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Figure
This part can be presented as food is being dried and stored. A number of lessors will evolve as students test the different dryers. Some vegetables and fruit may spoil as students run tests and learn the most productive drying methods. When this occurs, lessons on spoilage from mold and bacteria can be introduced as well as lessons reinforcing the use of preservation and pasteurization methods. The decomposition of food by mold and bacteria is similar to the digestive process in humans. As simple food tests and digestion tests are being run, students can also test spoiled foods and note differences between fresh, spoiled and dried foods. This will emphasize the value of drying and preserving foods as well as increase the students' awareness of the digestive process.
The sequence of chapters presented is a suggestion. It is best to sequence the chapters as students bring up issues, questions and concerns. Lessons on preservation and spoilage and decomposition may precede or follow simple food tests based on the students' questions. In this section, food drying tests are presented before simple food tests only as a suggestion for following upon the equipment constructed in Part II.
BACKGROUND INFORMATION ON MOLD AND BACTERIA
In this series of lessons, students learn more about the impact of mold and bacteria on the preservation of foods. This is important in studying food preservation by drying because bacteria and molds are found in foods. By ingesting foods contaminated with mold and bacteria, we can become infected so we need to preserve foods free of mold and bacteria. (p.178 )
These lessons show the behavior of mold and bacteria under different conditions and thereby reinforce the preservation and storage methods necessary to avoid the contamination and spoilage of foods. A lesson also shows the digestive process of mold and bacteria and thus emphasizes what will be learned in the food test and digestion test lessons.
The discussion of mold and bacteria is offered to assist the teacher in facilitating lessons and directing student research. It is not necessary to include all the detail in the lessons. It is your choice to interject various pieces of information in the discussion after the activities. You may want to discuss food storage in association with this chapter. (See p. 178 )
BACTERIA
Bacteria are considered plants primarily for classification, though many scientists would prefer to put them in a class separate from plants and animals. Bacteria have the following characteristics:
1. Small size: micro-organism.
2. Unicellular.
3. Rigid cell wall.
4. Reproduction: primarily binary fission; some produce spores.
5. Able to obtain food in a soluble form.
6. No chlorophyll.
Some examples of bacteria are:
1. Staphylococcus, which causes infections on the skin and in the respiratory tract.
2. Diplococcus pneumoniae, which causes pneumonia.
3. Salmonella typhi, which causes typhoid fever and is spread through contaminated water, milk and food.
4. Rhizobium, which is the nitrogen fixing bacteria on legumes' roots and is quite necessary and beneficial for plant growth.
Bacteria sources for the lessons include decaying fruit and the dirt under fingernails.
MOLD
There are many types of mold; they are classified by their reproductive processes. Molds have the following general characteristics:
1. Multicellular.
2. Majority of molds are composed of many thread-like filaments (exception - Slime Molds).
3. Filaments are thin walled.
4. Reproduction: asexual or sexual; most molds have both cycles. Each mold produces a fruiting body where spores are formed. The spores are thick walled.
5. Ability to obtain food in a soluble form.
6. No chlorophyll.
Some examples of mold are:
1. Rhizopus Nigricans, the “bread mold." It is a soft, white, cottony mass with black spore cases. It grows on moist bread, raw sweet potatoes, and other starchy foods.
2. Penicillium grows commonly on citrus fruits, forming blue-green spots on the fruit. It is used to make the antibiotic Penicillin and is also used in cheese production.
3. Aspergillus appears reddish or black depending on what it grows on; it is similar to Penicillium and is very common.
4. Neurospora grows in bread, on fruit and on grains. It is red. In culture, it has produced a number of enzymes including Lipase and Trypsin.
Mold can be found or produced for the lessons on moist bread, citrus fruits and/or by placing dead flies in stagnant water.
MOLD AND BACTERIA
Mold and bacteria differ in the first four characteristics listed above, but have other characteristics in common. As mentioned, both mold and bacteria contain no chlorophyll and both are able to obtain food in a soluble form. Also, all mold and bacteria are killed or made dormant by low or high temperatures or when moisture is low. These factors are very important when considering the preservation of foods and will be studied in this chapter. Although bacteria and mold differ in some ways, the factors important in a discussion of food preservation are common to both. For this reason, they will be studied together. Learning the advantages of preserving food by drying and employing good drying procedures will be the outcome of these lessons.
The following diagram on the effect of temperature on mold and bacteria growth is offered to facilitate discussion while the students prepare materials and during the tests. It is best that the students discover the relationships through the activities; presenting this diagram before the activities might inhibit some problem solving.
DIAGRAM 45
Preparation of Materials for Activities
Students will gain a better awareness of the need for cleanliness, sterilization and pasteurization in food preservation and preparation as they become involved in the preparation of materials for this chapter. Check in the local area for resources. Would the local meat market butcher be willing to donate bones? Or would he be willing to trade bones in return for the fat that is rendered while making gelatin? Could the farmer who slaughters an animal use some of the gelatin? The uses of gelatin can be a secondary objective learned in this series of lessons.
Agar, which is similar to gelatin, may be available. It is made with seaweed from the East Indies. It has some advantages over gelatin, one being a higher melting point. Gelatin can be used for these studies, though, and may be easier to secure or produce.
While the students are involved in the preparation of materials, concepts learned in other lessons (solutions, colloids, characteristics of fat, measurement, evaporation) can be reinforced through questioning and discussion.
CULTURE
Materials
Animal bones (uncooked or boiled)
Water
Scale
Pot
Procedure
1. Crush the bones to small pieces.
2. Put the bone pieces in a pot, cover with water and boil for 15 minutes.
3. Cool. Skim off the fat. (The fat can be used.)
4. Remove the bone pieces and retain the water.
5. Grind the bones to powder; weigh.
6. The water should equal 8-10 times the weight of the bones. Add more water if necessary to obtain this proportion.
7. Return bone powder to the pot.
8. Boil until evaporated to 1/2 the volume. The resultant liquid is gelatin.
9. Pour gelatin into sterile dishes for the mold and bacteria studies or keep gelatin warm while the additions are prepared for the activities.
ALTERNATIVE CULTURE
If gelatin cannot be produced, potato, cassava, cooked egg white, or margarine can be sliced and put in dishes with lids and sterilized. The test results with this procedure, though, are not as definitive. It may be useful to have both types of culture dishes prepared and used, especially if the students seem unsure about the results.
Another alternative culture for growing mold and bacteria can be made with well cooked cereal. Put cooked cereal in dishes or small jars, cover, and sterilize.
If each group of students runs the full series of tests, you will need 18-24 culture dishes total for each group. This may be difficult. It is possible to run a test/activity, record and discuss results and then clean, prepare and sterilize the dishes for the next test, With this procedure, you will need 2 or 3 dishes for each group. Alternately, you can assign one test/activity to each group of students and have them conduct the tests simultaneously. This would require 18-24 dishes total for the class (4-6 tests).
TO STERILIZE OR PASTEURIZE
Sterilizing, the killing of microorganisms, is done by placing the item (dish, stick) in an oven, heater, or dryer at a temperature of 45°- 50° C. for one hour. This is sufficient to kill most mold and bacteria, except the spore forming bacteria which require higher temperatures. Many spores resist higher temperatures and will sprout when placed in favorable conditions.
Pasteurizing its a modified, partial sterilization recommended for sun dried foods that may not have been kept at a high enough temperature for the length of time needed to kill microorganisms (mold and bacteria, pp. 172, 174). The process is modified so that the food is not cooked and the loss of nutrients is minimized. During the mold and bacteria lessons, it would be useful to emphasize the similarities between sterilizing, pasteurizing and food preservation methods.
Sterilization in on Oven
Materials
Items to be sterilized.
Oven or dryer able to heat to 70°- 80 C.
Procedure
Heat items in oven at 70° - 80° C. for 10 - 15 minutes.
Sterilization by Steam
Another sterilizing procedure uses steam and, thus, reaches higher temperatures and kills more molds and bacteria than the other procedure.
Materials
Items to be sterilized
Water
Source of heat
Large pot or can with rack or platform
Lid to pot or can
Procedure
Put 5 cm of water in the pot and place a rack or platform above the water. The dishes/jars to be sterilized are put on the rack in the pot. Bring the water to the boiling point. Steam will be visible, escaping from the cover. Boil for twenty minutes. Remove from the heat source to cool. Keep the pot covered while cooling.
There are many ways to adapt available materials for sterilizing and pasteurizing. Some models of food dryers can reach temperatures sufficient for pasteurization and partial sterilization and can be used to prepare culture dishes for the mold and bacteria studies. It is useful to have another alternative, preferable a steam sterilizer. Students can compare results in the dishes/jars sterilized with the different procedures; this increases the opportunities for learning.
Oven or Sterilizer
DIAGRAM 46
To Make Transfer Needles
Transfer needles are used to transfer mold or bacteria from their source to a sterilized dish or jar. Each time this is done, the student should sterilize the needle by heating the end of it in a flame before using the needle to transfer again. This transfer to a sterilized dish is called planting.
Materials
Soft wood twigs or branches about the size of pencils
Sewing needles
Procedure
Push the needle into the end of the wood leaving the needle eye about 3 cm from the end.
DIAGRAM 47
Activity III-1. PRELIMINARY INVESTIGATION OF MOLD AND BACTERIA
In this activity, students will observe some physical characteristics of mold and bacteria. This preliminary investigation is particularly important if the students have not discovered mold and bacteria during other food lessons and activities.
Materials
Source of bacteria and mold
Hand lens
Procedure
Have the students observe and record what they have noted about mold and bacteria. During the discussion, cover such questions as:
What does it look like?
Where is it found?
Have you seen it other places?
Are the samples different? How?
Are some larger?
How do they grow?
What is needed?
The preliminary discussion should bring out some questions to test. Sequence the test lessons according to the questions the students raise. If the students discuss the need for water for mold and bacteria growth, begin with this study. If the concern is focused on the type of food mold and bacteria grow on, begin with that study. Ask the students how they can check how bacteria and mold grow. For example: How can we test whether water is needed for mold or bacteria to grow? Have the students discuss and develop plans to answer the question. Let the students begin the tests/activities.
The following activities outline the kinds of tests students can perform for some of the basic questions about mold and bacteria. The students can gain more if they design the test procedures themselves; it is not necessary to limit the study to the questions presented here.
Activity III-2 DO MOLD AND BACTERIA DIGEST COMPLEX FOODS?
In this activity, students will discover that mold and bacteria themselves digest many of the foods which we eat. This will reinforce the concept that foods must be prevented from being contaminated by mold or bacteria. An example of a chart for students to use in recording their observations for this and the following activities is found after Activity III-6.
Materials
Sources of mold and bacteria
Sterilized culture dishes
Pieces of protein, carbohydrate and fat
Transfer needles
Procedure
1. Transfer mold and bacteria to sterilized dishes, each containing a different food type.
2. Label the dishes according to food type.
3. Put the dishes in a warm place (18-35° C) for 2 or 3 days.
4. Observe the various dishes. Are there differences in the size of the mold and bacteria from its previous size? Are there differences from one food type to another? What changes have occurred to the original foods?
5. Record your observations and conclusions.
Activity III-3 DO MOLD AND BACTERIA NEED WATER TO GROW?
In this activity, the necessity for water for bacteria and mold growth is investigated. This is done by planting bacteria in wet and dry cultures and observing the differences over a period of a few days.
Materials
Sources of mold or bacteria
Gelatin in sterile dishes
Light bulb dryer or other solar dryer with cover
Dry cereal or dried food in sterile dish
Cooked cereal or fresh food in sterile dish
Transfer needle
Procedure
1. Plant mold and bacteria in some gelatin dishes. Place half the samples on a light bulb dryer covered with a box or place them in a solar dryer covering the open dishes with a box or bowl. Place the other covered samples in a warm, dark place. Check all the dishes after a few days. Note the differences and record the results.
2. Place a spoonful of dry cereal or a few pieces of dried food in a sterile dish with lid.
3. Place a spoonful of cooked cereal or a few pieces of fresh food (same kind as dried) in a sterile dish with lid.
4. Plant each dish with mold or bacteria.
5. Put the dishes in a dark warm place for a few days.
6. Check them. What has happened? How do the dishes differ?
7. What can you conclude about the results?
Activity III-4 DO MOLD AND BACTERIA GROW WELL IN LIGHT AND IN DARK?
In this activity, students will study the effects of light and darkness on mold and bacteria.
Materials
Culture dishes
Source of mold and bacteria
Transfer needles
Procedure
1. Plant some dishes with mold or bacteria.
2. Place some of the dishes in a light place such as by a window.
3. Place the other dishes in a dark place.
4. After a few days, check the dishes. Observe the results and record your findings.
Activity III-5 DO MOLD AND BACTERIA GROW BEST IN COLD, WARM OR HOT PLACES?
In this activity, students investigate whether mold and bacteria grow best in cold, warm or hot places.
Materials
Culture dishes with covers
Dryer or oven
Source of mold and bacteria
Transfer needles
Procedure
1. Plant dishes as in the other tests and cover with lids.
2. Place one in a very cold place such as on a concrete floor in a well shaded corner.
3. Place one in a warm place.
4. Place one dish in a hot place such as a dryer or oven.
5. Check the dishes after a few days. Record your findings.
Activity III-6. DOES SUNLIGHT KILL BACTERIA OR MOLD?
In this activity, students will discover what effect direct sunlight has on the growth of bacteria and mold.
Materials
Culture dishes
Source of mold and bacteria
Transfer needles
Direct sunlight
Procedure
1. Put mold or bacteria in two sterile dishes.
2. Place one of the dishes in open sunlight for several hours.
3. Place the other dish in a warm dark place.
4. After a few hours, remove the first dish from the sun and place it with the other dish.
5. Check them after a few days. Record your findings.
Have the students prepare charts such as the on the following page. If the class has been divided into groups, with each group doing a different activity, have a table written on the blackboard, so that each group can record and share the results of its activity. Have the students discuss the differences they have noted and what these results mean for food storage.
What food sources did the mold prefer?
What sources did the bacteria prefer?
What conditions slowed or stopped the growth of mold and bacteria?
What conditions were necessary for bacteria and mold to survive?
What would you want to do to make food less appealing to mold and bacteria?
What does drying food in a solar dryer do that makes food last longer?
Although light and temperature affect the growth of bacteria, the amount of moisture is the significant difference. Lack of moisture alone is sufficient to prevent the growth of mold and bacteria. This should be emphasized as it might not be definitive from the tests and it is the major advantage of preserving food by drying.
Table
BACKGROUND INFORMATION ON FOOD TYPES
Several of the tests in this chapter are used by chemists to analyze chemicals. Chemists look at, feel, smell and taste substances as part of preliminary analysis. By working with the groups, you can encourage students to test and record their results.
You may want to perform the tests by yourself beforehand to become acquainted with the results. This also gives you the opportunity to develop directive questions to ask the students as they experiment. You can also anticipate opportunities to re-emphasize things learned in other lessons-for example, evaporation and dehydration while students conduct Test 5, or solubility if basic chemistry lessons have been taught earlier.
In this chapter the students will:
1. learn the basic food types: Sugar, Protein, Starch and Fat by experimenting and observing differences.
2. develop record keeping skills as demonstrated by the charts and tables produced after the food tests have been conducted.
3. keep diet records to learn what types of food they consume. Diet records, discussion and observation of animals will direct students to the need for balanced diets. Measurement of this learning can be done by having the students prepare menus or diets that contain the basic food types.
The activities are used to identify the basic food types: Sugar, Starch, Protein and Fat.
PROPERTIES OF SUGAR
1. Sugar is soluble (Test 1). Simple sugars are absorbed in the human body by direct diffusion. Digestion, or chemical breakdown, is not necessary.
2. Sugar turns brown when mixed with iodine (Test 2).
3. Sugar has a sweet taste (Test 1).
4. When burned, sugar turns black and gives off water vapor. This is because it contains carbon and water (Test 4). The presence of carbon and water indicate that sugar is a carbohydrate. It is a simple carbohydrate. Because it is absorbed in the body directly (soluble), it is separated from other carbohydrates (starches) which require degestive reactions, starting in the mouth with the action of the enzyme, ptyalin, in the saliva.
PROPERTIES OF STARCH
1. Starch is soluble.
2. Iodine turns blue when mixed with starch (Test 2).
3. When burned, starch turns black and gives off water vapor (Test 4). This is because starch, like sugar, is a carbohydrate.
PROPERTIES OF PROTEIN
1. Proteins, such as those in meat, fish and egg whites, are large chemical compounds and require a series of digestive reactions to be broken down to amino acids which are absorbed and used by the human body.
2. Protein is not water soluble (Test 1).
3. Protein begins to break down in the presence of hydrochloric acid (Test 5). This is what occurs in the stomach.
PROPERTIES OF FAT
1. Fats, such as palm oil or margarine, are large chemical compounds.
2. Fats are not water soluble (Test 1).
3. Fats are the only food type that change paper, leaving a smear on the paper, which appears translucent when held up to a light (Test 3).
There are several tests that students can perform in order to observe differences between the four basic food types: Protein, Fat, Starch and Sugar. The food tests will take 2 or 3 class periods. If students are interested and continue to test food items, this part of the unit could be extended.
You can divide the class into groups. Each group can run one or two of the tests and report to the rest of the class. Alternately, each group can run all the tests and compare their results with other groups.
The written directions for each test can be handed out to each group. This can save time and allow the teacher more time for questioning as the activities are in progress.
Choose food items that are locally available, but try to get at least one sample from each food type. The food samples can be cut ahead of time, or the students can cut or chop pieces from the items as they perform the tests.
Newspapers can be spread on the desks or tables to protect them as the chemical tests are in progress.
Have the students use only a small amount of food for each test. While testing is going on, you might question the students about mixing or keeping the food items separate. Emphasize the importance of control in science experiments.
Have the students practice using grass reed droppers or Bic pen droppers as accuracy with these takes trial and error. The diagram below shows how the grass reed dropper is held.
DIAGRAM 47
There should be an area of the room set aside for washing and rinsing used equipment such as jars and caps. The soap and water are also essential for students who accidently get HCl on their skin. They must wash the area liberally with soap and water. The soap will neutralize the acid.
Following are the directions to be given to the students. You may want to circulate among the groups questioning the students about their process. "How did you crush the food sample?" "What happened to the rice when you put iodine on it?" "Does the sample smell different now?" The questioning should direct the students toward observing the difference between foods, the changes that take place, The questioning also can reinforce problem solving skills and the scientific method.
Activity III- 7 FOOD TEST 1
This activity tests the effect of water on food samples.
Materials
Small jars
Samples of each food type
Water
Procedure
1. Place food sample in a small jar. If solid, crush it. Fill jar 1/4 full with water. Mix. What happens?
2. Taste a small amount of food. What does it taste like? Sweet, sour, bitter or no taste?
Activity III-8 FOOD TEST 2
In this activity students will test to see what effect iodine has on the food samples.
Materials
Bottle caps
Water
Iodine
Samples of each food type
Grass reed dropper or Bic pen dropper
Procedure
1. Place small food sample in a clean bottle cap. If solid, crush it first. Add a few drops of water.
2. Add a few drops of iodine to the sample. Do not taste this - iodine is POISON. What happens?
Activity III-9 FOOD TEST 3
Students will test to see if the food samples have any effect on paper.
Materials
Samples of each food type Brown paper
Procedure
1. On a small piece of brown paper, place a food sample. If solid, crush it. Wipe off extra food, leaving a spot on the paper.
2. Set this aside and check it later. What happens? Hold the paper up to the light. What do you observe?
Activity III-10 FOOD TEST 4
Here, students will observe the effect of heat on the food samples.
Materials
Food samples
Bamboo tweezers (see Appendix A).
Bottle caps
Candle
Piece of glass
Procedure
1. Place a small amount of food in a clean bottle cap. Crush it if necessary.
2. Using bamboo tweezers, hold the bottle cap over a flame of a candle. Trim the wick to get a small flame with no smoke. While doing this, hold a piece of glass over it. What happens? Continue heating it. What happens?
Activity III-11 FOOD TEST 5
In this activity, students will test the effect of hydrochloric acid (HCl) on the food samples.
Materials
Hydrochloric acid
Food samples
Small jars
Water
Tin labelled ACID
Candle or burner
Procedure
1, Place small amount of food sample in a small jar and cover with water.
2. Mix the solution thoroughly.
3. Heat slowly over a candle or burner. Record what happens.
4. Carefully add a few drops of HCl to the food sample. Record what happens.
Important. HCl is an acid and can burn your hand. When finished, empty the mixture into the tin marked ACID. Put the jar or test tube into the basin/bucket with soap and water. Wash.
During the next science period, the groups can report on their findings by developing a chart on the blackboard.
TESTS
Have the students discuss the results. Why do certain foods react to only some of the tests? Direct the discussion to bring out four basic reactions. Introduce the food type terms: Protein, Fat, Starch and Sugar. Have the students develop lists of foods in the four groups. Point out by referring to the test results that sugars are carbohydrates as are starches. The test results vary because of the size of the chemical compounds. In the future lessons, this difference will be clarified through dgestion experiments and activities. Have the materials ready should some conflict about food items come up in the discussion. If there is some conflict, have the students test the food items in question. Discuss the basic uses of the food types. Carbohydrates and Fats produce energy, while Proteins build and repair tissues as well as provide needed substances in the body. (Refer to "Food Preservation Resource Packet.")
Ask the students to write down what they eat (their diets) each day for the next week. A diet record form is found in Chapter 7.
What types of food do they eat each day?
How much of each food type?
What season is it?
Do they eat different foods at other times of the year?
What are the differences in diet throughout the year?
Why? What foods are available in each season?
If the students are finished with the food tests at this point, proceed with the lessons on digestion and nutrition including the need for vitamins and minerals. When the students have their diet records ready, use the reports on diets to develop a discussion on nutrition and the need for well-rounded diets.
DIAGRAM
48
This chapter can be presented in 6 to 14 lessons dependent on what concepts you choose to include and the interest and skill level of the science students.
For example, if the students have not studied solutions, colloids and suspensions, you may want to set up materials and activities for thes students to determine the differences. This activity could precede the food test lessons. This is appropriate at the beginning of digestion studies because the behavior of food substances in water is important in digestion (hydrolysis). This activity would involve samples of substances: sugar, gelatin (protein), starch and oil (fat). These samples would be mixed with water. Each mixture is shaken and allowed to stand for about 5 minutes. The students then record the results and discuss their findings. The format of the food test lessons can be used for this activity.
Through the activities and discussions, the students will develop an understanding of the following concepts and be able to apply them to their daily lives.
1. Digestion is the chemical change of foods into particles that can be absorbed by the body cells.
2. Fats, proteins and carbohydrates must be digested to make possible their absorption and entry into the body cells. Fats, proteins and carbohydrates all contain Carbon (C), Hydrogen (H), and Oxygen (0) used to produce energy. Proteins also contain Nitrogen (N), Sulfur (S), and Phosphorus (P) used to produce chemical substances essential to life. Proteins are used to build and repair body tissues. We are about 20% protein by weight. The body depends on proteins to produce enzymes, hormones and hemoglobin. In addition, proteins are used to regulate body fluids. An insufficient amount of protein in the diet causes fluids to build up in parts of the body. This is why children with protein deficiencies (Kwashiorkor) have distended stomachs.
3. Hydrolysis is the breaking down of a chemical compound by combining it with water (H2O).
4. An enzyme is a catalyst that speeds the hydrolysis of foods. The general equation for a digestive equation is:
Food + water 
food parts
The equations for the basic food types are:
Fat + water 
fatty acids -
glycerine
Protein + water 
amino acids
Carbohydrate + water 
glucose
5. Glands produce the digestive juices such as saliva, gastric juice, pancreatic juice and intestinal juice. These digestive juices contain enzymes.
6. Proteins, fats and carbohydrates are digested as they move through the alimentary canal which consists of five main parts: mouth and pharynx, esophogus, stomach, small intestine and large intestine.
7. Water, vitamins, simple sugars and minerals (inorganic salts) are taken in the body by direct diffusion; digestion is not necessary.
On the following pages is a table on the composition of some foods to assist you in generating discussion questions and clarifying students' research.
COMPOSITION OF SOME FOODS (Adapted
from Handbook of Chemistry, Lange ed.)
COMPOSITION OF SOME FOODS (Adapted
from Handbook of Chemistry, Lange ed.) (cont’d.)
Abbreviations
Ca - Calcium
P = Phosphorus
Fe = Iron
+ = vitamin
present
++ = good source of vitamin
+++ = excellent source of
vitamin
Blank space = no appreciable amount of substance
Activity III-12 DIGESTION INTRODUCTORY ACTIVITY
In this activity, students will begin to understand the digestive reaction, the breaking down of food for absorption, as they solve the introductory problem and discuss their solutions. (A written assignment can be used also to measure the students ' knowledge of digestion.)
Materials
DIAGRAM 49
Have one set of materials for each group or team of students. Set the task and have each team work on the problem collectively and then share their results. An alternative to this would be to have one set of materials and direct questions to the total class, although there is generally less problemsolving with this approach.
The box is completely enclosed; the walls have small round holes. These holes cannot be made larger. How can the dirt, root and wood be moved into the box?
Give the problem and let the groups work on solutions. While the groups are working you can move from group to group and ask questions to stimulate problem-solving.
What solution (s) have you come up with?
Does that solution require work (energy)?
What steps are involved in the solution?
What is doing the work?
What arrangement or change in the materials is necessary to get them in the box?
Are other materials (substances) needed to change the objects?
Are there other solutions to the problem?
Do the different objects require different solutions?
When the groups seem to be at a stopping point, ask for oral reports from the groups.
Again, ask directive questions during the reports and discussion. Some groups will offer breaking/cutting up the materials as the solution. Others may offer dissolving substances with water as another solution. Discuss these different solutions, emphasizing that different agents (knife, water) are required. Through the discussion, bring out that this process is like digestion in the human body. Food must be broken down mechanically and chemically by hydrolysis and enzyme action in order to be absorbed by body cells in much the same way as the objects had to be broken down, using such things as a knife and water, in order to be put in the box. Someone may offer the use of chemicals as a solution to the problem. Ask how the chemical is used. Does it go in the box as well as the material? Develop the use of enzymes for digestion from this response. Enzymes are catalysts/agents that speed up hydrolysis. If the problem-solving and discussion demonstrate that students understand the process, the general food equation can be presented.
FOOD + WATER 
FOOD PARTS
The terms: hydrolysis, enzyme, catalyst, digestion can be introduced as the students generate definitions out of the problem-solving.
Note: The next series of activities involve digestive reactions of the basic food types. Some of the activities require materials that may not be easily available. These can be eliminated without losing continuity although they do serve as reinforcers of the concepts. The teacher may wish to tell the students what the results of those activities would be.
Activity III- 13 DIGESTION OF CARBOHYDRATES
Through experimentation, the students will learn that digestion of carbohydrates begins in the mouth. Mechanical (chewing)and chemical (ptyalin in saliva) breakdown is necessary for hydrolysis of carbohydrates. Starches are broken down to simple sugars. The equation for this process is:
Carbohydrates + water 
simple
sugar
Materials
Starch
Cooked potato
Crackers, tortilla or bread
Benedict's solution (Indicator of sugar)
Food samples from food tests
Raw potato
Wax
Iodine (Indicator of starch)
Jars or test tubes
Candles or burners
The first step in these activities is to have the students test the food samples used in Chapter 6 with Benedict's solution to determine what it indicates. The solution changes to a yellow-red color in the presence of simple sugars. If you are not able to get Benedict's solution, you can proceed with the other exercises reinforcing the students' observations of changes in the presence of starch. Through discussion, you can develop the concept of starch breakdown to sugar.
A. WHAT DOES BENEDICT'S SOLUTION TEST?
Take a small food sample of protein, fat, sugar and starch, if solid, crush it and mix each sample with a little water in a jar or test tube. Heat the mixtures, then add a few drops of Benedict's solution to each jar. What happens? Record any change in color.
Discuss the results. When the students have determined what Benedict's solution indicates, proceed to the other activities.
B. DOES SALIVA CHANGE BENEDICT'S SOLUTION?
Have the students work in small groups. Each group member chews a different food sample for a few minutes and collects saliva in a jar or test tube. Have one scudent in each group chew a small piece of wax and collect saliva. After the saliva is collected, direct the students to add about 1 teaspoon (5 ml or cc ) of Benedict's solution. Heat the jars over burners or candles for about 30 seconds. What happens to the sample of just saliva?
C. HOW DO ENZYMES WORK - CARBOHYDRATES?
Ask groups of students to arrange eight jars containing the materials listed below. Suggest that the students find a way to be able to identify the contents of the jars (label, code, record).
1. 2 jars with 5 ml of water and a small piece of raw potato in each.
2. 2 jars with 5 ml of water and a small piece of cooked potato in each.
3. 2 jars with 5 ml of water, 10 ml of saliva and a small piece of raw potato in each.
4. 2 jars with 5 ml of water, 10 ml of saliva and a small piece of cooked potato in each.
Test one jar of each sample (1-4) with iodine. What are the results? Do the samples vary? Does the presence of saliva make a difference?
Let the other samples (1-4) stand for 15 minutes. Add 10 ml of Benedict's solution to each jar and heat each jar for thirty seconds. What happens? Record any changesthat occur in each Jar.
As the students are experimenting, move from group to group to question them. In addition to the questions in the above paragraphs, you may wish to discuss the use of controls with them.
Have the students report their findings by developing a chart on the blackboard. During the discussion, introduce the equation that describes the action the students observed. Introduce the term, Ptyalin, the enzyme in saliva that begins digestion of carbohydrates to sugars by speeding up hydrolysis of carbohydrates.
Carbohydrates + water 
Sugar
D. ANOTHER TEST - HOW DOES PTYALIN WORK?
Have the students test pieces of cracker, bread or tortilla with iodine. By this point, the students may be familiar with the food type. Ask the students what type of food the cracker. bread or tortilla samples are. If the students know this, begin the activity at the next step.
Chew a piece of cracker, bread or tortilla for a minute. Take the chewed cracker out and put some of it in one dish and some in another. Add a few drops of iodine to one dish. Add a few drops of Benedict's solution to the other dish. What happens? What can you conclude about saliva?
Activity III-14 DIGESTION OF FATS
These activities emphasize emulsifying fats. Here you can encourage thinking about increases in surface area. Why is physical or mechanical breakdown of food necessary? What are the advantages? Why is mixing food and water important? Can enzymes react with food more readily if the food is in smaller pieces?
The equation for fats:
Fats + water 
Fatty acids +
Glycerine
The chemical tests for fats, fatty acids and glycerine are complicated and involve solutions and equipment not readily available. Focusing on emulsification as well as comparing the reactions of different foods should give the students an understanding of digestion and the rudiments of nutrition.
Materials
Water
Hydrochloric acid
Vinegar
Jars
Oil
Soap
Gum Acacia
Bucket/basin
Assign groups of students the following problems:
1. Put equal amounts of water and oil (about 60 ml ) in a small jar. What happens? Mix them. What happens? What size are the drops?
2. Add an equal amount of vinegar. Mix or shake. What happens? What size are the drops?
3. In another jar, add equal amounts of water and oil. Add some gum acacia. What happens? Mix and note the change. Note size of drops.
4. In another jar, add equal amounts of water and oil. Add about 15 ml of hydrochloric acid. Mix carefully. Note any change.
As students discuss their findings, reinforce the concepts of hydrolysis and the advantages of mechanical and chemical breakdown of foods. Introduce the equation for the digestion of fats. You may want to include some explanation of fatty acids and glycerine and how the body uses these substances.
Activity III-15 DIGESTION OF PROTEINS
As with fats, a series of steps are necessary to break down proteins to amino acids. We must replenish our supply of essential amino acids daily because the body does not store them. Amino acids, like fats and carbohydrates, can be stored for energy but not as amino acids necessary to tissue repair and building or the production of hormones and enzymes.
The equation for protein digestion:
protein + Water 
Amino acids
The activities involve the first steps of protein breakdown, as occurs in the stomach. Further breakdown occurs in the small intestines.
Materials
Hydrochloric acid
Egg whites (boiled) or meat
Pepsin
Fresh pineapple or juice squeezed from papaya leaves
Water
Jars
Milk
Candles or burners
Procedure
1. Put a small amount of milk (about 60 ml ) in two small jars. Add 15 ml of hydrochloric acid to one jar. Add 15 ml of vinegar to the other jar. What happens? Why? Do the same changes occur in both jars? Why?
2. This activity takes 1-2 days to complete. The students can proceed with other activities, checking the results of this activity during the next lesson.
Set up four jars (test tubes) with pieces of egg white. Add one of the following to each jar of egg white. (Meat can also be used).
a. Water - 5 ml
b. Pepsin solution - (1g pepsin, 50 ml H2O, and a few drops of HCl.
c. Water - 15 ml and a few drops of HCl.
d. Pepsin - 15 ml and a few drops of HCl.
Allow the jars to set 24 to 48 hours. Observe and record the results.
Which jar showed the most change?
What can you conclude about pepsin?
Where in the body do these chemical reactions take place?
How did saliva react with egg white in the earlier experiments?
During the discussion of the results, introduce the equation for protein digestion. Emphasize hydrolysis and enzyme action in the stomach.
3. Set up 2 jars with egg white pieces. Add 15 ml fresh pineapple Juice to one jar. Boil an equal amount of Juice and add it to the other jar. Allow the mixtures to set for 48 hours. Observe and record the results. What can you conclude about pineapple juice? Why was one jar of juice boiled? (This experiment can be done with juice extracted 'from papaya leaves. They contain the same plant enzyme. Or egg white or meat pieces can be wrapped in crushed papaya leaves and allowed to set.)
Activity III-16 ANATOMY OF DIGESTIVE SYSTEM
Students dissect fresh fish to observe the digestive system (alimentary canal). This activity can be used to summarize the findings in the other exercises, keying the chemical reactions to the various parts of the system.
After the fish have been dissected, they can be cleaned and prepared and put in one of the food dryers!
Materials
Fish, frogs or toads
Knives or single edge razors
Newspapers for desks or Food dryer tables
The students can work individually or in pairs. Direct the students to cut the fish from the mouth to the anal area, taking care not to cut any organs. Trace the alimentary canal - the mouth, the esophagus, the stomach and the intestines to the anus. Can you find the liver and gall bladder? Move from group to group to check progress. Compare what you find with the diagram below.
DIAGRAM 50
At this point, you may want to summarize the digestive system activities or have the students prepare the fish for drying (refer to Part II), Following are Further Studies on vitamins and minerals which give the students more to work with on their diet records. In fact, the diet records can be used as the focus for the summary discussion.
On the following pages are vitamin and mineral charts to use for the lessons. Also, a sample of a diet record form which the students can use at the end of this study, follows the charts.
Further Study
Vitamins and Minerals
These lessons involve the transfer of information. As such they may be scheduled at a number of points in the nutrition studies. They supplement the digestion and other nutrition activities. They can be introduced in the summary discussions. The students can supplement their diet records and meal planning work with this information.
Activities studying vitamin and mineral needs are complex and take long term efforts. If the school has a poultry farm, students with high degrees of interest may study v-tamin and/or mineral needs in poultry as an independent special study.
Another supplementary activity could be a field trip to a local health center including discussion with center staff: a physician, public health nurse or health auxiliary for example. This may be especially useful in areas where there is a recognized deficiency that can be overcome with a change in diet. Alternately, a health practitioner can be invited to the school as a guest speaker or you may want to coordinate a community workshop with the local health facility staff, having the science students help with the planning and presentation.
Reproducing the charts that follow on a hectograph or similar device may be useful.
SampIe for Diet Record
(Record sheets con be reproduced on hectographs or copy machines.)
Name
Date
Daily Food Intake
MINERALS
VITAMINS
There are four steps in the preservation of food by drying: the pre-drying treatment, the drying, the post-drying treatment, and the storage. The actual drying of the food was studied in Part II. ( See p.87) This chapter addresses the remaining three steps of the preservation process.
BACKGROUND INFORMATION ON PRE-DRYING TREATMENTS
Fruits, vegetables, meat and fish are treated before drying to preserve nutrients and the natural color and to slow the enzyme action that breaks down the food. If the students have studied digestion (Chapter 7), they will be aware of the action of enzymes. Otherwise, you may want to use examples of food left out in the open to show the breakdown that occurs. Choose some food item that is not obviously overgrown with microorganisms. Comparing a just ripe mango to one that has fallen and begun to discolor and soften should illustrate enzyme action. The various treatment methods slow this process down. Treating vegetables by blanching, in fact, loosens the tissues and the drying is quicker.
Treating foods prevents the loss of nutrients. Vitamins A, E, and many of the B's are broken down by light and oxygen. Vitamin C is destroyed by heat. There will be some loss with any preserving method but some of the treatments will minimize the loss.
The temperature range of the dryer has an effect on the preservation of color and nutrients as was mentioned in the food drying section. The temperature of the dryer, the availability of treatment substances, the humidity of the air, and the availability of storage containers need to be taken into account as the students prepare food for drying. It is possible to clean, cut and dry food in dryers without having to use any of the treatment methods before drying. There is, however, more nutrient loss if drying without pre-drying treatment. If the temperature in the dryer reaches 60° C , enzyme action in vegetables can be stopped, making the vegetables palatable even after long term storage. If the temperatures are kept higher than 60° C for long periods, however, food can start to cook and scorch, and there is a high loss of nutrients.
Although it is possible to dry and store many foods without any treatment prior to drying, the various treatments are presented to give you and the students more options. There is a wide range of methods offered, and experts do not agree on the amount of treatment substance to use, the length of time of the treatment or the preparation of the food type for drying. This is due to the fact that many factors are involved in the drying of food. Also, the experts emphasize different results, some want to minimize nutrient loss while others want to extend storage life. During the lessons when the students are preparing food for the dryers, it is important to emphasize the factors affecting food preservation and the purpose of different methods.
Factors affecting food preservation by drying can be summarized as the following: (See "Food Preservation Resource Packet").
1. size of food pieces
2. temperature of dryer
3. moisture content of food
4. humidity
5. air movement - in dryer - in surroundings
6. treatment method used
7. type of storage containers available
8. type of food - fruit, vegetable, meat, or fish
The major reasons for treating foods before drying them can be summarized as the following:
1. preserve natural color
2. preserve nutrients
3. stop decomposition (enzyme action)
4. make drying even
5. extend storage life
Begin the food drying lessons with types of food that do not need treatment before drying. Onions and peppers can be used. Encourage the students to keep records. How was the food cut? (See p. 89, pp. 175 - 177). How thick were the pieces? How much did the food weigh before drying? What size? (Refer to food drying activity, Chapter 3).
As the lessons proceed, introduce the various treatment methods. Start with the less complex processes, such as blanching and adding an anti-oxidant, and move on to the more complex processes, such as suffering and salting. This can only be done if there is a type of food available for each of the treatment processes. If this is not the case, plan the lessons around the foods that are available to dry. This may change the sequence of treatment presentations. The important thing, though, is to encourage the students to test different procedures, keep thorough records and learn how to weigh the factors involved in drying and storing and develop methods useful for the local area. Have the groups of students experiment with different preparations and treatments. With thorough record keeping, by the end of this book, the students should have the information needed to produce a table listing local foods and the most effective preservation technique for each food. You may want to reproduce copies of the local food preservation tables for the students to take to their villages and for community residents who may have been involved or are interested. Another way to share this information with the community would be at the school open house. Have groups of students demonstrate the steps in food preservation using the equipment the science class(es) has built. Of course, special community workshops could be offered as well.
Explanation of each of the treatments follow along with tables of some fruits and vegetables to help you get started and to facilitate planning the sequence of lessons for treatment, drying and storing.
The information in this section was developed on the farm, in classes and in the kitchen. The book, Putting Food BY and the Organic Garden and Farming magazine and the report from the "Food Preservation and Storage" workshop in Tanzania were also used to develop this section.
PRE-DRYING TREATMENTS
ANTI-OXIDANTS
Some foods, when exposed to the air, oxidize quickly, turning brown. This especially is true of light colored fruit. Anti-oxidants are acids that prevent exidation. Ascorbic acid* (Vitamin C) is the most effective antioxidant.
It is water soluble. The solution is sprinkled on the fruit as it is being sliced for the drying trays. Turning the pieces over a number of times while slicing and sprinkling will assure a sufficient coating of ascorbic acid. The nutrient value of the fruit is improved also by adding vitamin C. One cup of solution will treat about 5 quarts of cut fruit.
Materials
Water
Ascorbic acid
Source of heat
Food to be treated
Procedure
Boil water for 20 minutes and cool it before preparing the solution. It is important to use pure water while preparing food for drying as water borne microorganisms can cause much food spoilage. The proportion for mixing the solution is 4 ml of ascorbic acid crystals to 240 ml of pure water.
BLANCHING
Vegetables contain enzymes which cause decomposition while drying if not destroyed by heat first. Blanching, exposing vegetables to full steam (100° C See pp. 175 - 177) stops enzyme action and protects the natural color. Also, because enzyme action is stopped, nutrients are preserved.
Materials
Water
Cover for pot
Wire rack, bamboo, or reed basket or clean cloth
Pot, bowl or basin
Source of heat
Tin or flat rock
Food to be treated
A large pot, bowl or basin can be used for blanching. Put about 5 cm of water in the pot. The cleaned and cut vegetables can be placed in a wire rack, a bamboo or reed basket or a piece of clean cloth tied loosely.
The rack is placed in the pot above the water when there is full steam. A lid or cover is put on the pot. Blanching time varies for the type of vegetable; thicker or denser vegetables are blanched for a longer period of time than leafy vegetables. It may be necessary to put a tin or a flat rock in the pot so that the rack or basket sits above the water. If a cloth is used, knot it around a stick that can rest on the top edge of the pot to keep the cloth out of the water.
DIAGRAM 51
After blanching, remove the vegetable pieces and lay them on a clean cloth to soak up the extra moisture and then arrange them on drying trays. Blanching times are listed on the tables at the end of this section. Experiment with local vegetables using the samples listed in the tables as a guideline.
SULFURING
Sulfuring fruits before air or sun drying slows down enzyme action and preserves the fruits' color. It protects vitamins A and C. It also protects against insects and mold, although if a closed dryer (such as a solar dryer) is used, insects are not a problem. Also, as mentioned earlier, if the temperature in the dryer is high enough, mold and bacteria growth are inhibited. As with other treatment methods, sulfuring is an extra assurance that the dried food will keep for longer periods of time and will be nutritious and palatable.
Sulfite Soak
Materials
Pure water
Food to be treated
Sulfite substances (see below)
Bowl or basin
This treatment involves preparing a solution with any number of sulfite compounds. The food pieces are then soaked in the solution for 15 to 30 minutes. Sulfite substances that can be used are:
sodium sulfite
sodium bisulfite
potassium metabisulfite
sodium metabisulfite
The solution releases sulfur dioxide into the food. The general ratio for the solution is one liter of water to about 10 ml of sulfite. The specific proportions for different types of food are listed in the tables. There are some problems with sulfite soak that make it less effective than using sulfur dioxide fumes, although it is an easier process. The soaking results in an uneven penetration of food. The food can become waterlogged which extends the drying time considerably. Also, there is a loss of water soluble nutrients while the food is being soaked.
Sulfur Dioxide Fumes
Materials
Food to be treated
Sublimed sulfur
Drying trays
Wooden box covered with heavy paper or pasteboard box
Dish
Food is sulfured by being enclosed in an area filled with sulfur dioxide fumes. The fumes penetrate the food pieces. This treatment is done outdoors as the fumes irritate the eyes and the breathing passages. Sulfur is burned in a dish under the box after the drying trays loaded with food are stacked and placed under the box. Sublimed sulfur or refined sulfur (sold in cake form with wick for fumigating buildings) can be used. Sulfur melts at 115° C and the proportion to use is 12 ml for each kilogram of cut fruit. Experiment with the burning sulfur. A thin layer in a shallow dish may burn more evenly than a thicker layer. The sulfur burns to a brown syrup that expels the fumes. Time the sulfuring after the sulfur has burned and the air vents have been closed off. When the sulfuring is finished, generally after 30 minutes for small slices and 60 minutes for larger pieces, unload the sulfur box by opening it away from you and on the leeward side if it is a windy day. By checking the wind first and lifting the box away from you, you can avoid having the fumes blow in your direction. You may want to discuss this with the students before sulfuring or while they construct the box. It may be useful to burn a small bit of sulfur beforehand to observe the changes and plan the sulfur treatment. It may be an opportunity to review change of state concepts. Also, the concept of convection can be reviewed and applied to the design of the box. A sample of a sulfur box is diagrammed below:
DIAGRAM 52
Sulfuring steps:
1. Weigh food and calculate the amount of sulfur needed.2. Sulfur the same type of food: mixing foods in the box can get complicated.
3. Put trays on rocks or wood blocks and stack trays with about 8 cm between each tray and 10-15 cm clearance from the ground and above the trays.
4. Set dish of sulfur beside the food trays and put the box over.
5. Light the sulfur and let it burn to brown syrup.
6. Block the air vents; the cut at the bottom of the box and the small hole at the top on the opposite side of the box.
7. Time the sulfuring after the sulfur has burned and the vents are blocked.
8. After the sulfuring, remove the trays of food, taking care to avoid the sulfur dioxide fumes.
9. Arrange trays in a food dryer.
Foods high in protein invite spoilage more than other foods and therefore require extra steps to dry and preserve. Salting meat and fish discourages the growth of microorganisms, preserves the color and speeds up the drying process. Protein foods also must be stored in a cool place, around 4° C , to avoid spoilage. Pickling salt is used for salting or making brine, a salt solution. It is coarse salt that has not been refined and no iodine has been added. Iodine will discolor some foods.
Meat
Materials
Food to be treated
Brine
Dryer
Meat can be dried without salting although it does not keep as long as salted meat. Use only lean meat. Fatty meat spoils too readily. Cut the meat into strips lengthwise of the grain. The strips should have a width of 2.5 cm and a thickness of a little more than 1 cm The strips are hung on the drying frame. Trays made of woven wire, bamboo or grass reed can be used, hanging the meat strips over the cross pieces. The dryer should have a temperature range around 49° C. The meat strips will be brittle when dry. The dry meat weighs about 1/4 the weight of fresh raw meat.
Salted meat can also be prepared by making a brine using approximately 1 liter of salt to 5(1/2) liters of pure water. The meat is cut as described above and then soaked in the brine for 1-2 days. The meat is removed then from the brine, wiped dry with a clean cloth and arranged in a dryer. When brittle and at least 1/4 the weight of the raw mess, the strips are removed, cooled and stored in air tight containers in a cool place. The cooler illustrated below can be used to store dry meat and fish. A model of this device was studied in Activity I-1. See also Activities I-5A and I-5B.
DIAGRAM 53
Fish
Materials
Food to be treated
Pickling sale
Knife
Dryer
The process for drying fish is more complicated than drying meat, but if fresh fish is readily available only part of the year, it may be useful to learn the process in the science class. Fish is an excellent source of protein. Adding a little fish to dishes with vegetable proteins, such as beans, grains or nuts and seeds greatly increases the protein value of the dish.
Fish has to be dried in the shade. Direct sunlight will cook fish, even at a temperature as low as 23° C. Frames that can be covered with cloth placed under a large shade tree work well.
Use fresh, lean fish. Split the fish and clean out the internal organs. The head can be removed. (The head and organs can be composted for the school garden. Add some lime.)
DIAGRAM 54
The split fish is coated with pickling salt. One half kg of spit for each kg of fish. The salted fish is arranged on trays flesh side up. The trays are placed on frames in the shade for 1 - 2 weeks. Each night, the trays should be brought indoors. Press the racks or frames to squeeze out extra brine. After 1 - 2 weeks, the fish is scrubbed to remove the extra salt and then set outside again to finish the drying. When the fleshy part of the fish can be pinched, leaving no imprint, it is dry. The dried fish can be cut into pieces and put in air tight containers and stored in a cool place.
POST - DRYING TREATMENTS
These treatments are extra assurance that mold and bacteria are killed and that the food has dried evenly before storing. Whether these treatments are necessary depends on the temperature of the dryer, the length and thoroughness of the drying and the amount of humidity in the air.
CONDITIONING
Conditioning gives fruit an opportunity to complete the drying process and prevents growth of mold. Food is conditioned to check for thorough drying. If the food is air or sun dried, it is possible that the dryness of some of the pieces may vary. If the food is stored immediately and one piece still has some moisture, the whole batch can spoil in the storage container. On the other hand, if the weather is humid, the dried fruit can take up moisture from the air while being conditioned.
Materials
Dried food
Large con-tainer
To condition, place cool, dried food in a large open container such as a crock or enamel bowl or basin and put it in a warm, dry room with good air circulation. Stir the food in the container two times a day for 10 - 14 days. Again, if it is humid, it may be better to cool and dry test the food pieces and store in airtight containers immediately.
The factors involved in pasteurizing and conditioning should be discussed with the students. Ask questions that make the students weigh the factors and develop methods that solve the problems in the local environment. Ask the students:
Why are high temperatures important in food dryers?
What would happen to dried food if the weather is humid?
The following tables outline the preparation, treatment and drying for some fruit and vegetables. Use them as a guideline and encourage students to develop processes for local foods. A suggested sequence to include all the treatment methods in the lessons is to start with onions (no treatment) and proceed with greens such as tampala, mustard or bok choy (blanching) and a fruit like bananas (anti-oxidant coating), then mangos or apricots (sulfuring) and finish with beef or a lean fish like cod, tilapia or congo (salting). Of course, choose food that is available. By picking foods that are available seasonally, the nutritional advantage of having dried foods can be reinforced.
PASTEURIZING
Pasteurizing is the partial sterilization of food to kill microorganisms without causing a chemical change in the food that is a loss of nutrients. Some experts recommend pasteurizing for air and sun dried foods. The drying time may not have been long enough to kill mold and bacteria. Others find that if a dryer is kept at 57° C for one hour (solar dryers can reach this range), the food is pasteurized sufficiently to avoid spoilage.
Materials
Dried food
Source of heat
Oven
Rocks
One method for pasteurizing is to expose dried food to a temperature of 80° C. This can be done in an oven or the container used for blanching can be put on a flat rock or brick that is set in hot coals. The dried food is layered (2 1/2 cm layers) on rocks in the oven or blanching pot. Fruit is pasteurized for 15 minutes; vegetables for 10 minutes.
DIAGRAM 55
Note: For foods that need shredding (ace pp.175 - 177) a food shredder can be made by pounding nail holes in a sardine tin, holding the nail at a 30° - 40° angle. The hoses are cutting edges that shred food. Shreds will dry faster than slices. Food can be cut up very fine with a knife also to make shreds.
DIAGRAM 56
PREPARATION, TREATMENT AND DRY TEST
OF SOME FRUIT AND VEGETABLES
PREPARATION, TREATMENT AND DRY TEST
OF SOME FRUIT AND VEGETABLES (cont’d-1)
PREPARATION, TREATMENT AND DRY TEST
OF SOME FRUIT AND VEGETABLES (cont’d-2)
FOOD STORAGE
Food storage methods can be covered in the lessons in Chapter 5. The key to safe storage is to keep the moisture content to a minimum. If this is done, other problems, such as insect or vermin invasions, can be avoided. The reasons for pasteurizing, adding preservatives and using airtight containers should be emphasized.
DIAGRAMS 57 - 60
If dried food is stored in baskets, ceramic pots or gourds, a lid or seal can be made by dipping a piece of cloth in melted wax (use candle stubs from other lessons) and quickly tying it over the top of the container.
Lessons on storage can be conducted in much the same manner as some of the other lessons by having groups of students work together to design and test various storage containers. It may be a good idea to initially store small amounts of foods in the various containers until the effectiveness of the containers is established by the students ' tests. Keeping moisture out of the storage containers is the most important factor to develop.
Removing 80 - 90% of the moisture from foods concentrates the sweetness (fruit sugar) in fruits and the nutrients in all foods, and since foods rehydrate to 90X of their original size, dried foods can be more nutritious than fresh foods.
Dry food also conserves storage space.
Examples:
|
1 kg fresh carrots |
= |
80 g dried carrots |
|
8 kg potatoes |
= |
1 kg dried potatoes |
|
12 kg onions |
= |
1 kg dried onions |
|
1 kg fresh fruit |
= |
200 g dried fruit |
A Special Note on Food Storage
Beans and other seeds con be protected from weevils and other insects by putting a dried hot pepper or a dry bay laurel leaf in each storage container of beans, peas or other dried seeds including those stored for the next growing season.
Bay laurel and other medicinal or culinary herbs should be dried in a dark, dry, cool place. Light and heat will cause the loss of the herb's volatile oils and, therefore, their flavor or medicinal value. See the food preservation materials in this packet.
This final chapter can be tied to the diet record work and meal planning that the students began at the end of the nutrition studies.
Some math can be included as students calculate the portions of protein, fat and carbohydrate in the meal plans. Also, converting proportions of fresh ingredients in local recipes to dried foods involves some math.
After this work, the students may want to prepare a balanced meal made from dried foods for the school. It may be beneficial to invite the community people who have been involved. This can help to transfer some of the skills and methods to the general population.
BACKGROUND INFORMATION ON REHYDRATION
Rehydration is the opposite of dehydration; it is the process of adding pure water to dried food. Dried foods absorb water and rehydrate to about 90% their original size. Generally, 1 kg of dried food will equal 2 - 2(1/2) kg of food when rehydrated. Dried food can be rehydrated and then prepared in recipes as fresh food or it can be added to recipes, absorbing liquid and cooking in one process. For example, dried vegetables can be added to soup stock without rehydrating beforehand.
A variety of rehydrating methods are used by nutritionists. As with food drying methods, a number of approaches work equally well, depending on taste and local food preparation methods. The variety of methods possible lends itself to testing by the students to develop acceptable methods for the local recipes.
Some general guidelines and methods will be offered here to develop the problem solving rehydration activities with the students.
Some experts feel the proportion of 1 part food to 2 parts liquid is adequate for all rehydration. Generally, water is used, but fruit juices and stocks can be used as well.
Fruit* 1 : 2 liquid (water)
- be sure to use pure water with
foods.
Vegetable 1 : 2 boiling water
- cover and wait 5 minutes;
then cook at low temperature to taste.
Other experts suggest a 1 : 3 ratio for dried vegetables. Again, this depends somewhat on taste.
Beans, such as soybeans, are covered with water and soaked overnight and then cooked for 1 - 2 hours in fresh water.
The bulkier foods will take up more water. You may ask the students to refer to the figures they recorded in the water content activity (Activity II-1) to figure how much water different foods may absorb when rehydrated.
Some experts suggest that soaking before cooking makes the food tough. This seems to be dependent, though, on the type of food and how it is prepared. These experts pour boiling water over the dried food and cover and cook at low temperatures. They adjust the water level while cooking the food, adding just enough water for the food to rehydrate and cook without getting tough or soggy.
As mentioned in the treatment charts in Chapter 8, dried foods can be pounded to powders. The powders can be stored mixed or separately. The powders can be mixed, added to boiling water and cooked low for soups, porridges or sauces. A mix of high protein, carbohydrate and fat dried food powder can be used for special food for babies and young children. A high protein food powder can be added to sauces and other dishes to supplement the protein intake if it is low in a particular region. Milk powder is commonly used this way, but others, such as soybean or groundnut powder, could be used as well.
Dried food that is to be eaten raw can be put in a bowl with enough boiling water to cover. A lid is put on the bowl and the food soaks for several hours.
The concept of balanced diets can be expanded and reinforced during these activities. The students can return to the diet records they began after the food and digestion tests (p. 157). At this point, you may introduce the need for average portions of protein, fat and carbohydrate in the daily diet.
The following chart depicts the daily protein, fat and carbohydrate needs of adolescents and adults.
Daily Protein, Fat and Carbohydrate
Needs in Grams
(This chart is adapted from figures given in Diet for a Small Planet and caloric value conversions in Today's Basic Science.)
Adults need about 1.1 g /kg of body weight of plant protein (grains, legumes, nuts) or about .88 g/kg of animal protein (meat, fish, eggs, milk, cheese, yogurt) each day. Growing people, children and young adults, need 1(1/2) - 2 times as much protein per pound of body weight each day. The fat and carbohydrate needs are approximations. Excess protein in the body will be converted to carbohydrates for energy, therefore altering the carbohydrate intake need
You may want to use average figures for each need based on the average age and weight of the science students in a class. The chart, or a portion of the chart of average figures, can be given to the students.
Activity III- 17 ANALYSIS OF DIETS
Using their diet records, the students can calculate the amount of protein, fat and carbohydrate they -consume in a day. You may want to pose' a conversion table or note some conversions on the blackboard. Ask the students to explain the procedure. Some math review may be needed.
After the students have finished their calculations, ask for reports. During the reports, bring out the need for the food types and vitamins and minerals in the diet.
Why do we need protein?
What do carbohydrates provide?
Why do we need green vegetables?
Are there protein foods that can be added to improve the diet?
For example, milk powder, nuts or seeds can be added to sauces or cooked rice to increase the amount of protein in the diet. Sesame seeds, bulgar wheat or soybeans can be cooked with rice if rice is a common part of the diet.
Activity III-18 MEAL PLANNING
At the end of the discussion, ask the students to begin to plan nutritious meals starting with local recipes. This can be done in the class or as a task outside the class. If the class is made up of people with different traditions and diets, divide the class into groups so that all the various diets are considered.
Activity III-l9 REHYDRATION
Materials
Dried foods - use small portions for the tests.
Bowls or pots with lids - some tins may be used for cooking.
Burners, charcoal pots or fire pits.
Pure water (boiled for 20 minutes).
Mortar and Pestle, pounding stones or similar utensil.
Conversion table and food portion need chart.
Milk powder, if available for special powder mixes.
Stirring, mixing tools - wood, metal, plastic.
Basin
Soap
Cloths
Water
Measuring spoons, plastic caps or something similar for measuring small amounts.
Direct the students to experiment wits, small portions of dried food to discover the best way to rehydrate a particular food either for cooking or eating raw. Groups of students can work together with one type of food per group or each group can test all the types available. Encourage record keeping.
How much water did you use?
Was it boiling or cold?
How did you decide on the amount of water to use?
(Did the students remember the water content activity results and apply them to these tests?)
How much dried food did you use?
(Encourage using only spoonfuls for the tests.)
How long did it take for the food to soak up the water?
Did you cook the food? How long? What temperature range? Low? Medium? High (boiling)?
Through questioning, alert the students to the variables involved:
Water - amount and temperature.
Food - amount and type.
Time - soaking and cooking.
After the testing, have the groups report their findings. The students can develop a chart such as the one that follows, on a large paper or the blackboard outlining the rehydration process that works best for each type of dried food. This information will be used again. It can also be compiled with the food drying methods developed earlier.
|
Food Type |
Amount of Food |
Amount of Water |
Water Temperature |
Soaking |
Time Cooking |
| |
| | |
| |
At this point, you may want to have the students compile all
their results into tables, charts and recipes. Assign the various parts of the
study to each group of students. Have each group give a final report.
If there are copying machines or hectographs available, the science students could produce a booklet on drying, preserving and preparing local roods for balanced nutritious meals the year round, even in the season of shortage.
Activity III-20 PREPARATION OF POWDERS FROM DRIED FOODS
Direct groups of students to pound various kinds of dried foods to make powders if this has not been done. Give a problem to each group to solve.
Problems:
1. What mix of powders would make a balanced nutritious food for babies and young children?
2. What mix of powders would make a sauce that could be served with rice (wheat, noodles, cassava, potatoes) to make a nutritious meal?
3. What mix of powders would make a soup or porridge that is complete (nutritious)?
The students will have to consider and calculate proportions of food types. Have the food type need chart and conversion tables posted. Some review of ratios may be needed to get started. Ask the students to use small portions. Later when recipes are developed, the amounts can be increased to usable portions for meals.
With milk powder available some mixes may be easier to develop. Having dried commonly used herbs also may facilitate developing sauce recipes. Also, having some cooked rice or similar food in the class may be useful for tasting the samples of new sauces being developed.
The steps involved in this activity are:
1. Calculate the portions of food types needed for a balanced meal (1/3 of daily need).
2. Decide which available powders fit each type.
3. Measure and mix samples from each type.
4. Add herbs if desired.
5. Cook sample mix in small tin with pure water.
6. Taste sample.
7. Adjust sample if necessary.
8. If acceptable, record the recipe increasing the portions to normal amounts for a meal.
While the students are working, move from group to group to question them. How did you calculate the portions to use? Do children need the same portions of food types as adults? What did you have to consider? Use this activity set to question and review the nutrition concepts from earlier lessons. Ask the students to gather and record local recipes -or various dishes. Using their dehydration and rehydration records and results, have the students convert local -recipes to the appropriate portions using dried foods.
Using the results of the various activities, have the students plan, prepare and give a meal at school for the other students. Invite interested community residents an well. If some people have donated food or time to the project, include them also.
SUMMARY
In Part I and Part II, the students learned the basic construction of solar dryers and the scientific principles needed in order to design and understand how solar dryers work.
In Part III, the students have investigated and learned why it is important to preserve foods by drying. They have also learned enough about basic nutrition for them to be able to plan well balanced meals the entire year.
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