Human Foods and Their Nutritive Value Part 19

Experiment No. 20

Testing for Watering or Skimming of Milk

_a._ Fat Content of Milk by Means of Babc.o.c.k Test.--Measure with pipette into test bottle 17.6 cc. of milk. Sample should be carefully taken and well mixed. Measure with cylinder 17.5 cc. commercial H_{2}SO_{4} and add to milk in test bottle. (See Fig. 25.) Mix acid and milk by rotating the bottle. Then place test bottles in centrifugal machine and whirl 5 minutes. Add sufficient hot water to test bottles to bring contents up to about the 8th mark on stem. Then whirl bottles 2 minutes longer and read fat. Read from extreme lowest to highest point.

Each large division as 1 to 2 represents a whole per cent, each small division 0.2 of a per cent.

_b._ Determining Specific Gravity by Means of Lactometer.--Pour 150 cc. of milk into 200 cc. cylinder. Place lactometer in milk and note depth to which it sinks as indicated on stem. Note also temperature of milk. For each 10 above 60 F. add 1 to the lactometer number, in order to make the necessary correction for temperature. For example, if milk has sp. gr. of 1.032 at temperature of 70, it will be equivalent to sp.

gr. of 1.033 at 60. Ordinarily milk has a sp. gr. of 1.029 to 1.034. If milk has sp. gr. less than 1.029, or contains less than 3 per cent fat, it may be considered watered milk. If the milk has a high sp. gr. (above 1.035) and a low content of fat, some of the fat has been removed.

(For extended direction for milk testing see Snyder's "Dairy Chemistry.")

Experiment No. 21

Boric Acid in Meat

Cut into very small pieces 5 gms, of meat, removing all the fat possible. Place in an evaporating dish with 20 to 25 cc. of water to which a few drops of HCl have been added and warm slightly. Dip a piece of turmeric paper in the meat extract and dry. A rose-red color of the turmeric paper after drying (turned olive by a weak ammonia solution) is indicative of boric acid.

1. How may meat be tested for boric acid? 2. Why is HCl added to the water? 3. Why is the water containing the meat warmed slightly? 4. What is the appearance of the turmeric paper after being dipped in the meat extract and dried? 5. What change takes place when it is moistened with ammonia, and why?

Experiment No. 22

Microscopic Examination of Cereal Starch Grains

Make a microscopic examination and drawings of wheat, corn, rice, and oat starch grains, comparing them with the drawings of the different starch grains on the chart. If the material is coa.r.s.e, pulverize in a mortar and filter through cloth. Place a drop or two of the starchy water on the slide, cover with a cover gla.s.s, and examine.

Experiment No. 23

Identification of Commercial Cereals

Examine under the microscope two samples of cereal breakfast foods, and by comparison with the wheat, corn, and oat starch grains previously examined tell of what grains the breakfast foods are made and their approximate food value.

Experiment No. 24

Granulation and Color of Flour

Arrange on gla.s.s plate, in order of color, samples of all the different grades of flour. Note the differences in color. How do these differences correspond with the grades of the flour? Examine the flour with a microscope, noting any coa.r.s.e or dark-colored particles of bran or dust.

Rub some of the flour between the thumb and forefinger. Note if any granular particles can be detected.

Experiment No. 25

Capacity of Flour to absorb Water

Weigh out 15 gms. of soft wheat flour into an evaporating dish; then add from burette a measured quant.i.ty of water sufficient to make a stiff dough. Note the amount of water required for this purpose. Repeat the operation, using hard wheat flour.

1. How may the absorptive power of a flour be determined? 2. To what is it due? 3. Why do some flours absorb more water than others?

Experiment No. 26

Acidity of Flour

Weigh into a flask 20 gms. of flour and add 200 cc. distilled water.

Shake vigorously. After letting stand 30 minutes, filter and then t.i.trate 50 cc. of the filtrate against standard KOH solution, using phenolphthalein as indicator, 1 cc. of the alkali equals 0.009 gms.

lactic acid. Calculate the per cent of acid present.

1. How may the acidity of a flour be determined? 2. The acidity is expressed in percentage amounts of what acid? 3. What per cent of acidity is found in normal flours? 4. What does a high acidity of a flour indicate?

Experiment No. 27

Moist and Dry Gluten

Weigh 30 gms. of flour into a porcelain dish. Make the flour into a stiff dough. After 30 minutes obtain the gluten by was.h.i.+ng, being careful to remove all the starch and prevent any losses. Squeeze the water from the gluten as thoroughly as possible. Weigh the moist gluten and calculate the per cent. Dry the gluten in the water oven and calculate the per cent of dry gluten.

Experiment No. 28

Gliadin from Flour

Place in a flask 10 gms. of flour, 30 cc. of alcohol, and 20 cc. of water. Cork the flask and shake, and after a few minutes shake again.

Allow the alcohol to act on the flour for an hour, or until the next day. Then filter off the alcohol solution and evaporate the filtrate to dryness over the water bath. Examine the residue; to a portion add a little water; burn a small portion and observe odor.

1. Describe the appearance of the gliadin. 2. What was the result when water was added? 3. When burned, what was the odor of the gliadin, and what does this indicate? 4. What is gliadin?

Experiment No. 29

Bread-making Test

Make a "sponge" by mixing together:

12 gm. sugar, 12 gm. yeast (compressed), 4 gm. salt, 175 cc. water (temp. 32 C.).

Let stand 1/2 hour at a temperature of 30 C. In a large bowl, mix with a knife or spatula 7.7 gms. of lard with 248.6 gms. of flour. Then add 160 cc. of the "sponge," or as much as is needed to make a good stiff dough, and mix thoroughly, using the spatula. With some flours as small a quant.i.ty as 150 cc. of sponge may be used. If more moisture is necessary, add H_{2}O. Keep at temperature of 30 C. Allow the dough to stand 50 minutes to first pulling, 40 minutes to second pulling, and 30 to 50 minutes to the pan. Let it rise to top of pan and then bake for 1/2 hour in an oven at a temperature of 180 C. One loaf of bread is made of patent flour of known quality as a standard for comparison, and other loaves of the flours to be tested. Compare the loaves as to size (cubic contents), color, porosity, odor, taste, nature of crust, and form of loaf.

Experiment No. 30

Microscopic Examination of Yeast

On a watch gla.s.s mix thoroughly a very small piece of yeast with about 5 cc. of water and then with the stirring rod place a drop of this solution on the microscopical slide, adding a drop of very dilute methyl violet solution. Cover with the cover gla.s.s and examine under the microscope. The living active cells appear colorless while the decayed and lifeless ones are stained. Yeast cells are circular or oval in shape. (See Fig. 46.)

(Adapted from Leach, "Food Inspection and a.n.a.lysis.")