Human Foods and Their Nutritive Value Part 17

Experiment No. 1

Water in Flour

Carefully weigh a porcelain or aluminum dish. (Porcelain must be used if the ash is to be determined on the same sample.) Place in it about 2 gm.

of flour; record the weight; then place the dish in the water oven for at least 6 hours. After drying, weigh again, and from the loss of weight calculate the per cent of water in the flour. (Weight of flour and dish before drying minus weight of flour and dish after drying equals weight of water lost. Weight of water divided by weight of flour taken, multiplied by 100, equals the per cent of water in the flour.)

How does the amount of water you obtained compare with the amount given in the tables of a.n.a.lysis?

Experiment No. 2

Water in b.u.t.ter

Carefully weigh a clean, dry aluminum dish, place in it about 2 gms. of b.u.t.ter, and weigh again. Record the weights. Place the dish containing b.u.t.ter in the water oven for 5 or 6 hours and then weigh. The loss in weight represents the water in the b.u.t.ter. Calculate the per cent of water. Care must be taken to get a representative sample of the b.u.t.ter to be tested; preferably small amounts should be taken with the b.u.t.ter trier from various parts of the package.

Experiment No. 3

Ash in Flour

Place the porcelain dish containing flour from the preceding experiment in a m.u.f.fle furnace and let it remain until the organic matter is completely volatilized. Cool, weigh, and determine the per cent of ash.

The flour should be burned at the lowest temperature necessary for complete combustion.

Experiment No. 4

Nitric Acid Test for Nitrogenous Organic Matter

To 3 cc. of egg alb.u.min in a test tube add 2 cc. of HNO_{3} (conc.) and heat. When cool add NH_{4}OH. The nitric acid chemically reacts upon the alb.u.min, forming yellow xanthoprotein. What change occurs in the appearance of the egg alb.u.min when the HNO_{3} is added? Is this a physical or chemical change? What is the name of the compound formed?

What change occurs on adding NH_{4}OH?

Experiment No. 5

Acidity of Lemons

With a pipette measure into a small beaker 2 cc. of lemon juice. Add 25 cc. of water and a few drops of phenolphthalein indicator. From the burette run in N/10 KOH solution until a faint pink tinge remains permanently. Note the number of cubic centimeters of KOH solution required to neutralize the citric acid in the lemon juice. Calculate the per cent of citric acid.

(1 cc. of N/10 KOH solution equals 0.00642 gm. citric acid. 1 cc. of H_{2}O weighs 1 gm. Because of sugar and other matter in solution 1 cc.

of lemon juice weighs approximately 1.03 gm.)

1. What is the characteristic acid of lemons? 2. What is the salt formed when the lemon juice is neutralized by the KOH solution? 3. Describe briefly the process for determining the acidity of lemon juice. 4. What per cent of acidity did you obtain? 5. How does this compare with the acidity of vinegar?

Experiment No. 6

Influence of Heat on Potato Starch Grains

With the point of a knife sc.r.a.pe slightly the surface of a raw potato and place a drop of the starchy juice upon the microscopical slide.

Cover with cover gla.s.s and examine under the microscope.

In the evaporating dish cook a small piece of potato, then place a very small portion upon the slide, and examine with the microscope.

Make drawings of the starch grains in raw and in cooked potatoes.

Experiment No. 7

Influence of Yeast on Starch Grains

Moisten a small portion of the dough prepared with yeast and with the stirring rod place a drop of the starchy water upon the slide. Cover with cover gla.s.s and examine under the microscope.

Repeat, examining a drop of starchy water washed from flour.

Make drawing of wheat starch grain in flour and in dough prepared with yeast.

Experiment No. 8

Mechanical Composition of Potatoes

Wash one potato. Weigh, then peel, making the peeling as thin as possible. Weigh the peeled potato and weigh the peeling or refuse.

Calculate the per cent of potato that is edible and the per cent that is refuse.

Experiment No. 9

Pectose from Apples

Reduce a small peeled apple to a pulp. Squeeze the pulp through a clean cloth into a beaker. Add 10 cc. H_{2}O and heat on a sand bath to coagulate the alb.u.min. Filter, adding a little hot water if necessary.

To the filtrate add 5 cc. alcohol. The precipitate is the pectose material.

1. Is the pectose from the apple soluble? 2. Is it coagulated by heat?

3. Is it soluble in alcohol?

Experiment No. 10

Lemon Extract

To 5 cc. of the extract in a test tube add an equal volume of water. A cloudy appearance indicates the presence of lemon oil. If the solution remains clear after adding the water, the extract does not contain lemon oil.

Why does the extract containing lemon oil become cloudy on adding water?

Experiment No. 11

Vanilla Extract