Human Foods and Their Nutritive Value Part 18

Pour into a test tube 5 cc. of the extract to be tested. Evaporate to one third. Then add sufficient water to restore the original volume. If a brown, flocculent precipitate is formed, the sample contains pure vanilla extract. Resin is present in vanilla beans and is extracted in the essence. The resin is readily soluble in 50 per cent alcohol. If the alcohol is removed from the extract, the excess of resin is precipitated, or if free from alkali, it may be precipitated by diluting the original solution with twice its volume of water. Test the two samples and compare.

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

1. Describe the appearance of each sample after evaporating and adding water. 2. Which sample contains pure vanilla extract? 3. State the principle underlying this test.

Experiment No. 12

Testing Olive Oil for Cotton Seed Oil

Pour into a test tube 5 cc. of the oil to be tested and 5 cc. of Halphen's Reagent. Mix thoroughly. Plug the test tube loosely with cotton, and heat in a bath of boiling saturated brine for 15 minutes. If cotton seed oil is present, a deep red or orange color is produced. Test two samples and compare.

Halphen's Reagent.--Mix equal volumes of amyl alcohol and carbon disulphid containing about one per cent of sulphur in solution.

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

Experiment No. 13

Testing for Coal Tar Dyes

Dilute 20 to 30 cc. of the material to 100 cc.; boil for 10 minutes with 10 cc. of a 10 per cent solution of pota.s.sium bisulphate and a piece of white woolen cloth which has previously been boiled in a 0.1 per cent solution of NaOH and thoroughly washed in water. Remove the cloth from the solution, wash in boiling water, and dry between pieces of filter paper. A bright red indicates coal tar dye. If the coloring matter is entirely from fruit, the woolen cloth will be either uncolored or will have a faint pink or brown color which is changed to green or yellow by ammonia and is not restored by was.h.i.+ng. This is the Arata test.

(Adapted, Winston, Conn. Experiment Station Report.)

1. Describe Arata's wool test for coal tar dyes. 2. What is the appearance of the woolen cloth when the coloring matter is entirely from fruit? 3. What effect has NH_{4}OH upon the color? 4. Why is NaOH used?

5. Why may not cotton cloth be used instead of woolen? 6. What can you say of the use of coal tar dyes in foods?

Experiment No. 14

Determining the Per Cent of Skin in Beans

Place in an evaporating dish 10 gm. of beans, 50 cc. of water, and 1/2 gm. of baking soda. Boil 10 minutes or until the skins are loosened, then drain off the water. Add cold water and rub the beans together till the skins slip off. Collect the skins, place on a watch gla.s.s and dry in the water oven for 1/2 hour. Weigh the dried skins and calculate the per cent of "skin."

1. What does the soda do? 2. What effect would hard limewater have upon the skins? 3. How does removal of skins affect food value of beans and digestibility?

Experiment No. 15

Extraction of Fat from Peanuts

Sh.e.l.l three or four peanuts and with the mortar and pestle break them into small pieces. Place in a test tube and pour over them about 10 cc.

of ether. Cork the test tube and allow it to stand 30 minutes, shaking occasionally. Filter on to a watch gla.s.s and let stand until the ether evaporates, and then observe the fat.

1. What is the appearance of the peanut fat? 2. What is the solvent of the fat? 3. What becomes of the ether? 4. Why should the peanuts be broken into small pieces?

Experiment No. 16

Microscopic Examination of Milk

Place a drop of milk on a microscopical slide and cover with cover gla.s.s. Examine the milk to detect impurities, as dust, hair, refuse, etc. Make drawings of any foreign matter present.

Experiment No. 17

Formaldehyde in Cream or Milk

To 10 cc. of milk in a ca.s.serole add 10 cc. of the acid reagent. Heat slowly over the flame nearly to boiling, holding the ca.s.serole in the hand and giving it a slight rotary movement while heating. The presence of formaldehyde is indicated by a violet coloration varying in depth with the amount present. In the absence of formaldehyde the solution slowly turns brown.

Acid Reagent.--Commercial hydrochloric acid (sp. gr. 1.2) containing 2 cc. per liter of 10 per cent ferric chlorid.

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

1. How may the presence of formaldehyde in milk be detected? 2. Why in this test is it necessary to use acid containing ferric chlorid? 3.

Describe the appearance of the two samples of milk after adding the acid reagent and heating. 4. Which sample showed the presence of formaldehyde?

Experiment No. 18

Gelatine in Cream or Milk

To 20 cc. of milk or cream in a beaker add 20 cc. of acid mercuric nitrate and about 40 cc. of H_{2}O. Let stand for a few minutes and filter. Filtrate will be cloudy if gelatine is present.

Add 1/2 cc. of a dilute solution of picric acid--a heavy yellow precipitate indicates gelatine.

Acid Mercuric Nitrate.--1 part by weight of Hg, 2 parts HNO_{3} (sp.

gr. 1.42). Dilute 25 times with water.

Experiment No. 19

Testing for Oleomargarine

Apply the following tests to two samples of the material:

Boiling or Spoon Test.--Melt the sample to be tested--a piece about the size of a chestnut--in a large spoon, hastening the process by stirring with a splinter. Then, increasing the heat, bring to as brisk a boil as possible and stir thoroughly, not neglecting the outer edges.

Oleomargarine and renovated b.u.t.ter boil noisily, sputtering like a mixture of grease and water, and produce no foam, or but very little.

Genuine b.u.t.ter boils with less noise and produces an abundance of foam.

Waterhouse Test.--Into a small beaker pour 50 cc. of sweet milk. Heat nearly to boiling and add from 5 to 10 gms. of b.u.t.ter or oleomargarine.

Stir with a gla.s.s rod until fat is melted. Then place the beaker in cold water and stir the milk until the temperature falls sufficiently for the fat to congeal. At this point the fat, if oleomargarine, can easily be collected into one lump by means of the rod; while if b.u.t.ter, it will granulate and cannot be collected.

(From Farmers' Bul. 131, U. S. Dept. of Agriculture.)

1. Name two simple tests for distinguis.h.i.+ng b.u.t.ter and oleomargarine. 2.

Describe these tests. 3. Why do b.u.t.ter and oleomargarine respond differently to these tests? 4. Are these tests based upon chemical or physical properties of the fats?