Experiments

Apple

15.1 - Grate an apple into a bowl. With a wooden spoon thoroughly mash the solid matter with the juice. What change in color is observed?

16. - Add about 2 tbsp. of water to the mixture obtained in Expt. 15, and strain the liquid through wet cheesecloth into a bowl. Filter the juice through a wet fluted filter and keep it for Expt. 17 and 18 below. To portions of the apple pulp apply: a. The Millon test2 for protein.

b. The iodine test for starch.3

17. - To small portions of the clear filtered apple juice obtained in Expt. 16, apply the following tests: a. Heat about 10 cc. to boiling in a test tube and notice whether coagulation takes place. Filter through a wet fluted paper and test the residue on the paper by adding a few drops of nitric acid. If protein is present, it will be turned yellow by the nitric acid.

b. Test for starch by adding iodine solution. (The portion of solution to which this test is applied must be cool.) c. Test for "reducing sugars" by mixing a small amount of the clear juice with an equal volume of the Fehling-Benedict4 solution, allow to stand a minute and note any change of color, then boil for two minutes. (Reference should be made to Leach's Food Inspection

1 For convenience the experiments are numbered consecutively throughout the book.

2 Milton's reagent: One part, by weight, of mercury dissolved in two parts of strong nitric acid. Dilute the solution with twice its bulk of water. After standing 24 hours, the supernatant liquid should be decanted from the precipitate. Proteins are colored red by this solution. Warming aids the development of the color.

3 Starch, iodine reaction: To the material to be tested for starch add a few drops of iodine solution (iodine dissolved in a water solution of potassium iodide). A blue, violet, or purple color indicates the presence of starch.

4 Fehling-Benedict solution:

34.65 gm. crystallized copper sulphate made up to 500 cc. with distilled water.

and Analysis, Sherman's Organic Analysis, or Woodmann's Food Analysis.) d. Test for proteins by means of Millon's reagent, making the test as closely comparable with that of the pulp as possible.

18. - Preparation of pectin.1 a. Neutralize the remaining apple juice with a sufficient quantity of caustic soda (sodium hydroxide) solution.

b. Heat the neutral fluid to boiling to complete the coagulation of the protein.

c. Filter on a wet fluted paper while the liquid is hot.

d. To the cold filtrate in a beaker or glass add alcohol, little by little, in sufficient quantity to produce a bulky, gelatinous precipitate of pectin. An equal volume of alcohol may be required. (Save this for Expt. 19.)

19. - Properties of pectin. Continuing the work begun in Expt. 18: a. Allow the alcohol to evaporate after decanting off as much as possible.

b. Dissolve the pectin in water and concentrate by heating.

c. Turn into beaker and let cool. The gelatinizing power of pectin will be shown.

Note : Other fruits or vegetables may be used to further demonstrate the above principles. Compare the experiments on vegetables, jellies, and gelatin described in later chapters.

20. - Decay of fruit (A). Place in a jar a number of apples that have been bruised or cut, packing them in rather tightly. Scatter in the jar some spores of the common mold which will usually be found on moldy lemon. Close the jar and set aside. Prepare a second jar with some whole clean apples and treat in the same way. Compare the two jars for a week or two to see if decay makes its appearance in either or both of the jars. Does bruising hasten the decay of the fruit?

1 Pectin, to which the essential gelatinous consistency of fruit jellies is due, is a substance belonging to the group of carbohydrates. It is entirely different from gelatin, which is a peculiar protein obtained from bone and other animal tissues and forms the basis of animal jellies.

21. - Decay of fruit (B). Make a cut through the skin of an apple with a knife blade that has been previously dipped into the midst of a mass of mold spores. Put the apple aside in a jar and examine carefully until it decays. Note that the decay begins rather quickly and starts at the point of the cut where the spores were inoculated.

22. - Experiment. Apple Sauce

1 apple 2 tbsp. sugar

5 tbsp. water 1/8 tsp. nutmeg

Prepare apple sauce by paring and slicing the apple and cooking it in the water until soft. Let half the class (a) add sugar at beginning of process; the other half (b) add sugar at end of process.

Use the thermometer constantly and compare the temperatures throughout the making of the apple sauce.

Account for differences in color, taste, and consistency.

23. Experiment. Baked Apple

Prepare baked apples in the following ways: in each case core and fill cavity with sugar.

a. Wash and remove skin from apple. Bake in slow oven. (Temperature?) b. Repeat with a second apple but bake in a hot oven. (Temperature?) c. Wash and core third and fourth apples. Do not remove skin. Bake one in slow, and one in hot oven.

d. Wash and core fifth and sixth apples. Make a slit around each apple, through the skin. Bake one in a hot oven, one in slow.

Which method and temperature produces best result?