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 Millon'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.
173 gm. Rochelle salt "I . ,
,. > made up to 500 cc. with distilled water.
100 gm. anhydrous sodium carbonate J
14 LABORATORY MANUAL OF FOODS AND COOKERY
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 coagu-
lation of the protein.
c. Filter on a wet fluted paper while the liquid is hot.
d. To the cold nitrate in a beaker or glass add alcohol, little
by little, in sufficient quantity to produce a bulky, gelatinous precipi-
tate 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.
FRUITS 15
Page 9
Presented as published in 1916. Historical recipes may not meet modern food-safety standards. Cook from the modern interpretation, not the original instructions.
AI-modernized reading of the original text
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 Millon'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.
173 gm. Rochelle salt "I . ,
,. > made up to 500 cc. with distilled water.
100 gm. anhydrous sodium carbonate J
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 nitrate 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.