Page:Foods and their adulteration; origin, manufacture, and composition of food products; description of common adulterations, food standards, and national food laws and regulations (IA foodstheiradulte02wile).pdf/347

 through a shelling machine, by means of which the pods are opened and the peas separated. The rest of the pods, stalks, leaves, etc., are very valuable for cattle food or fertilizing purposes. Peas, before canning, should be separated into different sizes so that all those entering one can may be as nearly uniform in size as possible. This separation not only makes the contents of the can appear more attractive but also renders the sterilization more certain and easy. If a large and small pea are put in the same can the heat of sterilization must be high enough and continue long enough to sterilize completely the large pea, and this might induce an over-cooking and impair the edible properties of the small one.

The technique of the canning process is not at all different except in the preparation of the material, as described above, from that of other vegetable canning factories.

Composition of Canned Peas.—The composition of typical varieties of canned peas compiled from a large number of analyses is shown in the following table:

Water,                85.47 percent Fat,                    .21 " Fiber,                  1.18 " Protein,               3.57 " Starch and sugar,       7.79 " Ash,                   1.11 " Salt,                    .67 "

From the above data it is seen that the canned pea does not have a high nutritive value, considering its bulk. In the canned pea one of the principal food elements in the wet material is the protein which it contains, both the pea and the bean being very rich in this important food material.

Adulteration of Canned Peas.—The principal form of adulteration which is practiced in the canning of peas is the addition of sulfate of copper for the purpose of producing an intense green color. The delicate shade of green of the fresh, succulent pea tends to assume a yellowish tint on canning, and especially after keeping for some time. To such an extent does this oxidation of the natural chlorophyl go on that in many samples when opened, instead of a green, we discover a decidedly yellowish tint. When a copper salt, such as sulfate, is heated in contact with a nitrogenous substance, such as that which exists in the pea, a chemical combination is formed between the copper and nitrogenous bodies which has an intensely green tint.

It is often supposed that the sulfate of copper is added to canned peas to preserve their natural color. This, however, is not the case. The copper combination, as above mentioned, produces a dye of a very bright green hue. Sulfate of copper is a highly poisonous substance, and for this reason should be excluded from food products. It is only fair to state that those who use this material claim that in the form of the combination produced it remains