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"Percentage of undissociated acid.

"Percentage of undissociated acid.

mance and why benzoates are not generally recommended above pH 4.5.

The use of acid to make heat preservation more effective, especially against spore-forming food spoilage organisms, is an established part of food technology. Under U.S. Federal Standards of Identity (12), the addition of a suitable organic acid or vinegar is required in the canning of artichokes (to reduce the pH to 4.5 or below) and is optional in the canning of the vegetables listed in Table 4. Vinegar is not permitted in mushrooms. Citric acid is specifically permitted as an optional ingredient in canned corn and canned field corn.

The advantage of acidification is especially well illustrated in the canning of whole tomatoes. When the pH of these is greater than 4.5, there is increased incidence of spoilage in the cans. When tomatoes of pH 3.9 are processed at 212°F, only 34 min are required to kill a normal or high spore load without decreases in color and flavor and deterioration of structure. In contrast, at pH 4.8 the cooking must be 110 min (13).

In the processing of fruits and vegetables, whether for canning, freezing, or dehydration, the prevention of discoloration in the fresh cut tissue is a major concern. Reactions in which polyphenolic compounds are changed by oxidation into colored materials play an important part in this discoloration which may be accompanied by undesirable flavors. The ascorbic acid naturally present in many fruits and vegetables offers some protection, but this is of relatively short duration because of destruction of ascorbic acid by natural enzymes and air. Heating, as applied in blanching, destroys the oxidative enzymes which cause discoloration but may alter flavor and texture if continued sufficiently to completely inactivate oxidative enzymes.

Lowering pH by addition of acid substantially decreases the activity of natural color producing enzymes in fruits. Citric acid also sequesters traces of metals which may accelerate oxidation. Even greater protection is obtained by using citric acid in conjunction with a reducing agent such as ascorbic or erythorbic acid. Some processors have found that a combination of sodium erythorbate and citric acid best serves their needs.

Leavening Agent

The basis for the formulation of effervescent beverage powders, effervescent compressed tablet products, and chem-

Table 4. Canned Vegetables in which Use of Acids is Optional

Asparagus

Celery

Potatoes

Bean sprouts

Greens, collard

Rutabagas

Beans, butter

Greens, dandelion

Salsify

Beans, lima

Greens, mustard

Spinach

Beans, shelled

Kale

Sweet peppers, green

Beet greens

Mushrooms

Sweet peppers, red

Beets

Okra

Sweet potatoes

Broccoli

Onions

Swiss chard

Brussels sprouts

Parsnips

Tomatoes

Cabbage

Peas, black-eyed

Truffles

Carrots

Peas, field

Turnip greens

Cauliflower

Pimientos

Turnips

ically leavened baked goods is the reaction of an acidulant with a carbonate or bicarbonate resulting in the generation of carbon dioxide. The physical state of some food acids as dry solids is a property appropriate for beverage mixes and chemical leavening systems. In the absence of water, there is essentially no interaction between such acids and sodium bicarbonate. Thus these dry mixes can be stored for long periods.

A desired property for an acidulant in a chemical leavening system is that it react smoothly with the sodium bicarbonate to assure desirable volume, texture, and taste. Leavening acids and acid salts vary quantitatively in their neutralizing capacity. This relationship is shown in Table 5. A new heat-activated leavening agent, dimagnesium phosphate, was recently reported for use in finished baked products (14).

The various acids differ in their rate of reaction in response to elevation of temperature. This must be taken into consideration in selecting an acidulant for a particular condition. Under some conditions, a mixture of acidulants may be most suitable to achieve desired reaction times. Table 6 compares the reaction times of GDL and cream of tartar.

Glucono-delta-lactone is an inner ester of gluconic acid that is produced commercially by fermentation involving Aspergillus niger or A. suboxydans. When it hydrolyzes, gluconic acid forms and this reacts with sodium bicarbonate. Although GDL is relatively expensive, there are certain specialized types of products such as pizza dough and cake doughnuts for which it is eminently suited as an acid component of the leavening system. Cream of tartar (potassium acid tartrate) has limited solubility at lower temperatures. There is a limited evolution of gas during the initial stages of mixing in reduced temperature bat-

Table 5. Neutralizing Value of Various Acidulants Used in Chemical Leavening
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