Falk and McGuire recommend the vacuum process of drying or dehydrating foods as a means of preserving the vitamin content. The absence of oxygen during drying favors the retention of the full vitamin potency. Banana flour is advantageously prepared in this manner.98

Givens and McClugage confirmed the findings of Hoist and FrSlich with regard to the destructive effect of drying on the antiscorbutic factor in potatoes, the amount of destruction varying greatly with the temperature and duration of drying. Fifty-five to 60° C. is apparently the optimum temperature, 2.5 g. per day of potato dried at this temperature affording some protection. The best results were obtained with potatoes which had been baked for a short time at a high temperature and then dried. Givens and McClugage99 remark that the influence of heat upon the antiscorbutic vitamin appears to be related not only to the degree of temperature but to the duration of the treatment, the reaction, the enzymes present, and the manner of heating. They consider a temperature of 35° to 40° C. for six to eight hours seems to be more destructive than 55° to 60° C. for two to three hours. This conclusion is based on the results obtained with potatoes dried at these temperatures and fed uncooked and cooked for 15 minutes at 100° C. With 2.5 grams of potatoes dried at 35° to 40° C. and fed without further treatment, death from scurvy was slightly delayed; with 5 grams life was certainly prolonged.

One out of four animals receiving daily 2.5 grams of potatoes dried at 55° to 60° C. showed signs of scurvy at death; also one out of three animals on potatoes dried at 75° to 80° C. showed signs of scurvy at death. If these dried products are further heated in water at a temperature of 100° C. for 15 minutes and then fed to guinea pigs in amounts equivalent to 2.5 grams of dried material no protection was observed with the 35-40° C. and 75-80° C. products while with the 55-60° C. material some favorable effect was noticed.

"When potatoes were baked for a short time at a high temperature and then dried, a product was obtained which afforded protection against scurvy. Thus it appears possible that the factors involved in the destruction of the antiscorbutic vitamin are not only the degree of heat and the duration of the heating but also the enzyme content and the reaction of the food being dried. Until further light is thrown upon the problem it seems plausible to assume that at any temperature below 80° C. the enzymes are functionating. For example, all potatoes dehydrated below this temperature darkened during the desiccation. Furthermore, samples of these same products tested nine months after drying showed that they still contained oxidases. The temperature of 35° to 40° C. is probably the optimum one for the enzyme action. The duration of drying at this temperature, being very long, allows several hours for continuous activity. In the case of drying at 55° to 60° C. and 75° to 80° C. there is undoubtedly some enzyme action, but the time is reduced.

The difference in the antiscorbutic value between the products dried at 55° to 60° C. and at 75° to 80° C. and then cooked, may be accounted for on the basis that at the higher temperature there is more destruction due to the duration of this greater heating and to enzyme action. In the case of baking and drying the enzymes are destroyed in a very short time; also the product is subjected to the high temperature for a short period and thus high heat and reaction have little time to bring about a joint effect.

98 Am. Food Jour. Oct 1021.

99Givens and McClugage, J. Biol. Ghem. 42, 407, 1020.

Drying at 35° to 40° C. for 32 to 52 hours appears to reduce the C content of tomatoes somewhat, the loss being greater if the dried tomatoes are cooked before feeding.100

Bassett-Smith101 kept a preparation of antiscorbutic material from lemon juice for three months at temperatures of 15°, 30° and 37° C. without appreciable loss of antiscorbutic power. The temperature of 37° was least satisfactory, the vitamin being slightly affected in this case.101a.

Harden and Robisonl02 report that the antiscorbutic property of orange juice is not appreciably destroyed by evaporation to dryness under suitable conditions. The dry residue retains considerable activity after storage for two years in a dry atmosphere at ordinary temperature, an observation which is confirmed by Givens and Macy.103 Hess and Unger,104 on the other hand, found that orange juice which had been kept in a refrigerator for some time had lost some of its nutritive value as indicated by the improvement in weight and general condition observed in the case of a guinea pig when the refrigerated juice was replaced by only half as much fresh orange juice in its dietary.

100 Givens and McClngage, Proc. Soc. Biol. Chem.; J. Biol. Chem. 41, xnv, 1920.

101 Bassett-Smith, Lancet 1020, 1102.

101a The preservation of citrus fruit juices from the standpoint of antiscorbutic potency has been studied by Davey (Biochem. J. 15, 83, 1021). Potassium metabisulphite is satisfactory at 0° but it is uncertain at room temperature and is ineffective at 37° C. Preservation with the rind oil, in the case of lemon and orange is satisfactory at temperatures up to room temperature. Even after two years the potency is very little diminished. Citrus fruit in cold storage therefore should maintain a high) degree of antiscorbutic value for an indefinite period. At 37° C. deterioration is rapid.

102 Harden and Robison, Biochem. J. 1020, 14, 171-177.