Givens and Macy105 have investigated the antiscorbutic properties of fruit juices dried by a commercial process. Lemon juice, acid and neutralised, tomato juice, grapefruit, and orange juice all contained a significant amount of the antiscorbutic vitamin; grape and raspberry juice were apparently devoid of it. The preparations used were for the most part 14 to 20 months old.106

Certain observations have suggested that enzyme action may be an important factor in the gradual destruction of the antiscorbutic vitamin and to test this suggestion, Smith and Medes106 heated orange juice, both in the presence and absence of an enzyme, at temperatures of 38°, 66° and 76° C. If enzyme activity causes destruction of the vitamin, presumably disappearance would be most rapid at 55° C, the temperature at which the activity of the enzyme is greatest. The enzyme employed was invertase, since it is a normal constituent of orange juice. This enzyme did not contribute to the destruction of the antiscorbutic vitamin when heated with the vitamin for four hours at 38°, 66° and 76° C. This does not preclude the possibility that other enzymes may have such an effect. Incidentally, Smith and Medes note that heating for four hours at a temperature of 76° C, either in the presence of invertase or in its absence, causes a more rapid destruction of the vitamin than heating at 55° C. Heating for four hours at 38° C, does not cause an appreciably greater loss of antiscorbutic value than keeping at room temperature.

Beef, which is poor in C, loses its antiscorbutic power completely when it has been dried in vacuo at 65° C, or lower, for 12 hours and then air-dried for several days.107

103 Givens and Macy, Proc. Am. Soc. Biol. Chem.; J. Biol. Chem. 46, xi, 1921.

104 Hess and Unger, J. Biol. Chem. 35, 487, 1918.

105 Qivens and Macy, loc. tit.

105 The effect of diying vegetables in the sun has been investigated by Shorten and Ray (Biochem. J. 15, 274, 1921). Dried tomatoes, potatoes and cabbage retain much of their antiscorbutic value. This is not true, however, of carrots, spinach or turnips. Dried cabbage, tomatoes, carrots, spinach and potatoes showed antineuritic properties.

106 J. Biol. Chem. 48, 323, 1021.

107 Givens and McClugage, Sci. 51, 273.

That very low temperatures may be deleterious as well as higher temperatures is indicated by Wiltshire's experience in Siberia, where scurvy broke out among the troops, although each man received a ration of frozen meat daily.108

108 Wiltshire, Lancet, 1918, ii, 811.

A summary of the destructive effects of oxidation and catalysis on vitamins is given by Hess (J. Ind. Eng. Chem. 1021, 1115).