None of the vitamines has been isolated in a pure state. The nearest approach to this desired end has been the work of Funk, who obtained the water-soluble vitamine in a state of such concentration that about 3 mg. sufficed to cure a pigeon of polyneuritis. In considering the attributes of the antiscorbutic vitamine, it must be borne in mind that this factor is referred to as it exists in various foods; for example, in orange juice or in cabbage, and furthermore, that the method of ascertaining its presence or concentration is limited to the crude biological test of animal feeding.
The antiscorbutic factor is distinguished by being the most sensitive of the three vitamines, the most unstable, the least resistant to physical or chemical processes. It may be regarded as one of the most delicate indicators of the biological integrity of foodstuffs; however, as Falk and his co-workers have shown, the enzyme property of living matter is still more readily destroyed. The antiscorbutic vitamine is soluble in water, and therefore is termed by some the “water-soluble C” factor. It is also soluble in alcohol, as shown by the experiments of Hess and Unger and of Harden and Zilva, and the therapeutic tests on infants of Freise and of Freudenberg.[23] It possesses, therefore, the solubility of the water-soluble vitamine. Some have suggested that it may be derived from this vitamine, others that instead of one there may be a series of antiscorbutic factors—suggestions based on pure hypothesis. Holst and Froelich showed that this vitamine passes, without appreciable loss, through dialyzing parchment, and Harden and Zilva (2) that it can pass through a porcelain filter. The latter, using the method of Seidell, demonstrated that this vitamine is not adsorbed by fine precipitates such as fuller’s earth, differing in this respect from the water-soluble vitamine; and that in a mixture of equal volumes of autolyzed yeast and orange juice, the antiscorbutic vitamine remained unaffected, whereas the water-soluble A was entirely removed.
One of the most distinctive characteristics of the antiscorbutic factor is its sensitiveness to even moderately high degrees of heat. In this respect it differs markedly from the water-soluble or so-called “antineuritic vitamine” which withstands exposure to high temperature. The reaction of the antiscorbutic vitamine in this regard is not a simple one, and cannot be expressed by a mere statement of the degree of heat and the length of exposure. Numerous other factors, especially the reaction of the medium, but also the physical environment, must be taken into consideration—for example, cabbage is more resistant to the action of heat than its juice. An understanding of the relation of antiscorbutics to heat may perhaps best be obtained by considering the subject in connection with some definite foodstuffs. The most exhaustive study from a quantitative standpoint is that of Delf. She showed that when cabbage is subjected for an hour to a temperature of 80° to 100° C., 90 per cent. of its antiscorbutic vitamine is lost, and that 80 per cent. is lost when a temperature of 90° to 100° is maintained for twenty minutes, or a temperature of 60° for a period of sixty minutes. This experiment shows that the destructive influence of heat is enhanced to a comparatively slight degree by a rise of temperature, only about threefold when it is raised from 60° C. to the boiling point. This result points to a temperature coefficient of about 1.5 to 10° C. of temperature. It is suggested by Delf that this low coefficient of destruction is opposed to the enzyme or protein-like theory of the nature of the vitamine, and suggests a simpler constitution. On the other hand, we must bear in mind that the proteins which have been used in experiments and found to possess a high coefficient of heat, have been tested in the pure state, whereas the vitamine of the cabbage is bound up in the cell.
Experiments with this vitamine as found in milk accord with the above investigation, demonstrating that intensity of heat is not as destructive as prolonged heating. This agrees with the clinical experience that milk which has been boiled for a few minutes does not induce scurvy as readily as pasteurized milk which has been heated for 45 minutes to 140° or 165° F. (Hess and Fish).
As demonstrated by tests with orange and with lemon juice, the antiscorbutic vitamine is greatly protected from the destructive effect of heat when it is associated with an acid. This was shown first by Holst and Froelich and has been confirmed by numerous observers. An excellent example of marked thermostability conferred on a food by its acid reaction is furnished by the tomato, which is strongly antiscorbutic even after it has been subjected to the canning process. Conversely, Harden and Zilva have shown that the vitamine is destroyed by alkali even when dilute (one-fiftieth normal sodium hydrate) and kept in contact at room temperature; this alteration does not take place at once, but in the course of several hours.
It is true that the antiscorbutic factor is peculiarly sensitive to drying, but there are exceptions to this rule, so that it is incorrect to state, as does the British Report of the Medical Research Committee, that “it may be regarded as an axiom that dry or dried foodstuffs will not prevent scurvy.” We have shown that fresh milk dried by the Just-Hatmaker process may retain by far the greater moiety of its virtue. In this regard rapidity of desiccation and subsequent protection from oxidative processes are important factors. The general rule holds true, however, that this vitamine, in contradistinction to the “water-soluble” vitamine, is readily damaged and destroyed by drying.
This vitamine is peculiarly sensitive to aging, especially when it is present in an alkaline or neutral medium; but even in an acid medium its potency soon diminishes. Harden and Zilva found this to be the case with lemon juice stored for a fortnight in the cold room, and our experience has been similar in regard to orange juice kept in the refrigerator under a layer of liquid petrolatum. In milk the antiscorbutic factor diminishes with age, especially following pasteurization, in the course of which most of the acid-forming bacteria have been destroyed. Aging has the least effect when the food with which the vitamine is associated has been dried. This is true not only of lemon and of orange juice as demonstrated experimentally and clinically, but even of milk, which even after it has been dried and stored for months, may still possess marked curative value.[24]
Experiments by Harden and Zilva showed that exposure of lemon juice to ultra-violet rays for eight hours does not influence its antiscorbutic activity, that exposure of autolyzed yeast for the same length of time likewise does not impair its “antineuritic” potency, but that under identical conditions the fat-soluble factor in butter becomes inactivated. Similar tests carried out by the author with orange juice led to the same result. It thus appears that one of the vitamines—not the most unstable—manifests a peculiar sensitiveness to a certain form of physical or chemical action.
In view of the fact that shaking partly destroys pepsin and rennin, as shown by Shaklee and Meltzer, it would be of interest to ascertain whether this process brings about any impairment of the antiscorbutic vitamine. Particular interest is attached to this question because it is generally recognized that milk loses some of its potency in the course of handling—whatever may be comprised by this term. In experiments on the fat-soluble vitamine Steenbock and his co-workers found that “somewhere in the course of the manipulation to which the butter fat had been subjected, factors had been introduced which were responsible for a vitamine destruction.”