II. The Chemical Properties of Vitamin "B"

When Funk first studied this substance he conducted all his evaporations in vacuo from fear that higher temperatures would prove destructive. Subsequent investigation however has shown that 100° has very little if any destructive effect if the vitamin is held in acid or neutral solution. Temperatures between 100° and 120° maintained in an autoclave at 15 pounds above normal pressure do tend to slowly destroy the factor. The extent of this destruction also varies with the character of the crude extract. In general, then, there is little fear of injuring this vitamin in ordinary cooking temperatures if the use of alkali is avoided.

The effect of alkali depends upon the temperature to a very marked degree. Osborne has recently reinvestigated this matter and finds that in the presence of a 0.1N solution of alkali at 20°C. there is very little destruction but that raising the temperature to 90°C. brings about a marked destruction. Seidell has shown that if the vitamin is absorbed by Lloyd's reagent and this reagent be then extracted with dilute alkali the vitamin passes into the alkaline solution. If the latter is neutralized quickly it is possible to recover most of the vitamin by this method. The effect of alkali becomes of practical importance to the housewife because of certain cooking habits. I refer to the well known practice of adding soda to the water in which vegetables are cooked to soften the vegetable and accelerate the cooking. Daniels and Loughlin in this country investigated this matter and came to the conclusion that this procedure did not produce enough destruction to be dangerous.

Later the matter was studied by Chick and Hume in England and these investigators brought out a feature that had perhaps been overlooked in the previous work. Their point was that in ordinary feeding tests the results merely tell whether there is enough vitamin present to produce normal growth. Hence if the substance tested has much vitamin, a large part of it might be destroyed and this fact not appear in the test because enough might still be left to induce normal growth. By reducing the amount tested so that it was just adequate for normal growth and then applying the soda-cooking experimentation they showed that this method of cookery does do serious harm to the vitamin. From the practical point of view it is of course sufficient to show that enough is left after a cooking process to suffice for normal growth when the substance is taken in the portion sizes ordinarily eaten. The effect of alkali deserves more attention on the part of cooks and food preparateurs and we need more data concerning the minimal dose necessary to protect the human animal.

In neutral and acid solution it is perfectly safe to assume little destruction of this vitamin through heat and it is now common practice to boil sources with the extracting reagent and to use the steam bath freely to concentrate and evaporate these extracts. We have recently investigated the effect upon cabbage of cooking in a pressure cooker at eight pounds pressure. The cabbage so cooked, when dried and mixed so as to form 10 per cent of a basal vitamin free diet, yielded all the "B" vitamin necessary to produce normal growth in rats.

The very name of this vitamin indicates its ready solubility in water. It is also soluble in 95 per cent alcohol and either of these extractants may be used to obtain the vitamin. It is not readily soluble in absolute alcohol and 95 per cent is not as good an extractant as water. Substances rich in the vitamin apparently yield the latter more readily if they have first been subjected to autolysis or if the extracting fluid is acidified. Funk was the first to show that yeast produced a greater yield if it was allowed to autolyse before extraction with alcohol. However, Osborne and Wakeman have produced a method of treating fresh yeast by boiling it with slightly acidified water which seem as efficient as autolysis in the yield produced.

The various methods of extraction now in vogue have already been discussed in Chapter II and need not be repeated here. In general it is apparent that to obtain concentrates of high potency it is permissible to employ temperatures of 100°C. if we will maintain an acid or neutral reaction but that alkali should be avoided wherever possible and when its use is imperative the temperature must be kept below 20°C. or destruction will result. In applying this rule to cooking operations the results should be determined by direct tests rather than by assumptions based on these generalizations. It should also be noted that the alkalinity of a solution should be determined on the basis of hydrogen ion concentration and not on amount of alkali added since many substances have a marked buffer reaction.

The water-soluble "B" is not only soluble in water but can be dissolved in other reagents. Thus McCollum has shown that while benzene is of little value as an extractant of this vitamin, if we will first extract the vitamin with alcohol or water and deposit this on dextrin by evaporation it is then possible by shaking the activated dextrin with benzene to cause the vitamin to pass into solution in benzene. Voegtlin and Meyers have recently shown that it is soluble in olive oil and in oleic acid and their data suggest a new means of concentrating the substance which may be of value in tracing its character.

The "B" vitamin is relatively easily absorbed by finely divided precipitates. We have already referred to the use of fuller's earth for this purpose by Seidell. This adsorptive power sometimes manifests itself in the treatment of plant extracts. A watery extract of alfalfa can be made to throw down its protein complex by diluting it to 40 per cent with alcohol. Osborne reports however that this process frequently removes the vitamin also which appears to be thrown down with the precipitated material. This adsorptive power therefore often appears as a difficulty in the handling of the substance as well as a means of extraction. We have used Osborne's method with alfalfa extracts and find the above result is not by any means invariable, for in some of our extracts we retained the greater part of the vitamin. Kaolin and ordinary charcoal are not very good adsorbents but the latter can be activated to serve this purpose.

The elementary nature of the "B" vitamin remains a mystery. Extracts which contain it show the presence of nitrogen. Funk's earlier researches on yeast and rice polishings both yielded crystalline complexes which he analysed.

Tags: Vitamins