Research Laboratories, SwiftCompany, Chicago, IllinoisAlthough the thermolabile properties of thiamin were recognized in early investigations of the vitamin B-complex, there is little definite information regarding the mechanism of loss of this vitamin during the cooking of natural products. Factors other than heat appear to be involved since various foodstuffs show different rates of thiamin loss under identical temperature conditions. A more complete understanding of the nature of thiamin decomposition during heating may lead to the development of cooking procedures which will permit greater retention of thiamin in the food.Since pure thiamin is cleaved into the thiazole and the pyrimidine constituents when heated in neutral solutions, Williams (1938), it has been commonly assumed that this cleavage is involved in the thermal destruction of thiamin in foods. However, thiamin in natural products is notably more resistant to heat than pure thiamin in aqueous solutionsLMelnick, Robinson, and Field (1941) and Greenwood, Beadle, and Kraybill (1943)-thus indicating the existence of factors which can modify the reaction. Greenwood et al. showed that cocarboxylase is only slightly more resistant to moist heat than thiamin itself. Hence, it does not seem probable that the natural occurrence of thiamin as part of the cocarboxylase molecule is sufficient to explain its superior retention in foods as compared with aqueous solutions.Beadle, Greenwood, and Kraybill (1943) confirmed earlier work showing thiamin to be much more stable in solutions of low pH than in neutral or alkaline solutions, and also pointed out the importance of the buffer systems.involved. According to these workers, retentions vary from 0 to 97 per cent in different solutions of the same pH, depending upon the buffer used. On the other hand, storage for a week at 49"C.(120.2"F.) has been shown to cause thiamin losses ranging from 10 to 80 per cent in food mixtures of approximately the same pH and having to a large extent the same buffer systems-Rice, Beuk, and Robinson (1943). Sealock, Livermore, and Evans (1943) have demonstrated the presence of a thiamin-destroying enzyme in fresh fish tissue. This enzyme, however, is heat labile and, hence, its presence could not explain differences in the rate of loss of thiamin during the cooking of foods. Moreover, natural products ordinarily lose thiamin more slowly than pure solutions, but the enzyme accelerates the breakdown of thiamin in fish.Many investigators have observed that the rate of loss of thiamin increases as the temperature is raised and that the amount lost increases with the duration of cooking. Whether or not such increases are strictly proportional to time and temperature has not been critically investigated heretofore, although several workers have stated that the losses are greatest 99 FOOD RESBARCE, VOL. 10, No. 2.
