| dc.description.abstract | Of the various nutrient factors that go to provide better health through letter nutrition, dietary protein is perhaps the most important and requires careful consideration. There is hardly any physiological function that does not call forth a particular combination of amino acids. The building up of body tissues, the formation of haemoglobin, the storage of liver proteins and similar other activities depend primarily on the dietary proteins. While the accessory food factors, the vitamins, serve their purpose in extremely small amounts, proteins form a major percentage of the total food intake. Also, most of the vitamins are synthesised by the varied bacterial flora of the intestinal tract, dietary medium is the only source of protein supply.
It is not merely the quantity of protein that counts; the quality is of paramount importance. Further, the protein should be capable of undergoing digestion by the body enzymes and releasing the constituent amino acids at a rate and amount facilitating simultaneous mutual utilisation. Only by such means, the dietary protein can be expected to satisfy the requirements of the body for its complicated and little understood functions.
The choice of protein is indeed limited, for people revolt vehemently to the idea of unfamiliar proteins irrespective of quality considerations; the problem is complicated in the case of vegetarians. Those consuming meat and allied products receive a good supply of all the essential amino acids. Vegetable proteins are invariably deficient in one or more of the indispensable amino acids. A judicious combination of two or more vegetable proteins may be expected to wholly or partly redeem the situation. But it is not a practicable solution to lay down the suitable combinations of proteins that people should take at any particular time. There should, therefore, be a simple procedure by which the quality of vegetable proteins could be very considerably improved.
The animal protein factor now known as vitamin B₁₂ is reported to make up all the difference between the animal and vegetable proteins. Several published reports show that the quality of vegetable proteins is greatly enhanced by the addition of vitamin B₁₂ at as low a level as 30 to 50 µg per kilogram of ration. The finding has undoubtedly advanced the scientific knowledge, and the practical utility of the discovery is considerable, for a simple and economic way of improving the quality of vegetable proteins and thus conferring important benefits on those depending mainly on vegetable proteins is made possible.
The work carried out by the present author on some of the aspects concerning this problem is detailed in this thesis. The author for the first time has made the observation that vitamin B₁₂ is able to counteract the adverse effects of the proteolytic and growth inhibitors present in raw soyabeans. By carefully planned growth and nitrogen-balance experiments, by adding vitamin B₁₂ to hyperthyroid animals fed raw soya protein, by studying the excretion in urine of amino acids under the influence of vitamin feeding and by determining the biological value of casein to which inhibitor extract is added and the influence of vitamin B₁₂ on casein–inhibitor mixture, the above conclusion was drawn.
The in vivo experiments were supported by the in vitro studies on the release of amino acids from raw soyabean protein to which vitamin B₁₂ was added.
Does vitamin B₁₂ play a part in protein metabolism? There are two schools of thought on this point. The present author carried out experiments by determining the biological value of autoclaved soyabean protein at graded levels in the diet. These studies yielded data which were interpreted as showing a significant relationship between vitamin B₁₂ and nitrogen retention. The level of protein in the diet was a deciding factor.
Thus, the observations collected and discussed in this thesis contribute materially to a better understanding of the present knowledge concerning vitamin B₁₂ and protein metabolism. In the course of these studies, the present author has developed a simple procedure for desalting urine and other biological fluids prior to estimating their amino acid composition by the circular paper chromatographic technique. | |
