Protein Digestibility and Trypsin Inhibitor Activity of Legume Seeds

Otras publicaciones, Werner Jaffe

Protein Digestibility and Trypsin Inhibitor Activity of Legume Seeds

The poor nutritional quality of some crude legumes has hem attributed in early studies to low digestibility( 1) and it has been shown that in vitro digestibility of crude beans is lower than that of cooked beans (2) . Later, factors have€ been found in a number of crude legumes which inhibit the in vitro activity of trypsin(3). However, a purified trypsin inhibitor ¡rom soy beans did not inhibit growth of rats and chicks (4) . Moreover, no correlation between improvement of growth promoting action of legumes after autoclaving and their trypsin inhibitor content was found in a recent study (5). Some legumes contain heat labile factors which inhibit growth and are probably not identical with trypsin inhibitors (6). No correlation could be detected between growth depression by crude legume seeds and their trypsin inhibitor activity (7). It therefore seemed to be of interest to study the in vivo digestibility of some legúmes in the crude and autoc1aved form and to compare them with their activity to inhibit the action of trypsin in vitro.

Experimental. The protein digestibility experiments were made with young SpragueDawley rats of about 100 g of weight. For each experiment 2 mal e and 2 female rats were housed in single screen bottomed cages. Food and water were given ad libitum. Food consumption was determined and feces were collected every 3 days, dried at 70°C, weighed, and analyzed for N. With the mentioned exceptions, the diets were composed mainly of starch and the amount of the dried and ground seeds to contain 10% of crude protein (Nx 6.25); the composition of these diets and the treatment of the legume seeds was the same as described earlier (8). The crude kidney beans and hyacinth beans were assayed as a mixture of 20% of the seeds with 80% of a commercial rat diet of known digestibility. This technic, although less accurate, had to be adopted as these seeds are toxic for rats and food consumption was very low when they were administered in the same diet as the other legumes studied. In a separate experiment, the protein digestibility of cooked kidney beans was determined using both experimental diets; the results differed only by 0.8%. To compute the true digestibility from the values of apparent digestibility, the endogenous nitrogen excretion in the feces of the strain of rats used was determined separately and found to correspond to an excretion Df 1.25ro of crude protein. This value was used for all the calculations. The digestibility Df each sample was determined from 3-8 times with 1-4 groups of rats. The results given in Table 1 are the averages of these experiments. Trypsin inhibitor activity was determined according to the technic of Borchers and Ackerson (3).

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