Protein digestibility of pigskin and bovine tendon in rats

The protein nutritional value of pigskins and bovine tendons, with collagen contents of 75 and 95% respectively, was evaluated using amino acid analyses and nitrogen balance experiments on rats. Pigskins contain somewhat higher amounts of tryptophan, meth-ionine, cystine and tyrosine than tendons. The amounts of several essential amino acids were low. The true digestibilities were for young (4 month old), unscalded pigskin 96.1%, old (5 year old), unscalded pigskin 92.5%, calf tendon 97.3% and cow tendon 92.4%. Small but statistically significant differences due to the animal age were observed. Insoluble collagen, extracted from bovine tendon, had a digestibility of 95.2%. Wet heat treatment of old pigskin and cow tendon samples at 74â°C for 30 min significantly increased the digestibilities to 96.3 and 97.3% respectively. The results indicate that prior denaturation of collagen, as obtained by, for example, heat treat-ment, is not necessary for the digestion of pigskin and tendon in rats.