Effect of Kiwifruit Juice on Beef Collagen

Abstract

The objective of this study is to clarify the difference in susceptibility to pro-tease digestion by kiwifruit juice between collagen domains under different conditions. In addition, the effect of pre-treatment with kiwifruit juice on collagen in meat during cooking processes was examined. Kiwifruit juice can degrade denatured collagen, but it can not cleave the triple helical domain of collagen. Thus, kiwifruit juice does not have collagenase activity. On the other hand, the cross-linked subunits of acid-soluble collagen were con-verted to monomeric subunits by kiwifruit juice treatment at acidic pH, suggesting that the globular domains, in which cross-links preferentially occur, can be degraded by kiwifruit juice. The pre-treatment with kiwifruit juice significantly decreased the shear force of con-nective tissue in comparison with other pre-treatments without protease activity, but inversely increased the liberation of collagen-related peptides in the outer solution by heat-ing processes at 50 and 70°C or by a shorter heating time at 100°C. This can be explained by the protease-mediated degradation of globular domains. However, this effect was not observed with a prolonged heating period at 100°C, and the liberation of collagen-related peptides by pre-treatment with kiwifruit juice at 100°C was less than that at 70°C for all heating periods. Thus, it can be suggested that the pre-treatment with kiwifruit juice might be useful in meat softening under vacuum-cooking and grilling, but not under stewing.