Effect of actinidin from kiwifruit (Actinidia deliciosa cv. Hayward) on the digestion of food proteins determined in the growing rat

This study aimed to determine the effect of dietary actinidin (provided as Hayward kiwifruit) on the gastric and small intestine digestion of six food protein sources in rats. For each protein source, two semi-synthetic test diets were formulated containing either freeze-dried Hayward kiwifruit (actinidin present) or freeze-dried Hort16A kiwifruit (actinidin absent). Actinidin activity is extremely low in Hort16A kiwifruit. Titanium dioxide was also included as an indigestible marker. Rats were fed freshly-prepared diets, euthanised and the gastric and ileal contents collected. The chyme and digesta samples were subjected to electrophoresis (SDS–PAGE), densitometry and titanium analysis and the degradability of individual proteins calculated. Dietary actinidin had no (p > 0.05) effect on the gastric degradability of zein and whey protein isolate but increased gastric degradability of beef muscle protein, gelatin, soy protein isolate and gluten by 40%, 60%, 27% and 29% units, respectively. Dietary actinidin had little or no effect on ileal protein degradability. Overall, dietary actinidin enhanced the gastric digestion of some food proteins.