Starch digestion enhancement by phytase, protease and xylanase/glucanase in milled maize, wheat and barley grains depends on cereal type and particle size

Abstract

Exogenous enzymes are used in animal feed formulations to enhance starch digestion in milled grains, but the effect of grain type and the underlying mechanisms are incompletely understood. This study compared the effect of three commercial in-feed exogenous enzymes (phytase, protease and xylanase/glucanase) and their combination on starch digestion of milled barley, wheat and maize in an in vitro model. Xylanase/glucanase enhanced starch digestion the most in barley and wheat, while phytase had the largest effect in maize. In each case exogenous enzymes showed greater enhancement of starch digestion for larger grain particles (1.18–2.36 mm). Microscopy showed that xylanase/glucanase treatment reduced cell wall encapsulation of starch for all three grains, suggesting that cell wall encapsulation is not rate-limiting for starch digestion of milled maize. Supplementing phytase in milled maize suppressed the loss of pancreatic amylase activity during small intestinal digestion in vitro. This provides a possible mechanism for the observed enhancement of starch digestion by phytase in grains. The data shows how the effects of enzyme treatment on starch digestion depends on the milled grain source and particle size, and that both de-encapsulation and protection of amylase activity can result in enhanced starch digestion.