Evaluation of the impact of maize endosperm vitreousness on in vitro starch digestion, dry matter digestibility and fermentation characteristics for pigs

The interest in the study of the effect of endosperm vitreousness (VT) on the nutritive value of maize is increasing in pig nutrition. Therefore, an experiment was conducted to determine the effect of maize VT on starch digestion, resistant starch (RS) content, dry matter digestibility as well as on large intestine fermentation kinetics and related end products by using several in vitro techniques specifically designed for pigs. A set of 30 maize grains was selected to represent a wide range of VT (as a proportion of vitreous in total endosperm) determined by a manual dissection method. Five distinct VT classes were designed [very low (vlVT), low (lVT), medium (mVT), high (hVT) and very high (vhVT)] and identified by a specific VT value (i.e., 291, 357, 432, 611 and 830 g/kg endosperm, respectively), calculated as the mean of VT values of maize samples entering the specific class. Starch digestion (expressed as predicted glycemic index) and the rate of starch digestion decreased linearly (ranging from 42.5 to 14.5 and from 0.018 to 0.006/min respectively, for vlVT and vhVT; P<0.05), whereas RS increased linearly (from 183 to 381 g/kg dry matter; P<0.05) with VT classes. The total tract in vitro dry matter digestibility decreased linearly (from 0.96 to 0.75; P<0.05) with VT classes. The in vitro fermentation showed that the rate of fermentation decreased (from 0.060 to 0.044/h; P<0.05), whereas the total short chain fatty acid (SCFA) production increased (ranging from 6.29 to 7.29 mmol/g dry matter incubated; P<0.05) linearly with VT classes. The molar ratio of acetate linearly increased, ranging from 0.50 to 0.55 (P<0.05) with VT classes, whereas no differences were observed for other individual SCFA. The loading plot of principal component analysis revealed significant relationships between VT and variables of interest. Results indicated that VT promoted marked effects on in vitro parameters related to starch and dry matter digestibility and fermentable kinetics for pigs. Further in vivo validations are required to validate these findings.