Starch digestion kinetics and mechanisms of hydrolysing enzymes in growing pigs fed processed and native cereal based diets

This study aimed to examine in vivo starch digestion kinetics of starches and to unravel mechanisms of starch hydrolysing enzymes. Ninety pigs (23±2.1 kg BW) were assigned to one of nine treatments in a 3x3 factorial arrangement, with starch source (barley, maize, high amylose maize) and form (isolated, within cereal matrix, extruded) as factors. We determined starch digestion coefficients (DC), starch breakdown products, and digest a retention times in four small intestinal segments (SI1-4). Starch digestion in SI2 of pigs fed barley and maize, exceeded starch digestion of pigs fed high amylose (HA) maize by 0.20 to 0.33 DC units (P<0.01). In SI3-4, barley starches were completely digested, whereas the cereal matrix of maize hampered digestion and generated 16% resistant starch in the SI (P<0.001). Extrusion increased the DC of maize and HA maize starch throughout the SI, but not that of barley (P<0.05). Up to 25% of starch residuals in the proximal small intestine of pigs was present as glucose and soluble α (1-4) maltodextrins. The high abundance of glucose, maltose and maltotriose in the proximal SI indicates activity of brush border enzymes in the intestin allumen, which is exceeded by α-amylase activity. Furthermore, we found that in vivo starch digestion exceeded our in vitro predictions for rapidly digested starch, which indicates that the role of the stomach on starch digestion is currently underestimated. Consequently, in vivo glucose release of slowly digestible starches is less gradual than expected, which challenges the predication quality of the in vitro assay.