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

Abstract

This study aimed to examine in vivo starch digestion kinetics and to unravel the mechanisms of starch hydrolysing enzymes. Ninety pigs (23 (sd 2·1) kg body weight) were assigned to one of nine treatments in a 3×3 factorial arrangement, with starch source (barley, maize, high-amylose (HA) maize) and form (isolated, within cereal matrix, extruded) as factors. We determined starch digestion coefficients (DC), starch breakdown products and digesta 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 HA maize by 0·20–0·33 DC units (P<0·01). In SI3–4, barley starch were completely digested, whereas the cereal matrix of maize hampered digestion and generated 16 % resistant starch in the small intestine (P<0·001). Extrusion increased the DC of maize and HA maize starch throughout the small intestine 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 small intestine indicates activity of brush-border enzymes in the intestinal lumen, 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 starch is less gradual than expected, which challenges the prediction quality of the in vitro assay.

Whole digesta properties as influenced by feed processing explain variation in gastrointestinal transit times in pigs

“…In our study, we observed a longer MRT of solid digesta in the SI of pigs fed IB compared with pigs fed GB. Numerically, the difference in MRT is largest in SI3 (Table 1), where the digestion coefficient of starch originating from GB (0•87) was lower than that of IB (0•96) (26) . Consequently, the longer MRT of IB seems to be caused by other components in the feed matrix than starch, which were mainly soyabean meal and soyabean hulls in the IB diet.…”

“…This relation appears more complex in the case of solids, as the behaviour of the solid fraction of digesta depends greatly on the properties of the particulate matter. Compared with the diets with ground and extruded cereals, the diets with isolated starch were richer in soyabean hulls, soyabean meal and sugar beet pulp (26) . These ingredients generally have higher WHC than maize and barley meals (47) .…”

“…The experiment described in the present paper was part of a larger study on starch digestion kinetics, which is described in detail elsewhere (26) . The experiment was approved by the Dutch Central Committee of Animal Experiments under the authorisation number AVD260002016550.…”

“…All diets were formulated to be identical in crude protein, fat and total dietary fibre content, using soyabean meal, soyabean hulls, soyabean protein isolate, soyabean oil and sugar beet pulp. Details on ingredients, production conditions and the analysed composition are described elsewhere (26) . Cr and Co were included as markers in the feed at a level of 170 mg/kg to study digesta passage behaviour of solid and liquid digesta fractions, respectively.…”

“…Prior to dissection, pigs were sedated and exsanguinated as described in detail elsewhere (26) . Immediately after exsanguination, clamps were placed between gastrointestinal sections to prevent the movement of digesta and the GIT was carefully removed.…”