Effect of different corn processing methods on starch gelatinization, granule structure alternation, rumen kinetic dynamics and starch digestion

Abstract

In this study, the effect of four corn processing methods including grinding (G), dry-rolling (DR), steam-flaking (SF) and super-conditioning (SC), on corn starch parameters viz. gelatinization, granule structure alternation, rumen kinetic dynamics and the extent and site of starch digestion were compared. In addition, physical properties, chemical composition, gas production (GP), pH, ammonia nitrogen (NH3-N) and volatile fatty acids (VFAs) of batch culture after 24 h were determined. The apparent density of the SC corn resembled that of the G corn (0.758 vs 0.837 kg/L); however, its geometric mean of particle size (3.39 mm) was greater than that of the G corn (1.56 mm) and smaller than that of the SF corn (5.43 mm). In addition, dry matter (DM), ether extract (EE) and neutral detergent fiber (aNDF) were not significantly affected (P > 0.01) by the processing method. The starch content of the SC and SF corns were greater (P < 0.01) than that of the DR and G corns. GP after 6, 12 and 24-h incubation and GP rate were greater (P < 0.01) in the SC corn; nevertheless, GP at 48-h incubation was the same in SC and SF corns (P> 0.01). The pH and NH3-N of batch culture after 24-h were significantly lower (P < 0.01) in the SC corn than in the other processing methods. The SF corn increased (P < 0.01) acetate and acetate to propionate ratio, but decreased (P < 0.01) propionate while the SC corn reduced (P < 0.01) acetate and acetate to propionate ratio, but raised propionate (P < 0.01). The time required for 25 % and 75 % fermentation of substrate was significantly reduced by the SC corn (P < 0.01). The highest starch gelatinization (P < 0.01) was obtained from SC, followed by SF corn. The rapidly soluble fraction (a) for DM, starch and CP was greater (P < 0.01) in the SC corn than in other processing methods; however, the slowly degradable fraction (b) for DM and starch was lower (P < 0.001) in the SC corn than in other methods. Although the effective rumen degradability of DM (ERDDM) remained unchanged (P> 0.01), the effective rumen degradability of starch (ERDS) and the effective rumen degradability of protein (ERDCP) were found to be greater in the SC corn than in other processing methods (P < 0.01). Ruminal and total tract digestibility of starch increased (P < 0.01) in the SC corn, but intestinal DM (P = 0.002) and starch (P < 0.01) digestibility of the SC corn diminished. The ruminal CP digestibility was lower (P = 0.06) in the SF corn than in the SC corn; however, SC and SF corns showed greater intestinal (P = 0.005) and total tract (P = 0.021) CP digestibility. The results indicated more starch gelatinization in the SC process in terms of higher exposure of particles to conditioning and homogenization, which enabled the alteration of starch granules and the protein matrix in the endosperm of corn. Furthermore, the SC process could influence the rumen kinetic dynamics, the extent and site of starch digestion as well as the efficiency of using starch under in vitro and in situ conditions.