Influence of corn hybrid, protease and methods of processing on in vitro gas production

An in vitro rumen gas production technique was used to compare four corn hybrids and two methods of processing. The hybrids varied in the proportion of vitreous starch in their endosperm. Hybrids were 553 (55VT), 606 (60VT), 632 (63VT) and 649 g/kg endosperm (65VT) vitreous starch. Each hybrid was dry rolled at 0.67 kg/L and steam flaked at 0.33 kg/L. The vitreous and floury endosperm fractions were isolated ground, processed corn particles were also pretreated with protease prior to incubation. Total gas produced at 8 h was highest for hybrid 55VT and lowest for hybrids 63VT and 65VT. Total gas production reflected in vitro fermentation of starch. Total gas produced after 24 and 72 h of incubation was not different among hybrids. Steam flaking increased total gas produced at 8 and 24 h of incubation compared to dry rolling but by 72 h there was no difference. Total gas produced was significantly higher at 8 and 72 h of incubation for floury than vitreous endosperm. Protease treatment markedly increased total gas produced at 8 and 24 h but not 72 h of incubation. There were significant interactions between hybrid and process and between process and enzyme treatment at 8 h of incubation. These interactions demonstrated that processing (dry rolling versus steam flaking), protease treatment, and difference in floury and vitreous endosperm reduced the differences in starch fermentation of different hybrids. In vitro rumen gas production can be used as a method to distinguish differences in starch fermentation of corn hybrids and the impact of various methods of starch processing and treatment on starch availability.