In vitro gas and volatile fatty acids production profiles of barley and maize and their soluble and washout fractions after feed processing

In vitro fermentation characteristics of soluble, washout, and non-washout fractions separated from barley and maize and their technologically processed (i.e., pressure toasting, pelleting and their combination) products were measured. The aim was to establish whether the soluble equaled the washout fraction, whether these fractions are rapidly and completely fermented, and whether their fermentation characteristics are the same. A simple fractionation method was developed to separate the whole grain into a soluble fraction, a washout fraction, an insoluble washout fraction, and a non-washout fraction. Proximate analysis of the different fractions revealed in the soluble fraction a large (>400 g kg−1 DM) residual organic matter component of unknown origin, while the insoluble washout fraction contained between 800 and 900 g starch/kg DM. Fermentation characteristics of all fractions as well as the whole grain were measured for 72 h using gas and volatile fatty acids (VFA) production in vitro. After fractionation, gas and VFA production profiles of the fractions with different chemical compositions were found to be different. Based on gas production profiles it was shown that the soluble fraction was easily fermentable and was fermented faster than the insoluble washout and the non-washout fraction. Differences were however much smaller than anticipated, which would suggest that the extent of fermentation of washout fractions in the rumen is incomplete. The maximum gas and VFA production from the soluble fraction was always lower than that of the insoluble washout, and the non-washout fraction. The combination of pressure toasting and pelleting reduced fermentability both in terms of gas and VFA production compared with the other treatments.