In vitro gas production as a method to compare fermentation characteristics of steam-flaked corn

An in vitro gas production technique was used to determine differences in starch availability that occurred with steam flaking of corn among eight feed mills (MILL) in California. Whole corn (WC) and steam-flaked corn (SFC) grain samples were obtained from six commercial mills and two mills at the University of California (Davis and El Centro, CA). The WC sample was collected prior to the steam chest and represented unprocessed corn. The SFC sample was collected at the rolls and represented a typically processed corn. Ground samples of WC and SFC were evaluated by incubation in buffered rumen fluid using an in vitro gas technique for a 72 h incubation period to compare processing (PROCESS) method. Starch reactivity was determined as the percentage of starch degraded to glucose by amylase after 4 h of incubation. Starch reactivity of SFC was higher (P<0.01) than WC. Starch reactivity was different for MILL (P<0.01) and the interaction of MILL and PROCESS was significant (P<0.01). Total gas produced at 8 h of incubation was higher (P<0.01) for SFC than WC, but total gas production did not differ for PROCESS at 24 and 72 h. Gas production after 8 h also differed for MILL (P<0.01). Time required for 25, 50, 75, and 90% disappearance of starch was estimated and in general disappearance of starch occurred sooner for SFC than WC. Fifty percent disappearance of starch occurred at 6.8 h for WC and at 5.5 h for SFC. Total volatile fatty acids (VFA) production did not differ for MILL or PROCESS at 8 or 72 h of incubation. Propionate production was higher (P<0.01) for SFC than WC at both 8 and 72 h. This in vitro gas production technique can be used to determine the effect of grain processing on fermentation rate and to identify differences among mills in potential digestibility of the processed grain.