In vitro studies of conditions required to protect protein from ruminal degradation by heating in the presence of sugars

Carbon-14 labelled casein was heated for various times at a range of temperatures in the presence of 8% glucose, sucrose or xylose or 12.4% cane molasses in order to determine the effects of heating with sugars on the digestibility and degradation of protein. Digestibility and degradation were determined in vitro by procedures using pepsin-pancreatin and mixed rumen microorganisms, respectively. As the time and temperature of the heating increased, degradation was affected before digestibility, such that an efficacy window for producing protected protein became apparent, in which degradability was depressed without affecting digestibility. Higher temperatures and longer times resulted in products with impaired digestibility. All sugars tested, including molasses, decreased the time/temperature requirement for efficacy. Each sugar gave a different pattern, with xylose causing the greatest shift in the treatment window. Protection was obtained with xylose following incubation at 80 °C for 4 h, for example, whereas similar protection of casein alone required incubation at 160 °C for 4 h. Although more xylose (4%) was required for protection than other sugars (1% with glucose), its efficacy under relatively mild conditions could prove advantageous in processing feed proteins for ruminants.