Impact of mammalian enzyme pretreatment on the fermentability of carbohydrate-rich feedstuffs

Several carbohydrate-rich substrates (spent brewer's grains, potato peel, potato starch, wheat bran, sugarbeet pulp and a maize-based standard diet for pigs) were pretreated with digestive enzymes, and the in vitro fermentability of these treated substrates and their untreated counterparts was assessed using the cumulative gas production technique. A comparison was also made between the enzyme-treated (ET) and untreated (UT) standard diet for pigs, and chyme which originated from pigs fed that diet, to determine whether the enzyme treatment resulted in material with similar fermentability to that reaching the large intestine in vivo. The enzyme pretreatment was performed according to a modified in vitro method of Babinszky et al (J Sci Food Agric 50:173-178 (1990)). Generally, it was shown that the fermentabilities of the ET and UT substrates were different. There was also a significant difference between the fermentation characteristics of the ET diet and chyme. Chyme produced less gas (P < 0.05), and the time at which half of the gas had been produced (C) occurred later (P < 0.05). The maximum rate of fermentation (R-M) was slower for chyme (P < 0.05). Fermentation of chyme led to more ammonia (P < 0.05) and a tendency to more volatile fatty acids at the end of fermentation. These differences in fermentability of the ET diet and chyme (from pigs fed the same diet) may be the result of differences which relate purely to the action of the enzymes chosen to work in vitro, compared with those which are actually present in vivo. However, the results also suggest that it is not only enzymatic digestion which is occurring in the small intestine. This is an important consideration when using ileal techniques to determine digestibility of feedstuffs. (C) 2003 Society of Chemical Industry.