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The Effect of Alcohol Treatments on Solubility and in Vitro and in Situ Digestibilities of Soybean Meal Protein

University of Illinois, Urbana 61801²

Abstract

Treatment of soybean meal (SBM) protein with alcohol-water solutions affected both solubility of protein in Burroughs mineral mixture and rate of disappearance from dacron bags between 2 and 8 h of in situ digestion. Minimum solubility was noted when solutions contained either 40% (v/v) isopropanol or propanol or 60% (v/v) ethanol. Denaturation of protein by propanol resulted in lower solubility than denaturation by ethanol or isopropanol (P<.05). For the alcohols combined, concentration of alcohol in the treatment solution produced a negative linear effect (P<.05) as well as a positive quadratic effect (P<.01) on rate of disappearance of crude protein from dacron bags. With propanol, rate of disappearance was lowest at 40% (v/v); with isopropanol, at 30% and with ethanol at 50%. After 8 h in situ digestion, the amount of protein residue from SBM treated with 50% ethanol was 163% of the protein left from untreated SBM. These values were 278% with 40% (v/v) propanol and 119% with 30% (v/v) isopropanol. No effect of alcohol treatments on the amount of protein residue remaining after 24 h in situ digestion was found, suggesting that alcohol treatment does not affect extent of protein digestion but rather rate of digestion. In vitro digestibilities of soluble proteins were quadratically affected by propanol and isopropanol treatments. Ammonia production from the soluble proteins was minimal after 24 h in vitro digestion at 40% (v/v) ethanol, 60% (v/v) propanol and 100% (v/v) isopropanol treatments. Ammonia release from total protein after 24 h in vitro digestion was lowest at 60% (v/v) ethanol, 40% (v/v) propanol and 40% (v/v) isopropanol. For all incubation times, the alcohol concentrations between 40 and 60% resulted in the lowest ammonia releases. These data suggest that alcohol treatment may increase the amount of SBM protein that escapes ruminal digestion when fed in practical diets.

¹ The senior author gratefully acknowledges the Stichting, Fonds Landbouw Export Bureau 1916/1918, Wageningen, the Netherlands, for partial financial assistance during his studies.

² Dept. of Anim. Sci.