Bacillus subtilis Fermentation for Enhancement of Feed Nutritive Value of Soybean Meal

Abstract In order to increase the nutritional quality of soybeanmeal (SBM) as an animal feed, Bacillus subtilis TP6, a previouslyisolated strain from an Indonesian traditional fermented soybeanfood, Tempeh, was used as a starter organism for solid-statefermentation. In the pre-treated SBM with water content of 60%(v/w), B. subtilis TP6 was grown to a maximum viable cellnumber of 3.5×10 9 CFU/g. Compared to control, crude protein inBacillus fermented SBM was increased by 16%, while raffinose,stachyose, and trypsin inhibitors were reduced by 31, 37, and90%, respectively. The Sodium dodecyl sulfate-polyacrylamidegel electrophoresis analysis showed that proteins in the fermentedSBM were remarkably hydrolyzed into smaller molecular masses,resulting in a decrease in large sized proteins. Our data suggestedthat B. subtilis fermentation could increase the nutritive value ofSBM through reduction of anti-nutritive factors and improvementof protein quality by hydrolysis of soy protein. In addition, B.subtilis TP6 produced a functional ingredient, poly-γ-glutamicacid which has various health benefits.Keywords animal feed · Bacillus subtilis · soybean meal · trypsin inhibitorIntroductionSoybean (Glycine max) is an oilseed crop belonging to the familyLeguminosae and one of the world’s largest and most efficientsources of plant protein. Soybean meal (SBM), which is abyproduct remaining after extraction of oil from soybean, hasbecome the most important source of protein for poultry and otherlivestock, due to its high concentration of protein and excellentprofile of essential amino acids in comparison to other plant proteinsources (Park, 1987; Adeola, 1996; Emmert and Baker, 1997;Boonyaratpalin et al., 1998). SBM contains around 40−50%protein and is a rich source of the amino acids including lysine,tryptophan, threonine, isoleucine, and valine that are deficient incorn, grain sorghum and other cereal grains used for animal feed(Emmert and Baker, 1997; Kim et al., 2012). Nutritive value of SBM is limited by several anti-nutritionalfactors such as protease inhibitor, oligosaccharide, and phytic acidthat interfere with digestion, absorption, and utilization of nutrientsin the diet (Liener, 1981; Grant, 1989). SBM possesses high contentof protease inhibitors that adversely affect protein digestibility andamino acid availability. Especially, the presence of trypsin inhibitorsin animal feed has been implicated in growth inhibition andpancreatic hypertrophy (Liener, 1981; Grant, 1989; Gumbmann etal., 1989; Friedman et al., 1991). Oligosaccharides such as raffinoseand stachyose are also poorly utilized by some species of animals,and fermentation of these oligosaccharides in the lower gut causesthe production of gastrointestinal gases (Krause et al., 1994). Mostphosphorus present in SBM is in the form of phytic acid, whichis generally indigestible by monogastric animals such as poultryand swine (Grant, 1989). The level of anti-nutritional factors canbe reduced by heating during the processing of soybean (Ratnerand Crawford, 1955; Friedman et al., 1991). However, an excessof heat may increase Maillard reactions between amino acids and