Abstract
Hypoallergenic antibacterial low-molecular-mass peptides were produced from defatted soybean meal in a membrane bioreactor. In the first step, soybean meal proteins were digested with trypsin in the bioreactor, operated in batch mode. For the tryptic digestion of soybean meal protein, optimum initial soybean meal concentration of 75 g/L, temperature of 40 °C and pH=9.0 were determined. After enzymatic digestion, low-molecular-mass peptides were purified with cross-flow flat sheet membrane (pore size 100 µm) and then with tubular ceramic ultrafiltration membrane (molecular mass cut-off 5 kDa). Effects of transmembrane pressure and the use of a static turbulence promoter to reduce the concentration polarization near the ultrafiltration membrane surface were examined and their positive effects were proven. For the filtration with ultrafiltration membrane, transmembrane pressure of 3·105 Pa with 3-stage discontinuous diafiltration was found optimal. The molecular mass distribution of purified peptides using ultrafiltration membrane was determined by a liquid chromatography-electrospray ionization quadrupole time-of-flight mass spectrometry setup. More than 96% of the peptides (calculated as relative frequency) from the ultrafiltration membrane permeate had the molecular mass M≤1.7 kDa and the highest molecular mass was found to be 3.1 kDa. The decrease of allergenic property due to the tryptic digestion and membrane filtration was determined by an enzyme-linked immunosorbent assay and it was found to exceed 99.9%. It was also found that the peptides purified in the ultrafiltration membrane promoted the growth of Pediococcus acidilactici HA6111-2 and they possessed antibacterial activity against Bacillus cereus.
Highlights
Leguminous soybean (Glycine max) is considered the largest edible protein source around the world [1]
Trypsin inhibitor activity is adequately reduced by the heat treatment during the production of soybean meal, the allergenic effect of soybean meal proteins renders this by-product an inadequate source of essential amino acids [5]
Buffered suspension of the soybean meal at appropriate concentration was prepared for enzymatic reaction and the substrate was preincubated under fixed operational temperature of 40 °C
Summary
Leguminous soybean (Glycine max) is considered the largest edible protein source around the world [1]. Soybean meal contains 40–45 % (on mass basis) protein and its application is mostly limited to broiler and fish feed [3,4]. Trypsin inhibitor activity is adequately reduced by the heat treatment during the production of soybean meal, the allergenic effect of soybean meal proteins renders this by-product an inadequate source of essential amino acids [5]. To avoid this problem, production of hypoallergenic low-molecular-mass (LMM) peptides (protein hydrolysate) from defatted soybean meal is considered a reliable approach [6,7]
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