Enhancement of selected essential amino acids via soy pulp solid state fermentation

This research evaluates the enhancement of essential amino acids namely tryptophan, lysine, methionine, valine and isoleucine from soy pulp by using solid state fermentation. The essential amino acids were selected based on their importance and functions in fish nutrition. In this study, eight bacteria were isolated from solid state fermented soy pulp and screened for isoleucine, valine, methionine, lysine and tryptophan enhancement activities. The potential bacteria strain (S1, S2, S3, S4, S5, S6, S7, and S8) were inoculated into solid state medium (soy pulp, 95.5%; yeast extract, 2 %; ammonium sulphate, 2 %; 0.5 % glucose v/v) and subjected to solid state fermentation for 8 days. Then, the fermentation period (0, 4, 8, 12 days) were screened using the bacteria that successfully enhanced total essential amino acids. After that, the bacteria were screened for carbon source type (glucose, molasses, and sucrose). The best carbon source was screened for the optimum concentration (0, 2, 4, 6, 8, and 10 % v/v) to be subjected in the solid state fermentation. The finding of screening test shows that bacteria S1 assay performs the highest total EAA bacteria (42.9±19.50gL-1). This is followed by S3 (28.2±5.21gL-1), S7 (23.2±5.29 gL-1), S5 (18.8±1.70 gL-1), S4 (30.0±14.0gL-1), S8 (19.9±2.38 gL-1), S2 (20.3±4.31gL-1) and S6 (13.9±0.46 gL-1). Bacteria strain S1 was then identified as Bacillus cereus strain (MH027625) by Polymerase Chain Reaction (PCR) assay and sequencing. The screenings of fermentation period, carbon source type and carbon concentration show that the highest enhancement of total essential amino acids were at day 8 fermentation using sucrose as carbon source with concentration of 2 % v/v. In order to optimize the enhancement of total essential amino acids from soy pulp solid state fermentation, a response surface method (RSM) involving a Central Composite Design (CCD) was applied. Two variables, namely fermentation period (0-12 days) and sucrose concentration (2% v/v) were selected as independent variables for the optimization using RSM. The dependant variable was quantified as concentration of total essential amino acids enhancement. The optimum conditions for total essential amino acids were enhanced by fermentation condition of 8 days of fermentation and 2 % v/v sucrose concentration and the predicted response by RSM (321.6 gL-1) closely matched the experimental response (316.0 gL-1). The results indicated that the total essential amino acids enhancement is high (345.99 gL-1).