Bioconversion of wheat bran into high value-added products and modelling of fermentations

The objectives of this study were to determine the particle size of wheat bran (WB), to optimize the pretreatment conditions of WB and to produce ethanol (EtOH), lactic acid (LA), and inulinase (Iase) from acid-pretreated and non-detoxified wheat bran. Another objective was to predict the experimental production data of the fermentations using mathematical models. It was found that the optimum acid-pretreatment conditions of WB were 1 min of pretreatment time, 1.99% (v/v) dilute-acid ratio, and 11.97:1 of liquid-to-solid ratio (v/w) at a fixed temperature (121 °C). Under optimal conditions, the levels of reducing sugar, phenolics, glucose, xylose, arabinose, acetic acid, 5-hydroxymethyl furfural, 2-furaldehyde and the catalytic efficiency (E, g sugar/g inhibitor) were 41.08 g/L (0.49 g sugar/g biomass), 468.10 mg/L, 17.66 g/L, 6.93 g/L, 3.78 g/L, 0 g/L, 247.84 mg/L, 7.27 mg/L, and 39.28 g/g, respectively. Maximum EtOH and LA yields were obtained as 30.44% (3.85 g/L, 59.57% of theoretical yield) and 66.68% (9.09 g/L) when the free Scheffersomyces stipitis (ATCC 58,784) and the immobilized Lactobacillus casei were used, respectively. Nevertheless, Iase activity (I), invertase-type activity (S) and S/I ratio were 116.85 U/mL, 44.88 U/mL and 0.38 when Aspergillus niger A42 was employed, respectively. As concerning mathematical modeling, Huang model was more successful than Baranyi model in predicting the experimental production data. Overall, WB can be used as a good substrate source for production of value-added products by microbial processes.