Optimization of dilute acid pretreatment of barley husk and oat husk and determination of their chemical composition

Abstract

The pretreatment of renewable resources is the first step to make them metabolically available for microorganisms for generation of value-added products by fermentation. In this research, barley husk (BH) and oat husk (OH) were used as renewable resources to study the optimization of dilute acid pretreatment conditions by using Response Surface Methodology (RSM). Temperature (T, 110–130 °C), solid-to-liquid ratio (S:L, 1:8–1:16 w/v), dilute sulfuric acid concentration (DSA, 1–5%, v/v), and pretreatment time (t, 30–90 min) were selected as independent variables. Their levels were specified by one-factor-at-a-time (OFAT) method according to statistically significance level (p = 0.05). OFAT results indicated that the independent variables for optimization of acid pretreatment conditions of the renewable resources were T (120–130 °C), S:L (1:8–1:12 w/v), and DSA (1–3% v/v) for BH; T (120–130 °C), S:L (1:8–1:12 w/v), and t (10–30 min) for OH. Optimum pretreatment values were 130 °C, 1:8 (w/v), 1.86% (v/v), and 30 min for BH and 130 °C, 1:8 (w/v), 1% (v/v), and 19 min for OH by using Box-Behnken RSM. Under optimal conditions, fermentable sugar concentration, total phenolics, and extract yield were determined to be 76.28, 1.12 g/L, and 55% for BH and 59.63 g/L, 0.70 g/L, and 56% for OH, respectively. Additionally, the chemical composition of hydrolysates was also evaluated in terms of maltose, glucose, xylose, arabinose, mannose, galactose, phenolics, 5-hydroxymthylfurfural, 2-furaldehyde (2-F), formic acid, and acetic acid. Catalytic efficiency values of sulfuric acid for BH and OH were 21.58 and 8.35 g/g, respectively. Consequently, this study clearly indicates that the hydrolysates from the renewable resources can be used as feedstocks for the production of value-added products by biotechnological processes.