Enzyme-free pretreatment of brewer’s spent grain for xylose recovery for potential xylitol production

Abstract

Brewer’s spent grains (BSG), a by-product in beer brewing, have historically been relegated to animal fodder. This study delves into the untapped potential of BSG as a valuable source of fermentable sugars, specifically xylose. Proximate analysis confirmed the presence of xylan-rich hemicellulose (21.5 ± 0.32%) in BSG, making it ideal for xylose production. The FTIR spectrum of BSG confirmed peaks at 900–950 cm⁻¹ corresponding to hemicellulose xylan. A combined pretreatment of BSG by hydrothermal (110 °C) and acid hydrolysis (100 °C) resulted in 50.11 ± 0.15% of reducing sugar recovery as quantified by Lane and Eyon method again reconfirmed by HPLC with 48.15 ± 0.05 g/L of xylose. GC-MS analysis of pre-treated BSG hydrolysate revealed presence of some inhibitory compounds with mass spectra viz. Levoglucosenone, 9,12-octadecadienoic acid, n-hexadecenoic acid and furfural derivatives. Further the BSG hydrolysate obtained after combined pretreatment was further used as a carbon source in addition to other ingredients of medium. A preliminary fermentation trial with Pichia fermentans was carried out at 30° C, at pH 7.0 for 24 h and resulted in 6.13 ± 0.05 g/L xylitol production at 30 °C at 150 RPM. The results validated the effectiveness of the pre-treatment in maximizing fermentable sugar recovery and give conformity for further optimization of xylitol production making it enzyme free and cost-effective approach.Graphical Abstract