Optimisation and Comparative Analysis of Alkaline Pre-treatment of Defatted Spent Coffee Ground to Increase Sugar Recovery
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UNIVERSITI MALAYSIA SARAWAK
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Spent coffee grounds (SCG) have the potential as a raw material for producing valuable products due to their cellulose and hemicellulose content. However, their complex lignocellulosic structure makes sugar extraction challenging. Effective pre-treatment and enzymatic hydrolysis are therefore essential to maximise sugar recovery. This study optimised the alkaline pre-treatment of defatted SCG following enzymatic hydrolysis using Response Surface Methodology (RSM) of 5-level, 3-factor Central Composite Design (CCD) by examining the effects of alkaline concentration, temperature, and incubation time on reducing sugar yield after enzymatic hydrolysis to maximise reducing sugar recovery. The optimal conditions for KOH pre-treatment were 3% (w/v) KOH concentration at 90 ℃ for 2 h, yielding a 2.97-fold increase, while NaOH pre-treatment at 3% (w/v) NaOH, 85 ℃ for 1 h achieved a 3.28-fold increase over the control. For second phase of the study, acid pre-treatment was combined with alkaline pre-treatment. Acid was included for its effectiveness in hydrolysing hemicellulose and was used synergistically with alkaline pre-treatment, which primarily removes lignin. Following pre-treatment, enzymatic hydrolysis with cellulase was applied to convert cellulose into glucose. To compare pre-treatment strategies, one-step pre-treatment methods using either alkali (KOH, NaOH) or acid (H₂SO₄), and two-step pre-treatment combinations (acid–alkali and alkali–acid), were statistically evaluated using One-Way ANOVA. Results showed that two-step pre-treatment achieved the highest sugar recovery (4.25–4.70 folds) which significantly greater than one-step pre-treatment methods (1.50–3.28 folds), demonstrating the synergistic effect of acid-base combinations to enhance lignin removal, hemicellulose solubilisation and enzyme accessibility, thereby improving reducing sugar release. This study explores the valorisation iv of SCG into reducing sugars by offering a sustainable solution to mitigate the environmental impact of SCG disposal.