Optimization of holocellulose extraction from spent coffee grounds using factorial design

Abstract

Spent coffee grounds (SCG) represent a substantial environmental challenge due to the massive generation of solid waste and its high organic load. However, SCG is a promising source of lignocellulosic biomass for the production of high-value biopolymers. This study aimed to optimize the extraction of holocellulose from SCG via oxidative bleaching using sodium hypochlorite (NaOCl), employing a 2³ factorial design with a central point. The effects of NaOCl concentration (1.0--2.5%), reaction time (15--45 min), and temperature (25--55 °C) on the extraction yield were evaluated. Statistical analysis revealed that temperature was the most significant variable, accounting for approximately 52% of the yield variation, followed by NaOCl concentration (~37%). High temperatures and concentrations led to excessive oxidative degradation and hydrolysis of the polysaccharide chains, drastically reducing yields to below 20%. Conversely, mild conditions resulted in insufficient delignification. The experimental results indicated that the central point conditions (1.75% NaOCl at 40 °C for 30 min) offered the optimal balance, providing a yield of approximately 38% with adequate brightness and reduced degradation. These findings demonstrate the feasibility of using statistical design to obtain holocellulose from SCG for future applications in biocomposites and packaging.