Promoting the High Solid Enzymatic Saccharification of Bamboo Shoot Shells via a Fed-Batch Strategy Based on Simplex-Centroid Mixture Design

This study aimed to enhance the enzymatic hydrolysis efficiency of bamboo shoot shell (BSS) and establish a high solid loading fed-batch enzymatic hydrolysis strategy for pretreated BSS. BSS was pretreated with five alkaline reagents (NaOH, KOH, NaHCO3, CH3COONa, and Na2SO3). NaOH demonstrated the best enzymatic performance, with glucose and xylose yields of 96.55% and 86.56% at 2% (w/v) solid loading, respectively. Based on this outcome, NaOH pretreatment conditions were further optimized, with 3% NaOH at 110 °C for 60 min identified as optimal. The yields of glucose and xylose under this condition were 98.11% and 93.64%, respectively. The hydrolysis kinetics of NaOH-pretreated BSS were analyzed using fractal kinetic modeling to understand its hydrolysis characteristics. This analysis indicated that a solid loading effect became apparent above 12.5% (w/v). Subsequently, the simplex-centroid mixture design was employed to optimize feeding ratios at 6 h, 12 h, 24 h, and 36 h to obtain maximum sugar concentration at an initial solid loading of 20% (w/v) and a final solid loading of 40% (w/v). The total sugar concentration reached 249.55 g·L−1 in the optimal fed-batch strategy by this model, which was higher than that of 225.91 g·L−1 in the batch group. When the solid loading was further increased to 45% (w/v), the total sugar concentration reached 269.49 g·L−1. Notably, the above strategy is limited by an enzyme loading of 15 FPU·g−1 glucan and product inhibition at high solid loading, with industrial scalability still needing further exploration. Overall, this model demonstrated significant potential for increasing the sugar concentration in fed-batch strategies for pretreated biomass.