Composition Retention Metrics Reveal Route-Specific Controls of Glucose Release from Pretreated Kenaf Core

Lignocellulosic sugar production relies on pretreatments that improve enzymatic digestibility without excessive loss of recoverable solids and carbohydrates. This study benchmarks autohydrolysis, dilute-acid (H2SO4), and alkaline (NaOH) pretreatments of kenaf core and introduces a retention-aware interpretation framework based on two complementary composition descriptors for cellulose, hemicellulose, and lignin: a relative composition ratio (R) that captures enrichment/depletion in the recovered solid and an absolute retention index (AR) that incorporates solid recovery to quantify true feedstock-basis retention. Glucose release was evaluated using paired yield bases (recovered-solid and raw-feedstock) together with solid yield and cellulose conversion to decouple digestibility from composition-driven enrichment effects. Across routes, recovered-solid-basis glucose yield reached 38.8% (autohydrolysis) and 37.6% (dilute acid) at moderate solid yields, whereas alkaline pretreatment combined higher recovery (up to 72.4%) with moderate-to-high digestibility (13.6–37.6%). Raw-feedstock-basis glucose yield ranged from 1.20–23.30% (autohydrolysis), 1.30–19.70% (dilute acid), and 8.70–18.00% (alkaline), showing that mass loss can offset apparent gains in digestibility. Route-resolved LOESS trends and quadratic response surfaces identify hemicellulose depletion as the most consistent predictor of glucose release, while lignin enrichment is not transferable across chemistries; AR-based lignin retention becomes a graded separator primarily under alkaline conditions. The results support routine paired reporting of R/AR metrics with solid yield, yield basis, and cellulose conversion for defensible cross-route comparison.