The Effect of Different Coffee Cherry Pulp-Retention Amounts on the Quality of Robusta Green Coffee Beans

Robusta coffee (Coffea canephora) possesses great industrial potential, whereas its intrinsic flavor defects compromise market competitiveness. Honey processing utilizing residual pulp and mucilage is capable of improving green coffee quality; nevertheless, the absence of quantitative research regarding graded pulp retention limits its industrial application. In this study, fermentation experiments with gradient retention of coffee cherry pulp were conducted to clarify the differential regulatory effects of varying coffee cherry pulp-retention amounts on physicochemical properties, functional components and volatile flavor precursor compounds of Hainan Robusta coffee. Quantitative scoring of coffee quality using international standard cup measuring instruments and the grey relational analysis was further employed to comprehensive quality assessment. Compared with the 0% coffee cherry pulp-retention treatment, all other treatments showed higher levels of selected functional components and volatile flavor precursor compounds. The 66% coffee cherry pulp-retention treatment enriched key roasting flavor substrates: sucrose, organic acids, pyrazines, and esters were increased by 8.74%, 26.58%, 80.66% and 30.18%, respectively. Meanwhile this treatment exhibited significantly lower protein and alkaloid contents than the 100% and 33% coffee cherry pulp-retention treatments, and significantly lower flavonoid content than the 0% and 33% coffee cherry pulp-retention treatments. This treatment exhibited remarkably excellent cup scores by 80.35 and superior comprehensive quality, outperforming the other treatments by 6.05–18.51%. This study identifies the optimal coffee cherry pulp-retention ratio for Robusta coffee post-harvest honey processing, providing theoretical basis and feasible technical references for the quality improvement, standardized processing and industrial promotion of local Robusta coffee.