Mechanistic insights into bitterness reduction of Robusta coffee by ultrasound-assisted oil solvent pretreatment: A combined experimental and computational study.

Robusta coffee is characterized by pronounced bitterness, which limits its consumer acceptance and application in high-end markets. This study proposed an ultrasonic-assisted oil-solvent (butter/coconut oil/palm oil/camellia oil/walnut oil) soaking pretreatment to modulate the taste quality of Robusta coffee. Electronic tongue analysis demonstrated that the pretreatment significantly reduced bitterness and astringency while enhancing the richness response. Targeted chemical analyses revealed decreases in key bitterness-related compounds, including caffeine and caffeoylquinic acids. Imaging analyses indicated that ultrasound-induced cell wall disruption facilitated oil penetration and improved mass transfer between the oil phase and the coffee matrix. Computational simulations further showed that fatty acids and bitter compounds formed stable non-covalent interactions mainly through van der Waals forces and hydrogen bonding. Although the pretreatment led to a reduction in the browning index and 5-HMF levels, it concurrently increased the formation of lipid oxidation products. Nevertheless, all safety indicators remained well within acceptable limits. Overall, this study provides a feasible food-grade strategy for flavor modulation of Robusta coffee.