Microencapsulated Spent Coffee Grounds Extracts Inhibit Enzymatic Browning In Vitro and In Silico

Abstract

Enzymatic browning, a reaction catalyzed by polyphenol oxidase (PPO), occurs when polyphenolic compounds in freshly cut produce are exposed to oxygen, reducing sensory quality and consumer acceptability. This study investigated the use of microencapsulated spent coffee grounds (SCG) as a natural inhibitor of browning in 100% apple juice. Phytochemicals were extracted using ultrasound-assisted solvent extraction and subsequently microencapsulated via freeze-drying with maltodextrin, gum arabic, and their combination (1:1) as carrier agents. The encapsulated extracts were evaluated for phenolic and flavonoid content, antioxidant capacity, and anti-browning activity using colorimetric analysis and molecular docking. At the same time, structural characteristics were confirmed using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and encapsulation efficiency assessment. The results indicated successful encapsulation, with efficiencies exceeding 70%, and morphology and spectra image confirmed the incorporation of phenolic compounds. Amongst the six identified phenolic compounds, trans-ferulic acid was identified as the predominant phenolic compound (14.50 mg/g), while p-coumaric acid was present at lower levels (0.60 mg/g). Application of microcapsules in apple juice significantly reduced the browning index (29.91, 22.43, and 21.48) and increased lightness (78.63, 82.24, and 81.42) over a five-day storage period, demonstrating potential anti-browning of activity. Molecular docking further revealed that flavonoids such as quercetin, luteolin, and apigenin exhibited strong binding affinity for PPO, suggesting their potential as enzymatic inhibitors. Overall, the findings provide primary evidence for the potential use of SCG-derived polyphenols as sustainable, natural antioxidants, contributing to agro-waste valorization.