Tea processing steps affect chemical compositions, enzyme activities, and antioxidant and anti-inflammatory activities of coffee leaves

Abstract

Coffee leaves have been processed into a tea-like beverage; however, how tea processing steps affect the chemical compositions and the bioactivities remain unknown. In the present study, the impacts of tea processing steps on the proximate compositions, phytochemicals, enzyme activities, and the antioxidant and anti-inflammatory activities of coffee leaves were investigated. The results showed that although soluble protein, soluble sugar, and phenolics were increased during withering, they were gradually decreased in the sequential processing steps associated with the decreases in the antioxidant activity and nitric oxide inhibitory activity in lipopolysaccharide (LPS)-induced RAW264.7 cells. Coffee leaves treated with the kill-green process possessed greater phenolics and antioxidant activity compared with the no kill-green counterparts due to the lower polyphenol oxidase and peroxidase activities found in the no kill-green coffee leaves. Coffee leaves significantly inhibited the expressions of proteins (tumor necrosis factor-alpha [TNF-α] and prostaglandin E2 [PGE-2]) proteins and genes (inducible nitric oxide synthase [iNOS] and cyclooxygenase 2 [COX-2]); however, tea processing steps have lesser effects on the anti-inflammatory activity. Our study indicated that kill-green is the crucial processing step to affect the phenolic composition and bioactivity of coffee leaf tea processed with the kill-green process; however, for the coffee leaves processed without the kill-green process, rolling and fermentation are the key influencing steps.