Evaluation of the chemical constituents, antioxidant and enzyme inhibitory activities of six Yemeni green coffee beans varieties

Coffee arabica L. is an economical crop cultivated in many countries including Yemen. The present study evaluated the phytochemical contents of the methanolic extracts, prepared by maceration, of six Yemeni green coffee beans varieties namely Esmaeli, Hamadi, Harazi, Mattari, Odaini and Yafei. Antioxidant (phosphomolybdenum, antiradical, reducing power and ferrous chelating), and enzyme inhibition activity of the extracts against acetylcholinesterase butyrylcholinesterase, tyrosinase, α-glucosidase, and α-amylase were also studied. Quantification of total phenols revealed that all green beans varieties were richer in their total polyphenolic (63.77–110.98 mg gallic acid equivalent per g of extract) content than their flavonoids one (2.86–5.57 mg rutin equivalent per g of extract). HPLC-MS/MS analysis of 30 selected bioactive compounds showed that all varieties had the same types of phytoconstituents with differences in their relative abundance. Caffeine (1613.89–2466.38 μg/g) followed by 5-caffeoylquinic acid (1017.63–1313.39 μg/g) were the dominant compounds in all varieties with caffeine more abundant in Esmaeli variety while 5-caffeoylquinic acid in Odaini variety. All varieties displayed a pronounced antioxidant property in all the in vitro assays with Odaini variety significantly (p < 0.05) exerted the highest anti-DPPH radicals (253.96 mg Trolox equivalent (TE)/g), metal chelating (19.73 mg Disodium edetate equivalents/g), Cu2+ (441.11 mg TE/g) and Fe3+ (221.04 mg TE/g) reducing activities. Furthermore, the majority of green coffee beans varieties showed comparable enzyme inhibition property with highest activity recorded against tyrosinase (39.35–46.96 mg kojic acid equivalents/g) and acetylcholinesterase (1.80–2.17 mg galanthamine equivalents/g) enzymes. In conclusion, all Yemeni green coffee beans varieties have proven to be rich source of biochemicals with beneficial impact on human health and could be of significant applications in food, pharmaceutical and cosmetics industry.