Antioxidant potential of low-grade coffee beans

Low-grade coffee beans (triage) are widely known to adversely affect the beverage quality. These represent about 15–20% of coffee production on weight basis and attempts are being explored for their utilization. These beans were evaluated for the physico-chemical characteristics and subjected to soxhlet extraction using the solvents (viz., hexane, chloroform, acetone and methanol successively). The extracts were evaluated for antioxidant potential through in vitro models such as radical scavenging activity (α,α-diphenyl-β-picrylhydrazyl radical), antioxidant activity (β-carotene-linoleate model system), reducing power (iron reducing activity) and antioxidant capacity (phosphomolybdenum complex). Highest yield of extract (12%) was obtained with methanol followed by hexane (8%) and chloroform (1.5%). Lowest was obtained with acetone (<1%). Also, it was observed that methanol extract was found to exhibit maximum radical scavenging activity (92.5%) followed by extracts obtained with acetone (81%) and chloroform (25%) at 100 ppm concentration. Further, the methanol extract showed antioxidant activity (58%) at 100 ppm concentration, while the other extracts viz., acetone, chloroform and hexane exhibited 44%, 28%, and 14%, respectively, at the same concentration. The antioxidant capacity of the methanol extract and propyl gallate showed 1367 ± 54.17 and 5098 ± 34.08 μmol/g (as equivalents to ascorbic acid). Reducing power of the extract and standard compounds is in the following order ascorbic acid > chlorogenic acid > BHA > methanol extract. The methanol extract was found to contain total phenolics (21.90 ± 0.50%), chlorogenic acid (34.16 ± 0.27%) and caffeine (8.25 ± 0.36%). The high antioxidant potential of the methanol extract of low-grade coffee beans is due to the presence of phenolic compounds including chlorogenic acids, which make them more suitable as a source of natural antioxidant and their utility can be explored in food industry.