Potential contribution of Amadori compounds to antioxidant and angiotensin I converting enzyme inhibitory activities of raw and black garlic

Abstract

Black garlic extracts had higher antioxidant and angiotensin I converting enzyme (ACE) inhibitory potential than raw garlic extracts. Black garlic extract contained large amounts of Amadori compounds (ACs), especially N-(1-deoxy-D-fructos-1-yl)-l-arginine (Fru-Arg) (1.0–5.0 mg/g), while no ACs were detected in raw garlic extracts. The antioxidant potential of eight individual ACs present in black garlic was characterized in FRAP, ABTS and ORAC assays. ACs had moderate FRAP values, 2–5 times lower than ascorbic acid (AA). The Fe3+ reducing mechanism of ACs probably includes 2, 3-enolization of the carbohydrate of ACs and formation of the enolate complex with Fe3+. Fru-Arg and N-(1-deoxy-D-fructos-1-yl)-l-phenylalanine could effectively scavenge ABTS radical, nearly the same scavenging activities as AA or Trolox. N-(1-deoxy-D-fructos-1-yl)-l-methionine (Fru-Met) followed by N-(1-deoxy-D-fructos-1-yl)-l-histidine had almost the same ORAC power with AA and at low concentrations, Fru-Met even showed higher ORAC value than AA. These results suggest that ACs probably contributed to antioxidant and ACE inhibitory activities of black garlic extract.