Anthocyanins and phenolics content of Thai black soybean extracts and their prevention against myoglobin autoxidation

Anthocyanin and phenolics found in black soybean are known as active antioxidants and have been linked to a variety of health benefits. The purpose of this study was to determine total monomeric anthocyanins (TMA), total phenolics (TP), and the retardation ability of protein autoxidation of an ethanolic extract of black soybeans planted in Thailand. We investigated the optimal conditions for extraction conditions. The ultrasonic-assisted approach successfully extracted both TMA and TP using 85% v/v ethanol as the solvent. The 15-min extraction time and solvent-to-sample ratio of 20:1 (v/w), at 30°C resulted in the highest concentration of TMA at 3.232±0.04 mg cyanidine-3-Oglucoside equivalent per gram dry weight whereas the longer time and higher temperature resulted in significantly decreased TMA content (P<0.05). The maximum TP concentration of 119.42±0.42 mg gallic acid equivalent per gram dry weight was obtained by using a method identical to that used to extract TMA, except that of the longer time, increased solvent consumption and temperature. The preventive effect of black soybean extracts on oxymyoglobin (oxyMb) autoxidation was investigated. The pseudo first-order rate constant of oxyMb oxidation is decreased in the presence of the extracts in comparison to oxyMb alone. Additionally, oxyMb's half -life was increased from 0.57 to 1.46 hrs in the presence of TMA-rich extracts and from 0.57 to 2.51 hrs in the presence of the highest concentration of TP extracts when compared to cyanidine-3- O-glucoside and gallic acid, respectively. The study revealed that the black soybean extract could stabilize the bound oxygen in the oxyMb lead to slow down autoxidation of the protein consumption of foods or products derived from black soybeans may help to reduce cellular oxidative stress and the risk of developing various diseases as the study's findings indicate.