Thermal processing effects on the chemical constituent and antioxidant activity of s-alk(en)ylcysteine s-oxides (alliin) extract

To explore the effects of thermal processing on antioxidant activity and the chemical composition of s-alk(en)ylcysteine s-oxides (alliin) extract from garlic, the alliin extract was thermally processed and the chemical constituents were analyzed by HPLC and LC–MS, and antioxidant capacities were investigated by 2,2-Diphenyl-1-picrylhydrazyl (DPPH) assay, hydroxyl free radical assay and ferric reducing/antioxidant power (FRAP) assay. The results showed that thermal treatments resulted in significant changes in the composition and antioxidant activities of alliin extract (p < 0.05). The contents of alliin were reduced from 85.7% to 60.8% and new chemicals including s-allylmercaptocysteine (SAMC), s-allylcysteine (SAC) and arginine were found after thermal treatment at 121 °C for 40 min. The IC50 value of alliin extract on DPPH assay was decreased from 46.6 mg/mL (untreated) to 7.3 mg/mL (treated). The antioxidant capacity on FRAP assay was increased from 1.45 mmol/L of FeSO4 equivalent (untreated) to 4.36 mmol/L of FeSO4 equivalent (treated) when alliin extracts was at the concentration of 16 mg/mL. These results suggest that thermal treatment is suitable to the antioxidant capacities of alliin extracts and SAC and SAMC might play important roles. These results could be useful for the processing of garlic related products in the food industry.