Optimization of S-allyl-L-cysteine extraction from black solo garlic (Allium sativum L.) by hydrothermal treatment

S-allyl-L-cysteine (SAC) is known to have high antioxidant and antibacterial activities. In this study, SAC was extracted from black solo garlic using hydrothermal treatment. Black solo garlic was obtained from fresh solo garlic through the aging process via the Maillard reaction at temperature of 80 ± 5 °C with a relative humidity of 80 ± 5% for 14 days, 21 days, and 28 days. Hydrothermal treatment was conducted in a semi batch process at temperatures of 120 ℃, 140 ℃, and 160 ℃ and pressures of 1 MPa, 3 MPa, and 5 MPa with water flow rate of 1 mL/min for 180 min. The extraction conditions were optimized using Response Surface Methodology (RSM) based on Central Composite Design (CCD) to evaluate the effects of temperature, pressure, and aging process on SAC content and yield. Based on the RSM CCD results, the best condition was 21 days of aging with temperature of 120 °C and pressure of 5 MPa, which produced extract with SAC content 4.21 (mg SAC/g sample) and a yield of 29.08%. The highest total polyphenol and flavonoid contents were 166.32 ± 2.10 mg GAE/g extract and 28.76 ± 1.06 mg QAE/g extract, respectively, obtained at 120 °C, 1 MPa, and 28 days aging process. At the same condition, black solo garlic extract had strong antioxidant activity and high antibacterial activity against Escherichia coli (E. coli), with an inhibition zone of 26.39 ± 0.59 mm, Minimum Inhibitory Concentration (MIC) 3.04 g/100 mL, and Minimum Bactericidal Concentration (MBC) 3.36 g/100 mL.