Preparation of S-allyl cysteine-enriched garlic by two-step processing

This study investigated the effect of ultrasonic and freezing pretreatment on S-ally cysteine (SAC) content in garlic during heat-processing at 40 °C for 15 days and also compared the browning degree and cell structure of ultrasonic and freezing pretreatment in garlic. Processing different times at the same frequency showed that ultrasonic pretreatment at 28 kHz for 3 h (2.51 ± 0.22 mg/g dry weight) is significantly higher than that for 1 h (1.83 ± 0.29 mg/g) after being heated at 40 °C for 6 days. The results of ultrasonic pretreatment for processing different frequencies at the same time finds that a frequency of 28 kHz for 2 h (3.15 ± 0.19 mg/g dry weight) has a better effect at increasing the SAC content in garlic than does 56 kHz for 2 h (2.69 ± 0.22 mg/g dry weight) after being heated at 40 °C for 15 days. A comparison of both pretreatments shows that the SAC content in garlic undergoing freezing pretreatment is significantly higher than that for ultrasonic pretreatment. Hence, ultrasonic pretreatment has a shorter processing time but needs more applications in the food industry to enhance the SAC content in garlic; however, it also maintains garlic's whole appearance and original color. •Discuss the effect of freeze and ultrasound on formation of SAC in garlic.•Freeze could induce structure damage obviously but not in ultrasound.•Freeze and ultrasound increase the SAC content about 3 and 6 times, respectively.