Various garlic nutrients bring about several health benefits. Allicin, the major bioactive component of garlic, has anticancer, antimicrobial, antioxidant, cardiovascular-preventive, and cholesterol-reducing effects. Using water as the solvent, the ultrasound-assisted extraction of garlic compounds were optimized through response surface methodology (RSM). The process was conducted at different times (10-30 min), temperatures (30-60°C), frequencies (37 and 80 Hz), and powers (40-100 W). The obtained extracts were assessed for DPPH scavenging activity, total phenolic content (TPC), and extraction efficiency. The optimal conditions were 10 min, 30°C, 37 Hz, and 40 W (R 2 = 0.93 for the DPPH assay, R 2 = 0.99 for the TPC, and R 2 = 0.94 for the extraction efficiency). Sonication time and temperature most affected the responses. In conclusion, ultrasound could be easily utilized for the extraction, because it accelerated the process and lowered the extraction time, which enhanced the extract quality with regards to antioxidant properties and the likelihood of extracting heat-sensitive substances.

The ever-present need for human communities to extract herbal active ingredients has necessitated many studies to be carried out in order to introduce more efficient and cost-effective extraction processes. The traditional extraction methods are very time consuming and use large volumes of solvents. The large volumes of solvents consumed in such methods not only increase costs but also pose many environmental problems. New extraction methods have been recently introduced to replace the traditional ones. These new methods reduce the volumes of required solvents, shorten the process and increase its efficiency and improve the quality of the products. In this study, the three methods of immersion, boiling, and ultrasound using water/ethanol solvents were employed for garlic extraction and compared with each other in terms of the extraction speed and time, the antioxidant property of the extract, and the quantity of the heat-sensitive active ingredient. The results showed that the highest allicin content (0.086%) was observed in the ultrasonic aqueous extract. The largest amounts of phenolic compounds (0.311 mg gallic acid equivalent) were observed in the ultrasonic aqueous extract followed by the aqueous extract prepared after 72 h in a shaking incubator. The highest inhibition rate (50% at 5000 ppm) was that of the ultrasonic aqueous extract and the shaken aqueous extract. Other extracts achieved an inhibition rate of 50% at 8000 ppm. Therefore, ultrasonic extraction can be a good alternative to traditional extraction methods.