Influence of hot-air drying methods on the phenolic compounds/allicin content, antioxidant activity and α-amylase/α-glucosidase inhibition of garlic ( Allium sativum L.)

Present investigation studies the effect of convective hot-air drying on the contents of allicin content and phenolic compounds, antioxidant activities, α-amylase and α-glucosidase-inhibiting properties of garlic ( Allium sativum L.). Thin garlic samples were chopped in single-layer dried in a high precision, ICT-controlled lab dryer at 50–80 °C, with specific humidity of 10 and 20 g water per kg of dry air and a constant air velocity of 0.5 m/s. Phenolic compounds were qualitatively and quantitatively measured. In addition, inhibitory potential against α-amylase and α-glucosidase in dried garlic was examined in vitro. The combination of lower hot-air drying temperatures and lower humidity levels of hot air caused the content of individual phenolic acids and allicin in garlic to increase while preserving a high percentage of α-amylase and α-glucosidase inhibition. A high negative correlation was observed between the total phenolic content, antioxidant activities, α-amylase inhibition and α-glucosidase inhibition, whereas a moderate positive correlation (0.752, p < 0.05) was observed between allicin, α-amylase and α-glucosidase inhibition. The findings indicated that dried garlic prepared at the hot-air drying temperature of 60 °C and specific humidity of 10 g/kg could effectively retain phenolic and organosulfur compounds. These extracted compounds can be potential functional ingredients used for dietary treatment during the early stage of hyperglycemic. The subsequent investigation could combine the traditional hot-air drying approach with microwave or vacuum drying, which may significantly minimize processing time while retaining a high retention rate of garlic's functional ingredients and bioactive activities.