Effect of convective drying pretreatment on the physicochemical properties of black garlic

摘要

Black garlic is produced commercially using traditional processes with high temperature (HT) and high relative humidity (HRH) during 30-60 days until the cloves turn black with a sweet and syrupy taste. The aim of this study was to reduce black garlicproduction time applying a convective drying pretreatment (CDP). Purple garlic bulbs (Allium sativum L.) sets were subjected to CDP process for 4 days at HT (70°C) and low RH (9%) followed by 4 days at HT (70°C) and HRH conditions (94%). Browning degree, water activity (aw), moisture, pH, total soluble solids (TSS), total phenols content, 5-hydroxymethyl-2-furaldehyde (HMF) levels, reducing sugar content (RSC) and pungency analyses of blacked garlic were performed. Black garlic production time was reduced to 8 days (4 days at CDP conditions, 70°C - 9% RH and 4 days at traditional processing conditions, 70°C - 94% RH). No differences in external (AE=62) and internal (AE=12) browning degree were observed (p>0.05) between CDP processed and commercialblack garlic (control group). Pungency values were 6 times higher in black garlic from CDP (12.87 umol pyruvic acid g1) when compared to control group (2.16 umol pyruvic acid g1). This observation is consistent with the lower RSC (13.69 mg fructose g-1)in black garlic from CDP. In comparison to control group, moisture, total phenols content and HMF levels decreased in the CDP group, whereas TSS increased. There were no differences (p>0.05) in pH or aw. The results suggest that it is possible to reduceblack garlic production time using convective drying.