Study on the Ageing Method and Antioxidant Activity of Black Garlic Residues

Garlic residue (GR), a co-product of garlic oil extraction, contains most of the nutrients of raw garlic (RG). Preparation of black garlic residue (BGR) is considered to be an effective method of processing GR. The main objective of this study was to optimise the ageing conditions of GR based on moisture, polyphenol and 5-hydroxymethyl-2-furaldehyde (HMF) levels. In addition, the antioxidant capacity of BGR was also evaluated in vitro and in vivo and compared with black garlic (BR) and RG. The results indicate that optimum ageing resulting in polyphenol and HMF contents of 25.80 mg/g and 3.84 mg/g, respectively, were achieved using a temperature of 90 degrees C and humidity of 95% for four days. Both BGR and BR had stronger capacities to scavenge alpha,alpha-diphenyl-beta-picrylhydrazyl (DPPH) than RG with half maximal inhibitory concentration (IC50) values of 0.454, 0.514 and 4.236 mg/ml, respectively. Experiments on mice demonstrated that there was no obvious difference in antioxidant activity between BGR and BR in vivo. BGR and BR consumption significantly decreased malondialdehyde (MDA) levels in serum and liver, in addition to markedly increasing superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities.