Effect of different combined mechanical and thermal treatments on the quality characteristics of garlic paste

The aim of this study was to investigate the effects of the sequence of different thermal and mechanical treatments on the physicochemical parameters and microstructure of garlic paste, in order to improve the quality of the product. The total organosulfur compounds (OSCs) decreased steadily in blended-heated garlic, whereas OSCs decreased sharply after 2 min at 75 degrees C or 5 min at 85 and 95 degrees C in heated-blended garlic. After blanching for 5 min, allicin could maintain over 4.0 mg/g only at 75 degrees C; and OSCs of heated-blended garlic paste were found to drop by 29.56%, 90.63% and 94.79% at 75, 85 and 95 degrees C, respectively. In blended-heated garlic, the color values of L*(lightness) and a*(redness) decreased (P < 0.05), while the b*(yellowness) and C*(chroma) increased (P < 0.05), obtaining green discoloration garlic paste. The total color differences of blended-heated samples were greater than 12.08, which were 2-6 folds higher compared with heated-blended garlic. Total phenolic content and antioxidant activity decreased (P < 0.05) in all thermal treatments, thermal treatment of heated-blended garlic less than 5 min maintained over 30% of antiradical activity. The sequence of unit operations determined the pattern of garlic microstructure disruption, resulting in various enzymic and non-enzymic reactions. Our results indicated that use of heat treatment prior to blend processing is an effective and feasible method to inhibit garlic discoloration and retain high content of bioactive OSCs. It is recommended that garlic paste be prepared using heated-blended processing, with thermal processing limited to 75 degrees C for less than 5 min.