Textural change and antioxidant properties of broccoli under different cooking treatments

Broccoli (Brassica oleracea L var italica Plenck) was used as a testing material and Sampled in four groups, including fresh, precooked (50 degreesC, 10 min), cooked (boiling, 8 min), and precooked followed by cooking (precooked + cooked), to investigate the effect of the cooking treatment on the textural change in the vegetable. After freeze-drying and extraction by the use of methanol, the antioxidant properties of the extracts from the four groups were estimated and compared with those of alpha-tocopherol and butylated hydroxyanisole (BHA). The antioxidant properties include reducing power, ferrous ion chelating power, alpha,alpha-diphenyl-beta-picrylhydrazyl (DPPH) radical-scavenging activity and inhibitory effect against lipid peroxidation. The data indicated that, after cooking in boiling water for 8 min, the broccoli tissue had a 51% relative peak force of the fresh tissue, whereas the tissue, after precooking at 50 degreesC for 10 min, and the tissue, after precooking + cooking, had relative peak forces of 172% and 119%, respectively, of the fresh tissue. These results revealed that cooked tissue with precooking softens more slowly than that without precooking; that is, precooked tissue can show a higher resistance to softening during cooking. The extracts from the precooked, cooked, and precooked + cooked broccoli exhibited high reducing powers. At a sample-to-solvent (mg/ml) ratio of 20 mg/ml, these extracts had 1.5 similar to 1.7 times as high reducing powers as those of alpha-tocopherol and BHA. These four extracts showed high ferrous ion chelating power, and the extracts from fresh and precooked broccoli had the highest, namely 90.5% at a sample-to-solvent ratio of 2 mg/ml. These extracts also exhibited high DPPH radical-scavenging activity, at 96.8, 97.3, 98.6 and 97.9%, respectively, for the fresh, precooked, cooked, and precooked + cooked samples, at a sample-to-solvent ratio of 20 mg/ml. The four extracts exhibited lower inhibitory effects against the peroxidation of a linoleic acid emulsion system than did alpha-tocopherol and BHA. (C) 2004 Elsevier Ltd. All rights reserved.