Effect of preliminary processing and method of preservation on the content of selected antioxidative compounds in kale (Brassica oleracea L. var. acephala) leaves

Vitamin C and polyphenol content: as well as total antioxidative activity were investigated in fresh leaves of kale; in leaves after blanching or cooking; and in frozen and canned leaves. In 100 g fresh matter, kale leaves contained 384.9 mg polyphenols and 112.1 mg vitamin C, with a Trolox equivalent antioxidant capacity (TEAC) level of 1175 mu M Trolox. Of the polyphenols identified in kale leaves, ferulic acid occurred in the highest amount (240.44 mg/100 g, constituting 62% of total polyphenols). Freezing was a better method of preserving kale leaves since the loss of nutritive constituents was lower than in the case of canning. Depending on preliminary processing and storage temperature, after one-year storage frozen leaves contained 82.9-171.3 mg polyphenols and 39.3-65.4 mg vitamin C, with TEAC at the level of 501-681 mu M Trolox in 100g. In canned leaves these values were: 91.3-94.1 mg polyphenols, 16.1-19.3 mg vitamin C and 268-293 mu M Trolox. (C) 2011 Elsevier Ltd. All rights reserved.