Effect of two cooking procedures on phytochemical compounds, total antioxidant capacity and colour of selected frozen vegetables

The effect of boiling and steaming on content of phytochemicals (carotenoids, chlorophylls, polyphenols and ascorbic acid) all evaluated by HPLC, total antioxidant capacity (TAC) measured by means of TEAC and FRAP assays and colour (L*, a*, b*, C, H°) of three frozen vegetables (carrot, cauliflower and spinach) was evaluated. Steaming increased the content of polyphenols in all vegetables and limited the depletion of carotenoids in spinach. Accordingly, TAC remained unvaried or increased both for steamed carrot and spinach. Boiling had a more marked effect on nutritional pattern of frozen vegetables in comparison with steaming, leading to a general loss of phytochemical compounds and TAC for all vegetables. Ascorbic acid was detected only in cauliflower and decreased after both treatments. Colour of frozen vegetables was only slightly influenced by cooking, probably due to blanching pre-treatment. Slight decrements of redness (a*) for carrot in relation with loss of carotenoids and greenness (-a*) for steamed spinach, due to a significant loss of total chlorophylls, were observed. Steaming increased TAC and bioaccessibility of polyphenols in all frozen vegetables while boiling led to a general loss of carotenoids and phenolic compounds and a TAC decrease.