Changes in the content of minerals, B-group vitamins and tocopherols in processed kale leaves

The human body cannot produce minerals, B-group vitamins or tocopherols, so these must be supplied in food. Kale and other Brassica vegetables are good sources of these substances, but food processing can affect their content. Therefore, the aim of this study was to determine the effect of the type of pre-treatment (blanching or cooking), the method of preservation (freezing or canning) and 12-month storage on the content of minerals, vitamins B-1 and B-2, and tocopherols in kale leaves (Brassica oleracea L. var acephala). Pre-processing of kale leaves prior to preservation led to a significant reduction in minerals and vitamins of 26-52 % (blanching) and 29-75 % (cooking). The most abundant macroelements in the products were potassium and calcium, whereas the microelements with the highest values were iron and copper. The highest content of minerals, B group vitamins and tocopherols was observed in frozen products from blanched raw kale leaves. After 12 months storage, the frozen products retained 24-74 % macroelements, 40-71 % microelements, 45-71 % vitamin B-1, 27-47 % vitamin B-2 and 69-85 % total tocopherols, while the canned products (leaves without brine) retained 41-70 %, 31-56 %, 21-23 %, 6-9 % and 44-48 %, respectively.