Effect of pretreatments on quality parameters and nutritional compounds of dried Galega kale (Brassica Oleracea L. Var. Acephala)

Galega kale (Brassica Oleracea L. var. Acephala) is a vegetable quite common in several countries. It presents high moisture content at harvest, so it can only be preserved for a few days under room temperature. Therefore, drying processes can be employed to increase its shelf-life. However, drying exposes the product to high temperatures that can result in some losses of flavour, texture, colour and nutrients. To minimize these detrimental effects, several pretreatments may be used as possible strategies to improve nutritional attributes and sensory properties, after dehydration and during long-term storage. The objective of this work was to evaluate the effect of six pretreatments on quality and nutritional contents of Galega kale submitted to convective air drying. Water and steam blanching, simple or combined with chemical treatments, were applied to kale samples before convective drying. When compared to the absence of pretreatment, steam blanching provided improvements on retention percentages of 7.3 and 13.6% for vitamin C and total antioxidant capacity, respectively. Regarding pigments, steam blanching enabled higher retention of total chlorophylls. Total phenolic content was the only nutritional parameter in which steam blanching preceded by chemical treatment with metabisulfite provided better results than isolated steam blanching. Steam blanching for 1 min, without the need of previous chemical treatment, applied to kale samples before drying, demonstrated to be a valuable approach to reduce deterioration of the majority of the parameters in study, and also improved significantly the appearance of Galega kale after the drying process.