Amino Acid Retention and Protein Quality in Dried Kale (Brassica oleracea L. var. acephala)

The aim of this work was to investigate the effects of technological processing (blanching), two drying methods: air‐drying (AD) and freeze‐drying (FD), and storage temperature on amino acid content and protein quality in dried kale products. The dominant amino acids in all samples were glutamic acid, aspartic acid and proline. The limiting amino acids in raw kale leaves were lysine (CS 96), isoleucine (CS 97), and cystine with methionine (CS 83), additionally valine (CS 85–91), isoleucine (CS 73–97) and leucine (CS 91–99) in the remaining products. Essential amino acids (EAA) comprised 47% of total amino acids in raw and blanched leaves and 45 and 46% in AD and FD products, respectively. The lowest EAA index in dried products (99–102) was recorded for the air‐dried product obtained from blanched raw material, while the highest (116–117) was found in freeze‐dried kale leaves produced from unblanched material. PRACTICAL APPLICATIONS: Kale is widely consumed vegetable, and is rich in many constituents. Drying is an important method of preserving plant material. This article describes widely the effects of technological processing, two drying methods, and storage temperature on amino acid content and protein quality in dried kale products. The results showed that raw kale leaves were a good source of valuable protein. Levels of individual amino acids were generally higher in freeze‐dried than in air‐dried products. From practical point of view it may be concluded that blanching is not a necessary procedure before drying kale leaves.