Abstract
Dried vegetables are widely used in food production. Kale leaves, due to their high health-promoting properties, can be a valuable raw material for drying. The aim of the study was to evaluate the effect of blanching, drying methods (air-drying, freeze-drying), the time and temperature of storage on the content of ash, minerals, vitamins B1, B2, and tocopherols in dried kale products. The dried products were evaluated directly after processing and after 12 months of storage at ambient temperature, 18–20 °C and cold temperature, 8–10 °C. In 100 g dry matter from fresh raw material the dominant minerals were potassium (2613 mg), calcium (1346 mg), phosphorus (432 mg), magnesium (129 mg). Kale leaves had 0.828 mg vitamin B1, 1.533 mg vitamin B2 and 16.55 mg total tocopherols per 100 g of dry matter. Blanching, applied prior to drying, significantly reduced the levels of minerals (3–38%) and vitamins (8–45%), except for calcium, zinc and manganese. This pre-treatment had, however, a beneficial effect, especially on vitamin retention during the storage of dried products. After 12 month storage, the losses of vitamin B1, B2 and total tocopherols in dried, previously blanched, raw materials ranged from 3 to 10%, 1 to 4%, and 1 to 16%, respectively, depending on the type of sample. In the dried products obtained from unblanched raw material, the losses were larger and amounted to 10–17%, 8–16% and 4–17%, respectively. Throughout drying and storage, the minerals examined were fairly stable. Dried kale is generally a good source of minerals and vitamins. However, blanching before drying is recommended. In addition, freeze-drying and storage in cold temperature allows for higher vitamin preservation in dried kale.
Highlights
Diet high in vegetables is widely recommended for its health-promoting properties
The study material consisted of raw kale (Brassica oleracea L. var. acephala) leaves; leaves after blanching; leaves after air-drying (AD); and leaves after freeze-drying (FD)
Kale added to a cereal-based diet enhances the intake of essential minerals to combat micronutrient malnutrition (Migliozzi et al 2015)
Summary
Diet high in vegetables is widely recommended for its health-promoting properties. Vegetables are consumed raw or numerous processed products. Intake of vegetables has been associated with a reduced risk of chronic diseases and body weight management (Pem and Jeewon 2015). Studies indicate that human nutrition should be based on fruit and vegetables. These provide many valuable substances and significantly reduce the incidence of cardiovascular disease and diabetes, along with the associated mortality (Aune et al 2017; Ulger et al 2018). We should eat fruit and vegetables as often as possible to improve overall health and reduce the risk of cardiovascular diseases and certain types of cancer. FAO/WHO (2015) suggests an intake of over 400 g of fruit and vegetables per day, which translates to about 5 portions per day. FAO/ WHO have been leading the global initiative ‘Promotion of Fruit and Vegetables for Health’ (PROFAV) to raise
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