The Effect of Hybrid Convective–Infrared–Ultrasonic Drying on Selected Properties of Kale and Nutritional Value of Kale Bars

The study aimed to determine the content of biocompounds and the nutrient composition of dried kale (with/without blanching) and bars containing it (fresh/dried). Kale leaves and bars were dried using convection (CD), convection–infrared–ultrasonic (HD), and freeze-drying (FD) methods to obtain potential snacks. The bar recipe consisted of 20% fresh kale (plus 30% water) or 10% dried kale (plus 40% water), 20% dried dates, 10% coconut flour, 10% flaxseed, and 10% hemp protein. Dried blanched kale contained from 524 to 618 mg of GAE/100 g d.m., which was 6.8–12.4% more than in unblanched kale, but about four times less in the bars. Similarly, blanched kale had a higher content of chlorophyll A + B and carotenoids. Both of these groups of compounds in blanched kale dried using the HD method were comparable to or slightly higher than in the raw material (approx. 932 and 174 mg/100 g d.m. of chlorophyll A + B and carotenoids, respectively), while in the bars their content was low, 34–64 and 7.6–13.2 mg/100 g d.m., respectively. The caloric content of the bars ranged from 325 to 348 kcal/100 g (1356 to 1452 kJ/100 g of product). Dried kale has proven to be a valuable snack due to its antioxidant content. In turn, the bars were rich in nutrients such as protein (approx. 14.4%), fat (approx. 9.3%), minerals (approx. 4.0%), carbohydrates (approx. 35.2%), and especially fiber (approx. 27.3%), which allows them to be classified as “high-fiber” products.