Characterization of phenolics, glucosinolates and antioxidant activity of beverages based on apple juice with addition of frozen and freeze-dried curly kale leaves (Brassica oleracea L. var. acephala L.)

- Apple juice supplemented by kale resulted in increase of antioxidant activity.
- Content of phenolics and glucosinolates in beverages depends on the kale form.
- Freeze-dried kale addition resulted in a higher level of bioactive compounds.
- Ascorbic acid content was significantly lower in beverages compared to apple juice.

The aim of this study was to determine the polyphenols, glucosinolates and ascorbic acid content as well as antioxidant activity of beverages on the base of apple juice with addition of frozen and freeze-dried curly kale leaves. Upon enrichment with frozen (13%) and freeze-dried curly kale (3%), the naturally cloudy apple juice was characterized by an increase in phenolic compounds by 2.7 and 3.3-times, accordingly. The antioxidant activity of beverages with the addition of curly kale ranged from 6.6 to 9.4 μmol Trolox/mL. The obtained beverages were characterized glucosinolates content at 117.6-167.6 mg/L and ascorbic acid content at 4,1-31,9 mg/L. The results of sensory evaluation of colour, taste and consistency of apple juice and beverages with the addition of kale did not differ significantly prior to pasteurization (P ≤ 0.05), whereas after the pasteurization the evaluated factors decreased significantly.