The use of alkalised cocoa powder in kefir: effects on physico-chemical, rheological, and functional properties

Abstract The aim of the study was to investigate the effects of cocoa powder alkalisation level and usage rate on the quality characteristics of cocoa kefir. For this purpose, kefir samples were prepared from cow’s milk using natural and alkalised (low and medium) low-fat cocoa powders at different concentrations (1.00, 1.50, 2.00, and 2.50 g/100 ml). The physico-chemical, flow behaviour, technological properties, total phenolic content (TPC), and antioxidant activity potential (AAP) of these samples were assessed. The pH values of the kefir samples ranged from 4.67 to 4.76 and increased with the use of alkalised cocoa powder and higher concentrations (p < .05). Additionally, the use of cocoa powder imparted a distinct visual characteristic to the kefir, allowing it to be identified as a cocoa-flavoured drink. The alkalisation level and cocoa powder concentration significantly affected the L*, a*, and b* values, which are used to describe colour characteristics. Furthermore, the addition of cocoa powders significantly influenced the TPC and AAP of the kefir samples (p < .05). However, the spectral signals of all kefir samples were similar, indicating that the overall compositions were closely related. The flow curves of the kefir samples were well-fitted to the Ostwald–de Waele model, with coefficients of determination ranging from 0.9763 to 0.994. This indicates that the flow behaviour of the samples was accurately described by the model. Interestingly, neither the degree of alkalisation nor the cocoa powder concentration significantly affected the consistency index values (p > .05).