Rheological and Chemical Characterization of Smoothie Beverages Containing High Concentrations of Fibre and Polyphenols from Apple

Beverages are an ideal food format to deliver health-promoting polyphenols (PPs) and dietary fibres (DFs) to consumers. In this study, complex beverage systems, smoothies, were formulated containing high concentrations of apple PPs (500 mg per 300 ml beverage), apple fibres of two different particle sizes (AF01, 250 μm; AF09, 300–700 μm; each containing soluble and insoluble fibres), and stabiliser carboxymethylcellulose (CMC; 0.05–2.00 %). The beverages were pasteurised at 85 °C for 15 s, and subjected to total extracted PP content (TEPC) and rheological measurements (viscosity, elastic modulus G′ and viscous modulus G″ at 4, 20, 37 and 60 °C). Scanning electron microscopy (SEM), FT-IR spectroscopy and N₂ physisorption measurements on the AF01 and AF09 fibre powders showed that they differed in particle size, yet were similar in particle surface morphology, chemical composition and specific surface area. Characterisation of smoothies prepared from the AF01 and AF09 fibres showed that the particle size of the apple fibres, testing temperature and CMC concentration strongly influenced the extractability of PPs and rheological behaviour of the smoothies. The peak TEPC values of the AF01 and AF09 beverages, 327 and 351 mg catechin equivalent per 300 ml beverage, occurred at 1.50 % and 1.00 % CMC, respectively. The temperature dependence of smoothie viscosity was examined, and an Arrhenius relationship was observed for both the AF01 and AF09 smoothie systems. The stabilising effect of CMC for this type of smoothie beverage was confirmed. CMC concentrations of 1.00–1.50 % afford high extracted PP content, good phase stability and beverage flow properties. These results presented here can be used to guide the development of stable beverages containing relatively high concentrations of PPs and DFs (including both insoluble and soluble).