Storage stability and simulated gastrointestinal release of spray dried grape marc phenolics

Maltodextrin (MD), whey protein isolate (WPI) and pea protein isolate (PPI) have been used in this work as carrier agents in the spray drying of grape marc extract, and the obtained microparticles have been characterized in terms of drying yield, morphology (SEM), size distribution, chemical structure (FTIR), chemical composition (total phenolic and anthocyanin content), and antioxidant activity (ORAC). WPI was found to be the most effective carrier for optimizing drying yield, requiring less than 0.5:1 carrier:extract solids ratio to achieve the usual 50% yield benchmark. In vitro gastrointestinal release of total phenolics and anthocyanins indicated Fickian diffusion, with the Higuchi and Korsmeyer-Peppas models providing the best fit for the data. An accelerated stability test carried out at 40 and 60 °C revealed first-order kinetics for anthocyanin degradation. WPI formulated microparticles showed severe degradation at 40 and especially 60 °C (complete degradation after 4 days), followed by MD and PPI microparticles. Similarly, a long term stability test carried out at room temperature (25 °C) over six months showed that total phenolic content did not diminish for any of the carriers, but anthocyanin content suffered a 20% loss after 6 months for PPI and MD formulated samples, and a 50-65% loss for WPI formulated samples.