Effect of hydrocolloid addition and microwave-assisted freeze drying on the characteristics of foamed raspberry puree

Abstract

Foamed fruit purees can be dried and consumed as snacks. This study compares the characteristics of foamed raspberry puree dried via microwave-assisted freeze drying and conventional freeze drying. The effect of potato protein (PP) (as a foaming agent), maltodextrin (MD) (as a foam stabilizer), and microwave power on the product characteristics was investigated. The puree contained 18%–20% higher content of anthocyanins and ascorbic acid than unprocessed raspberries. The retention of ascorbic acid and anthocyanins increased with increasing concentrations of MD and PP. Both drying methods resulted in 66%–81% retention of ascorbic acid and 53%–84% retention of total anthocyanins. The higher drying rates obtained at higher maltodextrin concentrations resulted in higher ascorbic acid and anthocyanin retention. The total color difference was significantly higher for the foam with 30% MD (w/w) at 2.0 W g−1, accounting for the formation of hot spots. Protein concentration did not have a considerable effect on product color. Increasing the maltodextrin concentration yielded a harder foam structure, while increasing the protein concentration had the opposite effect. Overall, microwave-assisted freeze drying was found to be a promising alternative to conventional freeze drying, as it offers a more efficient drying process with comparable product quality.