Monitoring mechanical, color and anthocyanin changes during rehydration of raspberry-based products

Abstract

BACKGROUND: Raspberry is a very popular berry, with a short postharvest life. Drying was proposed for obtaining different raspberry-based products. When rehydration is needed for foods direct consumption or use in composite products, a comprehensive understanding of the rehydration characteristics and quality attributes changes is necessary for a proper selection of processing. OBJECTIVE: The aim of the present work was to analyze the evolution of anthocyanin pigments and several physical properties upon rehydration of dried raspberries. METHODS: Raspberries were dehydrated (air- and freeze-drying) with sugar infusion pretreatments, and then rehydrated at different temperatures. Rehydration kinetics and several quality parameters were analyzed. RESULTS: Pretreated dried samples showed a significantly reduced rehydratability, and preserved dried fruit firmness. Upon rehydration, anthocyanins retention range was 8-42% in control raspberries and 40-90% in pretreated samples. Freeze-dried fruits showed a rapid water uptake but could not restore the water lost upon drying. These samples exhibited a high retention of anthocyanins and color, and a soft texture. When raisin-like fruits are required, samples with pretreatments and further drying should be selected, since they better maintained texture characteristics during a short period of consumption (5-20min); however, the anthocyanin content was lower than that for control samples. Both freeze- and air-dried control samples preserved the red hues, while maintaining the luminosity during rehydration. CONCLUSIONS: The evaluation of quality parameters of rehydrated raspberries, such as color, anthocyanin content, texture and volume, as well as the rehydration indices appeared to be useful to select the best drying and rehydration conditions.