The impact of alternate pretreatment methods and osmotic dehydration for the preservation of wild blueberries (Vaccinium angustifolium)

Abstract

This study investigated the effects of selected pretreatments and rigorous optimization of osmotic dehydration (OD) of lowbush blueberries using Response Surface Methodology (RSM) to produce dehydrated blueberries with high antioxidants content and long shelf life. Fresh wild blueberries (WB) were initially pretreated and then subjected to osmotic dehydration before they were oven dried to the required level (18g/100g of fresh sample). Microwave pretreated WB had shown better moisture loss during osmotic dehydration as compared to other pretreatment methods investigated. The highest levels of phenolics, flavonoids, and anthocyanin content of the dehydrated WB were found to be 742.61 mg/100 g, 263.12 mg/100 g, and 428.11 mg/100 g dry mass respectively, at optimized temperature of 40 °C, for 5 h with 65% (w/w) Brix osmotic solution at 1:5 ratio of sample to Brix%. With rigorous optimization of the critical osmotic dehydration parameters high level of antioxidants could be retained in the dehydrated product. Wild blueberries pretreated in the microwave before osmotic dehydration and oven drying had shorter drying time of 5h compared to the control sample and significantly maintained a higher rehydration ratio (p<0.05) and lower shrinkage ratio compared to the oven dried control. Preliminary mathematical modeling of the process was also carried out to determine the mass transfer coefficients of the system. The results suggest that the drying process developed was a promising alternative method that decreases drying time, achieves high product quality, uses simple process steps for superior drying and retains higher level of antioxidant in the final product.