Drying methods and their effects on bioactive compounds and quality of Georgia blueberries
Pallas, Laura Ann
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Blueberries have many suggested health benefits, most attributed to their high antioxidant content. To extend their short shelf life, fresh blueberries are frozen and then further processed. One method of preserving blueberries involves drying to a water activity (aw) < 0.63. Developing drying methods to optimize the final bioactive compounds content and understanding the impacts of drying on the nutritive and quality aspects are needed to create higher quality dried products. The main objectives were to produce dried whole blueberries (Vaccinium ashei Reade) with varying moisture content (MC) and aw values based on time and temperature combinations and to determine the effects of physical characteristics and processing conditions on the final quality and antioxidant activity in a vacuum belt dryer and jet-tube fluidized bed dryer. Pretreatments included freezing and mechanical abrasion in vacuum belt drying and scarification and sugar infusion in fluidized bed drying. Freezing blueberries prior to vacuum belt drying yielded lower final moisture contents, higher antioxidant activities (H-ORAC), and improved structural retention compared to drying of refrigerated fresh blueberries. Mechanical abrasion decreased vacuum belt drying time in fresh but not frozen blueberries. Total phenolics content (TPC) was not impacted by vacuum belt drying or fluidized bed drying while higher temperature and osmotic dehydration reduced total monomeric anthocyanins (TMA). Hydrophilic-oxygen radical absorbance capacity (H-ORAC) values were maintained or increased at all drying times compared to control values. Continuous vacuum belt drying shows promise for an uninterrupted method of drying blueberries in less time than freeze-drying while maintaining the bioactive activity in the dried product. Jet-tube fluidized bed drying offers a method for rapidly producing high-quality, shelf-stable sweetened and non-sweetened blueberries.