| Fruit drying is energy intensive (thermal efficiency 25-50%). However, improved efficiency is possible if phase change during the process is minimized. To minimize phase change and simultaneously increase product yield and quality, osmotic dehydration and pulsed-vacuum osmotic dehydration can be applied to maximize water removal before final drying. The objective of this study was to characterize the effect of vacuum, osmotic solution temperature and concentration, and treatment duration on blueberry mass transfer. Frozen blueberries were exposed to 2 temperatures (25 or 50°C), 2 sugar solution concentrations (45 or 65°Brix), 2 vacuum treatments (no vacuum or 50 mbar), and 3 duration treatments (180, 240, or 300 minutes). This design generated 24 treatment combinations that were nested in °Brix as a balanced incomplete block design. Following treatments, blueberries were conventionally dehydrated at 57.2°C for 6.5 hours. Higher concentration of osmotic solution increased blueberry sugar gains by 62% compared to sugar gains at the lower concentration. Time affected sugar gain at both concentrations (p<0.0001). Blueberry °Brix increased by 13.03, 17.29, and 17.68°Brix at 180, 240, and 300 minutes, respectively. Solution concentration, temperature, and time affected percent yield after conventional drying (p<0.0001, p=0.0004, p<0.0001, respectively). Higher temperatures increased yield of the final product compared to the lower temperature. Water activity appeared to be affected by an interaction between solution concentration and temperature (p=0.0210). These low temperature processes can be used commercially to reduce water activity of high moisture products and decrease the processing time; thereby, improving yield and producing minimally processed fruit products with marginal changes in color, texture, aroma, and flavor. |
