Effect of blanching on convective drying and osmotic dehydration of cranberries

Physical properties of frozen commercial cranberries were measured, including diameters, mass, sugar content, moisture content, and color. Density was calculated to be 0.89 g mL-1, and the moisture content averaged 87.0%. The effect of blanching on convective drying was investigated by dividing the cranberries into three size ranges and then subjecting them to convective drying after blanching in boiling water. Three blanching times (60, 120, and 180 s) were used, along with a control of no blanching. In a second set of experiments, cranberries were blanched prior to osmotic dehydration. The osmotic solution was either 50 or 65°Brix at a temperature of 50°C or 60°C. Samples were removed hourly, and mass and moisture contents were measured. The convective drying experiments indicated that blanching affected the subsequent drying rate, with a longer blanching time resulting in a faster drying rate. Results from the osmotic dehydration study indicated that blanching had a significant effect on the final dry basis moisture content of the berries compared to non-blanched controls. The actual mass of water removed from the cranberries did not differ between the blanched and non-blanched cranberries. Rather, the significant difference in the final moisture content was attributed to increased solid matter content due to the infusion of the sugar solution. Non-blanched cranberries had an average solids content increase of 41%, whereas blanched cranberries had an increase of 254%. © 2013 American Society of Agricultural and Biological Engineers.