Drying of pineapple by microwave-vacuum with osmotic pretreatment

Abstract

Drying of pineapple by microwave-vacuum (MW-V) with osmotic dehydration (OD) as a pretreatment was studied. Central composite design was used for the independent variables sugar concentration (40, 50, and 60 °Brix), immersion time (0, 3, and 6 hours) and product temperature in the microwave cavity (50, 60, and 70°C). The dependent variables were moisture content, shrinkage, rehydration coefficient, visual quality, color, and texture. The osmotic dehydration pretreatment was also evaluated with respect to weight reduction (WR), water loss (WL), and solid gain (SG). Maximizing moisture loss was the main objective of OD pretreatment for various combinations of sugar concentration and immersion time. OD preserved the color of the samples while drying. In the complete process composed by OD and MW-V, only the influence of temperature of the product on the drying rate was statistically significant (P < 0.05), whereas OD reduced shrinkage and improved rehydration capacity. The best visual quality was obtained when the independent variables were diminished. OD also significantly (P < 0.05) affected the texture of product producing softer, less surface-hardened product compared to untreated ones.