Foam-mat drying of starfruit (Averrhoa carambola L.) purée. Stability and air drying characteristics

Foams were prepared from starfruit (Averrhoa carambola L.) purée by adding various concentrations of methocel. Overrun and density of the foams from various concentrations of methocel were compared. Relative stability of the foam was determined by comparing amounts of juice separated from foam at 70°C. Drying rates at two drying temperatures (70 and 90°C) were also compared. Quality of the dry and reconstituted powder was evaluated with simple sensory evaluation and Hunterlab instrument. Overrun and stability of foams increased with increasing methocel concentration until maximum value was obtained at a methocel concentration of 0.4% w/w. Falling rate was observed for foam dried at both temperatures. Drying time could be shortened by as much as 30 min when drying temperature was increased from 70 to 90°C. However, obvious colour and flavour changes were observed in the product dried at 90°C. This study has indicated that, under the experimental conditions employed, reasonably good powder characteristics can be obtained.