Foaming and drying behaviour of ripe bananas

The foaming of ripe bananas and the forced air-drying characteristics of the resulting banana foam mats were studied. Fresh banana puree with a density of 0.93 g/ml was foamed to a density of 0.50 g/ml after 12 min of whipping by the addition of 10 g/100 g soy protein as a foam inducer. Glyceryl monostearate did not induce foaming while commercially available food ingredients, Dream Whip and Gelatine induced foaming but such foams were not suitable for subsequent drying. Banana foam mats were dried at temperatures from 45degreesC to 90degreesC in a forced air, cabinet dryer, to a hard, porous and brittle solid which was amenable to grinding so as to produce a dehydrated banana powder. The transient drying behaviour of such mats was described by a capillary model of the form ln(M/M-0) = -Kt and over the bulk of the moisture ratio range, 0.05 less than or equal to M/M-0 less than or equal to 1.0. The drying time (t) was directly related to the thickness of the foam mats. K values increased from 0.248 to 0.809 h(-1) as the drying air temperature was raised from 45degreesC to 90degreesC. Increasing the air velocity from 0.62 to 1.03 m/s did not profoundly influence the drying rate. (C) 2003 Published by Elsevier Ltd. on behalf of Swiss Society of Food Science and Technology.