Physical and Chemical Properties of Vacuum Belt Dried Tomato Powders

Abstract

Vacuum belt drying (VBD) was used to produce powders (aw = 0.2–0.3) from tomato pulp and skin-rich fractions. Drying times ranged from 3 to 14 h for pulp slices, when conduction heaters were specified at 100 to 60 °C, and between 1 to 3 h for thin layers of tomato skins. Modeling of moisture isotherms showed that dried pulp had greater monolayer moisture than dried skins and at a given aw had greater associated moisture content. Hygroscopicity measurements at 86 % relative humidity showed that while the pulp powders pick up more moisture, they do so at a rate similar to the tomato skin powders. Both fractions produced flowable powders, but skin powders had greater flowability than pulp powders. In general, tomato skin powders were darker and redder than tomato pulp powders, presumably as the fresh skins had greater lycopene content (2674 μg/g d.w.) than the pulp (1997 μg/g d.w.). The least decrease in trans-lycopene occurred for pulp dried at 60 °C (3.7 % decrease) and for skins dried at 80 °C (1.7 % decrease).