Spray drying of tomato pulp in dehumidified air: II. The effect on powder properties

Abstract

Tomato powders were produced by spray drying tomato pulp using a modified spray drying system. Modifications to the original dryer design consisted of connecting the spray dryer inlet air intake to an air dehumidifier. Samples of tomato pulp with a 14% constant total solids concentration were used. Sixty-four different experiments were conducted keeping constant the feed rate, the feed temperature and the atomizer pressure, and varying the compressed air flow rate, the flow rate of drying rate, and the air inlet temperature. In all experiments, the atomizer pressure, the feed rate and the feed temperature were kept at 5 ± 0.1 bar, 1.75 ± 0.05 g/min, and 32.0 ± 0.5 °C respectively. The variable operating conditions were within the following ranges: inlet air temperatures 110–140 (±1) °C; drying air flow rate 17.50–22.75 (±0.18) m 3/h, and compressed air flow rate 500–800 (±20) l/h. The tomato powders were analyzed for moisture content, bulk density and solubility. Analysis of experimental data yielded correlations between the powder properties and the variable operating conditions. Regression analysis was used to fit mathematical models to the data of each of the powder properties evaluated. Comparisons between the moisture content, the bulk density, and the solubility of powders produced by the two drying systems proved that the use of dehumidified air, promoting rapid particulate skin formation, decreased powder moisture content and increased powder bulk density and solubility. The modified spray drying system proved advantageous over the standard laboratory spray dryer. Preliminary air dehumidification improved not only product recovery, but, also product properties.