INFLUENCE OF COMBINED MICROWAVE-VACUUM DRYING ON DRYING KINETICS AND QUALITY OF DRIED TOMATO SLICES

The study investigated the influence of four microwave powers on the drying kinetics and quality of tomato slices in a microwave-vacuum dryer at vacuum pressures of 0.04, 0.05 and 0.06 MPa. The results showed that increase in microwave-vacuum drying conditions increased drying rates and resulted in decreased drying time from 84 to 14 min. The nonenzymatic browning index increased with microwave power whereas the overall flavor degradation was between 18.99 and 20.80%. The brightness and the yellowness of the dried tomatoes generally increased but there was a slight reduction in redness when compared with the fresh. The effective moisture diffusivity increased with microwave power and was 7.22 X 10-9, 9.10 X 10-9, 14.99 X 10-9 and 25.19 X 10-9 m2/s at respective microwave powers of 200, 300, 500 and 700 W. PRACTICAL APPLICATIONS Microwave-vacuum drying is one of the advanced methods with numerous advantages including high thermal efficiency, shorter drying time and improved product quality. Tomato is the second most important vegetable with enormous health benefits, which include reduction of cholesterol, improvement of vision, maintenance of gut, lowering of hypertension, alleviation of diabetes, and prevention of urinary tract infections and gallstones. The quality of dried products obtained using the microwave-vacuum dryer provides industries with method that can be used to enhance the quality of dried tomatoes. The dried product is a valuable ingredient in the preparation of soups and sauces, as well as in cosmetics and pharmaceutical formulations.