Effect of low temperature plasma pretreatment on drying process of vegetables with waxy layer

Abstract In this study, low temperature plasma technology was used as an efficient pretreatment method of vegetables with waxy layer before drying. The effects of different low plasma pretreatment power (200, 300, 400, and 500 W), low plasma pretreatment time (30, 40, and 50 s) and drying temperature on the thin layer drying process of vegetables (peppers, lentils, and peas) were investigated. Peppers after plasma pretreatment were dried at 45, 50, and 55°C. Lentils and peas after plasma pretreatment were dried at 65, 70, and 75°C. Results showed that low temperature plasma can effectively improve the drying efficiency, promote the moisture diffusion and shorten the drying time. After pretreatment power of 500 W for 30 s at 55°C, drying time of peppers was shortened by 18.75%, the maximum effective moisture diffusivity is 5.843 × 10 −10 m 2 ·s −1 , and lower activation energy ( E a) is 69.349 kJ·mol −1 in comparison with 71.118 kJ·mol −1 for the control group. After pretreatment power of 500 W for 30 s at 75°C, drying time of lentils and peas was shortened by 33.33 and 27.27%, respectively. The maximum effective moisture diffusivity of lentils is 2.526 × 10 −9 m 2 ·s −1 , and lower activation energy ( E a) is 27.359 kJ·mol −1 in comparison with 33.366 kJ·mol −1 for the control group. The maximum effective moisture diffusivity of peas is 1.867 × 10 −9 m 2 ·s −1 , and lower activation energy ( E a) is 23.583 kJ·mol −1 in comparison with 29.107 kJ·mol −1 for the control group. Results indicate that the higher plasma pretreatment power led to the higher drying efficiency but higher plasma pretreatment time cannot further shorten the drying time. Practical Applications Vegetable is important in daily life, but easy to dehydrate in a natural state. The transportation and storage are more convenient after drying. Low temperature plasma technology does not need high pressure and low energy consumption, which can maintain the color and nutrition of vegetables to a large extent. In industry, it can be applied to pretreat fruits, vegetables, and other foods before drying. It can effectively enhance the drying efficiency, and shorten the drying time.