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The objectives of this study were to analyze the effects of drying employing three different heat sources on drying kinetics and to evaluate qualities of parboiled rice after drying. Drying temperature was varied between 60 and 100C. Power of infrared (IR) heat source was fixed at 1,000 and 1,500 W and air flow rate was fixed at 1.0 ± 0.2 m/s. The three drying strategies composed of hot air (HA), IR and combined HA + IR drying. The experimental results were simulated using various equilibrium moisture content models and the mathematical drying model for prediction of drying kinetics and evaluation of effective diffusion coefficient (Deff) followed by Fick's law of diffusion. The results revealed that Deff values of HA and IR drying were in the range of 10−12–10−11 m2/s and relatively depended on temperature. For quality evaluation, conclusions reached that head rice yield using HA + IR drying had the highest value, while yellowness and whiteness of the parboiled rice are significantly affected by drying condition (P > 0.05). Practical Applications These results suggested that combined hot air and infrared (HA + IR) drying offers a great potential for preserving Leb Nok Pattani parboiled rice. Drying kinetics and quality aspects determined that IR drying is more efficient than the other drying method. However, the color degradation in the grain kernel is an issue for quality measurement.

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This work aims at investigating structural changes occurring in vacuum drying (VD) compared with conventional convective drying of bananas, pineapples, and apples, and to find the appropriate thin‐layer equation for predicting the drying kinetic of products. Drying experiments were carried out at the drying air temperatures of 100 °C, 110 °C, and 120 °C at 4 kPa. The experimental results showed that the VD method at high temperature for all three types of fruits showed the fastest drying time, lowest degree of lightness, lower shrinkage, more pores, more crispness, and more rehydration ability compared with conventional drying and low‐temperature drying. Consequently, the VD at drying air temperature of 120 °C was suggested as the best drying condition. Moreover, six mathematical models describing thin‐layer drying were investigated. The Logarithmic equation was considered adequate for describing the thin‐layer drying behavior of apples, while the Diffusion approach equation was deemed adequate for bananas and pineapples. Practical applications Dried agricultural products serve as important healthful snack items around the world. Vacuum drying (VD) is another process in which products are dried in a reduced pressure environment. The products obtained by the process were of exceptionally high quality. Moreover, none have investigated the effect of VD on structural changes (in terms of shrinkage, rehydration behavior, microstructure, texture, and color) of bananas, pineapples, and apples at drying air temperatures of 100 °C, 110 °C, and 120 °C and absolute pressure of 4 kPa. The result from this research can be applied to the development of dried agricultural product in Thailand.

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