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.

Drying at a microwave power of 300 W provided the highest nutritive and antioxidant values. The results of this study are useful in the selection of optimal drying conditions during microwave drying of germinated corn, as a baseline for other agricultural crops. © 2016 Society of Chemical Industry.

The effects of microwave power (MP, 100–600 W) on the drying kinetics, as well as the physical and antioxidant properties of papaya seeds dried under microwave vacuum drying (MVD) were investigated. The results found that moisture diffusivity increased in the order of 10−8 with an increase in MP. Shrinkage increased from 1.2 to 4.9% and bulk density decreased from 3,441 to 1,091 kg/m3, respectively, while the moisture content decreased. The antioxidant contents of all of the MVD samples were higher than those of the samples dried under ambient air ventilation. An increase in MP decreased the total phenolic content from 14.69 to 10.66 mg gallic acid equivalent per gram dry weight (DW), increased both the β‐carotene and the total flavonoid content in the ranges of 0.2–0.35 mg β‐carotene equivalent per gram DW and 20.71 to 23.51 mg catechin equivalent per gram DW, respectively. Higher values of antioxidant activity were obtained at higher MP. The results have shown that the use of novel MVD technique in appropriate conditions can improve the overall drying efficiency and enhance the total yield of antioxidant content. Practical Applications Papaya seeds have great potential for use as a source of antioxidants. However, the best novel techniques for retaining high values of antioxidant compounds, and therefore recouping value from the wasted seeds, has not been widely reported on. This study has found that combined microwave vacuum drying (MVD) is a very beneficial drying method for the preservation of antioxidant content. A better antioxidant yield from dried papaya seeds was obtained using MVD at a higher MP of 600 W. Trolox equivalent antioxidant capacity of seeds dried using MVD was 27.62% higher than the samples dried using ambient air ventilation.

The effects of hot air drying temperatures (40-80°C) on apparent density, void fraction, shrinkage, total phenolics, total flavonoids and reducing power in germinated corn were investigated. The physical properties: apparent density, void fraction and shrinkage at moisture contents ranging from 13 to 35% dry-basis were determined using standard techniques. The result found that apparent density and the void fraction were linear in relation to the initial moisture contents. The apparent density increased from 44 to 50 kg/m3. The void fraction decreased from 78 to 58% with increasing moisture content. The chemical property resulted in 40°C hot air convection drying enhances total phenolics and total flavonoids to 6.41% and 50.00%, respectively, when compared with the control. Higher drying temperature resulted in lower total phenolic, total flavonoid content and reducing power of germinated sweet corn compared with the control.

This research was to investigate some thermo-physical properties and to determine a mathematical model for describing drying kinetics for medium and long grain parboiled rice varieties. The thermo-physical properties in terms of equilibrium moisture content (EMC), apparent density, void fraction, specific heat capacity at moisture content ranging from 30 to 58% dry-basis (d.b.) for both Leb Nok Pattani (LNP) and Suphanburi 1 (SP 1) rice varieties were determined by conventional standard techniques.The evaluated results showed that EMC values for both rice varieties predicted by the GAB’s model yielded the best fitting with experimental data. To determine thermo-physical properties, the results stated that apparent density and specific heat capacity of parboiled LNP and SP1 rice varieties were linearly dependent on moisture content. In contrast, percentage of void fraction of medium grain LNP and long grain SP1 rice variety was inversely proportional to moisture content. For employing empirical thin-layer drying models, the Two terms model was the best fitting model to describe the experimental data for both rice varieties.