Nattapol Poomsa-ad

EFFECT OF TEMPERING ON SUBSEQUENT DRYING OF PADDY USING FLUIDISATION TECHNIQUE

ABSTRACT Drying and tempering models for paddy drying by a fluidised bed technique have been developed to describe the moisture movement inside a single paddy kernel. The grain shape was considered as a finite cylinder. The internal diffusion is an important contribution to control the drying rate of paddy. The dependence of effective diffusion coefficient on drying temperature can be adequately explained based on Arrhenius form. The parameters of this equation were evaluated in the range of temperatures between 110°C and 170°C by using the regression analysis with 189 experimental drying data. As compared with no tempering, the faster drying rate can be obtained by tempering treatment between drying stages. The effect of degrees of tempering on determining the moisture reduction in the second stage has also been explored. According to the simulation results, a prediction equation of the required tempering time for the tempering index of 0.95 has been established in which the drying air temperature, initial moisture content and drying time are taken into account. The tempering time for 35 min is recommended for the continuous fluidised bed dryers being operated in rice mills.

MANAGING MOIST PADDY BY DRYING, TEMPERING AND AMBIENT AIR VENTILATION

ABSTRACT This paper describes a strategy for reducing moisture in paddy by fluidized bed drying, tempering and ambient air cooling. Experimental results showed that after the three processes, moisture content was reduced from 33 % to 16.5 % dry-basis within approximately 53 minutes. During the first process, a fluidized-bed dryer was used to reduce the moisture content of paddy down to 19.5 % dry-basis within 3 minutes. Then the paddy was tempered for 30 minutes. Finally, it was cooled by ambient air (temperature and relative humidity of 30 °C and 55-60% respectively) with air velocity of 0.15 m/s for 20 minutes. Quality of paddy in terms of head rice yield and whiteness was acceptable.

Improving head rice yield of glutinous rice by novel parboiling process

ABSTRACT Most commercial parboiled rice is produced from high-amylose content rice. Glutinous rice, which is lacking in amylose content, is generally consumed in Southeast Asian countries. Rare study of parboiling glutinous rice has been observed. In this study, glutinous rice was improved in head rice yield by a novel parboiling process. Two rough glutinous rice, rice department 6 (RD6) and black glutinous rice (BGR) cultivars, were soaked in hot water at 70 ± 5°C for 3 h. The ricer 3moisture content after soaking was 50–52% (d.b.), it was dried with hot air and superheated steam (SHS) at 110, 130, and 150°C in a fluidized bed dryer. The results show that SHS at all drying temperatures can improve the high head rice yield in both parboiled glutinous rice cultivars better than hot air drying. Higher temperature drying caused L* value to decrease but the b* value increases in RD6, whereas in BGR, all color values decreased and ΔE* was increased when the drying temperature increased. Increasing drying temperature presented a softer texture of both glutinous rice cultivars. Upper 130°C, completed gelatinization of both varieties can be obtained and seen by scanning electron microscope and differential scanning calorimeter (DSC). This technique of using high-temperature fluidized bed drying can produce completely parboiled glutinous rice in a single process instead of two conventional processes, steaming and drying, in series.

Control of microwave assisted macadamia drying

ABSTRACT We studied the microwave-assisted macadamia drying, using surface temperature control and without surface temperature control as well as hot air drying, and assessed the drying time, drying rate, colour values, hardness and water activity of nuts and efficiency. The surface temperature of macadamia nuts was controlled between 60 and 80 °C using a thermal radiation detector. For drying without the surface temperature control, drying temperatures in the range of 40–60 °C and microwave power were controlled in the range of 1.6–4.4 Wg−1. We found that increase in microwave power and temperature had a positive effect with shorter drying time and increased drying rate. Microwave assisted hot air drying by surface temperature control led to a better quality product in respect of kernel brightness and suitable aw for storage, but a harder kernel. In addition, drying without surface temperature control had the highest energy efficiency followed by surface temperature control and hot air only. Considering quality, the recommended condition was drying by surface temperature control at 60 °C with 60 °C hot air combined with microwave.