The effects of drying temperature in paddy cleaner and relative humidity on rice grain yellowing were also studied. An empirical equation was developed to predict the rate of rice grain yellowing. The yellowing rate followed zero-order kinetics. The value of the yellowing constant increased exponentially with temperature and increased linearly with water activity. An analysis of variance showed that the interaction of temperature and water activity significantly influenced the rate of rice grain yellowing.
Drying characteristics of paddy (long grain variety PR-118 procured from PAU, Ludhiana) in an integrated dryer using single as well as combined heating source was studied at different air temperatures. The integrated dryer comprises three different air heating sources such as solar, biomass and electrical. Drying of paddy occurred in falling rate period. It was observed that duration of drying of paddy from 22 to 13 % moisture content (w.b.) was 5–9 h depending upon the source of energy used. In order to select a suitable drying curve, six thin layer-drying models were fitted to the experimental moisture ratio data.
Among the mathematical models investigated, Wang and Singh model best described the drying behaviour of paddy using solar, biomass and combined heating sources with highest coefficient of determination (r2) values and least chi-square, χ2, mean bias error (MBE) and root mean square error (RMSE) values. However, Page model adequately described the drying behavior of paddy using electrical heating source.
Determining the implicit contribution of the rice polisher attributes to the market price of rice varieties can be done through hedonic pricing analysis. Hedonic pricing regressions have been quite popular in the economics literature, being applied to various food commodities such as wine, tea, apples, and breakfast cereals. In all these commodities, the products could be grouped into quality classes or varieties. The hedonic pricing model has also been applied to study the effects of extrinsic and intrinsic quality attributes of rice to market prices; with the results suggesting that varietal improvement programs should not be limited only to yield-enhancing traits. Furthermore, dissemination and adoption of new varieties need to be supported. A recent study in Central Luzon found that out of the 200 modern rice varieties released, fewer than 10 varieties are being used by farmers in the Central Luzon area.