A Study of the Effect of Solar Drying System on Rice Quality

A thin layer solar drying method was compared with a traditional method (sun drying) of paddy drying, with their effects on quality characteristics of two varieties of Iranian rice (Kamphiroozi and Sazandegi) studied. Solar drying process was conducted in a passive, mixed mode type solar dryer at about ۵۰ºC for ۹۰ minutes. In sun drying method this process took ۸-۱۰ hours at a mean temperature of about ۲۶ºC. Samples were milled and polished. Quality factors including trade quality (head rice yield percent and whiteness), cooking quality (amylose content, gelatinization temperature, gel consistency, aroma and flavor) as well as nutritional quality (thiamine and lysine contents) were evaluated. For a determination of head rice yield, the percentages of de-husked and broken kernels were determined by hand-sorting of broken kernels, the calculation being done through the pertaining formula. Gel consistency was determined according to the method of Cagampang et al. (the consistency of milled rice paste that has been gelatinized by being boiled in dilute alkali and then cooled to room temperature). Amylose content was determined through the simplified assay method of Juliano (setting standard curve by spectrophotometer and comparing the adsorption with the sample’s). Gelatinization temperature was estimated by the extent of alkali spreading and clearing of milled rice soaked in ۱.۷% KOH for ۲۳ hours at room temperature. Organoleptic characteristics of cooked rice (iflavor, aroma) and apparent whiteness were judged by the taste panel using sensory evaluation method in triplicate. With respect to nutritional value, lysine amino acid was determined by using biological assay and applying Lactobacilllus delbrueckii while thiamine being measured through thiochrome fluorescence technique. The objective of this study was to examine the influence of solar drying process on the final quality of rice kernels and to compare the effects of this method with those in the traditional method of drying (natural sun drying). Results indicated that under the conditions prevailing in solar dryer, quality factors weren't affected except for whiteness of rice that too was better than that for sun dried samples. All other quality characteristics of the final product were acceptable in comparison with those in sun drying method.

Keywords:

Natural sun drying , Rice quality , Solar drying