Effect of drying and milling modes on the quality of white rice of an Indonesian long grain rice cultivar

Abstract

Background. Many studies have revealed the susceptibility of long grain rice to breaking during milling, while others have demonstrated the variation in the yield of head rice due to different rough rice drying methods. Thus, this study aims to determine appropriate drying and milling methods to improve the head rice yield and nutritional quality of long grain rice. Materials and methods. A series of drying experiments were performed on rough paddy rice employing shallow bed, oven and sun drying methods. Then, the dried rough rice grains were milled with various dehusking (H), separation (S) and polishing (P) configurations to obtain white rice. The resulting batches of white rice were analyzed and compared in terms of head rice yield, broken rice yield, brewer yield, whiteness and nutritional quality. Results. Milling configurations strongly affected the total, head rice, broken rice and brewer yields. The configuration of one dehusking, one separation and one polishing (H - S - P) resulted in the highest milling and head rice yields. Although the whiteness of the rice samples was significantly affected by the milling configuration, their values fell within an acceptable range preferred by consumers in Southeast Asia (39-47). The milling of dried rough rice obtained from shallow bed and sun drying using a concrete floor and white tarpaulin resulted in a comparable total (65%) and head rice yield (51%). However, the milling of rough rice dried using an oven and sun drying on black tarpaulin resulted in a slightly lower total yield (64.50%) and head rice yield (50.50%). The moisture, ash, protein and lipid contents of the white rice were significantly lower than those of manually dehulled rice, whereas the carbohydrate and amylose contents of the white rice were significantly higher. Conclusion. Application of shallow bed or sun drying on a concrete floor followed by milling with the H - S - P configuration produced the highest head rice yield with an acceptable whiteness and nutritional composition. These combined postharvest technologies are simple, efficient and economical for both small- and large-scale applications. Further research on consumer acceptance and on the nutritional and cooking qualities of the white rice obtained from these combined postharvest technologies is essential.