اثر نوع دستگاه سفيدكن، رقم و مدت زمان سفيدكني بر درصد شكست، درجه سفيدشدگي و شاخص سفيدشدگي برنج

Effects of Milling Machine Type, Variety and Milling Duration on Rice Breakage, Degree of Milling and Whiteness Index

Whitening as one of the stages in rice processing is performed following dehusking. Studies on performance of milling machines prevailent in Mazandaran province, as the biggest rice producer province in Iran, are essential and helpful in reducing rice losses. A research was undertaken to examine the effects of variety (Tarom, Hibrid, and Fajr), milling machine (frictional and abrasive baed milling machines) as well as milling time duration (25, 35, 45, 55, 65 and 75 seconds) on some such rice qualitative, and quantitative parameters as broken rice, degree of milling, as well as whiteness index. Statistical design was a randomized complete block design one 36 treatments and in three replications. Results indicated that increasing milling duration increased the degree of rice whitening up to 53.39 % due to a more stay time of brown rice in the milling chamber. Among the treatments, Hibrid and Fajr varieties devoted the highest and the lowest degree of milling to themselves, respectively. Based on statistical analysis, Tarom variety scored the highest whiteness index of 0.360, whereas Hibrid variety showed the lowest one namely 0.247. Results indicated that milling machine type, rice variety and milling time duration as well as interaction effect of milling machine type and rice variety exert significant effects on all parameters studied. Amount of broken rice for Fajr variety and for the two types of milling machines was found to be equal, whereas, that fiqure for Tarom variety was almost 10.23% lower for abrasive type machine as compared with the frictional one.