The influence of rice properties on flour milling and the relationship between rice flour quality and bread production

In rice flour manufacturing research, the relationship between the type of rice used and the milling quality is poorly understood. Regarding the fine rice flours used in rice bread, although the importance of both particle size and the degree of starch damage occurring during milling is recognized, other factors remain unexplained. Therefore, the milling characteristics of various types of polished rice and the features of sieved rice flour in relation to rice bread quality were examined. Labo-mill pulverization of 42 polished rice samples of 24 different types of rice was carried out until 60 % of each sample passed through a 200-mesh sieve. The results indicated that pulverization time decreases with increasing amylase content of the polished rice. Chalky and floury rice mutants pulverized quickly regardless of amylase content. A high correlation (0.81, p < 0.01) was observed between starch damage and the time required for pulverization. Furthermore, pulverization of rice samples of varying grain quality indicated that more immature grains required shorter milling time. In the case of pin-milling of polished rice immersed in water, the average particle diameter and degree of starch damage of the rice flour decreased and baking quality improved with increasing immersion time. The specific volume of the rice flour bread increased as the particle size decreased with further sifting of the rice flour, and the low degree of starch damage of the rice flour made the bigger specific volume in comparison with the same particle size. These results indicate that the properties of the rice and parameters of flour milling are important in rice flour bread manufacturing. Fine particle size and a low degree of starch damage are particularly important factors. Consideration of these factors is thus also necessary in the manufacturing of other products made from rice flour.