Preparation of fresh rice noodles using rice prepared by tempering moisture and semi-dry milling method and determination of its quality

Abstract: Traditionally, wet-milling of rice followed by an overnight soaking in water is commonly used as a processing for making rice noodles. However, the long soaking time resulted in bacterial growth on rice, leading to degradation in product quality. Therefore, the dry-milling method is used to break rice kernel, but the dry-milling can create more heat and mechanical damage which can lead to an increased damage of rice starch granules. As such, dry-milled rice flour exhibits a higher degree of starch damage compared to the wet-milled rice flour. Therefore, the quality of rice noodles produced from dry-milled rice flour is not acceptable by consumers despite the fact that dry-milling improved the safety and stability of rice products. In order to minimize the adverse effects of dry-milling on characteristics of rice flour and cooking qualities of rice noodles, the objective of this study was on developing a new process of semi-dry milling. To investigate the effect of semi-dry milling on rice flours characteristics and fresh rice noodles quality, the rice with 28% and 30% tempering moistures were milled by cyclone mill and Buller mill. Whiteness, gel properties and pasting properties of rice flours were analyzed, and then textural properties, cooking properties and sensory quality of fresh rice noodles were determined. The results showed that tempering moisture and milling equipments can affect rice flours qualities significantly. Milling rice with 28% and 30% tempering moisture can minimize the granules damage by machine and excess heat generated during milling. Flours whiteness of rice with 28% and 30% tempering moisture milled by Buller mill were significantly higher than wet-milled flours (P<0.05), but the use of cyclone milling on rice with 30% tempering moisture had a similar whiteness with wet-milled flours. Among the four kinds of semi-dry milled flour samples, the gel from cyclone-milled rice flour (30% tempering moisture) showed the highest hardness (3.45 N/cm2), which had no significant difference with wet-milled flour (P>0.05), whereas Buller semi-dry milled flours showed lower value than wet-milled flour (P<0.05). The pasting properties showed that tempering moisture and milling equipments did not affect the pasting temperature. Higher peak viscosity was observed in wet-milled rice flour, and lower one was observed in Buller -milled rice flour (30% tempering moisture) compared to dry-milled rice flour, the breakdown of flour samples milled from rice with 30% tempering moisture were lower than the wet-milled flour (P < 0.05), and lower value of setback was observed in Buller -milled rice flour (30% tempering moisture), which had no significant difference with the wet milled flour (P > 0.05), but cyclone-milled rice flour (30% tempering moisture) still had higher setback than the dry-milled rice flour. Based on the comparison of rice flour characteristics between semi-dry milled flours and wet-milled flour, the use of cyclone milling on rice with 30% tempering moisture was selected to be the best method. Compared to wet-milling, rice noodles produced by dry-milling can not be used for texture measurement due to its high broken rate, and it had the worst cooking qualities and sensory (visual and taste) evaluation. However the quality of rice noodles produced from cyclone-milled rice flour (30% tempering moisture) were significantly improved. The texture hardness was 35.10 N/cm2, the elasticity was 0.97, which were softer and more elastic than the wet-milling produced rice noodles. Moreover semi-dry milling method significantly affected the cooking loss and turbidity of rice noodles, which was 7.51% and 0.40 for the noodles prepared with cyclone-milled rice flour (30% tempering moisture), sensory evaluation was higher than the dry-milling produced rice noodles (P < 0.05), and there were no significant differences of cooking properties and sensory qualities between them (P > 0.05). Those results showed that the semi-dry milling can minimize the damage caused by mechanical forces and heat during milling. The method also reduced water use and the risk of microbial contamination in the traditional wet milling. Therefore, the semi-dry milling of rice with higher tempering moisture, such as cyclone-milled rice flour (30% tempering moisture), can be used to replace the wet-milling for industrial production, and the process can provide good rice noodles quality similar to or better than the traditional wet milling method but with low water usage and low risk of microorganism contamination.