Abstract: Objective: To investigate the effect of hot air drying on properties of semi-dry milled rice flour. Methods: Rice was hot air dried at 45 ℃ for 240 min, at 75 ℃ for 45 min or at 105 ℃ for 15 min and then used to prepare semidry-milled rice flour. The moisture absorption rate was determined and apparent cracks on the rice surface were examined. The whiteness and gel properties of semi-dry milled rice flours were analyzed, and the textural properties, tensile properties and breaking rate of fresh rice noodles made from the rice flours were determined. Results: Hot air treatments at 75 ℃ for 45 min and at 105 ℃ for 15 min could shorten the soaking time to reach maximum moisture content in semi-dry milled flour to 11 min. Surface cracks were observed in all three groups under stereomicroscopy. The whiteness and gel properties of semi-dry milled rice flour with hot air treatment at 45 ℃ for 240 min and at 75 ℃ for 45 min were not significant different from those of wet milled rice flour while the second hot air treatment resulted in a decrease in the gel hardness of semi-dry milled rice flour. There was no remarkable difference in the breaking rate of fresh rice noodles between semi-dry milling with hot air treatment at 75 ℃ for 45 min and wet milling (P > 0.05). Conclusion: Hot air treatment at 45 ℃ for 240 min and at 75 ℃ for 45 min can greatly shorten the soaking time to reach maximum moisture content in semi-dry milled flour and improve its properties. The quality of fresh rice noodles made from semi-dry milled flour with hot air treatment at 75 ℃ for 45 min is comparable to that of wet milled rice flour. This study provides a theoretical basis for overcoming the bottleneck problems of rice semi-dry milling such as long soaking time, high risks of microbial infection and difficulties in achieving continuous production.

Key words: hot air treatment, semi-dry milling, moisture absorption rate, cracks, quality