Improvement And Morphological Mechanism For Eating Quality Of Brown Rice By Reducing Agent Combined With Hydrothermal Treatment

Brown rice has a higher nutritional value than polished rice and is beneficial to human health.However,brown rice is generally difficult to cook,has poor taste,and is difficult to digest,so it is difficult to be accepted by consumers.In order to overcome the inherent disadvantages of brown rice,the effects of defatting,hydrothermal,reducing agent alone,or in combination treatment in improving the eating quality of brown rice were studied in this paper.Compared with untreated brown rice and polished rice,the differences in eating quality(texture,sensory score,and in vitro digestibility)of brown rice before and after treatment were systematically analyzed,and the mechanism of improvement was revealed from the changes in physicochemical properties,micromorphology and starch structure of brown rice.The main results are as follows:(1)Effects of reducing agent combined with hydrothermal treatment on the eating quality of brown rice.Firstly,the treatment conditions of defatting,hydrothermal,and reducing agent treatment of brown rice are defatting with absolute ethanol,hydrothermal 30 min at 80℃,and 100mmol/L ascorbic acid solution immersion,respectively.Brown rice was treated with defatted,hydrothermal and ascorbic acid alone or in combination.Compared with untreated brown rice and polished rice,the texture,sensory score and digestibility of brown rice before and after treatment were compared and analyzed.The results showed that defatted,hydrothermal and ascorbic acid treatments alone improved the eating quality of brown rice to some extent,but the effect of defatting combined with ascorbic acid hydrothermal treatment was the best.The texture results showed that after defatting combined with ascorbic acid hydrothermal treatment,the hardness and chewiness of cooked brown rice decreased to the level of cooked polished rice,and the stickiness and stickiness /hard ratio increased significantly to 76.20% and 73.96% of cooked polished rice,respectively,which was more than 5 times that of untreated cooked brown rice,and the drying process had no obvious adverse effect on the texture of cooked brown rice.The sensory evaluation results show that after the defatting combined with ascorbic acid hydrothermal treatment,the total sensory score of cooked brown rice is significantly increased from 68.9 to 84.0.In addition to the smell,the sensory scores of cooked brown rice and cooked polished rice were not significantly different in terms of appearance structure,palatability,flavor,and cold texture.The data of in vitro starch digestibility showed that the starch digestibility of cooked brown rice treated by defatting combined with ascorbic acid hydrothermal increased from 61.37% to 79.53%.At the same time,the glycemic index(GI)has also been significantly improved,but it has not reached the level of cooked polished rice,so it contributes to the improvement of nutrition.(2)Effects of reducing agent combined with hydrothermal treatment on the physicochemical properties of brown rice.Brown rice was treated with defatting,hydrothermal,and ascorbic acid alone or in combination,and then dried to the original moisture content as a sample.With untreated brown rice and polished rice as controls,the data of treated brown rice in cooking quality,water droplet contact angle,room temperature water absorption rate,and pasting viscosity was analyzed to explore the reasons for the improved eating quality of brown rice.The results showed that the optimal cooking time of brown rice was shortened by 25.25%(from 30.33 min to 22.67 min)after defatting combined with ascorbic acid hydrothermal treatment,and the heating water absorption rate,volume expansion rate,and solid loss rate were all increased to the level of polished rice.The cooking qualities were significantly improved.In addition,the surface water droplet contact angle of brown rice grains decreased from 113.39° to 64.93° after treatment,which was lower than the water droplet contact angle of polished rice(73.30°),and the surface of rice grains changed from hydrophobic to hydrophilic.Its room temperature water absorption rate increased from 11.13% to 30.24%,far exceeding the level of polished rice.After treatment,the peak viscosity,hold strength,final viscosity and breakdown of brown rice flour increased,the paste temperature decreased,which improved the gelatinization viscosity of brown rice.The reduction of water droplet contact angle and the increase of room temperature water absorption rate lead to the improvement of cooking quality and pasting viscosity which are the main reasons for the improvement of brown rice eating quality.(3)The effect of reducing agent combined with hydrothermal treatment on the micromorphology and starch structure of brown rice.The surface and cross-section of freeze-dried rice grains,the crystal structure changes of starch in freeze-dried rice flour,and the microscopic morphology changes of cooked brown rice were studied.X-ray diffraction showed that the defatting combined with ascorbic acid hydrothermal treatment significantly decreased the relative crystallinity of starch in the control group of brown rice from 32.74% to 22.55%,but did not change the crystal type,which was still an A-type crystal structure.Microscopic morphology of brown rice cortex surface and cross-section showed that defatting combined with ascorbic acid hydrothermal treatment caused obvious cracks,micropores and breaks on the surface and cross-section of brown rice cortex,and promoted the separation of starch granules inside the cooked brown rice.These microstructural changes promote the water absorption capacity of brown rice in the cooking process and are conducive to more uniform starch gelatinization,which is the intrinsic reason for the improvement of brown rice eating quality.In summary,defatting combined with ascorbic acid hydrothermal treatment can effectively improve the eating quality of brown rice and thus consumer acceptability.After treatment,the surface water droplet contact angle of brown rice grains is lower than that of polished rice,and the surface of brown rice grains changes from hydrophobic to hydrophilic,with the room temperature water absorption rate far higher than that of polished rice.The changes in water absorption capacity of brown rice improved the cooking quality and gelatinization viscosity of brown rice.In addition,cracks and micropores appeared on the surface and crosssection of brown rice after treatment promote the separation of starch granules inside cooked rice,contributing to more uniform starch gelatinization,which is the intrinsic reason for the improvement of brown rice eating quality.Therefore,the defatting combined with ascorbic acid hydrothermal treatment significantly improved the eating quality of brown rice,which was achieved by changing the cortex and internal structure to improve water absorption capacity and cooking quality,and the drying prefabrication process after treatment had no obvious adverse effect on the improvement effect,so the preparation of prefabricated brown rice is available.The research results have important practical value for improving the eating quality of brown rice and realizing its popular consumption as a staple food,and the process is green,environmentally friendly and safe,and has broad application prospects.