Study On Improving Cooking And Eating Qualities Of Brown Rice By Lactic Acid Bacteria Fermentation

As a kind of whole grain,brown rice is rich in dietary fiber and active ingredients,therefore it has a beneficial effect on human health.However,the large amount of dietary fiber and wax bring some disadvantages,such as the rough taste,hard texture and long cooking time,thus hinder the staple food consumption of brown rice.In this study,fermentation with lactic acid bacteria was applied to improve the cooking and eating quality of brown rice,meanwhile,the nutrient composition and storage stability were studied.This study can provide a new strategy for the improvement of cooking and eating quality of brown rice.Firstly,the identification and gradient domestication of experimental strains were studied.The experiments about the filter paper degradation and the determination of cellulase activity showed that the Lactobacillus plantarum JYI-3913 had the ability for degrading cellulose;In order to increase its cellulose utilization rate of brown rice medium,cellobiose was used for its gradient induction and domestication,and its cell density and vitality in brown rice medium were increased.Secondly,the process for improving the cooking quality of brown rice by lactic acid bacteria fermentation was optimized.Single factor and orthogonal experiments were performed and the optimum process parameters for fermentation were as follows: fermentation time 24 h,fermentation temperature 25°C,moisture content 35%,and inoculation amount 0.10%.Under this condition,the best cooking time of brown rice was 22.16 min,which was 20.17% shorter than that of raw brown rice,proving the great improvement of the cooking performance of brown rice.The pH of brown rice was 4.87,which was slightly sour.Then,the cooking and eating qualities of fermented brown rice were evaluated.After fermentation,the water absorption ability and the volume expansion rate increased,the hardness of brown rice decreased significantly by 29.63%(p<0.05),and the stickiness increased significantly by 81.88%(p<0.05),resulting in the tighter adhesion among rice grains and better sensory.In addition,the reasons for the improvement of cooking and eating quality were also explored.After fermentation,obvious gully and small holes appeared on brown rice cortex,and the starch connection became looser.The cellulose and hemicellulose were degraded to different degrees,and the bonds between them were partially broken or became loose,therefore the obstacles of water absorption was reduced;Meanwhile,the starch granules of brown rice were corroded after fermentation,the long chains of amylopectin were partially broken,the crystal structure of starch was destroyed and the gelatinization enthalpy decreased,making the starch to be gelatinized more easily.In particularly,the retrogradation value of starch decreased.These changes improved the cooking and eating quality of brown rice.Finally,the changes of nutrient composition and storage stability in fermented brown rice were studied.After fermentation,crude fiber content decreased by 0.42%(p<0.05).The total phenolic,flavonoid and GABA contents of fermented brown rice increased to 1.24,1.12 and 3.02 times respectively as compared to the raw brown rice.After being vacuum packaged,the fatty acid value and hexanal content of fermented brown rice increased slowly,the number of mold in fermented brown rice was significantly lower than that in raw brown rice,while the total number of colonies increased at first and then decreased in fermented brown rice.The results showed that fermentation by lactic acid bacteria can effectively inhibit the growth of other bacteria and extend the shelf life of brown rice.