Effects Of Rice Bran Rancidity On The Properties And Structure Of Rice Bran Dietary Fiber

The rice bran resource is very abundant in China,the annual output reached 14 million tons in recent years.Rice bran with 34?52%dietary fiber is a high quality resource for the preparation of rice bran dietary fiber.Rice bran contains strong activity lipase and lipoxygenase,leading to rice bran rancidity easily,and in China,rice bran is generally difficult to be stabilized in time and effectively,so the utilization of rice bran in China is low.Effect of rice bran rancidity on the properties and structure of rice bran dietary fiber was studied in this paper.Fresh rice bran which stored in a condition for different period were used as material to prepare rice bran insoluble dietary fiber(RBIDF)and rice bran soluble dietary fiber(RBSDF)after defatting.As storage time of fresh rice bran increased,water holding capacity,oil holding capacity,cation exchange capacity,and adsorption capacity of bile sodium of RBIDF firstly increased,and then decreased,and achieved the maximum value as fresh rice bran stored 1 d,3 d,1 d,and 3 d,respectively.water binding capacity of RBIDF fiber gradually decreased,no significant change of RBIDF expansion was observed,and powder brightness of RBIDF firstly increased,and then decreased.As storage time of fresh rice bran increased,reducing power,metal chelating activity,and free radical scavenging ability on ABTS+·,DPPH·,·OH,O2-·of RBSDF firstly increased,and then decreased.Fresh rice bran which stored in a condition for 0,1,3,5 and 10 d were used as material to prepare RBIDF,and effects of the addition of RBIDF which prepared by rice bran with different storage tine on rice flour pasting and gelatinization properties were investigated.The results indicated that when addition of RBIDF was the same,as storage time of rice bran increased,peak viscosity in the rice flour RVA profiles firstly increased,and then slightly decreased,and achieved the maximum as rice bran stored 5 d;setback value in the rice flour RVA profiles gradually increased;peak time and pasting temperature firstly decreased,and then increased,and achieved the minimum as rice bran stored 5 d and 3 d,respectively;storage modulus of rice flour gradually increased during rice flour gel formation as well as after rice flour gel formation,the loss angle tangent firstly decreased,and then increased after rice flour gel formation,and achieved the minimum as rice bran stored 5 d.Hardness,resilience,cumminess,and chewiness of rice flour gel firstly increased,and then decreased;adhesiveness of rice flour gel firstly decreased,and then increased.Hardness,resilience,cumminess,chewiness,and adhesiveness of rice flour gel achieved the extremum as rice bran stored 3 d.The results of correlation analysis indicated that acid value of rice bran crude oil was positively correlated with peak viscosity(P<0.05),negatively correlated with peak time and pasting temperature(P<0.01),and positively correlated with setback value of rice flour and storage time of rice bran(P<0.01).Rice bran rancidity had a significant effect on the structure of rice bran dietary fiber.As storage time of fresh rice bran increased,the O-H expansion vibration of RBIDF was slightly red shift,the absorption peak of the hydroxyl group of RBSDF was weakened,and the expansion vibration of C=O was significantly increased,the degree of oxidation and structure change of RBSDF in the storage process is greater than that of RBIDF;X diffraction pattern of RBIDF showed the typical crystal diffraction peak at 20=21.5°,but the peak shape and peak position did not change significantly.As storage time of fresh rice bran increased,RBSDF gradually formed aggregates and the average particle size gradually increased;analysis of monosaccharides showed arabinose,galactose,mannose,glucose and xylose in turn,the relative content of glucose and galactose decreased first and then increased,the relative content of arabinose,mannose and xylose increased first and then decreased.