Effect Of Rice Bran Dietary Fiber On Wheat Starch Retrogradation And Steamed Bread Quality

Starch is the main component of wheat grain.The high content of starch makes wheat flour products easy to retrogradation.Flour product’s color,hardness,taste,flavor and other functions have been changed significantly,which seriously affects the quality characteristics of wheat flour products.Therefore,studying the aging mechanism of wheat starch and delaying its aging are of great significance to the quality improvement of wheat flour products.In this study,the insoluble dietary fiber（IDF）and soluble dietary fiber（SDF）fractions（SDF-40,SDF-60 and SDF-80）were separated from defatted rice bran by enzymolysis and alcohol precipitation.Taking the amylose and amylopectin obtained from wheat grain as research objects,the effects of dietary fiber fractions from rice bran on the texture quality of wheat starch paste during retrogradation were evaluated by texture analyzer,and evaluated the anti-retrogradation mechanism of rice bran dietary fiber by analyzing the results of infrared spectrum and X-ray diffraction.On this basis,the following contents were studied:（1）the effect of SDF-40 on the quality of wheat steamed bread（WSB）;（2）the effect of ultrasonic assisted SDF-40 on dough fermentation and the quality of steamed bread.The experimental results are as follows:The SDF-40 could significantly improve the textural properties of the amylose and amylopectin.After 11 days of storage,the hardness of wheat amylose gel and amylopectin gel for adding SDF-40 were decreased by 6.97%and 24.27%,respectively.Their elasticities were increased by 5.97%and 4.24%,respectively.Their chewiness was decreased by 25.72%and 41.86%,respectively.Therefore,the SDF-40 component can delay the retrogradation of wheat starch and has a better effect on wheat amylopectin.Scanning electron microscopy showed that the amylopectin added with SDF-40 had more porous holes after being stored for the same time,the water content was larger,and the water holding capacity was better.Infrared spectrum and X-ray diffraction analysis showed that the absorbance ratio of 1047 cm^-1/1022 cm^-1 and the peak intensity at 2θ（17.0°）declined,crystallinity of amylopectin reduced after adding SDF-40.It is proved that SDF-40 can delay the retrogradation of starch by inhibiting the recrystallization of amylopectin.The SDF-40 has a certain influence on the quality of WSB.When the added amount of SDF-40 component was 5.0%,the hardness growth rate,chewing degree growth rate and elasticity of WSB were the slowest.After 5 days of storage,the hardness of WSB decreased by 37.86%compared with the control group.The elasticity increased by 8.99%,the chewability decreased by 36.48%,and the specific volume of WSB was 3.07 m L/g,which were significantly higher than that of the control group（P<0.05）.The swelling volume of WSB was 16.62%higher than that of the control group,and the color difference resolution was not significant.The comprehensive score showed that the quality of WSB was the best when 5.0%SDF-40 was added.The response surface factors were ultrasonic time,ultrasonic power and SDF-40addition amount,and the comprehensive weighted score（CWS）of texture index of WSB was taken as the response value.The optimal conditions of enhancing the WSB quality were obtained by response surface method:ultrasonic power 39 W,ultrasonic time 45.8min,SDF-40 content 4.3%.Under these conditions,the CWS measured in three replicates is 22.25,23.07 and 21.03,respectively.The average value is 22.12±1.03,which are basically consistent with the response surface model predictions of 22.09.The quality and retrogradation process of WSB in group A（SDF-40 0.0%,ultrasonic power 39 W,ultrasonic time 45.8 min）,group B（SDF-40 4.3%,no ultrasound treatment）and group C（SDF-40 4.3%,ultrasonic power 39 W,ultrasonic time 45.8 min）were evaluated.The results showed that the hardness and chewiness of group C were lower than those of the other two groups,and elasticity was the highest after 5 days.Compared with group B,the hardness,elasticity and chewiness decreased by 17.52%,15.79%and 13.76%,respectively.Infrared spectrum showed that the peak vibration of each group basically did not change,there was no new peak and new group;the order of 1047 cm^-1/1022 cm^-1 absorption value ratio was:group A>group B>group C.With the increase of storage days,the ratio of l047cm^-1/1022 cm^-1 absorption value of group C was the lowest,and the crystallized amount of WSB was the least,which indicated that the ultrasonic combined with SDF-40 significantly delayed the retrogradation of WSB.In summary,the SDF-40 has a good anti-retrogradation effect on wheat starch,which can delay the retrogradation of WSB.And the ultrasonic treatment strengthens the effect of SDF-40 on delaying the retrogradation of WSB.