Effects Of Rice Aging On Pasting Behavior Of Starch Granule Aggregates

Rice can be eaten as a staple food.Whether it is rice whole or flour,it has always faced the problem of deterioration of quality during the storage period after harvest.But the rice aging mechanism is very complex,and there is no unified conclusion on the related aging mechanism.The aging of rice involves changes in physicochemical,sensory,cooking and digestibility,resulting in deterioration of eating quality and production loss.Endicating the aging mechanism is an important way to delay aging rate.Rice starch is composed of a variety of components.The starch endosperm cell contains compound grains,and the compound grains contain multiple single grains,and the structure is very complex.The role of different grades of starch granules in rice in aging has been investigated so far,suggesting that the changes in starch granules deaggregation during gelatinization have important implications for aging.However,the current research is on the pasting properties of aged rice starch is mostly by adding functional polysaccharides,enzyme preparations,and pretreatment by microwave or ultrasonic to delay the aging to achieve the purpose of refreshing.However,interactions between starch and other food components are also mixed and chemical pretreatment may disrupt starch fine structure.Therefore,in this paper,by changing the particle size of rice flour,the effects of starch entities of different particle size levels,static heating temperature and dynamic pasting process on the deaggregation of starch granules in aged rice were investigated,showing the effect of the disaggregation between starch granules on the pasting behavior after aging.(1)Preparation of rice flour particles(starch aggregates)with different sizes and changes in pasting behavior at the starch granule scale.Heating for 5 min at four temperatures of 65℃,75℃,85℃ and 95℃,for starch single-grain aggregates(S3),The degree of disaggregation of fresh rice and aged rice at four temperatures was decreased at 75℃ compared with 65℃,increased at 85℃ compared with 75℃,decreased at 95℃ compared with 85℃,disaggregation is most likely to occur at 65℃,and the most difficult at 95℃.For aged S3,the peak particle size at 95℃ was significantly larger than that at other temperatures,reaching 240 μm,indicating that starch granules are difficult to disaggregation at high temperature.For single starch granules(S4),the peak particle size of fresh rice at 95℃ is significantly larger than that at other temperatures,reaching 631 μm,which is the result of starch granules cohesion after gelatinization;the peak particle size of aged rice at 95℃.The diameter of the starch was 240 μm,indicating that the single grain cohesion degree of aged rice starch was lower than that of fresh rice,which may be caused by the lower degree of pasting.From the light microscopic morphology of S3 and S4,it can be seen that at 95℃,both fresh rice and aged rice will cohesion,and the degree of cohesion of aged rice is lower.S4 itself is a single starch granule,and S3 is not suitable for studying the disaggregation between starch granules because there is no peak between single starch granules and multiple starch granules.The disaggregation of starch granules in endosperm cell aggregates(S1)and starch complex aggregates(S2)will be investigated later.(2)Using 20-40 μm rice flour particles(starch complex aggregates,S2)as the test material,the particle size of S2 of fresh rice and aged rice at four temperatures of 65℃,75℃,85℃ and 95℃ was studied.Particle size distribution,light microscopic morphology,hydration properties and rice gel texture.The results showed that with the increase of the heating temperature,the starch granules in both fresh and aged rice became difficult to disaggregate and disperse,and the aged rice was more difficult to disaggregate than the fresh rice.The observation of light microscope morphology shows that the disaggregation of both fresh rice and aged rice decreases with the increase of temperature:when the heating temperature is 95℃,there are more large particles in the fresh rice,although many small particles are also dispersed,while Most of the aged rice is large particles about 50 μm,and small particles are rare.Scanning electron microscopy showed that the starch granules inside the fresh rice also disaggregated,while for the aged rice only the starch granules on the surface of the rice flour particles disaggregated;but with the increase of the heating temperature,the disaggregation and dispersion of the starch granules in the fresh rice also became difficult,from the disaggregation of most of the starch granules inside the rice flour particle at low temperature to only the starch granules on the surface of the rice flour particle at high temperature disaggregated.The water binding capacity and swelling power increased with the increase of heating temperature.The water binding capacity of aged rice was not significantly different from that of fresh rice when heated at 65℃and 75℃,while the water binding capacity of aged rice was different at 85℃ and 95℃.It is significantly lower than that of fresh rice,indicating that aging reduces the water binding capacity,which may be the result of more difficult disaggregation of starch granules in aged rice at high temperature.With the increase of temperature,the amylose dissolution rate of fresh rice increased significantly,while that of aged rice decreased significantly.However,it was lower than that of fresh rice at 85℃ and 95℃,which may be caused by the rapid decrease of the disaggregation and dispersion degree of starch granules in aged rice with the increase of heating temperature.The dissolution rate of amylose in aged rice decreases with the increase of temperature,which may be due to the difficulty of disaggregation and dispersion between starch granules and the lack of release channels due to aging,or the dissolved solids are mainly amylopectin.The hardness and cohesion of S2 rice gel of fresh rice and aged rice increased significantly with the increase of heating temperature,but the hardness of aged rice rice gel was higher and the cohesion was lower,indicating that it is difficult to disaggregation between starch granules after aging.The hardness of rice gel is improved,but the resistance of the remaining large particles to external forces is reduced.It can be seen from the scanning electron microscope of rice gel that when the temperature rises to 85℃,the pore size of the fresh rice gel becomes larger,while the structure of the aged rice gel is denser,the most dense at 95℃.Therefore,aging makes it difficult to disaggregate and disperse between starch granules,which may be the internal reason for the structural change of aged rice.(3)Using 120-150 μm rice flour particles(endosperm cell aggregates,S1)as the test material,the differences in particle size distribution,light microscopic morphology,hydration properties and rice gel structure of S1 of fresh rice and aged rice at four temperatures were studied.Particle size analysis showed that with the increase of heating temperature in the range of 65℃ to 95℃,the disaggregation degree of starch granules increased first and then decreased.The degree of disaggregation of high starch granules was significantly reduced,and the degree of disaggregation was the largest at 65℃,but still lower than that of fresh rice.The results of light microscopy morphology showed that many large particles remained in aged rice after heating,and the degree of disaggregation was significantly lower than that of fresh rice.The pasting of aged rice was uniform at 65-75℃,and the pasting degree was uneven at 85-95℃,and the fresh rice was just the opposite.The water binding capacity of aged rice was always lower than that of fresh rice at four temperatures,and the hydration properties better supported the disaggregation changes of fresh rice and aged rice.Scanning electron microscope showed that the disaggregation degree of fresh rice at four temperatures was significantly higher than that of aged rice,and starch complexes in fresh rice could also disaggregate at 75℃.X-ray diffraction shows that with the increase of temperature,the FWHM of fresh rice and aged rice gradually increases around 23°,indicating that the increase of heating temperature reduces the crystallinity;and the FWHM of aged rice is always higher than that of fresh rice,indicating that in The crystallinity of aged rice was always lower than that of fresh rice under the four heating temperatures,which showed that the starch granule structure was easily broken due to aging.These results indicate that aging causes the starch granule structure to become denser but easily broken,which is the reason for the difficulty in disaggregation between starch granules during gelatinization.(4)Using 120-150 μm rice flour particles(endosperm cell aggregates,S1)as the test material,compare the S1 of fresh rice and aged rice at the four viscosity nodes of the pasting curve:onset,peak,valley and final value.Differences in particle size distribution,light microscopic morphology,crystalline structure,and rice gum texture.The particle size distribution shows that with the heating,the starch granules of fresh S1 have been completely disaggregated at the onset of the viscosity nodes(the volume fraction of the small particle size smaller than 26 μm reaches 100%),and then the peak viscosity nodes occurs due to pasting.Cohesion began,the peak volume fraction of small particle size decreased to 61.72%,continued to decrease to 42.66%at the valley value,and slightly increased to 52.31%at the final value due to the decrease in temperature;while the small particle size peak volume fraction of aged S1 It decreased from 83.88%at the onset to 41.42%at the peak,then decreased to 35.01%at the trough,until it decreased to 18.71%at the final value,and the light microscopic morphology supported the results of particle size analysis.Scanning electron microscope showed that the tissue structure of fresh rice was loose at the peak,while the tissue structure of aged rice remained compact with only a few holes.X-ray diffraction and Fourier transform infrared spectroscopy showed that at the four viscosity nodes of the pasting curve,the relative crystallinity(2.50%)and short-range ordering degree of the fresh rice were the lowest at the onset,while the aged rice was the lowest at the final value(3.66%),which indicates that the starch microcrystalline bundle structure in aged rice is strengthened and requires a longer heating time to destroy.The texture analysis of rice gel shows that the hardness of rice gel at the peak of the viscosity curve of fresh rice and aged rice is significantly higher than that at the peak,and the hardness of rice gel at the final value is lower than that at the valley value.The hardness and viscosity are always higher than those of fresh rice gel,which may be due to incomplete disaggregation of starch granules in aged rice,more large particles,and smaller specific surface area of particles.In conclusion,the disaggregation of granules in the static and dynamic pasting of aged rice can affect starch agglomeration structure,thereby affecting the pasting behaviors.Difficulty in disaggregation and dispersion among starch granules during pasting is the main reason for the deterioration of rice aging.In this paper,physical separation is used to minimize the impact on starch pasting due to the loss of nonstarch components.The multi-layered rice flour particles with different particle sizes are used as the research object.The effects of aging on the intergranular disaggregation of rice starch and the texture of gel and its mechanism were studied by means of particle size distribution,microscopic morphology observation,hydration properties,texture,crystallization analysis,crystallization analysis and other methods,which provided a theory for the effect of rice aging on starch pasting behaviors and related mechanisms.Experimental support to provide a basis for elucidating the rice aging mechanism,delaying the rate of aging deterioration,and reducing the grain loss caused by aging and deterioration.