Effects Of Environmental Conditions On The Retrogradation Characteristics Of Rice Starch And Its Application In Instant Rice Cakes

Ready-to-eat rice cakes have a soft,sweet and good taste.However,due to its high moisture content,rice cakes are easy to harden and breed bacteria,which lead to a short shelf life.The main ingredient of rice cake is starch,and its processing characteristics largely depend on the properties of starch.In order to delay the regeneration of rice cake and improve the taste of it,we should to reduce the regeneration of starch.At present,the effect of fine structure of starch on its regenerative properties has been widely reported,while the relationship between fine structure of different kinds of rice starch and its regenerative properties in ready-to-eat rice cakes has not been thoroughly and systematically studied,what more,the effect on the quality of rice cakes has not been clarified.Therefore,this paper selects four representative raw materials of rice flour（millet,black rice,glutinous rice and japonica rice）in rice cake products,extracted starch from them and systematically explored the influence and mechanism of fine structure of starch and environmental conditions on the regeneration of rice starch,and sought the optimal compounding to reduce the regeneration of rice cake and extend shelf life of ready-to-eat rice cake.Hoping to provide technical support and theoretical guidance for the quality control of ready-to-eat rice products.The main research contents of this paper are as follows:Firstly,the effects of the multi-scale structure of four different rice starches on regenerative properties were studied.The results showed that the amylose content of millet,black rice,glutinous rice and japonica rice was 15.55%,11.22%,4.66%and 8.87%,respectively.Compared with glutinous rice and japonica rice starch,the relative molecular weight of millet and black rice starch was larger,2.12×10⁷ and 2.25×10⁷ g/mol,respectively.The results of small Angle X-ray diffraction showed that the thickness of millet and black rice starch was lamellar,6.9784 nm and 6.6986 nm,respectively.Millet starch and black rice starch have the characteristics of high amylose content,relatively large molecular weight,thick lamellar thickness,and easy to aggregation and rearrangement between molecules.The content of amylose in japonica rice starch was lower,the short chain was higher（39.77%）,and the relative crystallinity was 25.92%.Compared with millet and black rice starch,it was not easy to regenerate.Glutinous rice starch has the lowest amylose content,and its breakdown is 162 m P·s,enthalpy value is 0.74 J/g,hardness increases from 22.7 g to 33.93 g after storage,which showing the lowest regeneration value,enthalpy value and hardness growth rate,and has good anti-regenerate performance.Correlation analysis showed that the degree of starch recovery was positively correlated with amylose content,Mw of amylopectin,B1 chain content,relative crystallinity and d value.Secondly,the influence of moisture content and storage temperature on the degree of starch regeneration was systematically investigated.The results showed that the enthalpy value,gel strength and relative crystallinity of the four starches increased with the decrease of water content.After 7 days of storage,the enthalpy of glutinous rice starch increased from 0J/g to 3.65 J/g with the decrease of moisture content.The relative crystallinity increased from5.07%to 22.63%.The cracking and folding of starch particles are more obvious.Water molecules initially exist as free water and changto bound water when the water content reducing 50%.The water molecular motility of millet starch is different.During the 14-day storage period,the transverse relaxation time T₂ of millet starch with 70%water content decreases from 29.05 ms to 15.59 ms and then increases to 34.59 ms,which indicating that with the extension of storage time,the ability of water molecules to bond with starch molecules first increases and then decreases.Compared with 25℃and 35℃,the retrogradation degree of starch at 4℃was the highest.At this temperature,T₂ of black rice starch continuously decreased from 24.77 ms to 7.06 ms,which showing a larger decreasing trend compared with the other two temperatures.The relative crystallinity of reclaimed black rice starch was 13.71%and 17.95%for 7 d and 14 d at 4℃,which were higher than other storage temperatures.Finally,based on the above studies,glutinous rice starch has the best anti-retrogradation capacity,therefore,this paper prepared three kinds of rice cakes through reformulation based on glutinous rice flour.The texture and sensory characteristics of rice cakes were used as the evaluation basis.With the increase of the amount of glutinous rice flour,the hardness and chewiness of the rice cake increase as well.The hardness of the rice cake with 25%glutinous rice flour increased from 711.696 g at the 1st day to 5099.296 g at the 7th day.Chewiness increased from 76.045 to 517.584.The sensory evaluation data showed that the overall acceptability of rice cakes was the highest when the amount of glutinous rice flour was 45%.