| Rice is the largest grain ration in China,and as rice is produced more than consumed,highquality storage is crucial.Conventional storage methods need to reduce the moisture content of the rice(≤14.5%),which will lead to the sensory quality of the rice and poor palatability.Starting from the water content of rice,this study selected two kinds of rice with water moisture(11.97% and 15.03%)and treated them by Electron Beam Irradiation(EBI)technology to explore the effects of Irradiation on the storage quality of rice with different moisture content and its rice starch.The purpose of this study is to use EBI to preserve rice with high water moisture,delay its quality deterioration and stabilize the high quality grain market in China.The main research contents and results are as follows:Firstly,the effects of EBI doses(1 kGy,2 kGy,4 kGy,8 kGy,10 kGy)on the storage quality of rice were explored,and the Fatty Acid Value(FAV),Lipase Acitivity(LA),gelatinization characteristics,starch micromorphology and thermal characteristics of irradiated rice were analyzed.EBI treatment had no obvious effect on FAV in rice,but significantly reduced the value of LA.The gelatinization characteristics of rice flour treated by EBI showed that the gelatinization viscosity of rice flour decreased sharply and the gelatinization temperature also shifted to the left under high dose(≥8 kGy)irradiation.At the same time,starch granule also showed the phenomenon of fragmentation and aggregation at high dose,and the particle size of starch granule became smaller.In addition,the thermodynamic properties of starch showed that the gelatinization temperature decreased with the increase of irradiation dose.Therefore,based on the consideration of the effect of irradiation on the properties of rice,this study selected a lower irradiation dose(≤4 kGy)to conduct storage experiments.Secondly,on the basis of the above research results,select the appropriate irradiation dose(1 kGy,2 kGy,3 kGy,4 kGy)to deal with two kinds of moisture content of rice,rice 60 days interval analysis of FAV and LA,the total bacterial colonies and mold,and moisture changes,at the same time,the Amylose Content(AC)of rice before and after the treatment,paste rheological,Swelling Force(SP)and Water Soluble Index(WSI),the texture and sensory assessment of rice,the water distribution and water migration of rice grains were analyzed.In the storage process,the growth rate of FAV under low moisture condition was faster than that under high moisture condition.The unirradiated low moisture condition and high water condition increased by 55.65% and 45.08%,respectively.At the same time,irradiation slowed down the formation rate of FAV of rice.After EBI treatment,the LA of rice under different moisture conditions decreased with the prolonging of storage time,and the LA reduction rate in low moisture condition was faster than that in high moisture condition.Compared with untreated rice,the microbial content of rice irradiated with 1 kGy,2 kGy,3 kGy and 4 kGy decreased by 1 and 2 orders of magnitude,respectively,indicating that EBI was very effective in killing microorganisms.Moisture content continued to decrease,and the decreasing rate of rice with high moisture content was faster than that of rice with low moisture content.Before and after storage,the proportion of bound water content of rice with high moisture content was higher than that of rice with low moisture content,and the stagnant water was converted or lost.With the change of storage time,the bond degree between water molecules and matter decreased.EBI was beneficial to water transfer in rice,and it was more obvious under low moisture condition.AC increases with different moisture content.The gelatinization and rheological properties showed that the irradiation effect of rice with high moisture content was weaker than that of rice with low moisture content.Irradiation and storage time had no significant effect on SP,but significant effect on WSI,and the change was more obvious in rice with high moisture content.Storage weakens the effects of irradiation on texture and sensory organs of rice,and rice with higher moisture content is better in quality.Finally,rice starch was isolated from rice,and the properties of rice starch before and after irradiation were studied,including its microstructure,crystallization properties,thermal properties,starch molecular weight and chain length distribution changes,as well as nutrient digestion properties of starch.The morphology of the particles showed that the irradiation effect of the particles weakened after storage,and the particles became uniform from aggregation.The crystal shape of rice starch did not change after storage and after EBI treatment.Thermodynamic properties showed that low dose irradiation has no significant effect on high moisture content.Irradiation had no significant effect on the distribution of chain length.After storage,the proportion of long chain and medium long chain decreased,while the proportion of short chain increased,which confirmed the above RVA results.The relative molecular weight decreased with the increase of irradiation dose and storage time.Irradiation had no significant effect on the digestibility of rice starch.The content of rapid-digesting starch was lower in rice starch with low water content,while the content of resistant starch was higher,which showed relatively good nutritional properties.The resistant starch was significantly reduced after prolonged storage time.The above results indicated that EBI had a weak effect on the properties of rice starch with high moisture content,while low dose irradiation had a slight effect on the properties of rice starch.Therefore,low-dose electron beam irradiation can be used to store rice with high moisture content in the future,which is of practical significance for rice quality maintenance and stability of high-quality grain market in China. |
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