| Rice is one of the important staple foods of Chinese residents,and it takes a lot of manpower,material and financial resources to manage after harvest.Under the current social background of advocating scientific and technological grain storage and green grain storage,nitrogen-filled and regulated grain storage has developed into a comprehensive grain storage technology.In order to explore its economics and explore a more economical nitrogen charging method,this study used the newly harvested Nanjing 5055 rice in Nanjing in October 2019 as raw materials.And the initial moisture content values were 13.5%,14.5%,15.5%,and 16.5% respectively.The japonica rice was packaged and stored for 300 d under low-temperature refrigeration at 4℃ and nitrogen filling at 30℃(nitrogen concentration: 98 ± 0.5%,95 ± 0.5%,92 ± 0.5%).With 30℃ air packaging as a control group,the storage effects of 30℃ nitrogen filling and 4℃ low temperature refrigeration were compared,in order to explore a more economical nitrogen filling process and improve the economic benefits of the grain storage process.1.After the end of the storage period,the fatty acid content and lipase activity both increased,but under the conditions of 4℃ low temperature and 30℃ nitrogen filling,the rising rate was inhibited.The inhibitory effect of 4℃ low temperature conditions on the increase in fatty acid content of japonica rice with initial moisture content of13.5%,14.5%,15.5%,and 16.5% were 70.49%,90.01%,92.22%,and 129.34%,respectively,and increased the stability of lipase by 236.04%,209.83%,242.95%,256.20%.The 30℃ + 98% nitrogen filling control increased the inhibition effect of fatty acid content by 63.25%,91.66%,89.03%,and 127.79%,respectively,and increased the stability of lipase by 193.69%,224.02%,236.24%,and 227.35%,respectively.The effect of 30℃ + 98% nitrogen charging for controlled storage is equivalent to 4℃ low temperature storage,both of which can effectively delay the increase of fatty acid content in japonica rice.And using kinetic analysis to establish a dynamic prediction model for the change of fatty acid content during storage of japonica rice,the prediction model at 4℃ low temperature is: F = 0.549 W + 0.038 D+ 5.760;the prediction model at 30℃ + 98% nitrogen is: F = 0.799 W + 0.042 D +1.864(F is the fatty acid content,W is the initial moisture content,and D is the storage days).Using this model,it is calculated that under 14.5% safe moisture,4℃ low temperature and 30 ℃ + 98% nitrogen atmosphere,the storage period of japonica rice can be extended by 149 d and 132 d,respectively,which effectively delays the deterioration of japonica rice quality.2.After the end of the storage period,the roughness rate and the whole rice rate of japonica rice decrease,the lightness L* value of the surface color decreases,the chroma a* value,b* value and the yellowness index YI value increase.In the texture characteristics,the hardness increases and the elasticity decreases.The malondialdehyde content increases.Compared with 30℃ air storage,under 4℃ low temperature conditions,the whiteness value of japonica rice with initial moisture content of 13.5%,14.5%,15.5%,and 16.5% increased by 11.60%,10.73%,9.61%,8.11%,respectively,and the content of malondialdehyde The inhibitory effects of the increase were 61.07%,73.96%,80.66%,100.36%,respectively.Under the condition of30℃ + 98% nitrogen filling,the whiteness value increased by 3.85%,5.18%,3.84%,4.61% respectively,and the inhibitory effect on the increase of malondialdehyde content was 55.73%,66.04%,70.80%,92.00%,respectively.3.During the simulated storage process,the volatile odor changes during the fat metabolism process.After the storage period,the peroxidase and catalase activities decrease with the extension of the storage time.Volatile odor substances such as aldehydes and alcohols The content of ketones,acid esters,etc.increased significantly,and the taste of aged rice appeared.Compared with 30℃ air storage,the peroxidase stability of japonica rice with initial moisture content of 13.5%,14.5%,15.5%,and16.5% under 4℃ low temperature conditions increased by 14.94%,12.56%,10.21%,respectively,15.11%;catalase stability increased by 17.36%,15.02%,12.64%,20.05%.The stability of peroxidase under the condition of 30℃ + 98% nitrogen increased by8.33%,8.50%,6.30%,14.12%;the stability of catalase increased by 10.76%,11.95%,11.14%,16.58%.Moreover,under these two conditions,the production of small molecular compounds such as aldehydes,alcohols,ketones and esters is reduced,the taste of aged rice is lighter,and the quality deterioration has been delayed.4.Under the same storage conditions,the quality of the 4 japonica rices with different initial moisture contents deteriorated with the extension of storage time during the storage period of 300 d,and the rate of quality deterioration accelerated with the increase of the initial moisture content.At the end of storage,the degree of quality deterioration is: 16.5%> 15.5%> 14.5> 13.5%.Low water content can appropriately slow down the deterioration of japonica rice quality,while high water content can aggravate the deterioration of japonica rice quality.After all,it can be concluded that 4℃ low temperature and 30℃ + 98% nitrogen filling can effectively delay the quality deterioration of japonica rice during storage and prolong the storage period of japonica rice.In the actual storage process of japonica rice,especially in southern China,the temperature is high throughout the year,the cost of cooling is high,and it is difficult.The use of low temperature storage will greatly increase the cost of grain storage and management.In this study,using 98% highconcentration nitrogen gas to adjust the storage of japonica rice,the effect is equivalent to the effect under low temperature storage at 4℃,and the quality of japonica rice during storage can be guaranteed without cooling,which can effectively improve japonica rice Economic benefits during grain storage. |
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