Quality Changes Of Mid-late Indica Rice Stored In Controlled Atmosphere With Nitrogen And At Different Storage Temperatures After Unsealing

With the nitrogen-controlled atmosphere storage technology being widely used in rice storage,in order to explore the influence of temperature on the quality of rice during nitrogencontrolled atmosphere storage,and to study the quality change law of rice in different temperature environments after nitrogen-controlled atmosphere storage,and to find the more economical nitrogen-controlled atmosphere storage temperature after unsealing.In this paper,the newly harvested mid-late indica rice was used as raw material,and the rice was packed with 99% nitrogen,which was stored in an incubator simulating high temperature(35℃,RH75%),normal temperature(25℃,RH75%)and low temperature(15℃,RH75%)for 180 d,and the rice after air conditioning was kept in these three temperature conditions for routine.Based on the determination of storage quality,biochemical quality,processing quality and eating quality of rice,combined with the further analysis of starch microstructure,moisture distribution,mechanical properties and texture characteristics,this paper studies the quality change law of rice stored under different temperature conditions after nitrogen-controlled atmosphere and sealed atmosphere,and explores the appropriate temperature conditions for rice stored under nitrogen-controlled atmosphere and unsealed atmosphere.The main results of this study are as follows:(1)The moisture,fatty acid value,amylose content,electrical conductivity and POD activity of rice will be affected by temperature during air-regulated storage,and the effect of low-temperature storage can be achieved by nitrogen-controlled atmosphere storage at normal temperature.Changes of moisture and fatty acid values were mainly related to temperature,and temperature difference had a certain effect on the changes of fatty acid values in the early stage of unsealing.After nitrogen-controlled atmosphere sealing,the rise of amylose can be better delayed under different temperature conditions during the storage process of 60 ～ 120 days.The increase of conductivity will be aggravated at different temperatures after high temperature gas encapsulation.In the early stage of storage after gas sealing,POD activity is protected by nitrogen gas at low temperature.Cracks appeared in different degrees between starch cells after nitrogen-controlled atmosphere and unsealing.With the increase of storage temperature,more starch particles were exposed.The crystallinity of starch decreased after nitrogen-controlled atmosphere and unsealing.With the increase of storage temperature,the adsorbed water in rice decreases continuously,and storage in high temperature environment after gas sealing will lead to the migration of free water to adsorbed water.In the process of air conditioning,the effects of different storage factors on rice quality were as follows: storage time > air conditioning temperature > gas composition.After nitrogen-controlled atmosphere sealing,the effects of different storage factors on rice quality were as follows: air-conditioned temperature > storage time > unsealing temperature > temperature difference.(2)Nitrogen-controlled atmosphere can delay the decline of roughness rate,and can delay the decline of milled rice rate and the increase of yellow grain rice rate at 15℃ and 25℃,and the effect is similar.Under the condition of high temperature and large temperature difference,the decrease of roughness and milled rice rate will be accelerated.In the early stage of airconditioned sealing storage,the effect of inhibiting the rise of yellow grain rice under the condition of 15℃ and 25℃ is still similar.With the extension of storage time,low temperature can inhibit the rise of yellow grain rice more.The triaxial dimensions of air-conditioned rice and brown rice were not affected after unsealing.Under the three forces,the compressive force > shear force > three-point bending force.After unsealing,the three-point bending force of rice showed an upward trend,and the three crushing forces of brown rice showed an upward trend.The change range of the three crushing forces of rice was larger than that of brown rice at the early unsealing stage and 180 d storage.Grain size was affected by water content,and grain length and thickness affected the percentage of roughening and milled rice,respectively.As the three-point bending force can better reflect the mechanical properties of rice,it is suitable to evaluate the mechanical breaking characteristics of middle and late indica rice during processing.(3)Nitrogen-controlled atmosphere at low temperature can maintain the edible quality of rice,and the low temperature condition is more conducive to delaying the decline of food quality after unsealing.The change of texture properties of rice after nitrogen-controlled atmosphere at different temperatures is different at different temperatures,25℃ and 35℃ will have a great effect on the texture properties of rice.The storage temperature after unsealing mainly affects the viscosity and elasticity of rice,and the processing quality of rice significantly affects the cooking quality of rice,which changes the hardness,viscosity,elasticity and resilience of rice,and thus leads to the decline of the sensory score of rice.After high temperature gas sealing,it is suitable to store 0 ～ 180 d at 15℃,0 ～ 120 d at 25℃,and 0～ 90 d at 35℃.After gas sealing at normal temperature,it can be stored at 15℃ and 25℃ for 0～ 180 d,and at 35℃ for 0 ～ 90 d.After low temperature gas sealing,it is suitable to store 0 ～180 d at 15℃ and 25℃,and 0 ～ 60 d at 35℃.At this time,the quality of rice is closer.Considering the storage economy,the temperature can be controlled at 25℃ when the nitrogen-controlled atmosphere is adjusted,and the temperature can still be controlled at 25℃after nitrogen-controlled atmosphere.To sum up,when the temperature of rice is too high during air conditioning,it needs to be stored at a lower temperature after unsealing in order to maintain the quality of rice in a long time.When the temperature of rice is kept at normal or low temperature during air conditioning,the quality deterioration of rice will be accelerated in high temperature environment after unsealing,leading to the shortening of storage time of rice.In practical application,the economical storage scheme can be obtained through the suitable storage period under different storage conditions.