Effect Of Cold Plasma Treatment On The Quality Of Rice

As a non-thermal processing technology for food,cold plasma technology currently focuses on two major aspects of breeding and sterilization.In this project,three different varieties of rice were treated with different power(120 W,320 W,520 W)cold plasma,to study the effects of cold plasma treatment on rice cooking quality,physical properties,physiological and biochemical properties and molecular structure;three different varieties of rice were treated with cold plasma at a power of 120 W and stored under different storage conditions of 15°C and 20°C for 10 months,to study the changes of cooking quality,physical properties,physiological and biochemical properties and molecular structure of cold plasma-treated rice during storage,providing a theoretical basis for the application of cold plasma technology in grain storage and processing.The main conclusions of the study are as follows:(1)After ?120 W cold plasma treatment,the rice cooking time is significantly reduced,the maximum can be reduced by 5.5 minutes at 520 W-60 s,the water absorption ratio and the solid content of the rice soup are increased,the contact angle of the water droplets of the rice grain is reduced,and the maximum can be reduced by 49.95°,Hydrophilicity increases.There was no significant change in imperfect grain,yellow grain rice rate and polished rice rate,but the rice breakage index,chalky grain rate and chalkiness increased significantly,among which the chalkiness of Dongbei japonica rice reached more than 2%,which was reduced from first-grade japonica rice to Second-grade japonica rice.The moisture content of rice decreased significantly by 0.26%-2.38%(P<0.05),and the electrical conductivity of Guangzhou indica rice and Dongbei japonica rice increased significantly(P < 0.05).The content of soluble protein and free amino acids showed an increasing trend;the fatty acid value and malondialdehyde content decreased,and the fatty acid value could be reduced by a maximum of 5.20 mg KOH/100 g,and the freshness increased.Flour and gelatinization characteristics showed that the formation time and the stabilization time were reduced,and the highest can be directly reduced by 2.22 min and 3.92 min,respectively,the degree ofweakening and peak viscosity increased,the viscosity disintegration value and amylase activity of Guangzhou indica rice and Dongbei japonica rice increased,Regeneration value has a tendency to decrease.Therefore,cold plasma treatment can improve the cooking quality and starch gelatinization characteristics of rice,and improve the freshness of rice.It can be used to extend the storage period of rice,but it has a certain effect on the quality of rice.From the perspective of energy saving,120 W cold plasma treatment is preferred as the processing condition for rice storage samples.(2)After cold plasma treatment,the content of sulfhydryl in rice can increase up to 1.29mg/g,and the content of ?-helix and ?-sheet of rice in protein secondary structure decreases by 0.44%-3.19% and 0.47%-2.97%,the content of ?-Corner and irregular curl increased by0.68%-5.76% and 0.15%-0.84%,respectively,indicating that the protein structure was damaged.Compared with the control sample,the content of rice amylose did not change significantly.In the starch crystal structure,the rice crystal structure did not change,and it was still the A-type crystal structure,while the crystallinity of starch could drop by up to2.97%.It shows that cold plasma treatment has destroyed the starch structure of rice to a certain extent;It was also observed under an electron scanning microscope that after the cold plasma treatment of rice,the surface was etched and cracks and depressions appeared.Therefore,cold plasma treatment can improve the cooking and flour pasting characteristics of rice by changing the surface morphology of rice grains and the internal protein and starch structure.(3)During storage,the rice cooking time and moisture absorption ratio increase,and the solid content of rice soup decreases.After 10 months of storage,the cooking time of rice increased by a maximum of 4.5 minutes.The cooking time of the cold plasma treated samples was always shorter than that of the control samples,and the solid content of the rice soup was still higher than the control samples by 0.46-1.99 mg/g.The yellow rice rate of rice is up to 0.25%,which is within the range of suitable storage.The higher the storage temperature,the faster the rate of rice chalkiness and chalkiness.At the end of the storage period,the chalkiness of Changzhou rice treated samples reached 4.51%,which decreasedfrom second-grade japonica rice(chalkiness?4%)to third-grade japonica rice(chalkiness?6%).Therefore,cold plasma treatment can improve the cooking quality of rice during storage,but it has a greater impact on its quality level.During storage,the formation time and stabilization time of rice increased,and the degree of weakening decreased.The formation time and stabilization time of the treated samples were lower than that of the control sample.The degree of weakening of the treated samples of Changzhou and Changchun rice was higher than that of the control sample.The peak viscosity,viscosity disintegration value,and amylase activity of rice were all decreased,and the retrogradation value was increased.The peak viscosity,viscosity disintegration value,and amylase activity of the treated samples were all higher than that of the control sample,while the retrogradation value was lower than that of the control sample.In the long-term storage,the cold plasma treatment makes the rice well maintain the gelatinization characteristics and taste quality of the rice.During storage,the moisture content of rice showed a trend of decreasing first and then increasing,and the conductivity of the treated samples was lower than that of the control samples,the highest difference was 34.43 ?s/cm/g,and the rate of increase was slow.Cold plasma treatment made the contents of soluble protein,free amino acids and damaged starch higher than the control samples during rice storage.At the end of the storage period,except for the fatty acid value of the treated samples stored at 15 ? in the storage range of Changzhou rice(21.93 mg KOH/100 g < 25 mg KOH/100g),the rest of them were mildly unsuitable,the highest increased to 31.94 mg KOH/100 g.In addition,the cold plasma treated samples had lower malondialdehyde content during storage than the control samples,and the freshness was higher than the control samples.Therefore,cold plasma treatment can improve the storage stability of rice and delay the deterioration of rice quality.(4)After 10 months of storage,the sulfhydryl content of the rice decreased,and the sulfhydryl content of the treated sample was higher than that of the control sample,with a maximum difference of 0.84 mg/g.The content of ?-helix and ?-sheet in the secondary structure of the protein decreased,and the content of ?-turn and random curl increased,thechange range was small,basically within 4%,and the ?-helix and ?-sheet of the treated samples The content is lower than the control sample,and the ?-turn and irregular curl content are higher than the control sample.The rice amylose content increased,the starch crystal structure type was still A type,but the crystallinity decreased.The amylose content and crystallinity of the treated samples were lower than the control samples.In the early period of storage,after cold plasma treatment,cracks and depressions appeared on the surface of rice grains,and starch granules in the endosperm did not change significantly,only minor cracks appeared.After 10 months of storage,the number of composite starch granules decreased at 15?,while At 20?,the starch granules are loosely arranged,and the damage and loss are more serious,and the corners of the starch granules in the treated samples become blurred and change greatly.Therefore,the cold plasma treatment damages both the protein structure and the starch structure during rice storage,which affects the rice cooking quality,flour pasting characteristics and quality grade.(5)Overall,when the cold plasma-treated rice is stored at a storage temperature of 15?,the quality deterioration rate is slower,and the soluble protein content of rice and the rate of yellow grain rice change are smaller,fatty acid value,chalky grain rate and chalkiness change the most.Based on the rice fatty acid value,cold plasma treated rice can be safely stored(suitable for storage)for more than 10 months at 15°C,and can be safely stored(suitable for storage)for 8 months at 20°C.Therefore,the cold plasma technology can be combined with low-temperature storage(storage at 15°C)to better suppress the deterioration of rice quality.