Study On Radio Frequency Inactivation Lipase Of Brown Rice And Its Storage Stability

Brown rice is a whole grain,which is increasingly popular among consumers because of its various health benefits.However,its cortex is rich in lipase and polyunsaturated fatty acids,which are prone to lipid oxidation during storage,resulting in lower eating quality and shorter shelf life,which hinders the consumption and distribution of brown rice.Therefore,this paper uses radio frequency(RF)technology to inactivate brown rice lipase and optimize the radio frequency treatment parameters from the perspective of controlling free radicals to explore the effect of radio frequency treatment in the storage stability of brown rice,the effect of different packaging types on the storage stability of brown rice and the effect on the physicochemical properties and cooking quality of brown rice,which provides theoretical guidance for the application of RF treatment in the shelf life extension of brown rice.Firstly,RF technology was used to moderately inactivate brown rice lipase and control the free radical intensity to improve its storage stability.The effects of electrode gap,temperature and supplementation rate on the inactivation rate and free radical intensity of brown rice were investigated,and the process parameters with the highest lipase inactivation rate and the lowest free radical intensity were obtained by single-factor and orthogonal experiments,respectively.The changes of fatty acid value,peroxide value,free radical intensity and hexanal during accelerated storage at 37℃for 28 days were compared between treated and untreated brown rice under two optimal process parameters,and the effect of RF technology on the improvement of brown rice storage stability was analyzed.The best processing parameters with the highest lipase inactivation rate(sample I)were obtained by single factor and orthogonal experiments:electrode gap of 145 mm,temperature of 105℃,water supplementation rate of 4.5%,and for lowest free radical intensity(sampleⅡ):electrode gap of 145 mm,temperature of 95℃,water supplementation rate of 4.5%were obtained.The lipase inactivation rate of the resulting sampleⅠand sampleⅡwere 62.65%and 41.77%,respectively,while the free radical intensity were 0.891 and 0.699,respectively.During accelerated storage,the peak fatty acids value of samples I and II were 22.42 mg/100 g and24.00 mg/100 g,respectively,both were within the suitable storage quality range of<25mg/100 g of rice,while that of the untreated sample was 33.17 mg/100 g,which exceeded the standard.The peak peroxide value of sampleⅡwas lower than those of sampleⅠand the untreated sample,was less than 0.35 g/100g within the acceptable range.The peak intensity of free radical peak and peak concentration of hexanal of sampleⅡwere lower than that of sampleⅠ,and the oxidation rate of polyunsaturated fatty acids was the slowest.The results of accelerated storage experiments showed that sampleⅡhad better storage stability than sampleⅠ.Secondly,the effects of two packaging types,self-sealing package and vacuum,on lipid oxidation and sensory evaluation of RF-stabilized brown rice were investigated for sample II stored at room temperature for 6 months(June to December).The results showed that(1)after6 months of storage,the fatty acid values of the RF group under vacuum and self-sealing bag packaging types were 21.45%and 31.73%of those of the ingredient group,respectively.The fatty acid values of the RF group were within the suitable storage range during the whole storage period,while those of the ingredients group exceeded 25 mg/100g by the second month of storage,exceeding the upper threshold of mild unsuitability for storage,the peroxide values of brown rice in the RF group were significantly lower than those of the corresponding ingredients group during the storage period(p<0.05),and the peroxide values of brown rice in the RF vacuum packaging were the lowest during the whole storage period and did not exceed the limit of 0.35 g/100g,while the raw material group had exceeded the limit at 4 months of storage.The free radical intensity and malondialdehyde content of the RF group were significantly lower than those of the corresponding ingredients group during storage(p<0.05),and the free radical intensity and malondialdehyde content of the RF vacuum-packed brown rice were the lowest,at 1.45 and 0.17μg/g,the degradation of unsaturated fatty acids in the RF group was lower than that of the raw ingredients group,and the degradation of unsaturated fatty acids in the RF vacuum-packed brown rice was lower than that of the raw ingredients group.The degradation of unsaturated fatty acids in the RF group was lower than that in the raw material group,and the brown rice under RF vacuum packaging had the lowest oxidation level and the fatty acid composition changed more slowly.(2)The sensory evaluation grade of the RF group was significantly higher than that of the brown rice in the ingredient group in both packaging types(p<0.05),and the brown rice in the ingredient group could smell the bad flavor at 2 months of storage,while the brown rice in the RF vacuum packaging could smell the bad flavor only at 6 months of storage.Finally,the effects of RF technology treatment on the physicochemical properties and cooking quality of brown rice were investigated.The results showed that(1)except for the reduction of moisture content by 1.45%,there was no significant effect of RF treatment on other components of brown rice(p<0.05).(2)The color differenceΔE value of brown rice was in the range of 2-4,and the brown rice was slightly yellowed.(3)Peak viscosity,disintegration value,final viscosity and regeneration value were significantly increased(p<0.05),starting temperature(T_o),peak temperature(T_p)and final temperature(T_c)were significantly increased(p<0.05),while the enthalpy of pasting(ΔH)was reduced from 4.99J/g to 3.69 J/g.(4)The original A-type crystalline structure was maintained,but the crystallinity decreased from 19.68%to 16.34%,the starch double helix structure was destroyed,which increased the water absorption rate from 22.70%to 28.02%.(5)Adhesion and elasticity increased,while hardness and chewiness significantly decreased(p<0.05),sensory score significantly increased from 69.50 to 78.10(p<0.05).RF treatment not only prolonged the shelf life of brown rice but also significantly improved the steaming quality and eating quality of brown rice.