| China is an important milled rice producing and consuming country in the world,and the consumption characteristics of milled rice determine that it often needs to be stored for a certain period of time to meet people's perennial demands and food security needs,but pests are extremely prone to occur during milled rice storage.Insect pests reduce the nutritional value of milled rice,and affect the quality of milled rice while depleting and contaminating it.However,there are many deficiencies in the existing chemical fumigation methods,therefore,many scholars have been actively studying more environmentally friendly and efficient methods of disinfestation.At present,a large number of scholars have studied and proved that radio frequency(RF)disinfestation methods have broad application prospects in milled rice disinfestation.Therefore,a 6 k W,27.12 MHz RF heating system was used to study the physicochemical properties and sensory quality of packaged milled rice under different RF treatment methods and sample weights,and determine the appropriate RF treatment protocol,then based on the research results of thermal lethal kinetics of the most heat-resistant pests in stored grains,verifying the feasibility of controlling insect pests by RF,and studying the relationship between mortality and heating uniformity to further optimize the RF treatment protocol,finally,the physicochemical quality differences of packaged milled rice under this RF treatment protocol was verified,which provides a theoretical basis for industrial continuous RF disinfestation.The main research results are as follows:(1)When RF treatment different weight milled rice samples(2.5,5 and 10 kg),adopts multi-layer accumulation method(different thickness)to control the weight of RF treatment,that is,the bottom area and thickness of each layer are the same,both 34.0 cm × 28.6 cm × 3.0 cm,weight 2.5 kg,and one layer is 2.5 kg sample,two layers is 5 kg,and four layers is 10 kg.Compared with the packaging method of the same sample thickness,the same bottom area packaging and layer cooling was feasible based on the cooling time and is suitable for mass treatment,and through the electrode gaps and heating rates tests,the optimal electrode gaps of 2.5,5 and 10 kg samples were determined to be 9,10 and 14 cm with corresponding heating rate of 5.68,5.78,and 5.76 ?/min,respectively,in order to ensure the low fissure ratio or broken rate of milled rice and high throughput of the RF treatments;(2)To achieve the 100% mortality of the most heat-tolerant pest adult lesser grain borer(Rhizopertha dominica [Fabricius]),three target temperatures and holding times 54 ? + 6 min,52 ? + 11 min and 50 ? + 26 min were used in RF treatment for different weights milled rice,and the results showed that three RF treatment protocols had some influence on moisture content,water activity and amylose content in packaged milled rice(average initial moisture content was 13.36 ± 0.06%(w.b.)),had no significant difference in fat,fatty acid,protein content,color,fissure ratio and broken rate,and the sensory quality evaluation results showed that the quality of cooked rice was better;(3)In the disinfestation verification,small batches(1 kg)packaged milled rice was compacted in sizes of 18.5 cm × 21.0 cm × 3.0 cm,electrode gap was selected 9.0 cm,and measured the corresponding heating rate was 5.53 ?/min,when the samples heated to 50,52 and 54 ? respectively by RF energy,the mortality of the pests in samples increased significantly with the sample temperature increased,and the maximum mortality was obtained at 54 ?,when holding at hot air for different times after RF and hot air heating samples to 54 ?,the results showed that the mortality of adult lesser grain borer in samples was positively correlated with the heating uniformity of the upper and lower surfaces of samples,when holding at hot air for 12 minutes,100% mortality was obtained,and the overall uniformity of temperature was best,besides,100% mortality of adult lesser grain borer in this protocol means that other or all pests can be effectively controlled when stored grains are affected by pests;(4)The quality verification results showed that the physical and chemical qualities and the cooked rice texture characteristics between the control and the RF-treated samples of 7 kinds of packaged milled rice under the optimal RF protocol of 54 ? + 12 min were not significant difference(P > 0.05),RF treatment had a certain universality;the storage stability analysis results showed that the milled rice treated by the RF disinfestation protocol was not significantly different from that of the control,the RF protocol was relatively reliable;the study of industrial application efficiency showed that the average heating efficiency of domestic RF treatment equipment with 27.12 MHz,15 k W at a electrode gap of 180 mm was 54.5%,and the maximum production efficiency was 476.2 kg/h,and the total electrical cost was US$ 3.13 per 1000 kg,the economic benefit was high;comprehensive research above showed that the disinfestation protocol of RF heated milled rice had certain universality,reliability and economic applicability. |
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