| Japonica rice has grain type of short circle and good taste,and typically the broken rice rate is low during processing,and is widely get people's favor.Now that people have satisfied their hunger,they pay more attention to the taste,safety and nutrition of food.In recent years,rice moderate processing has become the focus of attention.In this paper,three kinds of large variety japonica brown rice with regional representation(Yuanyang xinfeng No.2,Benxi liaojing and Jilin super rice)were selected.Moreover,this paper started from three aspects: rice processing characteristics,microscopic structure and nutrition,eating quality and flavor.The main research contents are as follows:Firstly,the effects of milling degree on processing technical indicators,appearance characteristics and mechanical properties were studied.In this study,the milling degree was characterized by degree of milling(DOM)and bran degree.An emery roller and an iron roller were used to mill rice.The appropriate degree of roughness was determined,and then rice samples of DOM(0%-14.0%)and bran degree(0.2%-100.0%)were prepared.The results showed that when DOM was 2.17%-2.89%,the whiteness(based on the whiteness of brown rice)increased by 4.2-5.5,the bran degree was 67.5%-79.4%,and the broken rice rate was less than 2.0%,the good roughening effect can be achieved.With the increase of milling time,DOM could be fitted into a quadratic curve and a linear equation.When rice milling degree was too high(DOM >10.0%),the increase of whiteness was slowly,and the improvement of rice appearance quality was tiny.This directly led to the high broken rice rate,which was as high as 17.55%.The crack rate before rice processing was positively correlated with the rice breaking rate.When the DOM was more than 4.0%,the effect of milling on the bursting strength of rice was not significant(P > 0.05).Meanwhile,the grains with intermediate thickness had better mechanical properties.Secondly,the effect of milling degree on grains was investigated by combining Scanning Electron Microscopy(SEM)and Energy Dispersive Spectrometer(EDS),and the nutrient composition and distribution were studied by gradient milling.The results showed that the aleurone layer of rice contained many aleurone grains and was rich in a large number of mineral elements.The aleurone layer on the dorsal side was thicker than that on the abdomen,generally contained 4-5 layers,and about 60?m-70?m.A lot of aleurone layer was lost in the milling process.A large amount of aleurone layer was left in the grains(DOM 6.0%),but the aleurone layer on the abdomen and dorsal side was ground away(DOM 12.0%).Milling degree and the moisture content,crude fat,crude protein content,ash content,dietary fiber had significant negative correlation relationship.At the same time,nutrients distribution was uneven in the rice.Thiamine was more distributed in aleurone layer,subaleurone layer and perisperm layer,whereas riboflavin was more evenly distributed in rice.Silicon was mainly distributed in the pericarp and seed coat,while Carbon and Oxygen were mainly distributed in the starch endosperm.Magnesium,Phosphorus,and Kalium mainly accumulated in the aleurone layer.Calcium mostly in the endosperm starch layer and its distribution was uniform.Milling had significant difference on some macro element(such as Magnesium,Phosphorus,and Kalium)(P < 0.05),and had little influence on Calcium.Finally,the influence of milling degree on rice eating quality was investigated by combining sensory evaluation with instruments,and the volatile contents and composition of rice with different milling degree were investigated by Simultaneous Distillation Extraction-Gas Chromatography-Mass Spectrometry method.The results showed that with the improvement of milling degree,the freshness of rice decreased,and the freshness of all three kinds of rice was lower than 70(DOM > 8.0%).With the improvement of milling degree,the food taste value and sensory score of rice increased.The processing did not always improve the eating quality,and the improvement of milling degree had no significant effect on the food taste value and sensory score(DOM ? 8.0%).With the improvement of milling degree,the hardness decreased,the viscosity increased and the degree of balance increased,but the milling degree has no significant effect on the elasticity.Compared with brown rice,the total amount of volatile flavor substances in sample(DOM 6.0%)and sample(DOM 10.0%)decreased by 34.4% and 71.9% respectively.High milling degree had a negative effect on the flavor of rice.Comprehensive processing characteristics,nutritional quality and edible quality results,on the premise of not affecting the taste of rice,to ensure that rice appearance and nutrition are both excellent,determine the appropriate processing technology accuracy: DOM 6.0%-8.0%,bran degree 0.7%-5.4%,moderate processing technical indicators are: whiteness(based on brown rice whiteness)is increased by 9.6-18.8,and the embryo retention rate is 23.66%-90.66%,which can reduce the broken rice rate and increase the rice yield,thus providing a suitable processing industry for japonica brown rice reference. |
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