Effect Of Milling And Microwave Treatment On Storage Properties Of Rough Rice And Sensory Characters Of Cooked Rice

The nutrient elements in rice such as Vitamins and y-aminobutyic acid are most located in the aleurone layer and germ.The higher of the rice milling,the lesser of the rice nutrients left.This study instead deep-milling method that always caused huge loss of nutrients,by proper-milling method that reduced the energy consumption,improved the milled rice rate and nutritional value of product.The subject researched the change rule of the color,eating quality and volatile composition of rice during milling,established the regression equation between colors index of rough rice and eating quality of cooked rice.If the outer layer is destroyed,the rice with high lipid content was easily occurred to oxidative rancidity during storage.So the research investigated the impact of milling degree on smell ingredients of rice during storage,explored the feasibility of microwave being used to inactivate enzyme,inhibit rice aging and rancidity,studied the effect of microwave treatment on the changes of rice composition,inner structure,thermal characteristics,storage properties and rice flavor.All this investigation provides research foundation for rice quality improvement.By exploring the effect of microwave treatment and vacuum package on the changes of rice flavor during storage,to provide research foundation for developing nutritional rice with better storage performance.Effect of degrees of milling on color parameters and sensory characteristics of rice(indica rice "Zaoxian 167" and japonica rice "Kongyu 131")were evaluated,and their relationships were established by the method of Pearson correlation analysis and regression analysis.Results showed that with the increase of milling degree,color value a*and b*gradually decreased while L*value and eating quality(including appearance,hardness,tastiness,stickiness,sweetness and overall judgments)correspondingly increased.The correlation analysis revealed that sensory characteristics were significantly negatively correlated with a*and b*value,and significantly positively correlated with L*value.In terms of color parameters,L*value had a significant negative correlation with a*and b*value,while a*and b*value were significantly positively correlated.Eating quality showed a linear relationship with a*,b*and L*value,and the R2 values for the relationship were in the range of 0.90-0.99.The establishment of relationship between color parameters of raw rice and sensory characteristics of cooked rice,assisted in quick locating the optimum degrees of milling to prevent poor judgment,and increasing the accuracy and efficiency of working.Effects of microwave irradiation(384 W and 539 W)on composition(lipase activity,lipoxidase activity and thiamine content),structure(microscopic structure),thermal and storage properties of rice with different milling degrees were investigated.Microwave irradiation partially inactivated the lipase and lipoxidase,damaged thiamine,and created puffed rice.In addition,the transition temperatures(To and Tp)of rice was 'shifted to higher temperatures,and the enthalpy of gelatinization decreased after irradiation.The effect was more obvious when the power of microwave was increased.After microwave irradiation of 384 W,some stress cracks were produced and propagated along the edges of pericarp of brown rice kernel.And the stress cracks on the rice kernel with 3%milling were narrower than that of the brown rice.There were no stress cracks along the edges of outer layer of rice kernels with DOM of 6 and 10%.Instead,some stress cracks were created in the endosperm of the rice kernels.After microwave treatment of 539 W,some stress cracks were found not only propagated along the pericarp and aleurone layers,but also caused some "explosion",or tore through some of the outer layer,dividing the outer layer and internal tissue into two pieces.In the rice kernels with DOM of 6 and 10%,the stress cracks were distributed in the endosperm.Moreover,compared with the rice kernels irradiated by 384 W,there were more stress cracks produced and the broken were heavier.Storage property analysis indicated that free fatty acids content of all rice samples increased gradually in the process of storage.Microwave irradiation suppressed new free fatty acids from emerging during storage.The higher of the power,the lesser of the free fatty acids generated.The results suggested that microwave irradiation was potentially applicable for improving storage properties of brown and milled rice.Volatile compounds emanating from cooked rice of three cultivars(Xiangzaoxian 21,Waiyin 7 and Kongyu 131)milled to different degrees(0,3,6 and 10%,based on brown rice),were identified by the method of Headspace solid-phase microextraction and gas chromatography-mass spectrometry.A total of 32,34 and 36 volatile compounds were assigned to the cooked rice of Xiangzaoxian 21,Waiyin 7 and Kongyu 131.The component cyclopentadecanolide was not previously reported in rice.At milling degrees of 0,3,6 and 10%,the volatile components identified were 30,32,32 and 30 for Xiangzaoxian 21,28,34,34 and 32 for Waiyin 7,whereas 35,36,36 and 34 for Kongyu 131.The major volatile components of cooked brown rice were aldehydes,aromatics,alcohols and acids,followed by esters,ketones and olefins.Lightly milling(3%)obviously increased the amount of them.Deeper milling(6 and 10%)result in a corresponding decreasing in the amount of the volatile compounds.Headspace solid-phase imtcroextraction and gas chromatography-mass spectrometry were used to analysis the effect of microwave treatment(384 W and 539 W)on the volatiles of rice with milling degrees of 0,3,6 and 10%.The results showed that after microwave treatment,the contents of olefins,acids and lipids in rice were declined to different degrees.Moreover,the decreasing amplitude of volatiles content in lightly-milled rice was highest,and the decreasing amplitude of volatiles content in partially-milled rice was higher than in well-milled rice.After microwave treatment of 384 W,aldehydes,alcohols and ketones content in lightly-milled rice increased most.After microwave treatment of 539 W,the content of alcohols,ketones,and partial aldehydes in brown rice increased most.Microwave promoted the generation of the heterocyclic compounds such as benzene and benzothiazole,accelerated the degradation of furan at the same time.Rice with milling degrees of 0,3,6 and 10%were used to the accelerated aging(25 and 40 days),the volatiles of cooked rice were analyzed.The results showed that in the process of aging,olefins content was gradually declined for all samples,while the contents of aldehydes,alcohols,ketones,acids,aromatic and ester compounds were gradually increased.After aging,the content of aldehydes,alcohols,ketones,aromatic,acids and esters compounds increased most in lightly-milled rice,followed by partially-milled rice,well-milled rice and brown rice.In addition,in the aging process,olefins compounds declined most in lightly milled rice,followed by partially-milled rice,well-milled rice and brown rice.After treated by microwave(539 w)or vacuum package,the rice with milling degrees of 0,3,6 and 10%were stored at 37? for 40 days,and the changes of rice volatiles were analyzed.The results showed that the rangeability of volatiles in rice with vacuum package for 40 days was lower than that in control for 25 days.It is concluded that vacuum package can be used to partially inhibit the rice aging,because the volatiles of rice still changed slowly during storage;among them the content of lightly-milled rice changed most,followed by partially-milled rice,well-milled rice and brown rice.In addition,after microwave treatment,the rangeability of volatiles in lightly-milled rice,partially-milled rice and well-milled rice were lower than that in control during storage,with the exception of brown rice.By contrasting the rangeability of volatiles during aging,it was obvious that vacuum package and microwave treatment had almost the same effect on inhibit the aging process for lightly-milled rice,partially-milled rice and well-milled rice.Moreover,vacuum package was more suitable for inhibiting the aging of brown rice than microwave treatment.