| Chinese rice warehouse stocks have grown rapidly since 2013,the inventory consumption increased by nearly 40%.The loss of quality in the storage process of rice can cause a lot of economic losses,Therefore,it is of great market significance to study the quality change of storage-resistant rice varieties during storage.The rice in Jiangsu and Northeast China is representative,so the rice varieties in these two regions were selected as the experimental objects in this paper.Eight kinds of indica rice harvested in 2016(four from Jilin and four from Jiangsu)were stored for 360 days(d)at 25~oC and RH 75%,and their physical and chemical properties were measured periodically every 30 days.The quality deterioration of different varieties of japonica rice during storage was analyzed,and the resistant varieties were found out.The results of the first stage experiment were used to study the effects of different temperature conditions on the quality index and volatile matter composition of the japonica rice.The four kinds of Jilin japonica rice harvested in 2017 were stored in artificial climate chambers of35~oC,30~oC,25~oC,20~oC,and15~oC for 3 months.The measured indicators are:fatty acid value,lipase activity,conductivity value,malondialdehyde content,color difference,gelatinization properties and volatile substances.The specific conclusions through experimental analysis are as follows:1.Under the same storage conditions,the fatty acid value,conductivity value and malondialdehyde content increased with the storage time.The increase of fatty acid value was between 12.4 mg/100g and 24.5 mg/100g,and the conductivity value increased by 31.92?s/cm~53.71?s/cm.The increase of malondialdehyde content was between 0.509?mol/L and 0.741?mol/L.The activity of lipase increased first and then decreased.The maximum value of lipase was between 9.22 mg/g and 12.69 mg/g.During the storage,the chromaticity L*value gradually decreases,and the a*value and the b*value gradually increase.There are differences in the variation range of different indicators of different varieties of japonica rice during storage.The growth rate of fatty acids in four kinds of japonica rice(Huai 5,Su Xiu,9108,9105)produced in Jiangsu Province ranged from 86.8%to 130.9%.The four indica rice(chaojidao,putongdao,qiutian,and changli)produced in Jilin ranged from 53.5%to 78.5%,and the increase rate was even slower.The lipase activity of 9105,9108 and Huai 5 reached the maximum of 10.85 mg/g to 12.69 mg/g in the 5th month.Su Xiu reached a maximum of 12.40 mg/g in the sixth month.Chaojidao and putongdao reached a maximum of9.22 mg/g and 12.30 mg/g in the seventh month.qiutian and changli reached a maximum of 11.00 mg/g and 10.53 mg/g in the 8th month.The largest increase in conductivity value is Su Xiu,53.71?s/cm.The conductivity value of changli is at least31.92?s/cm.Su Xiu's malondialdehyde increment is 0.741?mol/L.Ordinary rice has a minimum of 0.486?mol/L.Therefore,the four kind of japonica produced by Jilin are more resistant to storage.2.Analysis of volatile substances of different japonica rice varieties by solid phase microextraction(HS-SPME)and GC-MS.133 substances were selected,including 25kinds of alkane,11 kinds of olefins,13 kinds of alcohols,12 kinds of aldehydes,11kinds of ketones,9 kinds of aromatic hydrocarbons,37 kinds of acid esters and 15 kinds of heterocyclic compounds.As the storage time increases,the relative increase in hydrocarbon content is between 3.26%and 11.52%.The increase of acid esters is between 12.61%and 25.52%.The relative content of alcohols generally increased first and then decreased.The relative amount of aldehydes decreased by 8.03%to 12.15%.During the storage period,the relative content of alcohols,aldehydes and acid esters in the four japonica rice varieties produced in Jiangsu Province was significantly higher than that of the four japonica rice varieties produced in Jilin,so the four japonica rice varieties produced by Jilin were more resistant to storage.Principal component analysis(PCA)analysis showed three main components PC1(alcohol factor),PC2(olefin factor)and PC3(aldehyde factor),the contribution rates were 38.952%,24.494%,13.726%,respectively.Principal component analysis can be used to distinguish different varieties of japonica rice and find corresponding characteristic substances.3.Storage temperature has a significant impact on the quality index of japonica rice.For every 5~oC increase in temperature,the fatty acid value increases by about 3mg/100g to 6 mg/100g,and the conductivity value increases by about 3.0?s/cm.The lipase increase is between 4.8 mg/g and 9.2 mg/g under high temperature conditions.The lipase increment is between 1.0 mg/g and 3.9 mg/g at low temperature.The increase in malondialdehyde content reached a maximum at 25°C.The temperature has a significant influence on the a*value and the b*value.The higher the temperature is,the faster the increase of?a and?b.Temperature is not an influencing factor affecting the change of L*value,and the initial moisture content has a significant effect on the L*value.Fatty acid value(F),lipase(X),conductivity(P),and malondialdehyde content(Q)of indica rice were analyzed by two-way ANOVA and linear regression equations,and storage temperature and time were found.It is a significant factor affecting fatty acid value,lipase and electrical conductivity(p<0.01).Storage temperature is not a factor in the malondialdehyde content.These indicators are consistent with the binary linear relationship of W/F/X/P/Q=aT+bD+c(p<0.01).This model can be used to predict the relative indicators of japonica rice during storage at different temperatures.4.Detecting volatile substances at different temperatures by HS-SPME and GC-MS techniques,among the 79 substances selected,there are 19 kinds of alkanes,5 kinds of olefins,11 kinds of alcohols,7 kinds of aldehydes,6 kinds of ketones,3 kinds of aromatic hydrocarbons,19 kinds of acid esters and 9 kinds of heterocyclic compounds.With the increase of storage time,all kinds of volatile substances continue to accumulate.The higher the temperature is,the greater the increase of the content of alkane,olefin,aldehyde and acid ester,and the alcohols,ketones,aromatic hydrocarbons and heterocyclic substances are.The increment is independent of temperature.Temperature is a sensitive factor for the number of species of alkanes,alkenes,aldehydes and acid esters,and is a sensitive factor affecting the content of alkanes,alkenes,aldehydes and acid esters.The types and characteristics of volatile substances are different under different temperature conditions.The main contributing components at 35~oC are alcohol factors and acid ester factors.30°C is an alkane factor and an acid ester factor;25~oC is a heterocyclic factor and an olefin factor;20°C is an alkane factor and an aldehyde factor,15°C is a heterocyclic factor and an olefin factor.It can be concluded from principal component analysis that the characteristic substance of chaojidao is 3-methyl-2-(3,7,11-trimethyldodecyl)-furan,1-octadecene,hexamethyl Cyclotrisiloxane and pentadecene.putongdao is tannic acid.Qiutian is undecyl-cyclopentane.Changli is pentadecyl alcohol.Different varieties of rice can be distinguished according to different characteristic substances. |
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