Studies On The Effect Of Lipid On Rice Quality And Lipid Metabolism In Response To High Temperature And Weak Light Stresses

Rice,one of the most important food in the world,it is very significant to improve the rice quality for meeting the increased living standard.Many researches about rice lipid have been carried out indicating the closely relationships between lipid and eating quality.However,due to the poor content and difficult testing method of lipid,it has not gotten as much attention as it should be.Researches about rice protein and carbohydrate in response to temperature and light condition have been carried out for many years,however,few studies have reported related to rice lipid synthesis,especially the synthesis of key enzymes.Based on this,this study was carried out to(1)optimize the rice lipid extraction method by using ultrasound-assisted extraction,(2)analyze the relationship between rice lipid and qualities such as external quality and eating quality through defatted and un-defatted rice samples,and(3)explore the effect of high temperature and weak light on rice lipid metabolism during seed filling stage in field production conditions.These results are as follows:1.A new creative optimized extraction method for rice lipid was come up.In this work,a new method of ultrasound-assisted extraction(UAE)of rice lipid was proposed by using rice cultivar cv.Koshihikari as the materials.From the single-factor experimental design,extraction with hexane resulted in the highest yield compared to petroleum ether and isopropanol.The amount of extracted rice lipids yields enhanced with increasing sonication power,temperature and time,respectively.However,excessive sonication power,temperature and prolonged time would lead to the decrease of rice lipid.A response surface methodology(RSM)was used to optimize the parameters on UAE based on single factor experiment and the constructed regression equation is Y = 76.73-2.33x1-0.54x2-0.005x3-3.00x12-0.81x22-1.15x32-2.28x1x2 + 1.68x1x3 + 1.29x2x3,where xi represent the extraction yield,x2 represent extraction temperature,x3 represent extraction time.And also the predicted optimum combination for lipid extraction is proposed which is hexane,122.7W,42.1? and 37.2min and the predicted extraction yield is 77.31%.From the practical certification,the combination of hexane,123W,42oC and 37min obtained the greatest extraction yield(76.93%).Furthermore,the compositions of lipid were obtained by gas chromatography and mass spectrometry(GC-MS)and no significant differences were observed between UAE and conventional method.2.The lipid showed a significantly effect on rice external and eating qualities.Researches about the effects of starch lipid(SL),non-starch lipid(NSL)and fatty acid components on rice qualities are limited.To evaluate the relationship between lipid and rice qualities,15 cultivars(where 13 of them are japonica cultivars,and 2 of them are indica cultivars)were selected after harvest and analyzed the SL,NSL,fatty acid components,along with the chalkiness,pasting properties and eating quality.The predominant lipid in milled rice was SL,and the main fatty acids of both SL and NSL were linoleic,oleic and palmitic acids.The SL was negatively correlated with chalky rate and chalky degree while positively correlated with eating quality,whereas no clearly effect of NSL observed.Compared to un-defatted rice cultivars,the defatted rice significantly increased the hot viscosity,cool viscosity,setback and pasting temperature while decreased breakdown,suggesting poor qualities without lipid.Besides,the SL showed increased pattern with breakdown while decreased with setback.The unsaturated fatty acids of SL include linoleic and oleic acids evidently increased the rice eating quality while the accumulation of saturated fatty acids such as palmitic,stearic and arachidic acids contributed to the deterioration of rice qualities.These findings suggested that the SL was more responsible for the improvement of rice qualities besides other components such as starch and protein.3.The lipid and unsaturated fatty acid contents were significant decreased under high temperature during seed-filling stage.The rice cultivars cv.Koshihikari,Gangyou527 and IR72 were selected as the materials to evaluate the effect of high temperature on rice lipid metabolism during seed filling stage under field conditions.The results showed that the lipid content was evidently decreased under high temperature treatment compared to CK.The decrease of rice lipid was mainly attributed to the significant decreased PPase,G6PD and 3GPD activities,besides,the PEPC activity was evidently increased which was beneficial for protein synthesis and thus restrained the lipid accumulation.Furthermore,the unsaturated fatty acid was also decreased whereas the saturated fatty acid content increased under high temperature.The palmitic acid,linoleic and arachidic acids were significantly decreased,on the contrary,the oleic and stearic acids contents were evidently increased.4.The effects of high temperature on lipid and fatty acid accumulation during different seed-filling stage were different.To evaluate the effect of high temperature on lipid metabolism at different seed filling stage,the rice cultivars Koshihikari and IR72 were selected as the materials.The high temperature was initiated at 3 different stages during seed filling which were the early filling stage(H1),mid-filling stage(H2)and late filling stage(H3),respectively.Results showed that the lipid content,especially the unsaturated fatty acid were decreased at different levels under H1,H2 and H3 compared to CK where the lipid was affected most at H1 and H2.Decreased lipid content was mainly due to(1)the markedly decreased PPase,G6PD and 3GPD activities,(2)the evidently increase of PEPC activity which adversely increased the protein synthesis,and(3)the strong degradation of lipid under high temperature which resulted in increased free fatty acid.In general,the degree of influences of high temperature on rice lipid were H2>H1>H3.5.The rice lipid was decreased whereas unsaturated fatty acid was increased under weak light stress during seed-filling stage.Rice cultivars Koshihikari,gangyou527 and IR72 were selected as the materials to evaluate the effect of weak light on lipid metabolism during seed filling stage.Results showed that the lipid content was significantly decreased under weak light compared to CK,and the activities of PPase,G6PD and 3GPD were also decreased significantly.Besides,the evident increase of PEPC activity resulted in declined lipid indirectly.The weak light treatment was also resulted in decrease of saturated fatty acid and increase of unsaturated fatty acid.The decrease of saturated fatty acid was mainly resulted from declined palmitic,stearic and arachidic acids,and the increase of unsaturated fatty acid was mainly due to the heighted oleic and linoleic acids.6.There were differences between rice lipid and fatty acid under weak light stress during different seed-filling stage.2 of rice cultivars(cv.Koshihikari and IR72)were selected as the material to evaluate the effect of weak light on lipid metabolism at early filling stage(R1),mid-filling stage(R2)and late filling stage(R3),respectively.The results showed that lipid content was increased at different levels at either R1,R2 or R3,where the degree influences were R2>R1>R3.Furthermore,the unsaturated fatty acid(linoleic and oleic acids)was significantly increased under weak light,whereas the saturated fatty acid(palmitic,stearic and arachidic acids)was evidently declined.In general,he degree of influences of high temperature on rice lipid were R2>R1>R3.