Study On Aging Mechanism And Storage Quality Of Indica Rice

This paper studied the change in constituents of storage rice using nuclear magnetic resonance(NMR),and studied the influence of both storage temperature and package materials on the quality of indica rice.We also observed the microstructure of cooked storage rice by SEM.we hope this study can both aid in our understanding and further the research into the progression and phenomenon of aging rice.The main results are as follows:1.We investigated constituent differences between stored and fresh rice using multidimensional solution-state nuclear magnetic resonance(NMR)spectroscopy.Fourier transform infrared(FTIR)spectroscopy and gas chromatography–mass spectrometry(GC-MS)was also used to determine constituent changes during storage.Signal variations in alkyl,alkoxy,acyl,hydroxyl,amine,and amino groups revealed hydrolysis of neutral fats and phospholipids to free fatty acids or lower esters.Signals from double bonds showed changes in unsaturated substances,such as glycerides and phospholipids,which correspond to a phenomenon exposed by GC-MS detection,that is,a reduction in polyunsaturated fatty acids occurs on storage.Moreover,the hydrolysis or oxidation of unstable lipids result in a conversion from fresh to aging rice with respect to the development of disagreeable flavors.2.The storage conditions such as storage temperature,storage time and packaging material to influence physicochemical properties of Indica rice was studied.Rice samples were packed in PET/LLDPE vacuum-packed pouches,LLDPE zippered pouches and ventilated Paper cups for three months,respectively.Two endothermic peaks in DSC data were adjacent to each other.For peak 1,T_o and T_p increased after 50~o C,butΔH andΔT_g decreased after 50~oC.TheΔH andΔT_g of peak 2increased after 50~oC.DSC thermal data,were not distinctly influenced by packaging materials,but could be slightly postponed at lower storage temperatures.Peak viscosity of PET/LLDPE and LLDPE samples at 4~oC and at 23~oC increased before during first week and then kept constant for 12 weeks.The aerated samples at 65~oC decreased after one week storage and rose after 8 weeks.Breakdown of 4~oC and 23~oC in both three packaging decreased after one week.Aerated samples had lower setback values.Aerated samples at 4~oC,23~oC showed lower hardness than other packaging,but aerated samples at 65~oC showed higher hardness than others.DSC double peak of stored rice turned into singlet after the addition of 2-mercaptoethanol.According to the result of simulated storage sample in solution NMR,there were few change in constituents during short term storage.It was shown that temperature would affect rice quality during short term storage because the TPA and viscosity suffered changes.The conditions of package methods and temperature had few effect on rice during short term storage,but high temperature storage would turn rice into yellow.It may owing to unstable lipid suffered enzyme degradation or oxidation.3.We studied the surface morphology and structure of cooked storage rice using scanning electron microscopy(SEM).The result showed that more cracks appeared in endosperm.4.We studied the influence of package,temperature and storage period on the change in movement of water molecules by LF-NMR.The result showed that water molecules were easier to intrude into the rice owing to many cracks.