The Research Of Japonica Rice Quality Formation With Grain Grouting And Postharvest Drying Characteristics Of Grain

This paper is mainly to observe the changes of moisture states of grains during the grouting process of japonica rice,and to indirectly explore the internal relationship between accumulation of starch and protein and the formation of japonica rice qualities,and to analyze the effects of harvested period on the changes of japonica rice overall qualities,and to investigate the moisture diffusion characteristics of postharvest rice under low temperatures and low relative humidities.The spikes of "Yueguang" japonica rice were sampled at intervals for 63 days after heading(DAH).Hundred-grain weight,hardness,moisture content,starch content,and protein content were measured separately,which was used to compare the changes of whole qualities for grains at different growth periods of japonica rice after heading.The transverse relaxation parameters determined by LF-NMR were adopted to qualitatively and quantitatively analyze the moisture dynamic of grains.What’s more,the internal relationships between the formation process of japonica rice qualities and moisture state of grains were discussed.The spikes of Nanjing 5055 and Nanjing 9108 were harvested at intervals for 36～66 DAH.The thousand-grain weight,appearance qualities,milling characteristics,RVA profiles and cooking qualities of japonica rice grains were measured separately,which was used to analyze the internal relationships of physicochemical properties,and investigate the effects of harvested period on the changes of japonica rice overall qualities.The experimental samples with different initial moisture contents(18.9%,21.6%,23.9%,26.7%,and 29.6%)were prepared by freshly harested japonica rice(variety:Huaidao 5).Then the thin-layer drying experiments were conducted under low temperatures and low relative humidities.Mathematical models,drying duration and effective moisture diffusivity were used to investigate the effects of initial moisture content,drying temperature and air relative humidity on the external moisture diffusion characteristics of rice.LF-NMR was adopted to analyze the internal moisture dynamic of kernels during the drying process of rice.The main conclusions were showed as follows:1.Both hundred-grain weight and starch content for "Yueguang" japonica rice increased most quickly within 7～14 DAH,and they were highly significantly and positively correlated with each other(P<0.01).Hardness was highly significantly and positively correlated with starch content and protein content respectively(P<0.01),and negatively correlated with moisture content(P<0.01).The inversion spectrum of LF-NMR data showed that part of water in the grains moved towards the direction of high mobility within 7 DAH.Within 7-21 DAH,when inversion curves of LF-NMR data gradually moved towards the left,T2b peak representing for"bound water" with least mobility occurred,followed by the differentiation phenomenon of T22 peak representing for capillary water.Four kinds of transverse relaxation times including T2b,T21,T22 and T23,gradually decreased with growth periods,which indicated that whole proton degree of freedom in the kernels dropped obviously.2.The moisture content and transverse relaxation parameters(T2b,T21,T22,T23,A2b,A22 and A23)of grains varied with growth periods highly significantly(P<0.01),which were also highly significantly(P<0.01)related to the accumulation of starch and protein.It’s found that the ratio of "bound water" gradually increased,and the ratios of capillary water and free water significantly decreased in the grains.We can adopt LF-NMR to effectively analyze the whole moisture dynamic changes of grains at different growth periods of japonica rice after heading.3.The thousand-grain weights and starch contents of Nanjing 5055 and Nanjing 9108 harvested at 48～54 DAH were significantly higher than those harvested at other periods,respectively(P<0.05).The chalky rice rates of Nanjing 5055 and Nanjing 9108 didn’t change with harvested period significantly(P>0.05).The L*values of two milled japonica rice varieties gradually increased,while the a*and b*values of whose decreased little by little.The brown rice rates and head rice rates of Nanjing 5055 and Nanjing 9108 increased to the peak values at 54 DAH and 48 DAH respectively,and decreased slightly afterwards.With showing an V-shaped curve,the peak viscosity and breakdown values of rice RVA profiles changed with harvested period,and they highly significantly positively correlated with each other(P<0.01).While the setback and past temperature values showed the opposite variations of them.The consistency and peak time values didn’t vary with harvested period significantly(P>0.05).The hardness values of cooked rice decreased to the minimum values at 48～54 DAH,which highly significantly positively correlated with breakdown(P<0.01),and highly significantly negatively correlated with setback(P<0.01).The adhesiveness values gradually decreased,which was highly significantly influenced by harvested period(P<0.01).The qualities of japonica rice were greatly influenced by harvested period.The harvest at suitable periods would not only increase the appearance qualities and head rice rate of rice,but also improve the starch gelatinization properties and cooking qualities of rice.4.The lower drying temperature,the more significantly humidification could increase the drying rates during the drying process of rice under low temperatures and low relative humidities.The Page model was the most appropriate model used to decrible the thin-layer drying characteriscs of rice.Besides,the effective moisture diffusivity of rice was highly significantly(P<0.01)influenced by MC0,T and RH,which increased linearly with MC0.5.During the whole drying process of rice,it’s found that the inversion curves of LF-NMR data gradually moved towards the left,and both the A21 peak area representing for "bound water" and A22 peak area representing for capillary water decreased significantly,while the A23 peak area representing for free water kept steady.When the moisture content of rice was decreased to 14.5%～16.5%,the LF-NMR signal peak of capillary water disappeared and the moisture states of rice kernels transferred into "bound water" and free water.