| Rice is one of the three most important cereal in the world. It’s not resistant to storage, so the aging and quality deterioration of rice during storage are unavoidable. However, the rule of rice aging is still unclear. This paper will take the late indica rice as the research object, explore the rule of quality deterioration during storage, and find out the characteristic detection indexes which is closely related to the rice quality. First of all, the study will respectively adjust the moisture of the fresh test rice to (13.5 ±0.1)%, (14.5 ± 0.1)%, (15.5±0.1)%, and then put it into 2 liters of sealed jar at 15℃,25 ℃ and 35 ℃ in the artificial climate incubator to start simulated experiment of storage. The storage period is 180 days. Quality indexes of rice samples, including fatty acid value, gelatinization properties, surface color and volatile substances were detected regularly. The change rule of above-mentioned quality indexes of rice in the process of storage were explored. The characteristic volatile substances which are closely related to the rice quality were found out and the relationship between them were researched. This study will provide scientific basis for the safety of rice storage. The main research results are as follows:(1) Fatty acid value, gelatinization properties characteristic value and the surface color changed significantly along with the extension of storage. The temperature and moisture content were higher, the above-mentioned indexes also increased more quickly. On the contrary, increase amplitude of such indexes were small. The total factor analysis of variance showed that fatty acid value、hot viscosity、final viscosity、 and b value had the greatest influence by storage temperature. Peak viscosity、 breakdown value、setback value、△E value had the greatest influence by storage time. According to principal component analysis of rice quality indexes, it showed that fatty acid value、peak viscosity, hot viscosity, final viscosity, setback value and b value were the main indicators which could reflect the rice quality.(2) On the basis of single factor experiment, the response surface analysis was applied to solid phase micro-extraction conditions. The optimum processing conditions was obtained:75 ℃ extraction temperature,59 minutes balance duration, 60 minutes extraction duration and 5 minutes desorption duration. The total peak area of volatile substances of rice samples under the optimal conditions was 3.2036 x 109, and the relative error of prediction was 0.69%. There were 84 kinds of compounds, including hydrocarbons, aldehydes, ketones, alcohols and acid esters. The content of hydrocarbons and aldehydes were the highest, followed by nitrogen, chlorine, oxygen contained, heterocyclic compounds, acid esters, ketones, and alcohols.(3) Electronic nose and GC-MS were used to test and analyze indica rice samples during the period of storage. Principal component contribution rate of electronic nose was as high as 99%, Discriminant index is 81, which played a very good effect on distinguishing samples of different storage duration; GC-MS detected 102 kinds of volatile substances. The principal component analysis of different kinds of substances showed that the largest contribution to the overall flavor was alcohol, aldehyde and ketone. It is inferred that the characteristic volatile substances to leads to the deterioration of quality of indica rice were 2-hexyl-l-decyl alcohol, benzyl alcohol, hexanal, decanal, cis-2-decenal,2-dodecenal,2-undecanone and 5-tridecanone.(4) Regression model between volatile substances and rice quality indexes was established. It is concluded that the relationship between rice surface color, fatty acid value and volatile substances is the most significant among the rice quality indexes. Ketone volatile substances was the largest influence to the rice surface color and fatty acid value. According to the model ultimately, it is reflected that the fatty acid value and the surface color can be used to judge the quality of rice. |
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