| Today, the determination of the quality of rice was still using the traditional detection methods, such as measuring rice sugar, viscosity, fatty acids, conductivity and so on. To meet consumer’s higher demand for security and nutrition of rice, researches of modern analytical methods was very important, market was expecting a more reliable, faster, more accurate and cheaper determination method of rice quality. There was inevitable connection between the physicochemical index and volatile components group of rice, which reflected the quality of rice and the degree of microbial contamination by microorganism. The moisture content was the main quality index of rice, which can directly affect the level and changes of other indexes. Therefore, the quality of rice can be determined by the determination of moisture content. In this paper, a method for rice and rice contaminated by aflatoxin was initially established based on headspace solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS), the group of volatile components of rice as object; A new technique and method for the rapid detection of moisture content of rice was established, with the moisture content of rice. The main researches were as followed:(1) In this study, the method of analysing volatile components of rice based on HS-SPME/GC-MS for different storage period (5,15,30 and 50 days) was developed. First, the conditions of headspace solid phase micro extraction, including the balance of time, extraction time, extraction temperature, and the sample size were optimized, and identification and classification analysis of different rice volatile component was studied. The results showed that:the best conditions for analysising the rice volatile component were 30 min of equilibrium time,20 min of extraction time and 75 ℃ of extraction temperature of the amount of sample. There were 21 species rice volatile components detected, including four kinds of aldehydes, six kinds of alcohols, one kind of ketone, nine kinds of hydrocarbons and one kind of heterocyclic. The highest total content of rice volatile components was aldehydes and hydrocarbons, followed by alcohols, ketones and heterocyclic.(2) In this study, the volatile components of rices that had been stored for 5 day, 15 days,30 days and 50 days, which inoculated with 1.5 × 105 cfu/ml Aspergillus flavus, were detected using a fiber of 85 μm CAR/PDMS based on HS-SPME/GC-MS and NIST software. The main volatile components identified was a total of 26 species, including five kinds of aldehydes, six kinds of alcohols, one kinds of ketones, ten kinds of hydrocarbons, one kind of esters, one kind of heterocyclic hydrocarbons and one kind of acids. Identification of the volatile components may provide a theoretical basis for the identification of Aspergillus flavus and the inventions of biological sensors to monitor Aspergillus flavus.(3) In this study, a rapid non-destructive device for detecting moisture content of rice was constructed combine parallel plate electrodes with piezoelectric sensor, based on the theory that the dielectric properties of rice has a good correlation with moisture content and that piezoelectric sensor was sensitive response on frequency shift with the change of dielectric properties. Made use of the inverse piezoelectric effect of quartz piezoelectric sensors, with quartz crystal oscillation frequency and moisture content of paddy linked, combined GB 105℃ constant weight method, by linear fitting, established a specific calibration equation of rice sample moisture content and the piezoelectric characteristic frequency:y=-4.7X+9004940, r2= 0.996, n= 10. Then, the moisture content of the 8 rice samples in the linear range was rapidly detected by the calibration equation, and compared with the traditional national standard method. Results showed that:the piezoelectric sensor method was accurate, fast and simple, was expected to be applied to paddy moisture content rapid, real-time detection. |
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