Study On Characteristics Of Colorimetric Sensor Array And Application In Fish Freshness Evaluation

Fish is easily deteriorated.Fish spoilage reduces its economic value,and causes food safety concerns.Freshness is an important index to measure the quality of fish. As the routine examinations such as physical and chemical methods for fish freshness detection are so tedious and time-consuming,it is difficult to employ them for real-time detection in industry,or our daily life.The artificial olfaction technologies may be a proper method for fish freshness detection,due to their faste,scientific and objective figures.However,most of the gas sensors used in the traditional artificial olfaction system are based on the relatively weak chemical interactions(e.g.,physical adsorption).Those systems are sensitive to water vapor,unable to discriminate similar materials,and have a low sensitivity to detect metal-binding gases(e.g.,amines, thiols).In order to overcome the drawbacks mentioned above,this thesis describes a novel method,odour visualization technology,for detecting fish freshness.The main conclusions are as follows.1.This work researched the selection of gas sensing materials and the preparation way of the colorimetric sensor array(CSA).According to the chemical reaction principle between the chromogenic reagent and gas molecule,gas sensing materials(e.g.,metalloporphyrins,pH indicator) were screened to detect the common food odors.Depositing sensing materials as solidfilms onto a substrate was used for sensor array preparation.And how the concentrations of sensing materials solutions and depositing ways influenced the CSA consistency was explored.The result shows that low concentration of sensing material solution can enlarge sensor's color change range.A high reproducibility CSA could be obtained via a certain quantity solutions free diffusing on the C2 reverse phase silica gel plate.2.Some improvements in the odour visualization system have been made.Two gas collecting device were designed respectively to detect liquid or solid sampling object.The RGB value change was expanded to 0-255 by means of normality processing so as to enhance contrast of the characteristic image. 3.The basic characteristics of the CSA were primarily investigated.Combining with the previous work,the selectivity of the CSA was discussed.And the detection range,humidity sensing,stability of the CSA were also studied. Experiment results indicate that there is a good sensitivity,selectivity, stability and reproducibility for the CSA,the changes in humidity doesn't significantly affect the color fingerprints of vapor analytes.The CSA has a great potential to be applied in food quality rapid detection.4.A CSA which was used to detect the fish freshness was designed and its application in fish freshness detection was also studied.Via the analysis of volatile organic compounds(VOCs) change in fish headspace with different storage time,9 kinds of gas sensing materials were selected aim at assessing the freshness of the fish.Amines are the important compounds in the fish spoilage gas.In order to prove the qualitative and quantitative analysis ability of the CSA developed from 9 kinds sensing materials,several gaseous amines were discriminated by nicked eye,Principal Component Analysis(PCA) and Cluster Analysis(CA).Gaseous trimethylamine in different concentrations was also discriminated correctly by PCA and CA. The CSA developed form 9 kinds of sensing materials was used to evaluate the Silver Carp freshness.According to the color of the CSA,fresh and spoilage fish could be recognized via naked eye.The fresh,half-fresh, spoilage fish could be identified by means of computer analysis.This research demonstrates that the CSA has a great practical value in fish freshness detection.The method developed can also be used as reference for quality evaluation of other high protein food.And the CSA also has a great potential value in food aroma odor rapid detection and air quality monitoring.