| In this study,a sol-gel indicating card was prepared using bromocresol green as an indicator,and filter paper as a substrate.Firstly,properties of the indicating card including surface micro-structure,moisture absorption and thermal stability was characterized.Secondly,during the storage of red drum fish,the color response of the indicating card at room temperature and chilled condition were studied,and p H values and amount of TVB-N were determined.RGB values were extracted from the images of indicating card and calculate as H values based on HSV model,and the correlation between H values and TVB-N level was analyzed.Finally,the freshness indicating card we prepared in our study was successfully applied to other types of fish such as turbot and large yellow croaker for fish freshness monitoring.Characterization results showed that the sol-gel was successfully coated on the surface of filter paper entrapping bromocresol green dyes within it.Comparing with bare filter paper and traditional dip-coating bromocresol green indicating paper,moisture absorption property of our sol-gel indicating card was improved.The sol-gel coating yield of our indicating paper was calculated as 14.25% according to TGA analysis.The color response results showed that the color of indicating card changed from yellow to green and finally to blue during the spoilage of fish,which can be clearly distinguished by naked eyes.The TVB-N amount of red drum fish storing for 22 hours at room temperature and for 6 days at chilled condition was 23.11 ±2.22 mg/100 g and 24.12 ± 1.34 mg/100 g,respectively,reaching the threshold of spoilage.Correspondingly,the color of the indicating card turns to blue.The color change of freshness indicating card is linearly correlated with the response of TVB-N in a certain range.The linear fitting equation of H value and TVB-N can be used to judge the freshness grade of fish and the amount of TVB-N before the threshold of spoilage.The results of actual sample test showed that the color of indicating cardchanged from yellow to green and then to blue at room temperature.The H value was extracted from the color changing images and then TVB-N level was calculated.The results fitted the linear equation very well. |
