Sterilization technology of ready-to-eat isinglass

Isinglass is one of the traditional fish products in China, with unique flavor and taste. However, shortcomings such as soft taste and loss of nutrients after sterilization, limit its commercial development. In order to improve the heat sterilization process and reduce the deterioration of the quality of Sciaenops ocellatus isinglass after sterilization, the corresponding sterilization process at different sterilization temperature with F=4.5 min was investigated. Through the analysis of physical property, low-field nuclear magnetic and infrared chromatography, the effects of different sterilization temperature on the texture, color, collagen content, water distribution and protein structure of isinglass were investigated. The results showed that the isinglass products needed to be sterilized for 56.44, 15.85, 3.46 and 0.92 min at 110, 115, 121 and 125 °C, respectively, to reach the F=4.5 min, and corresponding products could reach the commercial sterile state. In the range of 110 to 125 °C, the brightness L^* value and b^* value decreased gradually from 59.78 to 49.65 and 17.80 to 11.25, while a^* value didn’t change notably (P>0.05), with the increase of the sterilization temperature. In addition, FTIR confirmed the triple helical structure of the collagens. The significant improvement of hardness and shear force of isinglass and the reduction of viscosity were also observed (P<0.05). After being sterilized at 125 °C, hardness and shear force values were 37.02 g and 34.2 g·s, respectively, the viscosity was –2.82 g. Meanwhile, the collagen content of the sample rose from 7.60% to 14.92% and the collagen concentration in the solution declined from 3.33 mg/mL to 0.15 mg/mL. After being sterilized at 110 °C, the degree of freedom of water in the isinglass was the highest, the proportion of free water in the isinglass gradually decreased with the increase of the sterilization temperature. Therefore, under the sterilization condition of higher temperature, the brightness of the isinglass was reduced, but the quality was improved with better texture and higher content of collagen. This study has important practical significance for promoting the processing and utilization of isinglass and improving the quality of sterilized ready-to-eat aquatic products.