Effect of Different Sterilization Methods on Isoflavone Profile and Quality Characteristics of Ready-to-Eat Dried Soybean Curd (Tofu)
YE Tao, CHEN Zhina, YE Qianwen, LIU Huiqian, WANG Yun, LU Jianfeng
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In order to explore the effects of different sterilization methods on the quality characteristics of ready-to-eat dried soybean curd (RTE-DSC), the impact of pasteurization (95 ℃ for 30 min), high-temperature sterilization (HTS; 121 ℃ for 15 min), high hydrostatic pressure (HHP; 400 MPa and 25 ℃ for 20 min) and pressure-assisted thermal sterilization (PATS; 400 MPa and 60 ℃ for 20 min) on the microbial load (total viable and coliform counts), texture, color, sensory quality, water-holding capacity and major soy isoflavone components of RTE-DSC coagulated with magnesium chloride was investigated. Total viable counts of RTE-DSC decreased to 420, 130, 180 and 120 CFU/g, respectively after pasteurization, HTS, HHP and PATS treatments, and no coliform bacteria were detected in all samples. Pasteurization had no significant effect on the texture of RTE-DSC (P > 0.05), but HTS, HHP and PATS could significantly increase the hardness by 68.04%, 36.51% and 43.02%, respectively (P < 0.05). The L value of RTE-DSC decreased from 80.99 to 74.76, and the a value increased from 3.24 to 3.70 after HTS; however, the other sterilization methods had no significant effect. In terms of sensory score, pasteurization and PATS had no significant effect on RTE-DSC (P > 0.05). The content of total isoflavones in unsterilized soybean curd was 1 031.8 μg/g (on dry basis). After pasteurization, HTS and PATS treatment, this value decreased significantly to 882.3, 846.1 and 893.8 μg/g (P < 0.05), respectively, but the effect of HHP (979.3 μg/g) was not significant (P > 0.05). Moreover, all treatments resulted in a decrease in total aglycone isoflavones, and heat treatment (pasteurization and HTS) resulted in greater losses. Therefore, PATS needs further research.