微酸性电解水对虾仁的杀菌效果及其动力学

    Disinfection effect and kinetics of slightly acidic electrolyzed water for white shrimp

    • 摘要: 为探明微酸性电解水(slightly acidic electrolyzed water,SAEW)对南美白对虾(Litopenaeus vannamei)虾仁表面杀菌效果及其动力学规律,选取料液比1:4、1:10、1:20,将虾仁分别浸洗杀菌2、5、10 min,对杀菌过程中虾仁表面及SAEW残存液中总菌落数,与有效氯质量浓度(available chlorine concentration,ACC)的变化进行测定,建立ACC衰减与微生物减灭的动力学模型,并通过颜色、硬度、pH值,及水分横向弛豫行为分析,探讨SAEW杀菌处理对虾仁品质的影响。结果表明SAEW对虾仁表面大肠杆菌有较强杀菌效果,并随处理时间的延长、作用量的增大,SAEW的杀菌效力不断增强,处理5 min时,随着料液比的增加,虾仁表面菌落数从最初的6.6 l(CFU/mL),依次降到5.0、4.7、4.4 lg(CFU/mL),料液比为1:20时,静置浸洗10 min后,虾仁表面菌落数由最初的6.6 lg(CFU/mL)降至3.9 lg(CFU/mL);同时SAEW浸洗液中残存菌落数也随处理时间的延长、作用量的增大,而不断减少,在处理2、5和10 min时,SAEW中的残存菌落数分别为4.18、3.47、2.78 lg(CFU/mL),处理时间为5 min时,随料液比的增加,SAEW中的残存菌落数分别为3.47、2.78、2.65 lg(CFU/mL);同时SAEW中ACC的消耗随处理时间的延长、而不断变大,杀菌处理5、10 min时,ACC质量浓度从初始的20.53 mg/L分别降至7.79、10.97 mg/L。动力学分析表明:SAEW在杀灭虾仁表面大肠杆菌的过程中,ACC的衰减可以用一级动力学模型描述,拟合后决定系数R2均大于0.9,而微生物的减灭遵循更为复杂的动力学模型;此外经过SAEW杀菌处理的虾仁,其颜色、pH值、硬度、以及水分的横向弛豫行为,与未处理样品相比,基本没有显著性变化。相关结果能为SAEW在水产品加工过程中的应用提供技术指导,同时也有助于SAEW杀菌技术理论的完善。

       

      Abstract: Abstract: Slightly acidic electrolyzed water (SAEW) with pH 5.0-6.5 is produced by electrolysis of dilute hydrochloric acid or salt solution in a chamber without a membrane. SAEW can effectively kill various pathogenic bacteria as one of the most potential green disinfectants. However, SAEW is susceptible to being exposed to time, air, and illumination etc. The influence of SAEW for inactivation of Escherichia coli on white shrimp (Litopenaeus vannamei) under different washing conditions was investigated. At room temperature, the effectiveness of SAEW (with available chlorine concentration (ACC) of 20 mg/L, pH value of 6.1 and ORP of 812 mV) to inactivate Escherichia coli with different dipping times (2, 5 and 10 min), weight ratio of shrimp to SAEW (1:4, 1:10 and 1:20) was evaluated, and changes of ACC were also measured. For inoculation, each shrimp was determined to be intact, and then exposed to a 90°C water bath boiling for 20 min. to inactivate bacteria on the surface of shrimps. Each sample was inoculated with E. coli by spreading 0.5 mL onto each surface respectively and then placed in a clean bench for 20 min. to allow for the attached E. coli. The level of E. coli on the shrimp surface was ensured to be of approximately 6.0-7.0 lgCFU/mL, and bacterial cells on surfaces of shrimp or in residual solution after treatment were counted using a dilution plate count at 37°C for 24h onto nutrient agar, and shrimp that were not washed were used as a control. Moreover, the decay kinetics models of ACC in SAEW during disinfection were established. The effect of SAEW on meat quality was also evaluated, respectively from color, pH value, hardness, and the moisture distribution. The results showed that SAEW has a strong bactericidal activity against E coli. on white shrimp, while distilled water has a relative weaker role. As the action time prolonged, and the amount of SAEW increased, the bactericidal effect of SAEW was intensified. Meanwhile, the residue bacteria colony in SAEW was also reduced and expenses of active chlorine was increased as the action time was prolonged, and the amount of SAEW increased during the disinfection process. The effective order of time on the bactericidal activity of SAEW was 10 min > 5 min > 2 min under the same ratio of shrimp to SAEW, dipping in SAEW (weight ratio of shrimp to SAEW was 1:4) for 10 min reduced E. coli population from 6.6 to 3.9 lgCFU/mL, which better than the control treatment. E. coli counts in a residual solution can reduce by 1-2 lgCFU/mL. Increasing the amount of SAEW enhanced the bactericidal effect obviously. The decay of ACC and bactericidal kinetic followed first-order kinetics during the disinfection process, and the model had good predicted results. In addition, there was no significant differences between the treated meat quality by SAEW and the controls, respectively from color, pH, hardness, and the moisture distribution of white shrimp meat. Therefore, SAEW has a strong bactericidal activity, and does not affect the meat quality of white shrimp, and has a great potential for application compared with the traditional thermal treatment.

       

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