Effect of temperature, pH and citrus essential oil on the reduction of Listeria monocytogenes in smoked fish by hot and cold method

Document Type : Research Paper

Authors

1 Department of Fisheries, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran

2 Department of Food and Science Technology, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran

Abstract

The aim of this study was to investigate the effects of temperature, pH and orange essential oil on reducing the growth rate of L. monocytogenes. The variables included 45 ° C (for 144 hours), 50 ° C (for 72 hours), 55 ° C (for 6 hours), 4 pH levels (4, 5, 6) and essential oil citrus (Citrus aurantium L.) in 0.2, 0.4 and 0.6% levels on the growth rate of L. monocytogenes in cold smoked silver carp fillet. The results showed that the number of bacteria increased with increasing pH at the studied temperatures (P<0.05), But correlation analysis showed no correlation between L. monocytogenes and pH. The increase in temperature significantly reduced the number of bacteria in cold and hot smoked silver carp fillets, so that the lowest bacterial count in both cold and hot smoked fillets was counted in a temperature of 55 ° C. The correlation between number of bacteria and temperature also confirmed this. Regarding the effect of citrus essential oil on the number of bacteria, the results showed that in the conditions of pH and constant temperature, increasing the percentage of essential oil, the number of L. monocytogenes decreased and this decrease, especially in the treatment of 0.6% of orange essential oil. Also, at the same temperature and pH, hot smoking compared to cold smoking was more effective in reducing the number of L. monocytogenes. Given that the number of bacteria counted in both methods of smoke at different temperatures and pH was not higher than the107 Log cfu/ g standard, it could be argued that smoke is a reliable way to increase the shelf-life of silver carp fillet and the best temperature and time to smoke was 55 ° C for 6 hours, at pH = 4, and essential oil level was 0.6%.

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