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Depending on the conditions of each facility and the time that it would take the product to return below -18 degrees Celsius (-0.4 degrees Fahrenheit) in all points, and taking in consideration the cumulative effect of future temperature oscillations until the product reaches the final consumer, I believe that organizations should address this issue and propose the adoption of the Safe Dipping Time (SDT) concept. SDT should be defined by each organization according to its operational conditions (e.g. temperature of product and glazing solution, production room temperature, time to product return to frozen storage and its temperature) and will represent the maximum time that a product can be dipped without the temperature raise constituting a hazard.
Antimicrobial Activity of Chitosan Solution
Freezing is a commonly used method for long term preservation since it is well known for the capacity for inhibiting microbial growth and slowing down enzymatic activity. The Fish and Fishery Products Hazards and Controls Guidance – Fourth Edition presents in its Appendix 4 a list of common pathogens in the fish industry and temperatures that enable growth and toxin formation. According to the guide, the two pathogens that are able to grow at the lowest temperatures are Yersinia enterocolitica and Listeria monocytogenes at -1.3 degrees Celsius (29.7 degrees Fahrenheit) and -0.4 degrees Celsius (31.3 degrees Fahrenheit), respectively. These temperatures are much higher than the -18 degrees Celsius (-0.4 degrees Fahrenheit recommended for storage of frozen fish and therefore, during frozen storage, temperature is the main factor to inhibit microbiological growth. In fact, in an experiment where salmon was glazed with water or chitosan solution (0.5 percent w/v) and stored at -5 degrees Celsius (23 degrees Fahrenheit), the total viable count (TVC) did not show any trend during the 14 week experiment and fluctuated between 5.0 X 102 and 1.0 X 104 colony-forming units/gram for both glazing solutions tested.
Nevertheless, as soon as the temperature rises, as is the case when fish is thawed at home before cooking, microorganisms can growth again, start spoiling the product, or even produce toxins depending on the time/temperature of exposure. The use of water glazing will not affect in any way microbial growth but the use to a 1.5 percent (w/v) chitosan solution has been proven to reduce the TVC in salmon stored at -22 degrees Celsius (-7.6 degrees Fahrenheit) during 181 days. In this experiment, two different TVC evaluations were performed. Both were based on BS EN ISO 4833:2003 but one was done immediately after storage and the other after the product was kept in a refrigerator at 5.9 degrees Celsius (42.6 degrees Fahrenheit) during 24 hours, simulating conditions of home thawing. Table 1 presents TVC results for both experiments.
The results clearly show that using a chitosan solution to glaze the product can actively reduce the microbial contamination of the product and even help ensure that it is safe during a 24-hour thawing process.
Glazing has been used too long just as a mechanical barrier. At a time where safety, added-value products, and product differentiation are so important for consumers and therefore for the fish industry, organizations should revise the use of glazing, bringing new benefits to the product and consumers.
Reducing the amount of glazing to the thickness necessary to guarantee the protection from cold air and introducing substances that can guarantee a safer product, not only during storage time but also at consumers’ home, are paradigm changes that can shape the industry in the forthcoming years and increase the consumers’ confidence regarding frozen fish.
Soares is quality manager at Vanibru, Lda. He is also author of the book Food Safety in Seafood Industry: A Practical Guide for ISO 22000 and FSSC 22000 Implementation. Reach him at email@example.com or @foodsafetybooks.