Fish Microbiology and Quality Assurance

Unit 7 - Sanitation and microbiological quality

7.2. Quality indicators
From the microbiological point of view, the product quality (shelflife) can be assessed by determining the presence of certain microorganisms as indicators of quality, presence of metabolic products of microorganisms and total viable counts. This information will help not only in assessing the existing quality of product but also in predicting product shelflife.

7.2.1. Presence of certain microorganisms as indicators of quality
The microbiological quality of a product depends on the associated spoilage organisms whose increasing numbers results in loss of product quality, and human pathogenic microorganisms whose presence leads to health risk to consumers. Presence of pathogenic microorganisms can be assessed by detecting an organism called indicator organism which can indicate likely presence of pathogens in food. Thus, the overall microbial quality of the product is a function of number of organisms, and therefore shelflife can be increased by their control.

Microbial indicators are more often used to assess food safety and sanitation rather than quality. Among the several food associated microorganisms the most commonly used organism as indicator is feacal coliform bacteria, E. coli and fecal streptococci. These microorganisms are associated with human faeces and their presence in food indicates poor sanitation, likely presence of other pathogens and fecal contamination.

Characters of indicator organisms

• Present and detectable in all foods whose quality to be assessed.
• Their growth and numbers should have a direct negative relation with product quality.
• Have history of constant association with pathogen and their numbers should correlate with pathogen of concern.
• Easily detectable and distinguishable from other organisms in short period of time.
• Growth should not be affected adversely by other food-associated microorganisms.

E. coli or coliform criteria
Presence of coliform or E. coli in foods is highly undesirable as it indicates faecal contamination, and handling and processing of food under unsanitary conditions. However, it is usually impossible to eliminate them in all foods (fresh/ frozen). Therefore, limits for coliform have been set for certain sensitive foods where coliforms are permitted in low numbers ranging from 1 – 100/g or 100 ml. These values are considered feasible and expected to ensure product safely.
Although coliforms are widely used in shellfish sanitation programme, these often fail as good predictors of sanitary quality because of presence of pathogens in waters meeting coliform standards. However, coliform criteria have been widely used in most foods as good indicator of fecal contamination.

Fecal streptococci as indicators
Faecal streptococci are a Gram positive bacteria associated with human intestine and thus encountered in fecal matter with their numbers variying from 105 to 108/g of feces. Species of streptococci such as Enterococcus faecalis and E. faecium are commonly associated with feces. These are fastidious in their nutritional requirements and grow over a wide pH range than other food borne bacteria. These being microaerophilic grow in reduced Eh condition. Generally do not multiply in water especially when organic matter load is low. Compared to E. coli these are less numerous in human faces. Ratio of 4 or higher between E. coli and streptococci is considered as indicative of fecal contamination.
Enterococci die off at slower rate than coliforms in water. Live longer in water than coliforms thus outlive the pathogen in water. These are found to be better indicators of food sanitary quality in frozen foods as they are more resistant to freezing condition. Also exibit resistances to adverse environmental conditions, and have better survival in dried foods than coliforms. These show poor relation with the incidence of food borne intestinal pathogen. Though they possess qualities suitable to be considered as indicator organisms they have not gained importance, as coliforms.

7.2.2. Metabolic products as indicators of quality
Metabolic products of microorganisms may be used to assess and predict microbial quality in some products. In fishes, the production of nitrogenous compounds by spoilage organisms has been used as indicators of product quality. These include;

• Trimethy amine (TMA)
• Total volatile bases (TVB) such as ammonia and dimethyl amine,
• Total volatile nitrogen (TVN).

Increase in their value indicates the spoilage, and their concentration increases as the spoilage progresses.

7.2.3. Total viable counts as indicators of sanitary quality
The natural counts of microorganisms vary depending on the environment from which the fish is caught. Besides, microorganisms are added during processing and handling of food.
Number of microorganisms present in fish starts increasing once the fish dies unless steps are taken to halt their multiplication. As the quality deterorates with increase in microbial count, the total viable counts are used as indicators of product quality. Thus, to ensure quality, limits or standards are set for total viable load for fresh and processed foods. Further, Increase in microbial build up in processed foods during storage is attributed to likely changes in storage/ preservation conditions. Total viable counts are of greater value as indicators of existing condition of given product than as predictors of shelflife, because the portion of counts responsible for ultimate spoilage are difficult to ascertain.