Growth of aerobic mesophilic bacteria and Pseudomonas species on carp tissues during chilled storage

Spoilage is the degradation of food such that the food becomes unfit for human consumption. Food can be spoiled by a number of means, including physical and chemical means. However, the most prevalent cause of food spoilage is microbial growth and residence in the food, which results in numerous undesirable metabolites being produced in the food that cause unwanted flavors and odors. Approximately 25% of the world’s food produced post harvest or post slaughter is lost to microbial degradation of food alone (Gram and Dalgaard, 2002; Begum et al., 2010). Compared to the other foods, fish is unique as a substrate for microbial growth. This uniqueness stems from several important factors: the poikilotherm nature of fish, a high post mortem pH in the flesh (typically greater than 6.0), the presence of non-protein-nitrogen (NPN) in large quantities, and presence of trimethylamine oxide (TMAO) (Huss, 1995). The bacterial ecology of fish products is connected to environmental factors such as water pollution, anthropic activities, fish feed quality, hygienic procedures of slaughter, handling, transport, commercialization and storage conditions (Begum et al., 2010, Banja, 2002). Microbes are found on the outer body covering and the inner surfaces of fresh fish, such as the skin, gills, and GI tract. The poikilotherm nature of fresh fish allows a wide variety of bacteria to grow, including the Gram-negative, rod-shaped bacteria which belong to the genera Pseudomonas, Moraxella, Acinetobacter, Shewanella, Flavobacterium, Aeromonadaceae, and Vibrionaceae, and Gram-positive organisms such as Bacillus, Micrococcus, Clostridium, Lactobacillus, and Corynebacterium. Psychrotrophs are bacteria that can tolerate cold temperature and grow at 0 ºC but grow optimally around 25 ºC. The edible muscle tissue of fish is normally sterile at the time of capture and bacteria are usually present on the skin, gills and the intestinal tract. The rate of fish spoilage depends on several factors, the most important of these are temperature, processing and atmospheric conditions during storage (Gram and Dalgaard, 2002; Huss, 1995). The objective of the present research was to determine the total bacteria count and Pseudomonas spp. on the skin and in muscle tissue of cold stored carp.