An investigation was carried out to develop and evaluate a Quality Index Method (QIM) scheme for Frigate tuna (Auxis thazard) for the prediction of past and remaining storage time in ice. The quality index method (QIM) provides weighted evaluation of the key parameters in deterioration of individual species, assigning demerit points according to the importance of each parameter. For the development and evaluation of QIM scheme, Frigate tuna were stored in ice and assessed raw and cooked. The QIM developed for raw Frigate tuna comprised of 11 parameters (appearance of skin and stiffness: cornea, form and colour of eyes; colour, smell and mucus of gills; condition of viscera; colour of blood and fillets) covering attributes, which gave a total of 25 demerit points. Sensory analysis of cooked Frigate tuna using Torry scheme were carried out in parallel to determine the shelf life. In order to obtain more information about the quality of Frigate tuna, Total viable counts (TVC), hydrogen sulphide (H2S) producing bacteria, trimethylamine (TMA), total volatile basic nitrogen (TVN) content and pH value were determined. The sensory evaluation was carried out by a panel of 6-7 judges and the rejection level was found to be 22 days. The QIM scheme developed for Frigate tuna showed a linear relationship between QIM scores and storage time in ice, (r2 = 0.9378) with slope of 0.755. The TVC varied from 102 cfu g-1 to 106 cfu g-1 within 7 to 22 days and H2S producing bacteria at 102 cfu g-1 within 22 days of storage in ice. The TMA and TVN amounts increased with time and the amounts ranged from 1.2 mg/100g to 2.5 mg/100g and 17.2 mg/100g to 34.9 mg/100g respectively. The variation of pH ranged from 5.4 to 5.9 within the storage. The QIM calibration curve obtained for Frigate tuna indicates it’s applicability to determine the storage life of fish in ice. Further, it will facilitate the requirements of buyers and sellers while fulfilling the demands of inspection authorities and the consumers.
Dried fish is one of the traditionally preserved foods in Sri Lanka.Since dried fish is often an important component of daily meal, this study was aimed to assess the quality of selected dried fish varieties in the local market. Dried fish samples of nine selected varieties were collected under three categories, viz. locally produced, imported dried fish before and after distribution to retail market. They were analyzed for microbiological and chemical parameters. Water activity of the samples was also measured. Samples were found to be negative for Escherichia coli, Staphylococcus aureus and halophilic bacteria. Aerobic Plate Count and yeast and mould count of the majority of the samples were within the acceptable limit. Histamine content exceeded 100 mg/kg level in 33% and 13% of imported and local samples respectively. Water activity of the samples was <0.75 except for imported prawn samples of retail outlets. There was no significant difference (p>0.05) between the analyzed parameters of all three categories.
The prevalence of the pathogenic bacteria, Salmonella sp. Vibrio cholerae, Vibrio parahaemolyticus, total conforms, faecal coliforrns and Escherichia coli in cultured shrimp, pond sediments, water and the pelleted feed were analysed. Raw frozen shrimps were also analysed for total plate count, coliforms, faecal coliforms, E. coli, Staphylococcus aureus, Salmonella, Vibrio parahaemolyticus and Vibrio cholerae.In shrimp, water and sediments the total coliform counts were <3- 93 MPN/g, 0-45 MPN/100m1 and 3.6-93 MPN/g, while the faecal coliform counts were <3-15 MPN/g, 0-11 MPN/100m1 and <3-23 MPN/g respectively. E. coil were in the ranges of 0-8 MPN/100 ml (water), <3-9.1 MPN/g (sediment) and <3-7.3 MPN/g (shrimp). In one occasion, feed was highly contaminated with coliforms (>1100 MPN/g), faecal conforms (>1100 MPN/g) and E. coli (460 MPN/g), Salmonella sp were not recovered from samples of shrimp, pond water, sediments and feed. V. parahaemolyticus was detected in farm shrimp, sediment and water at a density of 101-102 cfu/g.The total plate counts for frozen shrimp were 102-107 cfu/g. In 27% samples it ranged from 105 cfu/g to 106 cfu/g while in 59% it was 106- 107cfu/g. The E. coil count of frozen shrimp ranged from <3 to 10 MPN/g with 94% counts less than 3 MPN/g. Vibrio cholerae, Vibrio parahaemolyticus, Salmonella sp. and Staphylococcus aureus were not found in frozen shrimp samples.
This study aimed to identify histamine-forming bacteria (HFB) and the sources of introduction of such bacteria to recommend control measures to mitigate histamine formation in yellowfin tuna (YFT). Field samples were collected from multi-day boats that landed at Dikkowita, Negombo, Trincomalee and Dondra fishery harbours. Ice from the fish holds (n=63) and chill transport vehicles (n=63), and swabs from the fish holds (n=63), the boat decks (n=63) and the skin of YFT (n=63) were collected. Fish loin samples (n=15), ice samples (n=36) and swabs from the skin of YFT (n=18), floor (n=18) and chill transport vehicles (n=18) were collected from fish processing plants. Presumptive HFB isolated from Nivens medium and Violet Red Bile Glucose (VRBG) agar were screened for histamine forming ability in Tripticase soy broth (TSB) supplemented with 1.0% L-histidine. HFB isolates were characterized by sequencing approximately 1400 bp of the 16S rDNA. Seven isolates that produced histamine in the range of 3000–4000 ppm in TSB isolated from ice samples, and a swab sample collected from the boat deck, were confirmed as Klebsiella aerogens (n=6) and Morganella morganii (n=1) respectively. Hafnia alvei (n=1), Serratia sp. (n=2), Citrobacter freundii (n=1), Rahnella sp. (n=1) and Aeromonas salmonicida (n=8) were also among the isolated histamine forming bacteria. Pseudomonas sp. (n=24) and Shewanella baltica (n=7), which are known as spoilage bacteria were also isolated and showed weak histamine formation. Hence, it is evident that histamineforming bacteria could be introduced into the fish from ice and contacting surfaces. This necessitates the practice of rigorous cleaning procedures and adaptation of proper postharvest handling procedures to minimize contamination of the fish.
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