Studies on Changes in Chemical and Microbial Load in Fresh and Frozen Farmed Carp Fish Species for Comparison to International Fish Quality & Food Safety Standards

Abstract

This study was intended to evaluate the quality and food safety of the locally produced farmed fish at different marketing channels with the objectives of heavy metals determination, time series chemical change and increase in microbial loads, in comparison to the international standards. Microbial quality and shelf life of Labeo rohita, fish was also examined during the freezing storage, under varied delayed freezing regimes. Two sets of experiments were involved. Under 1st set, four farmed carp fish species were sampled from fish farming cluster around Qadirabad Barrage area (district Gujranwala) and the metropolitan city of Lahore, form four fish distribution channels. These samples were analyzed for three heavy metals (Cd, Pb and Cr), microbial loads, viz, APC, TCC, FCC, E. coli, V. cholera and S. aerous and the histamine production, to check the farmed fish quality in totality. In the 2nd set of experiment, the microbial quality and production of histamine, in the most popular farmed fish, Labeo rohita, stored at -12 ± 0.2○C, under various delayed freezing regimes was analyzed with 10 days’ intervals, during total 30 days’ frozen storage. All of the three tested heavy metals were detected in fish samples collected from all four sampling sites. Individually, among species, the metals accumulations though nonsignificant, were slightly higher in L. rohita and H. molitrix, as compared with other two species. Overall in fish, the concentrations of lead were highest, followed by chromium and the cadmium. Mean concentrations of Cd, Pb and Cr were found highest in fish samples collected from the retailers’ shops, when compared with other three fish sampling points. Values of Cd and Cr, in all fish samples, were found within the permissible limits of FAO, while of Pb were beyond the acceptable limits, suitable for human consumption. Among microbial loads, APC, TCC and FCC were positive in all fish species collected from four experimental sites and these parameters showed a consistent increase from fish farms to wholesale and the retailers markets under varied patterns. E. coli were absent in samples collected from fish farms and the localized fish markets but found in samples collected from the other sampling sites i.e. main fish market and the retailers’ shops, with an increasing trend from wholesale to the retailers. Mean APC in fish samples of all four species collected from fish farms were below the acceptable limits, while at other three sites, of all species were beyond acceptable limits except samples of L. rohita and C.

idella, collected from the localized fish markets. APC in fish sampled from retailers’ shops were found significantly higher than the fish sampled from other three points. Levels of TCC, in fish collected from fish farms, the localized fish markets, and main fish market were below the accepted limits of ICMSF (1986), while in fish of retailers’ shops, these were higher than the permissible limits, except in C. mrigala. FCC in fish collected from fish farms were within the suitabl limits while most of the samples at other sampling points were beyond the acceptable limits. E. coli showed a significant increase from main fish market to the retailers’ shops in all fish species except L. rohita. E. coli were found beyond acceptable limits of FAO, in all samples collected from both sites, except C. mrigala and the C. idella, sampled from the main fish market. V. cholera, S. aureus and histamine was not detected in any fish species, from any of the sampling sites. In delayed freezing, the initial APC, TCC, FCC and E. coli, augmented with the increase in delay, with different patterns. APC and TCC crossed the acceptable limit before 24 hrs, while FCC and the E. coli crossed respective acceptable limit, even before 16 hrs. During 30 days freezing storage, the mean APC in 0, 8, 16 and 24 hrs delay crossed the safe limits of fish consumption on the day 30, 20, 10 and the 0, respectively. TCC in 8 hrs delay crossed acceptable limits on the day 30, while in 16 and 24 hrs delay these crossed these limits on the day 10. TCC in 0 hrs delay group remained under permissible limits through storage period. FCC in 0 and 8 hrs delay crossed acceptable limits on day 10, while in 16 and 24 hrs delay groups these crossed the suitable limits on the day 0. E. coli, in 0 and 8 hours’ delay, crossed the acceptable limits, on the day 20 while in 16 and 24 hours’ delay, on the day 0. The S. aureus, V. cholerae and histamine were however, found altogether absent, throughout freezing storage experiment. Overall, quality of the fish, marketed at various marketing channels was not upto the mark, to fulfill the international standards of quality and the food safety. Labeo rohita also steadily deteriorated its quality after catch and during the 30 days freezing storage, shortening its shelflife. The delayed storage and microbial development caused consistent increase in microbial loads. Therefore, the consumption of fresh fish should a preferred option. If however required, quick and immediate freezing, after catch may be opted to increase the shelflife of fish. This was perhaps the first study, ever conducted in Pakistan, on quality freshwater farmed fish species in totality and the effect of delayed freezing during storage.