Authors : O.A. Oyelese
Abstract: Hypoxanthine levels, chemical studies, organoleptic assessment and bacteria flora/count were studied for a 12 week period on market simulated fresh samples of the Chub Mackerel (Scomber japonicus) in order to assess its keeping quality and shelflife under cold storage conditions of – 40C. Twenty-two (22) fresh samples of average weight of 260gm were used for the study. Two pieces were exposed for 12 hours to thaw and defroze biweekly to simulate market conditions before taken them for further chemical analysis and microbiological assessment. Initial proximate analysis were carried out on the fresh fish and also final proximate analysis at the end of the 12 week experiment. The chemical parameters analysed are Hypoxanthine levels, trimethylamine (TMA), peroxide value (PV), free fatty acid (FFA) (fortnightly) and bacteria identification and count (monthly). Organoleptic assessment was also carried out on the fresh and cooked fish samples forthnightly. The final proximate analysis showed increase (74.36%) in the moisture content compared to (69.25%) the initial. There were decreases observed in crude fibre (2.42% as against 2.78%), ether extract (fat) (16.89% as against 17.38%) and ash (2.86% as against 3.18%), but increase in crude protein content from 19.65% to 21.34%. The other chemical parameters assessed increased e.g peroxide value (PV from 26.40 to 34.60 Meq/kg), trimethylamine (TMA from 29.62 to 39.20mg/100gm fish), free fatty acid (% FFA from 1.74 to 2.32%) over the assessment period. The hypoxanthine level also increased considerably from 28.24mg/100gm fish to 37.54mg/100gm fish at the end of the experiment (hence the increasing bitter taste with length of study). The organoleptic assessment also ranged from very good (2.0) to just fair (6.0) quality at the end of the 12 week study. The number of bacteria identified also increased with storage time. The overall bacteria total viable count varied from 0 week (1.82 Cfu/gm) – 14.70 Cfu/gm) in the 12th week with 29.36 Cfu/gm overall count recorded for the 12 weeks. A total of 10 bacteria specie were detected in the study with Lactoccocus acidophilus showing the highest prevalence of 6.14 Cfu/gm fish) also showing its presence from the 0 week (1.82 Cfu/gm fish) to 1.60cfu/gm fish recorded in the 12th week. Second to it is Pseudomonas aureginosa (3.50cfu/gm) detected from (8th – 12th week), while the third bacteria prevalent was Clostridium welchii with 2.72 Cfu/gm detected at the end of the 4th week and 12th week of study. The other bacteria species detected (arranging them in their order of prevalence) include Bacillus substilis (2.40 cfu/gm), Proteus morganii (2.40 Cfu/gm); Eschericha coli (2.36 Cfu/gm fish); Bacillus cereus (2.10 cfu/gm), Micrococcus acidiophilus (1.50 Cfu/gm), Staphylococcus aureus (1.30 Cfu/gm) and lastly Streptococcus faecium (1.10 Cfu/gm). All parameters measured showed drastic rises in their values as from the 8th week to the 12th week. Hence the limit of acceptability and shelflife of the market simulated Chub Mackerel (Scomber japonicus) under cold storage conditions of – 40C is 8 weeks (2 months).
O.A. Oyelese , 2007. Hypoxanthine Levels, Chemical Studies and Bacteria Flora/Count of Frozen/Thawed Market Simulated Chub Mackerel (Scomber japonicus) under Cold Sotrage Temperature Conditions. Research Journal of Applied Sciences, 2: 295-300.