Effect of post-slaughter frozen storage on protein, lipid, moisture, calorie content and microbial development of male and female Heterobranchus longifilis and Clarias gariepinus flesh

Abstract

The effect of post-slaughter frozen storage and exposure on proximate composition and microbial development respectively, were studied in two commonly cultured catfish species, Heterobranchus longifilis and Clarias gariepinus. Samples of minced fillets of males and females of both species were analyzed for protein, lipid, moisture, and calorie content, at slaughter and at 3 and 6 days of deep freezing at -18oC. Bacterial development in samples of minced unpreserved fillets was quantified at slaughter, and at 3, 6, and 9 hours interval using fluorescence microscopy. Protein, lipid, moisture, calorie levels, and bacterial counts were statistically analyzed to detect differences using the ANOVA. Fischer’s LSD_(0.05) was used to separate means. Means of variables were compared between species using t-test. There were significant differences in moisture levels (P<0.02) at 6 days post-slaughter frozen storage, between H. longifilis and C. gariepinus. Protein, lipid, and calorie levels did not significantly vary between species (P>0.05). There were significant differences in protein, lipid, moisture and calorie levels between sexes of both species with post-slaughter freezing (P<0.05). Protein loss ranged from -3.22±0.08% of initial levels in female H. longifilis, to -1.19±0.1% in male C. gariepinus. Generally, males of both species lost significantly less protein due to frozen storage than females. Lipid levels increased at all intervals. Males gained significantly more lipid than females (P>0.05) over the intervals. Moisture loss ranged from -5.24±0.32% of initial levels in H. longifilis males, to -13.92±0.22% in H. longifilis females. At 9 hours post-slaughter exposure, bacterial load in both species recorded higher levels in females (4.88x10⁷ cells g^-1, and 3.5x10⁷ cells g^-1 in H. longifilis and C gariepinus respectively), than males (0.50x10⁶ cells g^-1, and 0.45x10⁶ cells g^-1 in H. longifilis and C. gariepinus respectively).

Key words: Heterobranchus longifilis, Clarias gariepinus, frozen storage, protein, fat, moisture, bacterial development.