International Journal of Aquaculture, 2016, Vol.6, No.19, 1
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10
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Figure 5 Total volatile bases-Nitrogen (TVB-N) and
Trimethylamine levels in Lake Malawi Tilapia (
Chambo
)
stored in ice for 21 days
Figure 6 pH for Lake Malawi Tilapia (
Chambo
) muscle stored
in ice for 21 days
4 Discussions
4.1 Sensory evaluation
Results suggest that whole fresh Chambo stored in ice can remain in acceptable condition for consumption until
between day 16 and day 19. Also apart from explaining the significant relationship between fish freshness and
quality deterioration with storage time in ice (Figure 2), the strong correlation also demonstrated the reliability of
the sensory evaluation in determining freshness and quality attributes using the developed QIM scheme with
minimal errors. The estimated shelf life of 16 days for Lake Malawi tilapia (Chambo) in this study appear to fall
within the previously reported for tilapias (Surendran et al., 1989; Adoga et al., 2010). Results reported for this
study also echoed earlier and most recent reports that tropical fish kept in ice exhibit a longer shelf life compared
to temperate fish (Huss, 1995; Goliat et al., 2016).
4.2 Microbiological analysis
Bacterial populations in the study were within the recommended safe range of bacterial counts (5×105 cfu/g and
5×107 cfu/g) for good quality fish product stipulated by the International Commission on Microbiology Safety for
Foods (ICMSF, 1986). Spoilage of fish under aerobic conditions becomes apparent when specific spoilage
bacteria (SSO) reach the values of 108-109 cfu/g flesh or cm
2
(Gram and Huss, 1996). This suggests that despite
the fish being sensorily unacceptable, microbial load had not yet exceeded levels that could be deemed dangerous
to human consumption. While Hernandez et al. (2009) observed a correlation between bacterial viable counts and
sensory parameter scores, findings in this study suggest the contrary supporting the observation by Ólafsson (1999)
that bacterial total count and sensory evaluation do not always agree. This study observes a likelihood of
condemning as unfit, products that are microbiologically safe for human consumption and hence, underscoring the
importance of validating sensory results with other methods. Fish gills and intestines contain huge load of bacteria
(Huss, 1995; Singh et al., 2011) underscoring the need for quick removal of these appendages to reduce microbial
spoilage of fresh fish.
4.3 Biochemical analysis
Values for TBN-N and TMA-N reported in this study at sensory rejection were within the acceptable limits
(Connell, 1975) and similar to those reported by Okeyo et al. (2009), but slightly lower while within range of
those reported by Guo et al. (2011). The noticeable increase in TVB-N and TMA-N between day 8 and 12 may be
attributed to the sharp increase in bacteria population (Table 2). TVB-N and TMA-N are volatile amines that are
produced by spoilage bacteria hence their increase tends to be positively correlated with microbial population in
fresh fish (Huss, 1995). In iced fish, TVB-N contents decrease over the first few days before rising again
(Howgate, 2006; Okeyo et al., 2009). Although growth of bacteria starts immediately after resolution rigor,
formation of TMA-N in stored fish only commences after several days (Connell, 1975). The relatively smaller
observed values for TVB-N could be due to the washing effect (leaching) of ice as the melted ice in the cooler box
