International Journal of Aquaculture, 2016, Vol.6, No.19, 1
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2 Materials and Methods
Whole fresh Lake Malawi Tilapia (Chambo) fish (Figure 1) were bought from fish sellers early in the morning
between 4 am and 5 am soon after landing their catch at the southeast arm of Lake Malawi in Mangochi district,
southern Malawi. The fish were immediately packed in cool boxes preserved with block ice without washing with
water to avoid influencing the sensory analysis process (Huidobro et al., 2001). To avoid bias in the shelf life
estimation process, thus reducing variability factors (Azam et al., 2005); fish of approximately the same size
(about 25 cm TL average) were deliberately selected during purchase. Size of fish is one of the intrinsic factors
that affect the rate of spoilage in fresh fish stored in ice (Huss, 1995).
Figure 1 Collection and preservation in ice of fresh Lake Malawi Tilapia (
Chambo
)
2.1 Sensory evaluation of the whole fresh tilapia
A sensory evaluation panel of six students in the age ranges of 21 and 23 was pre-trained according to de Kock et
al. (2002) and ISO (1993). The sensory panel then described daily changes in freshness and quality during storage
of whole fresh Chambo in ice using the developed quality index method (QIM) Scheme (Mai et al., 2009) (Table
1).
Sensory quality of the fish was decided by scoring the attributes in Table 1 between 0 and 3 where 0 and 3 entailed
highly and poorly liked freshness of the fish sample respectively. Lower scores (demerit points) were given to
sensory attributes that are not very important as far as acceptability of raw fish is concerned and as such,
appearance of skin and scales; stiffness of the belly and the backside of the fish were allocated lower scores while
higher scores were given to commonly used parameters (Nielsen, 1997) mainly colour and mucus on the gills and
colour of the eye cornea.
2.2 Microbiological analysis
A sample of fresh tilapia fish stored in ice was removed every two to three days for microbiological assessment
for a period of 21 days. Samples for aerobic psychrotrophic bacteria counts were obtained on the external surfaces
(skin), flesh (tissue/muscle) and gills; and enterobacteriaceae counts from samples on kidney and intestine.
Microbiological analysis was done following a procedure described by Slaby et al. (1981).
Skin surface
A sterile cotton wool swab dipped in 0.10% sterile peptone water was rubbed over the surface of the fish on the
area covered by the wire swab guide. The swab was then immediately placed in a sterile sample vial containing
100 mls of 0.10% (w/v) peptone water. The vial was vigorously shaken for 10 minutes and allowed to stand for 20
minutes. 6 fold decimal serial dilution of the bacterial suspension in peptone water was prepared in duplicate and
viable aerobic bacterial counts were enumerated in standard plate count agar after incubation at 37°C for 48 hrs as
outlined by Okoro et al. (2010) and Slaby et al. (1981). All data on skin bacterial counts reported are based on this
method. Results were reported in log cfu/cm
2
of skin surface.
