Abstract:
This study was conducted to validate the Quality Index Method (QIM) scheme and
determine storage days on ice for domestically processed Nile perch (Lates niloticus).
Samples collected from the fishermen at landing site were used to develop the QIM and
for shelf life study at 0oC to -1oC for 33 days. Those collected from fish factories and cold
stores were used for validation. The study assessed the sensory, microbiological and
chemical quality changes of Nile perch on ice. The QIM scheme had the maximum total
demerit points score 23 and 24 for gutted and ungutted fish, respectively. The Total Viable
Count (TVC) and Specific Spoilage Bacteria (SSB) at the end of storage time (33 days)
were 7.64 and 7.36 log 10 cfu/g for ungutted and 6.93 and 6.83 log 10 cfu/g for the gutted
fish, respectively. The TVC and SSB exceeded the limit of acceptability set by Tanzania
standards, beyond 14 storage days. Total Volatile Basic Nitrogen (TVBN) value increased
slowly with storage time, reaching 11.48 and 12.18 mgN/100g in day 33 of storage for
gutted and ungutted fish, respectively. Peroxide values (PV) increased gradually for
ungutted Nile perch up to 21 days whereas, rapid increase was observed in gutted Nile
perch up to14 days. The Quality Index (QI) scores had a positive correlation (0.91 for
TVC, 0.97 for SSB, 0.79 for TVBN) and negative correlation (- 0.40 for FFAs and - 0.33
for PV). There was a significant decrease (p<0.05) in quality of cooked Nile perch from
day 14 onwards. The storage time for good freshness quality is 14 days on ice. For good
sensory and microbiological quality, Nile perch should not be stored on ice for more than
two weeks. Adoption of QIM to determine the freshness level and storage time of Nile
perch is necessary.
