Development and validation of indices of quality of Lake Victoria Nile perch (lates niloticus) marketed in Tanzania

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.