The Effects of Different Storage Temperatures on the Microbial, Physicochemical and Organoleptic Quality Changes in the Shellfish "Ngolo" (Thais califera) from Nigeria

Aims: To investigate the effects of different storage temperatures (-15±2°C; 4±2°C and 29±2°C) on quality changes in ‘Ngolo’ (Thais califera) to evaluate the potential enhancement or otherwise of its domestic and global trade.

Study Design: “Ngolo” samples were subjected to different temperatures and evaluated for microbiological, physico-chemical and organoleptic changes during short and long-term storage.

Place and Duration of Study: Department of Microbiology (Food and Industrial Division), University of Port Harcourt and Research and Development Division, Nigerian National Petroleum Corporation (NNPC), Moscow Road, Port Harcourt, Nigeria between January 2006 and December 2008.

Methodology: Freshly shucked “Ngolo” samples were divided using sterile polyethylene bags into sub-samples of 150 g per bag and stored at (-15±2°C; 4±2°C and 29±2°C) respectively and analysed at daily or weekly intervals for microbial, physico-chemical and organoleptic quality attributes.

Results: Variations in quality attributes of “Ngolo” samples were induced by the temperatures resulting in significant (P=.05) minimum total viable counts (2.12 log CFU/g) in samples stored at -15±2°C compared with 8.72 log CFU/g in samples stored at 29±2°C. Little or no change in pH occurred within two weeks in samples stored at -15±2°C and 4±2°C respectively but decrease in pH within 24h occurred in samples stored at 29±2°C. Total volatile nitrogen (TVN) and trimethylamine (TMA) contents remained low (32 mgN/100 g TVN and 25 mgN/100 g TMA) in samples stored at -15±2°C and were acceptable throughout storage while the contents of those stored at 29±2°C increased significantly (P=.05) from day 0 to 72 mgN/100 g and 48 mgN/100g respectively on day 4 and were rejected within 24h. Significant (P=.05) positive correlations between TVCs and TVN occurred indicating their usefulness for prediction of quality changes in “Ngolo” (and could be applied to other related seafoods).

Conclusion: Overall, the quality attributes of samples stored at -15±2°C remained significantly (P =.05) acceptable throughout storage thereby enhancing their potential for international food trade.