Assessment of insect contamination, acid insoluble ash content and colour characteristics of traditionally sun-dried and oven-dried dagaa (Rastrineobola argentea)

Abstract

Objective: To determine and investigate the influence of selected pre-washing treatments and drying temperatures on the colour characteristics, insect infestation and insoluble ash content of sun-dried dagaa (a small pelagic fish found in Lake Victoria). Methodology and results: Insect infestation, colour (lightness L*; redness a*; yellowness b*) and acid insoluble ash contents were analyzed on dagaa that were sun-dried or oven-dried at 30, 40 and 50 o C after pre-washing with salted water (3% NaCl), chlorinated water (100ppm) solutions and potable tap water (control). Insect fragments including blowfly (Lucilia spp), Beetle (Dermested spp), larvae and mites were present on the sun-dried dagaa. The acid insoluble ash in the sun-dried market samples (0.46% dry weight basis, dwb) was significantly higher (p<0.05) than in the fresh dagaa (0.11% dwb). The L* values of fresh dagaa (47.98) were significantly (p<0.05) lower than in market samples (67.16). Chlorinated-wash treatments had significantly (p<0.05) higher L* values compared to those washed in salted water and tap water (control). Conclusion and application of findings: The study established that sun-drying dagaa in the field predisposes them to contamination by insects and grit. In the oven-dried dagaa, the chlorinated-wash treatments exhibited higher L* values and lower a* and b* values than the control-wash treatments. The apparent increase in the L* and b* values and decline in a* values could be attributed to the reactions of lipid oxidation products. This study emphasize the importance of improved handling and drying of dagaa in order to prevent occurrence of insects, grit and sand contamination; and colour degradation of dagaa. The knowledge will improve the capacity of local fishing communities on appropriate washing and drying methods for fish.