Influence of selected washing treatments and drying temperatures on proximate composition of dagaa (Rastrineobola argentea), a small pelagic fish specie.

Abstract

Proximate analysis for moisture, crude protein, crude fat and total ash was carried out on dagaa (Rastrineobola argentea), a small pelagic fish specie found in Lake Victoria. The first phase of the study involved sampling of fresh, sundried (for 1 day, 2 days, 3 days, 4 days) and retail market dagaa. The second phase of the study involved pre-washing of fresh dagaa with selected solutions namely, salted solution (3% NaCl), chlorinated solution (100 ppm) or potable tap water (control) and thereafter oven-drying the respective pre-washed samples at 30^oC (31hrs), 40^oC (23hrs) or 50^oC (15hrs). Results showed that the crude protein composition of fresh dagaa (74.4% dry weight basis, dwb) was significantly higher (p<0.05) than values in market samples (62.5% dwb). After oven-drying at 30oC, the salted-wash treatments resulted to significantly lower (p<0.05) crude protein content of 60.4% (dwb) when compared with the chlorinated (64.6% dwb) and control-wash treatments (64.1% dwb).The crude fat content in fresh dagaa (14.8% dwb) was significantly higher (p<0.05) than levels in market samples (13.9% dwb).The salted-wash treatments showed significantly lower (p<0.05) crude fat content (15.9% dwb) than the chlorinated (17.0% dwb) and control (16.9% dwb) wash treatments after ovendrying at 30^oC.The total ash content in fresh dagaa (10.3% dwb) was significantly lower (p<0.05) than levels in market samples (13.5% dwb).The salted and chlorinated-wash treatments exhibited significantly higher (p<0.05) total ash content (19.9%, 16.7% dwb, respectively) than the control-wash treatment (15.9% dwb) after drying at 40^oC. In this study, oven-drying of dagaa at 40^oC after washing with chlorinated (100ppm) solution was suggested with regard to the optimal retention of the crude protein and fat levels of the dried dagaa.These conditions are achievable at the local community level through use of solar driers whereas sodium hypochlorite products are accessible to most of the households involved in dried fish processing.

Key words: fish, moisture, protein, fat, ash