Acidity/Rancidity Levels, Chemical Studies, Bacterial Count/Flora of Fermented and Unfermented Silver Catfish (<i>Chrysichthys nigrodigitatus</i>)

Abstract

The keeping quality and shelf life of fermented and unfermented Chrysichthys nigrodigitatus were monitored in this study. Four kilograms of fresh Chrysichthys nigrodigitatus was minced into fine particles (with an initial pH of 7.2 before distribution into 8 samples). Samples 1-4 are unfermented cooked while Samples 5-8 were fermented, not cooked. All the 8 prepared samples barely lasted for two weeks, while samples 1, 3 and 7 lasted for six weeks. Total Volatile Base (TVB) ranged higher (24.12 - 29.43) mg/100gm in Samples 1-4 than (14.23 - 18.09) mg/100gm recorded in Samples 5-8. In Samples 1-4, FFA values were not significantly (P > 0.05) different; also followed a narrow range of (6.14 - 6.45)% while higher range of (6.42 - 12.27)% recorded in samples (5-8). Peroxide values (PV) increased in all the 8 samples in the second, fourth and sixth week, however higher values were recorded in Samples 5-8. Acidity generally increased with length (weeks) of fermentation with a gradual drop in pH from 7.2 (in the fresh fish) to pH 4.5 (sample 7), the worst sample at six weeks. Sample 4 with bacteria load of 5.05 × 105 at second week and sample 7 (8.2 × 105) at sixth week became unfit for consumption having exceeded the 5.0 × 105 ICMSF standard for safe fish product. Five bacteria species (Lactobacillus sp, Proteus spp, Staphylococcus aureus, Staphylococcus epidermis, Bacillus sp) with the exception of Proteus spwere not represented in sample 1 (due to salt content). Strong positive correlation (r = 0.97, P < 0.01) exists between PV and FFA. Acidityof the fermented products increased over the weeks with strong negative correlation (r = -0.121, P < 0.01) exists between pH and FFA. Acidity (i.e drop in PH) with increasing rancidity since (r = -0.313, P < 0.05) exists between PV and pH.