Microbial evaluation of Carica papaya leaf extract pre-treated smoke cured grass eater (Distichodus rostratus Gunther 1864)

Abstract

The sensory and microbial evaluation of Carica papaya leaf extract pre-treated smoke cured Distichodus rostratus (Grass eater) was studied. Twelve (12) fish samples weighing between 0.80-1.80 kg were weighed eviscerated and washed properly with tap water. These were randomly divided into 4 groups of 3 fish each (T₁, T₂,T₃ andT₄). T₁ was immersed into 3% Brine only. T₂ was immersed in a mixture of 3% brine and 2.5% C. papaya leaf extract). T₃ was immersed into 3% Brine and 5% C. papaya leaf extract.   T₄ was immersed into 3% Brine and 8% C.papaya leaf extract. These mixtures were thoroughly mixed and allowed to stand for three hours. Soaked samples were poured out on muslin clothing for draining and cured with wood smoke on a brick kiln for four hours at a temperature range of 85-95°C. The cured samples were left overnight to cool and were wrapped in sterile polythene bags and kept in a refrigerator for microbial analysis. The samples were subjected to microbial analysis, culturing, incubating, colony count and statistical analysis.  Increasing concentrations of water extract of C. papaya leaf inhibited microbial growth at all dilutions (highest T₁ {control} was 2.6 x 10⁷ cfu/ml while T₂= 2.2×10⁵ cfu/ml, T₃ =  1.5 x 10⁵ cfu/ml and T₄= 1.24 x 10⁴ cfu/ml ,decreased in that order). Probable organisms in T₁ were Staphylococcus aures. T₂ and T₃ had Proteus sp. T₄ had Klebsiella sp. Biochemical characterisation of pure culture isolates confirmed the presence of these organisms. The fungi found were Aspergillus (T₁), Penicillum (T₂ andT₃) and Mucor (T₄). These results show that usage of C. papaya in processing and preservation of fish will improve the shelf life of stored fish.