Warm water containing wood ash as a novel sterilant to reduce microbial and aflatoxin B₁ levels in smoked-dried fish

Abstract

This study evaluated the effects of warm water containing wood ash on the microbial aflatoxin B1, and nutritional contents of smoked dried croaker (Micropogonius undukiuts), catfish (Siluriformes sp.), and tilapia (Oreochromis niloticus) sold in Akure, Nigeria. Raw and treated samples (cold water, warm water, and warm water with wood ash) were analyzed for microbial load using standard cultural methods, aflatoxin B1 by spectrophotometry, and nutritional composition by chemical methods. Bacterial counts ranged from 20.0 × 10³ to 29.0 × 10³ CFU/g, and mold counts ranged from 2.0 × 10³ to 12.0 × 10³ SFU/g across different markets. Pre-treatment with the sterilizing solutions, particularly warm water containing wood ash, significantly reduced microbial and aflatoxin B1 levels while preserving nutritional quality. Identified microorganisms included pathogenic and spoilage species such as Escherichia coli, Staphylococcus aureus, Klebsiella sp., Bacillus subtilis, Pseudomonas aeruginosa, Aspergillus flavus, A. niger, and Rhizopus stolonifer. The results demonstrate that warm water containing wood ash effectively reduces microbial and aflatoxin contamination in smoked fish without compromising nutritional value, suggesting it as a practical, low-cost decontamination method for improving fish safety and quality in local markets.