Potential biological control of aflatoxins in dried fish

Fish contributes 63% of the protein intake to the Indonesian diet. Fungal contamination is a common problem and can cause significant spoilage. However, little is known about the potential for fungal commensals of dried fish to be used to inhibit aflatoxin contamination. This study investigated metabolites extracted from Debaryomyces hansenii, Aspergillus wentii, Eurotium rubrum, Polypaecilum pisce and non-toxigenic A. flavus to prevent growth and aflatoxin production by A. parasiticus and A. flavus. Aflatoxigenic strain, aw and substrates all affected the concentration of aflatoxins. Both aflatoxigenic fungi produced the highest toxin concentration at aw 0.99 and the lowest at a\(_w\) 0.89. Endogenous degradation occurred after prolonged growth. Fungal inhibitor species affected synthesis and degradation of AFB\(_1\), AFB\(_2\), AFG\(_1\) and AFG\(_2\). Metabolites of D. hansenii demonstrated strong antiaflatoxigenic activity on different substrates. The metabolites eliminated AFB\(_1\) concentration (compared to 0.220-0.555 μg g\(^{-1}\) in the control), AFG\(_1\) (control contained 0.352-0.672 μg g\(^{-1}\)) and AFG\(_2\) (control contained 0.259 μg g\(^{-1}\)). Furthermore, there were no other fluorescent compounds found on fish dried to a\(_w\) 0.85 in the presence of D. hansenii extract, indicating that the aflatoxins were completely degraded and/or synthesis was completely blocked. These results indicate that the metabolites may be suitable for use as a form of biological control on dried fish in tropical regions. The active inhibitor compounds of metabolites of D. hansenii contained β-1,4 glycoside bonds and were heatstable, active over pH 2-10 with an optimum at neutral pH and did not fluoresce under UV. It is possible that a cyclic peptide is involved because the metabolites lacked a free carboxyl terminal group, but were sensitive to trypsin and pepsin. The metabolites of the other four fungi tested were relatively heat-stable and their activity directly reduced aflatoxin concentrations without affecting the growth of aflatoxigenic fungi. Inhibitory compounds of P. pisce and A. wentii metabolites maybe complex compounds with β-1,4 glycoside links and Lamino acids with lysyl or argynyl residues and with highest activity at pH near neutral to basic. Inhibitors of non-toxigenic A. flavus metabolites were possibly a sugar group with β-1,4 glycoside bonds attached to a peptide and were active at pH neutral. Degradation activity by non-toxigenic A. flavus occurred over a\(_w\) 0.89-0.99. Metabolites of E. rubrum were not effective in reducing aflatoxins. Results suggest that modification on extraction and possibly production in a dried form could increase activity of the metabolites. Further study particularly of D. hansenii would be necessary to characterise the active inhibitors and evaluate their usefulness