Contaminated fungi in dried salted fishes: Isolation, identification, and their inhibition by chitooligosaccharide-gallic acid conjugate.

Abstract

Contaminated fungi on dried salted fish of three species including Talang queenfish (TQF, Scomberroides commersonianus), Hamilton's thryssa fish (HTF, Thryssa hamiltonii), and Cobia fish (CF, Rachycentron canadum) were isolated and identified. One hundred and sixty-nine isolates were obtained from TQF and HTF, respectively, while no fungi were detected in CF. The dominant genera were Aspergillus spp. (n =79), Penicillium spp. (n =60), and non-sporulating fungi (n =30). The representative groups of Aspergillus spp. (n =6) and Penicillium spp. (n =3) based on different morphological characteristics were selected for species identification by molecular methods involving ITS1-5.8s-ITS2 region and Matrix-Assisted Laser Desorption/Ionization Time-of Flight Mass Spectrometer (MALDI-TOF MS)analysis. The nine isolates were identified to be Aspergillus versicolor (n =2), Aspergillus montevidensis (n =3), Penicillium citrinum (n =3), and Aspergillus sp. (n =1). The antifungal activity of chitooligosaccharide-gallic acid (COS-GAL) conjugate against A. versicolor F1/10M9, A. montevidensis F1/30M20, and P. citrinum F1/23M14 was examined. The minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) values were in the range of 0.625-2.5mg/mL and 1.25-10mg/mL, respectively. COS-GAL conjugate at the concentration of 5mg/mL completely inhibited the spore germination of A. versicolor F1/10M9 and P. citrinum F1/23M14 after 72h of treatment. COS-GAL conjugate at 4×MIC mainly affected the mycelium of A. versicolor F1/10M9 and P. citrinum F1/23M14 after treatment with COS-GAL conjugate for 3 days by coating mycelium surface and reducing the size of mycelium. Therefore, COS-GAL conjugate could be used as a food additive to inhibit or prevent the growth of fungi contaminated in dried salted fish or other relevant products. PRACTICAL APPLICATION: During processing, dried salted fish can be contaminated with fungi, which may cause food poisoning and food spoilage. The contaminated fungi are capable of producing mycotoxin that is harmful to consumers. Synthetic food preservatives have long been used to inhibit fungal growth, but the side effects to consumers are of concern. Chitooligosaccharide is a nontoxic chitosan derivative produced from shrimp shell and its conjugate namely chitooligosaccharide-gallic acid conjugate showed high efficacy in inhibiting the growth of fungi including Aspergillus spp. and Penicillium spp. Therefore, it can serve as a natural alternative preservative for the prevention of fungal growth in dried salted fish.