Fumonisin production by Aspergillus species associated with Australian Vineyards: Implications of fumonisins for grape and wine industries

Research output: ThesisDoctoral Thesis

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Abstract

Grapes and grape products have the potential to be contaminated with several mycotoxins due to the presence of black aspergilli, of which fumonisins are the most recently identified mycotoxins produced by some isolates of A. niger and A. welwitschiae. Although black aspergilli have been reported from Australian vineyards, no research has been conducted to investigate the potential of these organisms to produce fumonisins in Australian wine grapes. This research presents information on the occurrence of fumonisin producing Aspergillus isolates in Australian wine grapes and the implications of fumonisins for grape and wine industries.
A total of 38 Aspergillus isolates were collected from Australian wine grapes. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis of culture extracts revealed that six isolates were positive for fumonisins. These isolates produced from 0.9 to 30.6 mg/kg and 0.4 to 19.4 mg/kg of FB2 in Czapek yeast extract agar with 5 % NaCl and synthetic grape juice medium (SGJM), respectively. Molecular detection based on calmodulin sequencing data revealed that all fumonisin producing isolates were A. niger and A. welwitschiae.
The effects of temperature and water activity for growth and production of fumonisins were studied using two A. niger and an isolate of A. welwitschiae on SGJM at 20 °C, 25 °C, 30 °C and 35 °C, and 0.92 aw, 0.95 aw and 0.98 aw levels. All isolates grew and produced fumonisins in the water activity levels of 0.95 aw and 0.98 aw at 20 °C, 25 °C and 30 °C. The highest growth rate was observed at 0.98 aw / 35 °C, whereas the highest toxin production was observed at 0.98 aw / 20 - 25 °C for all the isolates assessed. None of the isolates produced fumonisins at 35 °C within the water activity levels assessed.
Passage of fumonisin throughout white wine vinification was investigated using Chardonnay grapes inoculated with a fumonisin producing Aspergillus isolate identified as a part of this study. Vinification resulted in removal of 90% of fumonisins mainly through binding to solids (marc and lees), and only a 3% was found to pass into wine. Cold stabilisation of white wine had only a minor effect on the amount of fumonisins in wine.
The stability of fumonisins in white wine was investigated using Chardonnay wine spiked with FB2. Results showed that FB2 was less prone to degradation during wine storage and handling conditions, and maximum reductions of 14% and 42% were observed after storage for nine months at 17 °C and 25 °C, respectively.
Fining agents currently commercially used in clarification of white wine in Australia were investigated for their ability to remove fumonisins in Chardonnay wine spiked with FB2. Of the five fining agents (activated charcoal, PVPP, calcium bentonite, yeast hulls, NO (OX)) tested, activated charcoal and calcium bentonite were the most effective agents in removal of fumonisins from white wine. Usage of these two agents at concentrations below the maximum recommended by Australian Wine Research Institute were effective in removing more than 90% of FB2 within 24 hours of contact time.
Data from this study may enhance the current understanding related to the occurrence of fumonisins in grapes and grape products and will be useful to develop strategies to minimise the exposure to fumonisins through consumption of grape and grape products.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Charles Sturt University
Supervisors/Advisors
  • Steel, Christopher, Principal Supervisor
  • Savocchia, Sandra, Co-Supervisor
  • Prenzler, Paul, Co-Supervisor
Place of PublicationAustralia
Publisher
Publication statusPublished - 2020

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