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Keywords:

  • Aspergillus carbonarius;
  • environmental factors;
  • grape-based products;
  • mould growth;
  • mycotoxigenic fungi;
  • natural preservatives

Abstract

Aims:  To examine the efficacy of natamycin produced by Streptomyces natalensis against strains of Aspergillus carbonarius growth and ochratoxin A (OTA) production under different environmental factors on a grape juice-based medium.

Methods and Results:  Detailed studies in the range 0–20 ng ml−1 for control of growth and ochratoxin production by strains of A. carbonarius at 0·98, 0·96 and 0·94 water availabilities (aw) and 15–25°C on a fresh red grape extract medium were examined. Inhibition of growth was depending on temperature and aw level. At 15°C, 5–10 ng ml−1 natamycin was effective in reducing growth almost completely. However, at 20–25°C and all the three aw levels, growth was only slightly inhibited by 5–10 ng ml−1 natamycin. There were strain differences with regard to inhibition of OTA production. At 15°C and 0·98 aw, 10 ng ml−1 was required to inhibit production by >90%. However, at 0·96 and 0·94 aw, almost complete inhibition occurred. At 20°C, OTA production was only significantly inhibited by 10 ng ml−1 natamycin at 0·94 aw. At 0·96 and 0·98 aw, some inhibition occurred with 5–10 ng ml−1, but greater concentrations would be required for effective inhibition. At 25°C, 5 ng ml−1 was effective at all aw levels. However, at 15°C and 25°C and a wide range of aw levels, natamycin effectively controlled OTA production.

Conclusions:  Natamycin appears to be a very effective for controlling growth and OTA production by strains of A. carbonarius over a range of aw and temperature conditions on grape-based media.

Significance and Impact of the Study:  This is the first detailed study to demonstrate the impact of natamycin against A. carbonarius. This study suggests that use of natamycin at 50–100 ng ml−1 can give complete inhibition of growth of A. carbonarius and OTA production over a range of environmental conditions. Natamycin could be an important component of a system to prevent OTA contamination of wine as well during the drying and production of vine fruits.