Efficacy of natamycin for control of growth and ochratoxin A production by Aspergillus carbonarius strains under different environmental conditions

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. 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. 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. 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.