Biochemical and morphological characterization of a new fungal contaminant in balsamic and cider vinegars

Abstract

In this study we have determined the morphological, some physiological and biochemical characteristics of a fungal strain isolated from balsamic and cider vinegars. The examination of fungal contamination of 100 balsamic and cider vinegar samples showed that 90% contained more than 10⁴ colony forming units (CFU ml⁻¹), but in most samples (65%) values of more than 10⁵ CFU ml⁻¹ were obtained. The most frequent contamination was with Monascus sp. (80% of the samples examined showed 2 × 10³ to 6 × 10⁵ CFU ml⁻¹). This mould can produce secondary metabolites such as citrinin and monacolin K_L (lactone form), and monacolin K_A (acid form). Using high-performance liquid chromatography (HPLC) with fluorescence detection, citrinin was found in 68% of the samples. The concentration of these mycotoxins varied between 1.6 × 10⁻² µg ml⁻¹ and 7.2 × 10⁻² µg ml⁻¹. The concentrations of citrinin were very low, and we can anticipate that this compound at these concentrations has no toxic effects on renal cells. Monacolin was not detected in any sample studied.

Keywords:

• acetic acid bacteria
• balsamic and cider vinegars
• Monascus spp.
• contamination
• citrinin and monacolin

Acknowledgements

The authors gratefully acknowledge financial support from the European project Winegar (Grant Number COOP-CT-2005/017269) and Academic Society of Geneva (F. B.). Thanks are due to Professor R. Strasser for interest in the project and encouragement, L. Chappuis for technical assistance, A. Fehr for secretarial assistance, and Dr M. Ojha for revising the manuscript.