Ochratoxin A occurrence and formation in Portuguese wine grapes at various stages of maturation

Abstract

A total of 93 Portuguese grape samples destined for wine production were examined for the presence of ochratoxin A (OTA) and the OTA producing fungi Aspergillus carbonarius and A. niger aggregate. Samples came from 11 vineyards from four winemaking regions in the North and South of the Portuguese mainland, during the harvest seasons of 2001, 2002 and 2003. Grapes were examined at 3 maturation stages, from setting to the harvesting period, to evaluate when contamination with OTA producing fungi and OTA synthesis occur. The detection of fungi in grape samples was made by plating methods with and without surface disinfection. OTA was formed by 14% of the 650 isolates tested. Most of the OTA producing strains (96%) were isolated at harvest time. At this stage, the percentage of grape samples with OTA producing strains detected without surface disinfection was 56%. With surface disinfection, A. carbonarius was isolated from 10% of the samples. OTA was detected in grapes at the 3 maturation stages. The average OTA concentrations in 60 samples at pea berry (28 samples), early veraison (22 samples) and ripe berry (20 samples) were 263, 149 and 35 ng/kg, respectively. Experiments with an A. carbonarius strain demonstrated that OTA production differs significantly with the composition of the berries at different maturation stages (P<0.001), with a mean value of OTA production at pea berry, early veraison and ripe berry of 3402, 1530 and 22 mug/kg, respectively. The production of OTA by A. carbonarius was correlated positively and negatively with the total acidity of grapes (r(s)=0.855, P<0.001) and reducing sugars content (r(s)=-0.835, P<0.001), respectively. Our data demonstrate that OTA synthesis in grapes occurs since early maturation stages.

How will climate change affect mycotoxins in food?

“…Grape sample. Samples from 11 vineyards from four winemaking regions in the North and South of the Portuguese mainland, during the harvest seasons of 2001, 2002, and 2003 were assessed for ochratoxin A and fungi (Serra, Mendonca, & Venancio, 2006). Significant differences were observed in ochratoxin A content of grapes between 2002 and 2003 which may have been related to temperature, although isolation of ochratoxin A fungi were only '' insignificantly different" upon the application of statistics between 2001 and 2003.…”

“…with Portugal in Serra et al, 2006). The aim was to study the fungi associated with grapes and their ability to produce ochratoxin A on synthetic media.…”

Inhibition of ochratoxin A production of Aspergillus carbonarius by yeast species

“…A previous study by Cabañes et al (2002) observed that A. carbonarius isolates produced maximum OTA on unmodified YES agar and Czapek yeast agar after about 14 days. In a recent study, Serra et al (2006) found that the levels of OTA produced by black Aspergillus strains on the grape juice medium were lower than those produced on Czapek yeast agar. The ability of yeasts isolated from wine-grapes of Turkey to inhibit OTA production by A. carbonarius were assessed both in YES medium and grape juice.…”

Wine Contamination with Ochratoxins: A Review

“…Several works have studied ecophysiological factors affecting fungal growth and OTA production by Aspergillus section Nigri strains in grape-based medium [37][38][39][40]. A. niger and A. carbonarius present an optimum temperature for growth around 30-35 • C although maximum OTA production is reached at lower temperatures (15)(16)(17)(18)(19)(20) • C) closer to that found during night when OTA accumulation might occur. High water activity levels favor both growth and OTA production; therefore, rainfall close to harvest might potentiate toxin accumulation on grapes.…”