Natural occurrence and production of tenuazonic acid in wine grapes in Argentina

A survey was carried out to determine natural occurrence of tenuazonic acid (TA) in healthy and rotten wine grapes samples from different varieties (n=37) collected during 2016 vintage in the region of DOC San Rafael (Argentina). In addition, inoculation experiments with three Alternaria alternata strains in wine grapes were done to elucidate TA production and its major influencing factors. The 16.2% (6/37) of total wine grape samples showed TA contamination with 4% (1/25) of incidence in healthy samples (77 mu g.kg(-1)) and 42% (5/12) in rotten samples (10-778 mu g.kg(-1)). Malbec, Cabernet Sauvignon, and Syrah varieties showed TA contamination, whereas Bonarda, Ancelota, Torrontes, Semillon, and Chenin did not. During inoculation experiments in wine grapes, two of three strains were able to produce TA among the evaluated conditions and the highest TA production was observed at 15 degrees C and 25 degrees C after 24days of incubation. Nutritional composition of grapes results appropriate for A. alternata infection and TA production and, together with the adequate field conditions, favors TA natural occurrence in wine grapes.