Identification of ochratoxigenic fungi and contextual change on dried raisins (Sultanas)

Abstract

Mycotoxins are secondary toxic metabolites synthesized by various filamentous fungi that grow on organic material frequently occurring in agricultural products, including grapes and dried vine fruits. Ochratoxin A (OTA) is a nephrotoxic compound produced mainly by the members of Aspergillus section Nigri and Circumdati in grape and grape derived products. Lower hygienic drying conditions may cause increase in microbiological contamination. Total mold counts were between 3.567 and 6.053 log10 CFU g-1 in unprocessed seedless raisin (Sultana) samples belonging to 20 different vineyards in Denizli region during 2011. Total of 330 strains of filamentous fungi were isolated and 301 isolates belonged to Aspergillus spp. (91.21%), while 29 (8.79%) isolates belonged to other genus such as Penicillium, Alternaria, Cladosporium, Mucor, Ulocladium and Stachybotrys spp. Black aspergilli constituted 91.03% of the Aspergillus strains isolated, namely A. niger (77.58%) and A. aculeatus (5.98%). All Aspergillus isolates were tested for the ability to produce OTA. A. niger, A. aculeatus and A. ochraceus had highest OTA production ability with maximum production of 441.830±100.554, 975.460±9.294 and 10.450±1.914 ng g-1 50% grape juice extract (GJ50) agar, respectively. However, OTA was also produced by other Aspergillus isolates at lower levels compared to A. niger and A. ochraceus isolates in vitro. In a total of 20 samples, OTA was not detected in 13 samples (65%), OTA levels were 0.0-0.16 ?g kg-1 (LOQ) in 1 sample (5%), 0.05-1.0 ?g kg-1 in 5 samples (25%) and 1.0-2.0 ?g kg-1 in 1 sample (5%). None of the 20 samples (100%) contained OTA exceeding current the EC limit (10 ?g kg-1) set for dried vine fruits.