Removal of Ochratoxin A in Saccharomyces cerevisiae Liquid Cultures

Abstract

The capacity for removal of ochratoxin A (OTA) during alcoholic fermentation was evaluated in batch systems with one commercial strain and one wild strain of Saccharomyces cerevisiae. Batch alcoholic fermentations were carried out in yeast extract-malt extract broth (YM) medium, with 18.0% glucose and OTA added to final concentrations of 3.48 and 4.95 ng/mL respectively. The removal capacity of each yeast strain was examined after completion of fermentation in batch culture and after extended contact with yeast biomass. The removal capacity of the yeast strains was also examined in stationary phase cultures. Stationary phase yeasts were studied with biomass harvested from the stationary phase of anaerobic fermentation, by incubation in phosphate buffer, with the addition of 5.00 ng/ mL of OTA. Removal studies with stationary phase cells were performed with viable and non-viable cells inactivated with Na-azide. The study showed that in growing phase cultures, OTA removal was significant only after extended contact with yeast biomass; up to 29.7% and 25.4% for wild yeast ZIM 1927 and commercial yeast Lalvin EC-1118 respectively, but not during alcoholic fermentation. In stationary phase cultures, viable and non-viable cells were not significantly different in OTA removal from the medium. This demonstrated that OTA was not metabolised, but possibly adsorbed by the yeast cells. The presence of OTA in synthetic media influenced yeast metabolism, causing the production of higher volatile acidity by 0.08 and 0.13 g/L for Lalvin EC-1118 and ZIM 1927 respectively, and lower concentrations of reducing sugar, by 0.32 g/L, but only for ZIM 1927.

Potential Mechanisms Underlying Response to Effects of the Fungicide Pyrimethanil from Gene Expression Profiling in Saccharomyces cerevisiae

“…Concentrations close to the lowest values herein found toxic for the yeast (e.g., between 5 and 10 mg/L) have been detected in must from grapes treated with PYR under extreme agricultural practices, 1,4,5 volatile acidity) of spontaneous and inoculated wine fermentations. 6,7 On the other hand, for example, the PYR IC20 value estimated is of an order of magnitude similar to that of the concentrations reported as cytotoxic toward the yeast antiandrogen test system (EC20 ∼ 33 mg/L) 8 or inhibiting ATP production in human neuronal and glial cell lines (IC50 ∼ 9 mg/L). 9 In the environmental context also, they are relatively close to or moderately higher than levels of concern reported for nontarget freshwater primary producers (e.g., chronic EC50 ∼ 23.1 mg/L for Scenedesmus acutus, or chronic EC50 ∼ 46.1 mg/L for Lemna minor) 15,16 or organisms in higher trophic levels (e.g., chronic EC50 = 1.18 mg/L or acute LC50 = 2.9 mg/L for Daphnia magna, and acute LC50 = 10.6 mg/L for fish).…”

“…42−44 However, these results point to potential interference of PYR in the network of pathways that influence the patterns of volatile aroma compounds during alcoholic fermentation (e.g., fatty acid and amino acid metabolism, lipid and sterol biosynthesis) in the yeast, 42−44 thus possibly imparting variable organoleptic properties and influencing the quality of the final wine, at least in worst-case situations associated with fungicide misuse. 4,6,7 Alterations on Genes Related to Stress Response. As expectable for transcriptional responses initiated in response to growing chemical challenges in the yeast, 18,22,24 a significant number of gene expression alterations related to cell rescue, defense, and detoxification increased considerably in cells exposed to the IC50 of PYR compared with the IC20s (Table 1, and Table S5 in the Supporting Information).…”

“…These insights deserve further in-depth studies in relevant wine yeast strains and phytopathogenic fungi to gain better understanding of PYR action, with possible repercussions on control of fungicide resistance in target fungi 10−12 and in enology. 4,6,42−44 In this respect, it is noteworthy that, besides PYR, 4,6,7 other new fungicides that may be used alone or together with anilinopyrimidine fungicides to treat vineyards, and whose residues can persist in grapes, have been reported to alter wine yeast biosynthesis of volatile products that contribute to the wines' sensorial properties. 50,51 In the (eco)toxicological context, we are aware that there are differences in xenobiotic susceptibility across species and a discrepancy exists between the fungicide concentrations herein used and those usually found in aquatic compartments under regulatory agricultural practices (e.g., <22−90 μg/L in vineyards).…”

“…4 There are thus concerns about potential risks to wine properties because residual PYR in must might affect wine yeasts and the outcome of fermentations. 4,6,7 In addition, consumers of grape products may be also at potential risk, which may be even enhanced when PYR is mixed with other currently used pesticides. 8,9 On the other hand, development of PYR resistance and/or multidrug resistance in field strains of B. cinerea 10 and other phytopathogenic fungi 11,12 have increased in recent years and can be of high economic importance.…”

Mycotoxins – prevention and decontamination by yeasts

“…Oenological S. cerevisiae and S. bayanus strains were shown also to adsorb OTA in grape and fruit juice and in liquid culture too . OTA removal was shown to be a very rapid process .…”