Vinification and repassage as effective processes to remove ochratoxin A from contaminated grape

Ochratoxin A (OTA) contamination of red wine grape might be quite severe in certain high-risk regions and vintages thus requiring corrective measures to fulfill acceptable standard for human consumption. Knowledge about the fate of OTA during vinification and its distribution in wine and winery by-products is important to manage OTA risk in red wine grape. The distribution of OTA in red wine and winery byproducts during vinification (at laboratory and winery scale) of naturally contaminated Negroamaro and Primitivo was thoroughly monitored. Musts and wines were analysed by the EN 14133 standard method while a new HPLC method was developed for the analysis of grape pomaces, seeds and lees. Experimental results showed that during the 5-6 day fermentation and maceration of crushed grape berries the amount of toxin dissolved in juice/must and adsorbed on pomace reached a dynamic equilibrium with only 4% OTA dissolved in the wine, 95% retained in the pressed grape pomaces and 1% in the lees. OTA was homogeneously distributed within pomaces during fermentation/maceration of crushed grape berries (5-7% variability in triplicate analyses from the same tank). After fermentation/maceration OTA concentration remained unchanged in all liquid fractions collected during vinification (free run wine, press wine and wine after first and second decantation) as well as in wine after one year aging. Similar results were obtained from experiments conducted at winery scale for two consecutive vintages. Although most of the toxin is retained by pomaces during vinification process, OTA concentrations higher then 2 µg/kg (EU limit) can be found in must/wine produced in certain high-risk regions and vintages which requires additional decontamination measure. The high affinity of grape pomaces for OTA suggested that repassage of contaminated must/wine over pomaces with no or low OTA levels could be used to remove the toxin. Time course experiments showed that OTA adsorption by pomaces is a rapid process, reaching the equilibrium in less than 10 h, and is not affected by the tested toxin concentrations. Specific experiments carried out at laboratory and winery scale showed that up to 65% of toxin was removed when contaminated red must spiked with 2-10 µg/kg OTA was repassed over clean red pomaces. Grape pomaces maintained a good efficacy in removing OTA after four time re-usage. Unlike other oenological fining agents, the use of grape pomaces to remove OTA from red wines of the same grape variety (Primitivo) did not affect relevant wine quality parameters, including color intensity and health promoting phenolics content (trans-resveratrol, quercetin, total polyphenols). The proposed repassage process can be applied in a modern winery to decontaminate must/wines that still contain OTA at concentrations higher then 2 µg/kg at the end of vinification process.