Dispersive liquid-liquid microextraction for the quantification of terpens in wines

Abstract

In a highly competitive worldwide market, a current challenge for the beverage sector is to diversify the range of products and to offer wines and spirits with typicity and character. 

During alcoholic fermentation, wine yeasts generate a large variety of volatile metabolites, including acetate esters, ethyl fatty acid esters, higher alcohols, volatile fatty acids and volatile sulfur compounds that contribute to the aroma profile of wine. These molecules, refered as fermentative aromas, are the most abundant volatile compounds synthetized by yeasts and the metabolic pathways involved in their formation have been well characterized. Furthermore, other molecules with a major organoleptic impact may be produced during wine fermentation including terpene derivatives. However, little information is available on the contribution of yeasts to the formation of these molecules, in particular on their ability to synthethise de novo the terpens derivatives or to produce hydrolytic enzymes involved in the release of varietal precursors. 

To study the yeasts ability to produce these molecules, a dispersive liquid-liquid microextraction (DLLME) gas chromatography mass spectrometry was developed for their quantification in white wines, synthetic wine and fermented synthetic medium. A mixture of acetone (dispersive solvent) and dichloromethane (extractive solvent) was added to 5 ml of sample. The proposed method showed no matrix effect, a good linearity in enological range (from 10 to 300 μg/L), good recoveries, inter-day precision and good reproducibility. The developed method was applied to the analysis of the capacities of 41 yeast strains to produce terpene compounds in Chardonnay must and in synthetic meidum. Interestingly, the majority of the studied compound has been detected and quantified in the resulting wines. 

This sample-preparation technique is very interesting for high-throughput studies and for economic and environmental reasons because it is fast, easy to operate with a high enrichment, and consumes low volume of organic solvent.