Ksenia Morozova

High resolution mass approach to characterize refrigerated black truffles stored under different storage atmospheres

Freshly harvested Tuber melanosporum samples were packed and stored at 4°C under reduced atmospheric pressure or modified atmosphere for four weeks. Multivariate analysis was employed to correlate the antioxidant power of the ethanolic extracts of the samples with the chemical composition determined by high resolution mass spectrometry. High performance liquid chromatography coupled with a coularray detector was applied to select the chemical species associated with the antioxidant power. Four classes of chemical compounds were investigated in more detail by a targeted approach: derivatives of glutathione, adenine (such as S-adenosyl-homocysteine), oxidized linoleic acid and ergosterol. Adducts containing glutathione and adenine with oxidized linoleic acid were observed in TM for the first time and can be considered markers of freshness of the product. S-adenosyl-homocysteine, the acetyl-carnitine adduct with cysteinyl-glycine and several oxidized linoleic acid derivatives were among the markers of degradation.

Effect of light irradiation on the antioxidant stability of oleuropein

The stability of oleuropein, a natural antioxidant from Olea europaea, has been often studied in connection with thermal or enzymatic treatments, but very little is known about the effects of UV light. This work aimed at studying the UV-C effects on oleuropein standard solutions once dissolved in ethanol or water. During irradiation, aliquots were taken and analyzed by a flow injection system equipped with a multi-channel coulometric detector and a high-resolution mass spectrometer. The effects of irradiation were also studied by UV spectroscopy. The results show that oleuropein is relatively stable in water or ethanol, but that under UV-C light undergoes a series of fast decomposition reactions leading to hydroxytyrosol and elenolic acid. Overall, this study provides evidences that the degradation of oleuropein by UV-C light follows a mechanism dependent on the solvent used. Moreover, the solvent affects the resulting redox properties of the solution.

Indirect effect of glyphosate on wine fermentation studied by microcalorimetry

The use of herbicide such as glyphosate is a common practice in viticulture to limit nutrients and water competition between vine/weed plants. However, the impact of such herbicide on the resulting grapes juice quality and, later, on wine fermentation has not yet been proven. In this work, grapes of Vitis vinifera L. cv Gewürztraminer harvested from plants subjected to the weed control with glyphosate were analysed for their fermenting capacity by isothermal microcalorimetry after inoculation with Saccharomyces cerevisae. The resulting heat flow traces were fitted by two additive Gompertz functions and used to describe the yeast growth rate. The comparison of the fitting parameters showed that glyphosate decreased the heat generated by yeast growth. This effect was consistent with a change in the amino acids and sugars contents in grapes. However, the results also show that the impact of the herbicide on yeast fermentation can be partly overcome with an additional N fertilization (i.e. urea) in the vine. Microcalorimetry has revealed for the first time these effects on the fermenting process of grapes.

Fining of Red Wine Monitored by Multiple Light Scattering

This work describes a new approach based on multiple light scattering to study red wine clarification processes. The whole spectral signal (1933 backscattering points along the length of each sample vial) were fitted by a multivariate kinetic model that was built with a three-step mechanism, implying (1) adsorption of wine colloids to fining agents, (2) aggregation into larger particles, and (3) sedimentation. Each step is characterized by a reaction rate constant. According to the first reaction, the results showed that gelatin was the most efficient fining agent, concerning the main objective, which was the clarification of the wine, and consequently the increase in its limpidity. Such a trend was also discussed in relation to the results achieved by nephelometry, total phenols, ζ-potential, color, sensory, and electronic nose analyses. Also, higher concentrations of the fining agent (from 5 to 30 g/100 L) or higher temperatures (from 10 to 20 °C) sped up the process. Finally, the advantage of using the whole spectral signal vs classical univariate approaches was demonstrated by comparing the uncertainty associated with the rate constants of the proposed kinetic model. Overall, multiple light scattering technique showed a great potential for studying fining processes compared to classical univariate approaches.