Identification of Saccharomyces cerevisiae strains for alcoholic fermentation by discriminant factorial analysis on electronic nose signals

An electronic nose (E-nose) coupled to gas chromatography was tested to monitor alcoholic fermentation by Saccharomyces cerevisiae ICV-K1 and Saccharomyces cerevisiae T306, two strains well-known for their use in oenology. The biomass and ethanol concentrations and conductance changes were measured during cultivations and allowed to observe the standard growth phases for both yeast strains. The two strains were characterized by a very similar tendency in biomass or ethanol production during the fermentation. E-nose was able to establish a kinetic of the production of aroma compounds production and which was then easy to associate with the fermentation phases. Principal Component Analysis (PCA) showed that the data collected by E-nose during the fermentation mainly contained cultivation course information. Discriminant factorial analysis (DFA) was able to clearly identify differences between the two strains using the four main principal components of PCA as input data. Nevertheless, the electronic nose responses being mainly influenced by cultivation course, a specific data treatment limiting the time influence on data was carried out and permitted to achieve an overall performance of 83.5%

Défauts d'arôme : formation et protection

Chapitre 5absen

The use of active PET to package rosé wine: Changes of aromatic profile by chemical evolution and by transfers

Active Polyethylene Terephthalate (PET) bottles containing 1 or 3% of oxygen scavenger (named 1osPET and 3osPET) were used to pack rosé wine. Changes in the aromatic profiles were monitored during 12 months and compared to those of a wine packed in glass bottles. Wine in 1osPET bottles was differentiated from wine in glass or 3osPET bottles by ten aging markers such as cis-dioxane, ethyl pyruvate or furfural. Only trans-1,3-dioxolane allowed to discriminate wine in glass and in 3osPET bottles. Methionol, an oxygen sensitive aroma compound, was preserved in glass and 3osPET bottles but was slightly degraded (15%) in 1osPET bottles. Chemical reactions were the main cause of the aroma compound degradation. Indeed, the total amount of compounds sorbed only reached 160 μg considering the bottles and the joint of cap after 12 months of storage. The use of PET with 3% of oxygen scavenger is adapted to pack wine for at least 12 months

Protection of methionol against oxidation by oxygen scavenger: An experimental and modelling approach in wine model solution

The aim of this study was to evaluate the impact amount (1% and 3%) of oxygen scavengers (os) incorporated in a PET matrix on methionol oxidation in model wine solutions with different initial oxygen concentrations. At saturated oxygen concentration, the studied amount of oxygen scavenger did not affect the methionol preservation. In more realistic oxygen concentration of wine (0.117 mmol/L), methionol was only protected after contact with 3% of oxygen scavenger. For a minimal concentration of oxygen (0.024 mmol/L), the presence of scavenger slowed down the methionol degradation by 1.2 and 1.9 times for 1osPET and 3osPET respectively. For the strongest oxygen concentrations, a mechanistic model was proposed to predict methionol degradation in relation to scavenger amount. This model based on second order reactions for methionol degradation and oxygen consumption by scavenger fitted well with the experimental data. An improvement of this model has been developed for the low initial oxygen amount

Modified atmosphere packaging using environmentally compatible and active food packaging materials

International audienceIn response to consumer demand and the market trend for more convenient, safer products that can be stored longer despite containing low quantities of preservatives, active packaging has become more of a factor in food packaging innovations. Packaging that was limited to protecting food products against external influences is no longer considered as an inert barrier and might be termed active when it interacts with food, or its surrounding environment, to delay degradation and extend shelf-life. Currently, there is an increasing interest in the possible use of natural solutions to delay and prevent microbial growth in food items, responding to consumer pressure to reduce chemical additives in foods and/or strong, detrimental thermal treatment. Antimicrobial packaging is expected to improve the shelf-life and microbial quality of packaged food. The antimicrobial effect of packaging materials could be achieved either by direct contact with food surfaces, using antimicrobial, non-migratory, or controlled diffusion systems, or by indirect contact, using volatile antimicrobial-releasing systems to create a modified antimicrobial atmosphere in the headspace of packaging. Many preservatives, such as bacteriocins, organic acids, various plant extracts, volatiles from essential oils, and silver-substituted zeolite, have been incorporated in packaging materials to provide antimicrobial activity

Losses of methionol in PET-packed rosé wine in presence of SO2: Comparison between oxidation and scalping via uncertainty analysis

International audienceAn uncertainty analysis was performed on a mechanistic model describing the transport and oxidation of methionol, a model aroma compound, in PET-packed rosé wine. This allowed to quantify the relative importance of the losses to the wine/packaging material (scalping) with respect to those due to oxidation over a year of storage. Additionally, the oxygen scavenging effect of SO2, was also evaluated. Results showed that the predictions of the wine concentrations of the three studied species –methionol, oxygen and SO2- are reasonable, and that the reaction pathway is largely dominant with respect to losses of methionol and SO2 through the wine/packaging interface. Contrarily, the oxidation reaction appears to be almost equally governed by the kinetic reaction constants and by the oxygen barrier properties of PET in some of the tested scenarios, and thus likely responsible of a large proportion of the uncertainty

Coupling gas chromatography and electronic nose for dehydration and de-alcoholization of alcoholised beverages. Application to off-flavour detection in wine

International audienceAroma characterization of alcoholic beverages with sensor array electronic noses is a difficult challenge due to the masking effect of ethanol. Back-flush gas chromatography is proposed as a novel tool for the pretreatment of vapour samples before analysis in the electronic nose. The dehydration and desalcoholization step can be conducted in parallel with electronic nose detection, reducing significantly the analysis overall duration. As demonstration application, five molecules responsible for off-flavours in wines have been detected with a FOX 4000 system, after total dehydration and desalcoholization. Principal component analysis showed that discrimination between the control wine and off-flavour doped-wines became easy, even at concentrations corresponding to the human expert perception threshold. Back-flush gas chromatography is proposed as a novel tool for the pretreatment of vapour samples before analysis in the electronic nose. The dehydration and desalcoholization step can be conducted in parallel with electronic nose detection, reducing significantly the analysis overall duration. As demonstration application, five molecules responsible for off-flavours in wines have been detected with a FOX 4000 system, after total dehydration and desalcoholization. Principal component analysis showed that discrimination between the control wine and off-flavour doped-wines became easy, even at concentrations corresponding to the human expert perception threshold

Designing of a wheat gluten/montmorillonite based system as carvacrol carrier: Rheological and structural properties

E-mail [email protected] audienceAn antimicrobial delivery system was designed from film-forming solutions containing wheat gluten 20% (wt/vol) (WG) as matrix, montmorillonites (Mmt) as structuring agent and carvacrol as active agent (15% wt/wt dry WG). The objectives of this work were to understand how the addition of montmorillonites (0-10% wt/wt dry WG) affects the carvacrol retention capacity of both the film forming solution and the resulting film obtained by casting. For this purpose, structural, granulometric and rheological changes that occurred in the film-forming solutions were studied. The introduction of carvacrol in a WG solution containing increasing amounts of Mmt resulted in dramatic changes in its rheological behaviour. Depending on the Mmt amount added (=5%), the viscosity evolved in different ways indicating an unexpected and specific effect of Mmt on the WG solutions that contain carvacrol. In the presence of a sufficiently high Mmt content (>=5%), particles size measurements and microscopic observations pointed out large aggregated structures. These aggregated structures were supposed to result in an entrapment of carvacrol molecules that could be responsible for a higher carvacrol retention exhibited by both WG film-forming solutions and cast films. Further indications of this assumption were provided by XRD measurements that confirmed the establishment of specific interactions between Mmt, carvacrol and WG. The investigated delivery system based on a WG matrix reinforced by high content of Mmt fillers (>=5%) was clearly efficient to retain and protect an antimicrobial active agent such as carvacrol during the processing stag

Factors determining the transport coefficients of aroma compounds through polyethylene films

International audienceAroma sensitivity of two PE films having different composition was evaluated with four aroma compounds by measuring (i) aroma permeation (ii) aroma uptake by immersing films in pure aroma compounds, (iii) aroma vapour sorption by exposing films to saturated vapour phase and finally (iv) aroma sorption under realistic conditions by immersing films in water solution containing low concentration of aroma compounds. From permeation and sorption kinetics, diffusion coefficients were determined by modelling the curve over time. Results were clearly related to the conditions of measurement, to the aroma compounds characteristics such as hydrophobicity and size. Regardless of the method used, the crystallinity of PE films was found to be the most critical factor