Today, chitosan (CS) is probably considered as a biofunctional polysaccharide with the most notable growth and potential for applications in various fields. The progress in chitin chemistry and the need to replace additives and non-natural polymers with functional natural-based polymers have opened many new opportunities for CS and its derivatives. Thanks to the specific reactive groups of CS and easy chemical modifications, a wide range of physico-chemical and biological properties can be obtained from this ubiquitous polysaccharide that is composed of β-(1,4)-2-acetamido-2-deoxy-d-glucose repeating units. This review is presented to share insights into multiple native/modified CSs and chitooligosaccharides (COS) associated with their functional properties. An overview will be given on bioadhesive applications, antimicrobial activities, adsorption, and chelation in the wine industry, as well as developments in medical fields or biodegradability.

The yeast species Brettanomyces bruxellensis is associated with important economic losses due to red wine spoilage. The most common method to prevent and/or control B. bruxellensis spoilage in winemaking is the addition of sulfur dioxide into must and wine. However, recently, it was reported that some B. bruxellensis strains could be tolerant to commonly used doses of SO2. In this work, B. bruxellensis response to SO2 was assessed in order to explore the relationship between SO2 tolerance and genotype. We selected 145 isolates representative of the genetic diversity of the species, and from different fermentation niches (roughly 70% from grape wine fermentation environment, and 30% from beer, ethanol, tequila, kombucha, etc.). These isolates were grown in media harboring increasing sulfite concentrations, from 0 to 0.6 mg.L-1 of molecular SO2. Three behaviors were defined: sensitive strains showed longer lag phase and slower growth rate and/or lower maximum population size in presence of increasing concentrations of SO2. Tolerant strains displayed increased lag phase, but maximal growth rate and maximal population size remained unchanged. Finally, resistant strains showed no growth variation whatever the SO2 concentrations. 36% (52/145) of B. bruxellensis isolates were resistant or tolerant to sulfite, and up to 43% (46/107) when considering only wine isolates. Moreover, most of the resistant/tolerant strains belonged to two specific genetic groups, allowing the use of microsatellite genotyping to predict the risk of sulfur dioxide resistance/tolerance with high reliability (>90%). Such molecular diagnosis could help the winemakers to adjust antimicrobial techniques and efficient spoilage prevention with minimal intervention.

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Brettanomyces bruxellensis is the main spoilage microbial agent in red wines. The use of fungal chitosan has been authorized since 2009 as a curative treatment to eliminate this yeast in conventional wines and in 2018 in organic wines. As this species is known to exhibit great genetic and phenotypic diversity, we examined whether all the strains responded the same way to chitosan treatment. A collection of 53 strains of B. bruxellensis was used. In the conditions of the reference test, all were at least temporarily affected by the addition of chitosan to wine, with significant decrease of cultivable population. Some (41%) were very sensitive and no cultivable yeast was detected in wine or lees after 3 days of treatment, while others (13%) were tolerant and, after a slight drop in cultivability, resumed growth between 3 and 10 days and remained able to produce spoilage compounds. There were also many strains with intermediate behavior. The strain behavior was only partially linked to the strain genetic group. This behavior was little modulated by the physiological state of the strain or the dose of chitosan used (within the limits of the authorized doses). On the other hand, for a given strain, the sensitivity to chitosan treatment was modulated by the chitosan used and by the properties of the wine in which the treatment was carried out.

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Nowadays, the use of sulfur dioxide (SO2) during the winemaking process is a controversial societal issue. In order to reduce its use, various alternatives are emerging, in particular bioprotection by adding yeasts, with different impacts on yeast microbiota in early winemaking stages. In this study, quantitative-PCR and metabarcoding high-throughput sequencing (HTS) were combined with MALDI-TOF-MS to monitor yeast population dynamic and diversity in the early stages of red winemaking process without sulfites and with bioprotection by Torulaspora delbrueckii and Metschnikowia pulcherrima addition. By using standard procedures for yeast protein extraction and a laboratory-specific database of wine yeasts, identification at species level of 95% of the isolates was successfully achieved by MALDI-TOF-MS, thus confirming that it is a promising method for wine yeast identification. The different approaches confirmed the implantation and the niche occupation of bioprotection leading to the decrease of fungal communities (HTS) and Hanseniaspora uvarum cultivable population (MALDI-TOF MS). Yeast and fungi diversity was impacted by stage of maceration and, to a lesser extent, by bioprotection and SO2, resulting in a modification of the nature and abundance of the operational taxonomic units (OTUs) diversity.

<p style="text-align: justify;"><em>Brettanomyces bruxellensis</em> is well adapted to high ethanol concentrations and low pH which allows it to develop in difficult environments, such as wine. <em>B. bruxellensis</em> is mainly found in red wine and is regarded as a spoilage yeast due to its production of ethylphenols and other compounds responsible for organoleptic defects. The detection and quantification of this yeast is essential to preventing wine spoilage. Several specific detection and quantification kits based on real time quantitative PCR are commercially available. Although these kits are frequently used by private enological and research laboratories, no scientific report on the reliability and performance of these kits, including inter-laboratory and inter-assay comparisons have been published. The aim of this work was to compare available kits to quantify <em>B</em>. <em>bruxellensis</em> in red wine to classical method (plate counting on selective medium) in an interlaboratory study. Three different commercial kits were tested on three different wines from Bordeaux, Côtes du Rhône, and Burgundy inoculated with <em>B</em>. <em>bruxellensis </em>at four different concentrations. Five naturally contaminated wines from different French wine regions were also tested. Our results suggest that all the kits tested probably over or underestimate the quantity of <em>B</em>. <em>bruxellensis</em> in red wine and, under specific conditions, give false positives. Quantification may be very heterogeneous depending on the wine, laboratory, or population level. Underestimations or false negative results may have serious consequences for winemakers. Overestimation may be partly due to the quantification of dead cells qPCR.</p><p style="text-align: justify;">This study highlights that quantification of<em> B</em>. <em>bruxellensis</em> in red wine using commercial kits requires a high level of expertise in molecular biology. We recommend that all users use a microbiological internal control to validate DNA extraction yield.</p>