Description of Ewiss cheese, a new ewe's milk cheese processed by Swiss cheese manufacturing techniques: microbiological, physicochemical and sensory aspects.

Typically, Swiss-type cheese is made from cow's milk. However, in the present work an attempt to expand the sheep supply chain and product offering in this field was made by developing a new type of cheese using Swiss-type cheese technology. The cheese was manufactured under industrial conditions, and fermentations were carried out using freeze-dried commercial starters that are traditionally used in the production of Swiss cheese. Two experimental "Ewiss cheese" (EC) products were produced using raw milk (RM-EC) and pasteurized milk (PM-EC), respectively. Fourteen microbial groups were investigated by plate counts from curd until ripened cheeses. According to microbiological analyses, no statistically significant differences were found between the 2 productions with respect to the group of lactic acid bacteria (LAB). The curds were mainly characterized by mesophilic LAB cocci (7.45 log10 cfu/g in RM-EC and 7.33 log10 cfu /g in PM-EC). However, at the end of the ripening period (9 mo), the cheeses exhibited a higher presence of mesophilic LAB rods. Undesired microbiological groups were found only in the curd of raw milk cheese in the range of 104-105 cfu/g, but reaching undetectable levels by plate count in the cheese at the end of ripening. RM-EC and PM-EC were characterized by 76% and 68% of dry matter, respectively. These cheeses contained 29.30% and 34.36% of protein, and 51.31% and 50.38% of fat, respectively. Textural analysis showed differences in terms of hardness, chewiness, and gumminess between the experimental cheeses and Swiss cheese sold on the market. These differences could be attributed to the higher protein content of ewe's milk. The main fatty acids in the cheeses were palmitic acid, myristic acid, oleic acid, and capric acid. Among the organic acids, RM-EC had higher concentrations of lactic acid, while PM-EC was higher in propionic acid. The ewe's cheeses emitted 46 volatile compounds, including acids, aldehydes, ketones, esters, alcohols, and other compounds. PM-EC was characterized by the main compounds of Swiss-type cheese: acetic acid, butyric acid, ethyl butyrate, ethyl caproate, propanoic acid, and tetramethylpyrazine. Sensory evaluation showed that the new dairy products were generally appreciated, and PM-EC was the most preferred by the judges. This research has enabled the development of new ewe's milk products, which could stimulate the valorization of a sector that has been long neglected and still has a large margin of improvement.

Biosynthesis of the antioxidant γ-glutamyl-cysteine with engineered Yarrowia lipolytica.

The dipeptide γ-glutamylcysteine (γ-GC), the first intermediate of glutathione (GSH) synthesis, is considered as a promising drug to reduce or prevent plethora of age-related disorders such as Alzheimer and Parkinson diseases. The unusual γ-linkage between the two constitutive amino acids, namely cysteine and glutamate, renders its chemical synthesis particularly challenging. Herein, we report on the metabolic engineering of the non-conventional yeast Yarrowia lipolytica for efficient γ-GC synthesis. The yeast was first converted into a γ-GC producer by disruption of gene GSH2 encoding GSH synthase and by constitutive expression of GSH1 encoding glutamylcysteine ligase. Subsequently genes involved in cysteine and glutamate anabolism, namely MET4, CYSE, CYSF, and GDH1 were overexpressed with the aim to increase their intracellular availability. With such a strategy, a γ-GC titer of 464 nmol mg-1 protein (93 mg gDCW-1 ) was obtained within 24 h of cell growth.

Exploring yeast-based microbial interactions: The next frontier in postharvest biocontrol.

Fresh fruits and vegetables are susceptible to a large variety of spoilage agents before and after harvest. Among these, fungi are mostly responsible for the microbiological deteriorations that lead to economically significant losses of fresh produce. Today, synthetic fungicides represent the first approach for controlling postharvest spoilage in fruits and vegetables worldwide. However, the emergence of fungicide-resistant pathogen biotypes and the increasing awareness of consumers toward the health implications of hazardous chemicals imposed an urgent need to reduce the use of synthetic fungicides in the food supply; this phenomenon strengthened the search for alternative biocontrol strategies that are more effective, safer, nontoxic, low-residue, environment friendly, and cost-effective. In the last decade, biocontrol with antagonistic yeasts became a promising strategy to reduce chemical compounds during fruit and vegetable postharvest, and several yeast-based biocontrol products have been commercialized. Biocontrol is a multipartite system that includes different microbial groups (spoilage mold, yeast, bacteria, and nonspoilage resident microorganisms), host fruit, vegetables, or plants, and the environment. The majority of biocontrol studies focused on yeast-mold mechanisms, with little consideration for yeast-bacteria and yeast-yeast interactions. The current review focused mainly on the unexplored yeast-based interactions and the mechanisms of actions in biocontrol systems as well as on the importance and advantages of using yeasts as biocontrol agents, improving antagonist efficiency, the commercialization process and associated challenges, and future perspectives.

A Thorough Investigation of the Microbiological, Physicochemical, and Sensory Properties of Ewe's Yoghurt Fermented by a Selected Multi-Strain Starter Culture.

This work was carried out with the aim to investigate the microbiological, physicochemical, and sensory properties of an innovative yoghurt produced from ewe's milk. Experimental yoghurt productions were performed with a commercial freeze-dried starter preparation and a natural milk starter culture (NMSC) of Streptococcus thermophilus and Lactobacillus delbrueckii. The two yoghurts did not differ for colour parameters, showing an average value of lightness, redness, and yellowness of 94.99, -3.74, and 9.37, respectively. The yoghurt produced using the NMSC as a fermenting agent was characterised by a significantly lower fat percentage and a higher antioxidant potential than commercial starters. Microbiological analysis confirmed the safety of the final product and a level of living lactic acid bacteria of 108 CFU/g. Sensory analysis revealed some differences among yoghurts regarding unpleasant odour, homogeneity, and persistence in the mouth, but the yoghurt processed with NMSC was more appreciated. Thus, the production of ewe's yoghurt fermented by a selected multi-strain starter culture represents an interesting strategy to enlarge the functional ovine dairy product portfolio.

The influence of Torulaspora delbrueckii on beer fermentation.

In this study, the effect of five different Torulaspora delbrueckii strains in combination with an ale type Saccharomyces cerevisiae on physical, chemical, microbiological, aroma composition, and sensory profiles of beer were examined. The ethyl alcohol content of produced beers ranged from 5.46% (v/v) to 5.93% (v/v), while the highest alcohol amount was obtained using a pure culture of S. cerevisiae. The major volatiles among beer aroma compounds was acetaldehyde, n-propanol, 3-methyl-butanol, 2-methyl-butanol, ethyl acetate, isoamyl acetate, 2,3-butanedione, and 2,3-pentanedione. It was ascertained that the total amount of higher alcohols was higher in the S. cerevisiae control beer compared to all mixed fermentations. Total ester levels were higher in all the mixed culture beers than the control beer. Sensory evaluation showed that all the mixed cultures of S. cerevisiae and T. delbrueckii positively influenced the sensory profile of the beers. Strain Y1031 was the most preferred and was characterized as rich in hop aroma and full bodied. It is therefore a suitable strategy to use T. delbrueckii in mixed fermentations with S. cerevisiae to produce beer with a distinctive flavor. The results demonstrate that, T. delbrueckii strains isolated or commercialized for winemaking can be equally employed as well in brewing.

Identification of yeasts in fermented foods and beverages using MALDI-TOF MS.

Yeasts are an important group of microorganisms and contribute to the fermentation of a broad range of foods and beverages spontaneously or as a starter culture. Rapid and reliable microbial species identification is essential to evaluate biodiversity in fermented foods and beverages. Nowadays, high-throughput omics technologies and bioinformatics tools produce large-scale molecular-level data in many fields. These omics technologies generate data at different expression levels and are used to identify microorganisms. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a powerful analytical technique in proteomic technology. It is a tool used to analyze the peptides or proteins of microorganisms for identification. MALDI-TOF MS has been used for the taxonomic identification of microorganisms as a fast, high-throughput, and cost-effective method. This review briefly discussed the application of MALDI-TOF MS in identifying yeasts in fermented foods and beverages.

Evaluation of the variations in chemical and microbiological properties of the sourdoughs produced with selected lactic acid bacteria strains during fermentation.

This research aimed to analyze variations in chemical properties, microbiological characteristics and generated volatile organic compounds (VOCs) profile during sourdough fermentation. Sourdoughs were collected from different cities in Turkey at two different times and lactic acid bacteria (LAB) in the samples were identified with culture-independent and culture-dependent molecular methods. According to culture-dependent methodology, thirteen LAB species were identified. Lactobacillus spp. were identified as the major group according to MiSeq Illumina analysis. Technological potential of commonly isolated LAB species was evaluated. Due to high frequency of isolation, Fructilactobacillus sanfranciscensis and Lactiplantibacillus plantarum strains were better investigated for their technological traits useful in sourdough production. Experimental sourdoughs were produced with mono- and dual-culture of the selected strains and chemical properties and microbiological characteristics, as well as VOCs profile of the sourdoughs, were subjected to multivariate analysis which showed the relevance of added starter, in terms of acidification and VOCs profile.

Non-Saccharomyces yeast for lowering wine alcohol levels: partial aeration versus standard conditions.

Non-Saccharomyces yeasts have been suggested for use in wine production for lowering alcohol content. In this study, 23 non-Saccharomyces yeasts were investigated in laboratory-scale trials using previously frozen grape must. Both aerated and standard fermentation conditions were investigated and the fermentations were co-inoculated with a commercial Saccharomyces cerevisiae reference yeast strain. Sugar consumed for percentage alcohol formed was calculated from sugar and alcohol measurements. The non-Saccharomyces yeasts showed greater variability in sugar consumption compared with the S. cerevisiae reference yeast. Two of the yeast strains (Starmerella bacillaris and Wickerhamomyces anomalus) consumed more sugar than the S. cerevisiae reference yeast under the same conditions. These two strains were subsequently used in a small-scale wine production trial following a similar aeration and standard fermentation strategy. The wine production trials using aeration compared with the standard strategy showed shorter fermentation times, increased biomass formation and more sugar utilized for alcohol produced, but reduced wine quality. The same yeasts under standard fermentation conditions also showed increased use of sugar, but neutral or positive effects on wine quality. The S. bacillaris strain showed the most potential for use in wine production for lowering alcohol content.

Effect of different mineral salt mixtures and dough extraction procedure on the physical, chemical and microbiological composition of Salgam: A black carrot fermented beverage.

NaCl is utilized in Salgam at 1-2% (w/w). The aim of this study was to reduce the NaCl content by addition of different concentrations of KCl and CaCl2 during production and evaluate their effects on quality. An innovation in production process was also employed, specifically dough extraction and use of the resulting liquid as a starter inoculum. Lactic acid bacteria (LAB) species (13) were identified using a combined approach of (RAPD)-PCR and 16S rRNA gene sequencing. Lactobacillus paracasei and Lactobacillus plantarum were dominant, but Leuconostoc mesenteroides subsp. jonggajibkimchii, Lactococcus lactis subsp. cremoris, Lactobacillus coryniformis subsp. coryniformis, Lactobacillus paraplantarum were also found. Mineral compositons were determined using ICP-OES and the most abundant were potassium, sodium, calcium, magnesium and phosphorus, respectively. A mixture of NaCl and KCl protected anthocyanin contents and improved colour parameters. Dough extraction also accelerated production of salgam.

The influence of backslopping on lactic acid bacteria diversity in tarhana fermentation.

Tarhana is produced at batch systems in which the microbiota has changed accordingly to the microbial load from ingredients. In order to stabilize the microbiota, the effects of backslopping carried out under different temperature regimes (25 and 30 °C), pH (3.70 and 4.00) and inoculation rates (5, 10 and 15%) on lactic acid bacteria (LAB) diversity were determined in tarhana dough. LAB and Total Aerobic Mesophilic Bacteria (TAMB) numbers increased in all tarhana dough samples subjected to backslopping. Temperature and pH significantly affected the microbiological diversity of tarhana whereas the different inoculation rates did not. Tarhana dough showed complex tarhana microbiota following backslopping at pH 4.00 independently on the temperature applied. When backslopping was carried out at pH 3.70 and 25 °C, tarhana microbiota stabilized and became steady after several cycles. The LAB species found in all dough samples after the final backslopping were Lactobacillus plantarum, Lactobacillus alimentarius and Lactobacillus brevis which were able to carry out the fermentation in all conditions tested. In order to obtain a stable presence of LAB populations at industrial level for tarhana production, this work showed that backslopping is recommended at pH 3.70 and 25 °C with any inoculation ratios.

Lipids by Yarrowia lipolytica Strains Cultivated on Glucose in Batch Cultures.

Oleaginous microorganisms, such as Yarrowia lipolytica, accumulate lipids that can have interesting applications in food biotechnology or the synthesis of biodiesel. Y. lipolytica yeast can have many advantages such as wide substrate range usage and robustness to extreme conditions, while under several culture conditions it can produce high lipid productivity. Based on this assumption, in this study, 12 different Yarrowia lipolytica strains were used to investigate microbial lipid production using a glucose-based medium under nitrogen-limited conditions in shake-flask cultivations. Twelve wild-type or mutant strains of Yarrowia lipolytica which were newly isolated or belonged to official culture collections were tested, and moderate lipid quantities (up to 1.30 g/L) were produced; in many instances, nitrogen limitation led to citric acid production in the medium. Lipids were mainly composed of C16 and C18 fatty acids. Most of the fatty acids of the microbial lipid were unsaturated and corresponded mainly to oleic, palmitic and linoleic acids. Linolenic acid (C18:3) was produced in significant quantities (between 10% and 20%, wt/wt of dry cell weight (DCW)) by strains H917 and Po1dL.

Molecular analysis of the dominant lactic acid bacteria of chickpea liquid starters and doughs and propagation of chickpea sourdoughs with selected Weissella confusa.

Fermented chickpea liquid is used as a leavening agent in chickpea bread production. In the present study, traditional chickpea liquid starter and dough samples were collected from bakeries in Turkey and microbiologically investigated. Culture-independent analysis for microbiota diversity, performed by MiSeq Illumina, identified Clostridium perfringens as major group in all samples, while Weissella spp. Dominated LAB community. A culture-dependent methodology was applied and 141 isolates were confirmed to be members of the LAB group based on 16s rRNA gene sequence analysis. In particular, 11 different LAB species were identified confirming the high frequency of isolation of weissellas, since Weissella confusa and Weissella cibaria constituted 47.8 and 12.4%, respectively, of total LAB isolated. The other species were Enterococcus faecium, Enterococcus lactis, Lactobacillus brevis, Lactobacillus plantarum, Leuconostoc mesenteroides, Leuconostoc mesenteroides subsp. Dextranium, Pediococcus acidilactici, Pediococcus pentosaceus and Streptococcus lutetiensis. Due to high frequency of isolation, W. confusa strains were investigated at technological level and W. confusa RL1139 was used as mono-culture starter in the experimental chickpea sourdough production. Chemical and microbiological properties, as well as volatile organic compounds (VOCs) of the chickpea liquid starters and doughs were subjected to a multivariate analysis. Control and W. confusa inoculated chickpea liquid starter and dough samples were close to each other in terms of some characteristics related to chemical, microbiological and VOCs profile, but the inoculated sourdough showed a higher generation of certain VOCs, like butanoic acid (81.52%) and ethyl acetate (8.15%) than control sourdough. This is important in order to maintain typical characteristics of the traditional chickpea dough, but at the same time improving the aroma profile. This work demonstrated that W. confusa RL1139 can be applied at large scale production level without compromising the typical characteristics of the final product.

Predominant yeasts in the sourdoughs collected from some parts of Turkey.

In the present study, a total of eight sourdough samples were collected from three different bakeries at two different times in Turkey. Also, laboratory-scale sourdough production was conducted by daily back-slopping for 7 days. Microbiological and chemical properties of the sourdoughs were investigated. Yeast species in the sourdoughs were identified by subjecting all presumptive yeast cultures to internal transcribed spacer region amplification of the 5.8S rRNA gene, restriction fragment length polymorphism analysis using Hae III, Hha I, and Hinf I endonucleases, and sequence analysis of the D1/D2 domain of the 26S rDNA gene. A total of seven profiles were determined according to the restriction fragments. Totally, 148 yeast isolates were identified at the species level (≥400 bp, 99% identity) as Saccharomyces cerevisiae (106), Kazachstania bulderi (11), Pichia fermentans (nine), Pichia membranifaciens (eight), Kazachstania servazzii (seven), Kazachstania unispora (four), and Hanseniaspora valbyensis (three). Although collected sourdoughs were produced without using baker's yeast, S. cerevisiae was the most frequently isolated yeast species. This can be related to the contamination of the bakery environment with commercial baker's yeast during the production of other bakery products. The pH and acidity levels of the collected sourdough samples ranged from 3.71 to 3.96 and 6.78 to 23.93 mL 0.1 N NaOH/10 g dough, respectively. Mean values of the content of maltose + sucrose, glucose, fructose, lactic acid, and acetic acid were 2.43, 1.57, 2.67, 7.30, and 1.40 g/kg, respectively. Due to the artisan and region-dependent handling of the sourdough, different biochemical patterns were observed among the collected samples.

Biocontrol ability and action mechanisms of Aureobasidium pullulans GE17 and Meyerozyma guilliermondii KL3 against Penicillium digitatum DSM2750 and Penicillium expansum DSM62841 causing postharvest diseases.

Epiphytic yeasts were isolated from different cultivars of apples and lemons and identified by a combination of PCR-RFLP of 5.8S rRNA region and sequencing of D1/D2 domain of the 26S rRNA gene. Among 69 isolates, Aureobasidium pullulans GE17 and Meyerozyma guilliermondii KL3 strains showed the greatest antagonistic activity against two significant apple and lemon postharvest pathogens, Penicillium expansum DSM62841 (blue mold) and Penicillium digitatum DSM2750 (green mold), after preliminary screening. Yeasts were applied as single and mixed cultures with two different cell concentrations of 106 and 108 cells/ml in the present study. It was determined that antagonistic activity of two yeast strains studied emerged with a combination of several mechanisms of action including competition for space and nutrients, production of volatile organic compounds (VOCs), secretion of extracellular lytic enzymes and inhibition of fungal spore germination. The highest inhibition of mycelial growth on P. expansum DSM62841 and P. digitatum DSM2750 (83.4% and 74.7%, respectively) was achieved by utilization of single culture of A. pullulans GE17. Otherwise, the application of mixed culture at the ratio of 108 cells/ml inhibited spore germination of both pathogens from 86% to 95%. Results of this study suggest that an increase in yeast cell concentrations positively affected their biocontrol activity against blue and green molds. According to the results, employing single culture of M. guilliermondii KL3 did not exhibit effective antagonistic activity against blue and green molds. However, utilization of A. pullulans GE17 alone and mixed culture showed succesfull controlling against both P. expansum DSM62841 and P. digitatum DSM2750.

Structural and technological characterization of ropy exopolysaccharides produced by Lactobacillus plantarum strains isolated from Tarhana.

Exopolysaccharide producing starter cultures enable manufacturing "clean labeled" foods with improved textural and nutritional properties. The structural and technological analyses were performed on the ropy exopolysaccharides of six Lactobacillus plantarum. The incubation temperature, time and pH affected the exopolysaccharide production and high exopolysaccharide was produced in the presence of sucrose and maltose. The viscosity of exopolysaccharide was high at acidic conditions except PFC311E that showed viscous at neutral pH. Lactobacillus plantarum strains produced between 120 and 400 mg/L exopolysaccharide in which the highest was observed at L. plantarum PFC311. Exoploysaccharides were degraded over 300 °C except PFC311E that degraded at 295.7 °C. The NMR analyses revealed that the exopolysaccharides were synthesized by α1-6, α1-3 and α1-4 bonds with glucose, galactose and fructose moieties. In conclusion, L. plantarum PFC311 produced ropy exopolysaccharide with different structural, rheological and thermal properties and reveals potential to be used in food industry.

Screening various Yarrowia lipolytica strains for citric acid production.

Citric acid (CA) productivity by Yarrowia lipolytica dependents on strain type, carbon source, carbon to nitrogen (C/N) molar ratio as well as physicochemical conditions (pH, temperature, oxygen transfer rate, etc.). In the current study, 10 different Y. lipolytica strains were first challenged in shake-flask culture for CA production in a glucose-based media under nitrogen-limited conditions. For the most promising one, strain K57, CA productivity was monitored during culture in batch bioreactor for three initial C/N molar ratio (167, 367, and 567 Cmol/Nmol). The highest CA yield (0.77 g/g glucose), titre (72.3 g/L CA), and productivity (0.04 g/g.h) were found for C/N ratio of 367. However, the highest growth rate was obtained for an initial C/N ratio of 167. From these results, Y. lipolytica strain K57 could be considered to produce CA at higher titre on glucose-based medium in batch bioreactor than others Y. lipolytica strain reported in the literature.

Aroma composition of shalgam: a traditional Turkish lactic acid fermented beverage.

Shalgam, a traditional red, cloudy and sour soft beverage, is produced by lactic acid fermentation of black carrot, sourdough, salt, bulgur flour, turnip and adequate water. The present study was designed to characterize the volatile compounds of shalgam obtained from different methods. The aroma compounds of shalgams produced by traditional and direct methods, and addition of Lactic acid bateria (LAB) cultures were examined. Volatile components of shalgam samples were extracted by liquid-liquid extraction technique with pentane/dichloromethane and analyzed by gas chromatography-mass spectrometry (GC-MS). Sixty aroma compounds were identified in shalgam samples including 20 terpenes, 9 esters, 9 alcohols, 5 volatile acids, 6 volatile phenols, 5 lactones, 3 naphthalenes, 2 carbonyl compounds and 1 C13-norisoprenoids. It was found that the aroma profiles of shalgams were quite similar. However, the total volatile content of the shalgam samples increased with addition of Lb. plantarum.

Yeast biota of naturally fermented black olives in different brines made from cv. Gemlik grown in various districts of the Cukurova region of Turkey.

In this study, the yeast microbiota of naturally fermented black olives made from cv. Gemlik, grown in three different districts of the Çukurova region of Turkey, were investigated. Fermentations were conducted for 180 days in three different brines, including NaCl 10% w/v, NaCl 8% w/v and NaCl 8% w/v added with glucose 0.5%. In total, 223 yeasts were isolated and then identified by PCR-RFLP analysis of the 5.8S ITS rRNA region and sequence information for the D1/D2 domains of the 26S rRNA gene. A broad range of yeast biodiversity was identified, including eight genera and nine species. Candida boidinii (41%), Wickerhamomyces anomalus (32%) and Saccharomyces sp. (18%) were predominant yeasts throughout the fermentations. To a lesser extent, the other species, Candida aaseri, Meyerozyma sp., Zygoascus hellenicus, Pichia kudriavzevii, Schwanniomyces etchellsii and Candida atlantica were also members of the olive-fermenting microbiota. In Tarsus and Bahçe districts C. boidinii and in Serinyol district Saccharomyces sp. were the most frequently identified species. W. anomalus was the most frequently isolated species (by 48% of total yeasts) in NaCl 10% brines. C. boidinii was the most dominant species in the brines, including NaCl 8% and NaCl 8% + glucose 0.5%, with frequencies of 42% and 61%, respectively. At the end of the 180 days of fermentation, total acidity values of the brines were in the range 1.04-8.1 g/l lactic acid. Copyright © 2016 John Wiley & Sons, Ltd.

Influence of Lachancea thermotolerans on cv. Emir wine fermentation.

The present paper describes the behaviour of Lachancea thermotolerans and Saccharomyces cerevisiae in pure, co-cultured and sequential fermentations in cv. Emir grape must. Faster fermentation rates were observed in wine made with a pure culture of S. cerevisiae and wine produced with simultaneously inoculated cultures of L. thermotolerans and S. cerevisiae. Both L. thermotolerans and S. cerevisiae gave high population numbers. The use of L. thermotolerans in mixed and sequential cultures led to an increase in final total acidity content in the wines, varying in the range 5.40-6.28 g/l (as tartaric acid), compared to pure culture S. cerevisiae, which gave the lowest level of total acidity (5 g/l). The increase was in the order of 1.18-2.06 g/l total acidity. Increase in final acidity by the use of L. thermotolerans might be useful to improve wines with low acidity due to global climate change. Volatile acidity levels (as acetic acid) were in the range 0.53-0.73 g/l, while the concentration of ethyl alcohol varied in the range 10.76-11.62% v/v. Sequential fermentations of wines and pure culture fermentation of L. thermotolerans resulted in reduction in the concentrations of acetaldehyde and higher alcohols, with exception of N-propanol and esters. According to the sensory analysis, wine obtained with sequential inoculation of L. thermotolerans followed by inoculation of S. cerevisiae after 24 h, and simultaneous inoculation of these yeasts, was the most preferred. Copyright © 2016 John Wiley & Sons, Ltd.

Effectiveness of chitosan against wine-related microorganisms.

The antimicrobial action of chitosan against wine related microorganisms, including Lactobacillus plantarum, Saccharomyces cerevisiae, Oeonococcus oeni, Lactobacillus hilgardii, Brettanomyces bruxellensis, Hanseniaspora uvarum and Zygosaccharomyces bailii was examined in laboratory media. In order to assess the potential applicability of chitosan as a microbial control agent for wine, the effect of chitosan, applied individually and/or in combination with sulphur dioxide (SO2), on the growth of microorganisms involved in various stages of winemaking and on the fermentative performance of S. cerevisiae was investigated. Of the seven wine-related microorganisms studied, S. cerevisiae exhibited the strongest resistance to antimicrobial action of chitosan in laboratory media with a minimum inhibitory concentration (MIC) greater than 2 g/L. L. hilgardii, O. oeni and B. bruxellensis were the most susceptible to chitosan since they were completely inactivated by chitosan at 0.2 g/L. The MIC of chitosan for L. plantarum, H. uvarum and Z. bailii was 2, 0.4 and 0.4 g/L, respectively. In wine experiments, it was found that chitosan had a retarding effect on alcoholic fermentation without significantly altering the viability and the fermentative performance of S. cerevisiae. With regard to non-Saccharomyces yeasts (H. uvarum and Z. bailii) involved in winemaking, the early deaths of these yeasts in mixed cultures with S. cerevisiae were not probably due to the antimicrobial action of chitosan but rather due to ethanol produced by the yeasts. The complex interactions between chitosan and wine ingredients as well as microbial interactions during wine fermentation considerably affect the efficacy of chitosan. It was concluded that chitosan was worthy of further investigation as an alternative or complementary preservative to SO2 in wine industry.