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.

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.

Impacts of selected lactic acid bacteria strains on the aroma and bioactive compositions of fermented gilaburu (Viburnum opulus) juices.

Gilaburu fruit and its products have gained popularity due to their nutritional content, taste and health benefits. Even though fermented gilaburu juice is widely preferred and consumed in some regions, there is no detailed study on the optimization of the production conditions of this popular beverage. In this study, gilaburu fruit juices fermented naturally (NFJ) and with three commercial lactic acid bacteria (LAB) (L. plantarum: FJLP, L. delbureckii: FJLD, L. caseii: FJLC) were examined for the first time. The microbial properties, phenolics, aroma compounds, minerals, amino acid contents and sensory properties were examined. It was found that the phenolics and volatiles were richer in the samples fermented with LAB but their amino acid contents were in lower amounts as compared to the NFJ sample. The juices produced with L. plantarum (FJLP) and L. delbrueckii (FJLD) presented better aroma, colour, flavour, and overall acceptability.

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.

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.

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.