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Kefir is a high nutritional fermented dairy beverage associated with a wide range of health benefits. It constitutes a unique symbiotic association, comprising mainly lactic acid bacteria, yeasts, and occasionally acetic acid bacteria, which is strongly influenced by the geographical origin of the grains, the type of milk used, and the manufacture technology applied. Until recently, kefir microbiota has been almost exclusively studied by culture-dependent techniques. However, high-throughput sequencing, alongside omics approaches, has revolutionized the study of food microbial communities. In the present study, the bacterial, and yeast/fungal microbiota of four home-made samples (both grains and drinks), deriving from well spread geographical regions of Greece, and four industrial beverages, was elucidated by culture-dependent and -independent analyses. In all samples, classical microbiological analysis revealed varying populations of LAB and yeasts, ranging from 5.32 to 9.60 log CFU mL–1 or g–1, and 2.49 to 7.80 log CFU mL–1 or g–1, respectively, while in two industrial samples no yeasts were detected. Listeria monocytogenes , Salmonella spp. and Staphylococcus spp. were absent from all the samples analyzed, whereas Enterobacteriaceae were detected in one of them. From a total of 123 isolates, including 91 bacteria and 32 yeasts, Lentilactobacillus kefiri , Leuconostoc mesenteroides , and Lactococcus lactis as well as Kluvyeromyces marxianus and Saccharomyces cerevisiae were the mostly identified bacterial and yeast species, respectively, in the home-made samples. On the contrary, Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus , and Lacticaseibacillus rhamnosus along with Debaryomyces hansenii and K. marxianus were the main bacterial and yeast species, respectively, isolated from the industrial beverages. In agreement with the identification results obtained from the culture-dependent approaches, amplicon-based metagenomics analysis revealed that the most abundant bacterial genera in almost all home-made samples (both grains and drinks) were Lactobacillus and Lactococcus , while Saccharomyces, Kazachstania , and Kluvyeromyces were the predominant yeasts/fungi. On the other hand, Streptococcus, Lactobacillus , and Lactococcus as well as Kluvyeromyces and Debaryomyces dominated the bacterial and yeast/fungal microbiota, respectively, in the industrial beverages. This is the first report on the microbiota of kefir produced in Greece by a holistic approach combining classical microbiological, molecular, and amplicon-based metagenomics analyses. [ABSTRACT FROM AUTHOR]

The microflora of four batches of traditional Greek Graviera cheese was studied at 5 weeks of ripening, and 200 lactic acid bacteria (LAB) isolates were phenotypically characterized and screened for antilisterial bacteriocins. The cheeses were also analyzed for organic acids by high-performance liquid chromatography and for the potential presence of 25 known LAB bacteriocin genes directly in cheese and their microbial consortia by PCR. All batches were safe according to the European Union regulatory criteria for Listeria mohocytogenes, Salmonella, enterobacteria, and coagulase-positive staphylococci. The cheese flora was dominated by nonstarter Lactobacillus caseilparacasei (67.5%) and Lactobacillus plantarum (16.3%) strains, whereas few Streptococcus thermophilus (3.8%), Lactococcus lactis subsp. lactis (0.6%), and Leuconostoc (1.9%) organisms were present. Enterococcus faecium (9.4%) and Enterococcus durans (0.6%) were isolated among the dominant LAB from two batches; however, enterococci were present in all batches at 10- to 100-fold lower populations than mesophilic lactobacilli. Sixteen E. faecium isolates produced antilisterial enterocins. In accordance, enterocin B gene was detectable in all cheeses and enterocin P gene was present in one cheese, whereas the consortia of all cheeses contained at least two of the enterocin A, B, P, 31, L50A, and L50B genes. Plantaricin A gene was also amplified from all cheeses. Mean concentrations of lactic, acetic, citric, and propionic acids in the ripened cheeses exceeded 1.5% in total, of which approximately 0.9% was lactate. Thus, organic acid contents constitute an important hurdle factor for inhibiting growth of pathogens in traditional Graviera cheese products, with LAB bacteriocins, mainly enterocins, potentially contributing to increased cheese safety. [ABSTRACT FROM AUTHOR]

Highlights • Microemulsions based on four essential oils were used to encapsulate nisin. • Structural changes were revealed regarding the micellar interface flexibility. • Nisin loaded systems showed antimicrobial efficacy against pathogens. • Dittany-based microemulsions had the best antimicrobial efficacy against pathogens. • The system's antimicrobial efficacy depended on microemulsions' characteristics. Abstract During the last years, the food industry is working on the replacement of high energy methodologies with more sustainable techniques for the encapsulation of natural preservatives, in order to enhance their effectiveness as food additives. In the present study, nisin, an antimicrobial agent, was encapsulated in essential oil-containing microemulsions. More specifically, rosemary, thyme, oregano, and dittany essential oil-containing microemulsions were formulated to encapsulate nisin enhancing the system's overall antimicrobial activity. The systems were investigated for the interfacial properties and size of the surfactants' monolayer using electron paramagnetic resonance spectroscopy and dynamic light scattering. Subsequently, nisin-loaded microemulsions were tested for their antimicrobial activity against Lactococcus lactis , Staphylococcus aureus, Listeria monocytogenes, and Bacillus cereus, using the well diffusion assay. Finally, this technique was validated by a killing assay. Overall, this study provides important information on the antibacterial activity of nisin-loaded nano-carriers enhanced by essential oils, in relation to the microemulsions' structure. [ABSTRACT FROM AUTHOR]

Reverse micelles (RMs) as nanocarriers of nisin were optimized for the highest water and bacteriocin content. RMs formulated with either refined olive oil or sunflower oil, distilled monoglycerides, ethanol, and water were effectively designed. Structural characterization of the RMs was assessed using Electron Paramagnetic Resonance Spectroscopy and Small Angle X-ray Scattering in the presence and absence of nisin. No conformational changes occurred in the presence of nisin for the nanocarriers. To assess efficacy of the loaded systems, their antimicrobial activity against Staphylococcus aureus and Listeria monocytogenes was tested in lettuce leaves and minced meat, respectively. Antimicrobial activity was evident in both cases. Interestingly, a synergistic antimicrobial effect was observed in lettuce leaves and to a lesser extent in minced meat between nisin and some of the nanocarriers’ constituents (probably ethanol). Our findings suggest complex interactions that take place when RMs are applied in different food matrices. [ABSTRACT FROM AUTHOR]