Effect of mesophilic lactobacilli and enterococci adjunct cultures on the final characteristics of a microfiltered milk Swiss-type cheese

Deciphering microbial communities of three Savoyard raw milk cheeses along ripening and regarding the cheese process

Different Savoyard cheeses are granted with PDO (Protected Designation or Origin) and PGI (Protected Geographical Indication) which guarantees consumers compliance with strict specifications. The use of raw milk is known to be crucial for specific flavor development. To unravel the factors influencing microbial ecosystems across cheese making steps, according to the seasonality (winter and summer) and the mode of production (farmhouse and dairy factory ones), gene targeting on bacteria and fungus was used to have a full picture of 3 cheese making technologies, from the raw milk to the end of the ripening. Our results revealed that Savoyard raw milks are a plenteous source of biodiversity together with the brines used during the process, that may support the development of specific features for each cheese. It was shown that rinds and curds have very contrasted ecosystem diversity, composition, and evolution. Ripening stage was selective for some bacterial species, whereas fungus were mainly ubiquitous in dairy samples. All ripening stages are impacted by the type of cheese technologies, with a higher impact on bacterial communities, except for fungal rind communities, for which the technology is the more discriminant. The specific microorganism's abundance for each technology allow to see a real bar-code, with more or less differences regarding bacterial or fungal communities. Bacterial structuration is shaped mainly by matrices, differently regarding technologies while the influence of technology is higher for fungi. Production types showed 10 differential bacterial species, farmhouses showed more ripening taxa, while dairy factory products showing more lactic acid bacteria. Meanwhile, seasonality looks to be a minor element for the comprehension of both microbial ecosystems, but the uniqueness of each dairy plant is a key explicative feature, more for bacteria than for fungus communities.

Screening of Lactiplantibacillus plantarum with High Stress Tolerance and High Esterase Activity and Their Effect on Promoting Protein Metabolism and Flavor Formation in Suanzhayu, a Chinese Fermented Fish

In this study, three Lactiplantibacillus plantarum, namely 3-14-LJ, M22, and MB1, with high acetate esterase activity, acid, salt, and high-temperature tolerance were selected from 708 strains isolated from fermented food. Then, L. plantarum strains MB1, M22, and 3-14-LJ were inoculated at 107 CFU/mL in the model and 107 CFU/g in actual Suanzhayu systems, and the effects during fermentation on the physicochemical properties, amino acid, and volatile substance were investigated. The results showed that the inoculated group had a faster pH decrease, lower protein content, higher TCA-soluble peptides, and total amino acid contents than the control group in both systems (p < 0.05). Inoculation was also found to increase the production of volatile compounds, particularly esters, improve the sour taste, and decrease the bitterness of the product (p < 0.05). L. plantarum M22 was more effective than the other two strains in stimulating the production of isoamyl acetate, ethyl hexanoate, and ethyl octanoate. However, differences were discovered between the strains as well as between the model and the actual systems. Overall, the isolated strains, particularly L. plantarum M22, have good fermentation characteristics and have the potential to become excellent Suanzhayu fermenters in the future.

Slovak Local Ewe's Milk Lump Cheese, a Source of Beneficial Enterococcus durans Strain

Slovak ewe's milk lump cheese is produced from unpasteurized ewe's milk without any added culture. Because of the traditional processing and shaping by hand into a lump, this cheese was given the traditional specialty guaranteed (TSG) label. Up till now, there have existed only limited detailed studies of individual microbiota and their benefits in ewe's milk lump cheese. Therefore, this study has been focused on the beneficial properties and safety of Enterococcus durans strains with the aim to contribute to basic dairy microbiology but also for further application potential and strategy. The total enterococcal count in cheeses reached 3.93 CFU/g (log 10) ± 1.98 on average. Based on a MALDI-TOF mass spectrometry evaluation, the strains were allotted to the species E. durans (score, 1.781-2.245). The strains were gelatinase and hemolysis-negative (γ-hemolysis) and were mostly susceptible to commercial antibiotics. Among the strains, E. durans ED26E/7 produced the highest value of lactase enzyme β-galactosidase (10 nmoL). ED26E/7 was absent of virulence factor genes such as Hyl (hyaluronidase), IS 16 element and gelatinase (GelE). To test safety, ED26E/7 did not cause mortality in Balb/c mice. Its partially purified bacteriocin substance showed the highest inhibition activity/bioactivity against Gram-positive indicator bacteria: the principal indicator Enterococcus avium EA5 (102,400 AU/mL), Staphylococcus aureus SA5 and listeriae (25,600 AU/mL). Moreover, 16 staphylococci (out of 22) were inhibited (100 AU/mL), and the growth of 36 (out of 51) enterococcal indicators was as well. After further technological tests, E. durans ED26E/7, with its bacteriocin substance, can be supposed as a promising additive to dairy products.

Microbial transfers from permanent grassland ecosystems to milk in dairy farms in the Comté cheese area

The specificity of dairy Protected Designation of Origin (PDO) products is related to their “terroir” of production. This relationship needs better understanding for efficient and sustainable productions preserving the agroecological equilibrium of agroecosystems, especially grasslands. Specificity of PDO Comté cheese was related to the diversity of natural raw milk bacterial communities, but their sources need to be determined. It is hypothesized that raw milk indigenous microbial communities may originate from permanent grazed grasslands by the intermediate of dairy cows according to the sequence soil–phyllosphere–teat–milk. This hypothesis was evaluated on a 44 dairy farms network across PDO Comté cheese area by characterizing prokaryotic and fungal communities of these compartments by metabarcoding analysis (16S rRNA gene: V3–V4 region, 18S rRNA gene: V7–V8 region). Strong and significant links were highlighted between the four compartments through a network analysis (0.34 < r < 0.58), and were modulated by soil pH, plant diversity and elevation; but also by farming practices: organic fertilization levels, cattle intensity and cow-teat care. This causal relationship suggests that microbial diversity of agroecosystems is a key player in relating a PDO product to its “terroir”; this under the dependency of farming practices. Altogether, this makes the “terroir” even more local and needs to be considered for production sustainability.

Microbiome Associated with Slovak Traditional Ewe’s Milk Lump Cheese

Worldwide consumers increasingly demand traditional/local products, to which those made from ewe’s milk belong. In Slovakia, dairy products made from ewe’s milk have a long tradition. A total of seventeen farmhouse fresh ewe’s milk lump cheeses from various local farm producers in central Slovakia were sampled at farms and then analyzed. Based on the sequencing data analysis, the phylum Firmicutes dominated (60.92%) in ewe’s lump cheeses, followed with the phylum Proteobacteria (38.23%), Actinobacteria (0.38%) and Bacteroidetes (0.35%). The phylum Firmicutes was represented by six genera, among which the highest amount possessed the genus Streptococcus (41.13%) followed with the genus Lactococcus (8.54%), Fructobacillus (3.91%), Enterococcus (3.18%), Staphylococcus (1.80%) and the genus Brochotrix (0.08%). The phylum Proteobacteria in ewe’s lump cheeses involved eight Gram-negative genera: Pseudomonas, Acinetobacter, Enterobacter, Ewingella, Escherichia-Shigella, Pantoea and Moraxella. The phylum Bacteroidetes involved three genera: Bacteroides, Sphingobacterium and Chrysobacterium. Results presented are original; the microbiome of Slovak ewe’s milk lump cheese has been not analyzed at those taxonomic levels up to now.

Microbial shifts in Minas artisanal cheeses from the Serra do Salitre region of Minas Gerais, Brazil throughout ripening time

The Minas artisanal cheese is a traditional product in its way of producing. Produced in the Minas Gerais state, Brazil, this cheese is made using raw cow's milk with the addition of an endogenous starter culture called "pingo", responsible for inoculating specific microorganisms that could enhance flavor and sensorial aspects. There are seven regions able to produce and commercialize this product - Araxá, Campo das Vertentes, Canastra Cerrado, Serra do Salitre, Serro and Triângulo Mineiro. This study aimed to assess the bacterial community of raw milk, endogenous starter culture and to uncover possible shifts in the bacterial community of the rind and core of cheeses at sixty days of ripening located in the Serra do Salitre region by Illumina MiSeq 16S rRNA gene amplicon sequencing. Raw milk and starter culture are responsible for inoculating specific bacteria into the cheese, with Planococcaceae and Streptococcaceae being prevalent throughout ripening time. The Planococcaceae family seems to develop strong interactions with the Leuconostocaceae family on the surface of these cheeses, and is associated with environmental aspects of the region, probably leading to a microbial signature of these products. Additionally, abiotic factors such as geographical location, moisture and acidity are major drivers in the microbial shift.

Selection of potential probiotic Enterococcus faecium isolated from Portuguese fermented food

Four Enterococcus faecium strains isolated from fermented products were evaluated for potential use as probiotic strains. In addition to efaAfm gene, commonly found in E. faecium food isolates, none of the isolates possessed virulence genes and none had positive reactions for the production of tyramine, histamine, putrescine and cadaverine in the screening medium used. All of these four isolates proved to be resistant to 65 °C. E. faecium 119 did not show antimicrobial activity against any of the target bacteria investigated. E. faecium 85 and 101 inhibited Listeria innocua and E. faecium DSMZ 13590. The strain E. faecium 120 inhibited seven target bacteria (Listeria monocytogenes 7946, L. monocytogenes 7947, L. innocua 2030c, L. innocua NCTC 11286, E. faecium DSMZ 13590, Enterococcus faecalis ATCC 29212 and Staphylococcus aureus ATCC 29213) and was chosen as the representative to assess the ability to survive gastrointestinal tract passage simulation, as well as the protective role of two food matrices (skim milk and Alheira) during its passage. For both matrices used, no significant differences (p<0.05) were obtained between the types of digestion - quick and slow passage simulation. In the skim milk matrix the isolate was reduced to values below the detection limit of the enumeration technique by the end of the two digestions, in contrast to the Alheira matrix, for which isolate 120 showed a reduction of only ca. 1 log CFU/ml. The E. faecium strain 120 was shown to be a potential candidate for further investigations as a potential probiotic culture.

Traditional cheeses: rich and diverse microbiota with associated benefits

The risks and benefits of traditional cheeses, mainly raw milk cheeses, are rarely set out objectively, whence the recurrent confused debate over their pros and cons. This review starts by emphasizing the particularities of the microbiota in traditional cheeses. It then describes the sensory, hygiene, and possible health benefits associated with traditional cheeses. The microbial diversity underlying the benefits of raw milk cheese depends on both the milk microbiota and on traditional practices, including inoculation practices. Traditional know-how from farming to cheese processing helps to maintain both the richness of the microbiota in individual cheeses and the diversity between cheeses throughout processing. All in all more than 400 species of lactic acid bacteria, Gram and catalase-positive bacteria, Gram-negative bacteria, yeasts and moulds have been detected in raw milk. This biodiversity decreases in cheese cores, where a small number of lactic acid bacteria species are numerically dominant, but persists on the cheese surfaces, which harbour numerous species of bacteria, yeasts and moulds. Diversity between cheeses is due particularly to wide variations in the dynamics of the same species in different cheeses. Flavour is more intense and rich in raw milk cheeses than in processed ones. This is mainly because an abundant native microbiota can express in raw milk cheeses, which is not the case in cheeses made from pasteurized or microfiltered milk. Compared to commercial strains, indigenous lactic acid bacteria isolated from milk/cheese, and surface bacteria and yeasts isolated from traditional brines, were associated with more complex volatile profiles and higher scores for some sensorial attributes. The ability of traditional cheeses to combat pathogens is related more to native antipathogenic strains or microbial consortia than to natural non-microbial inhibitor(s) from milk. Quite different native microbiota can protect against Listeria monocytogenes in cheeses (in both core and surface) and on the wooden surfaces of traditional equipment. The inhibition seems to be associated with their qualitative and quantitative composition rather than with their degree of diversity. The inhibitory mechanisms are not well elucidated. Both cross-sectional and cohort studies have evidenced a strong association of raw-milk consumption with protection against allergic/atopic diseases; further studies are needed to determine whether such association extends to traditional raw-milk cheese consumption. In the future, the use of meta-omics methods should help to decipher how traditional cheese ecosystems form and function, opening the way to new methods of risk-benefit management from farm to ripened cheese.

Enterococci as probiotics and their implications in food safety

Enterococci belong to the lactic acid bacteria (LAB) and they are of importance in foods due to their involvement in food spoilage and fermentations, as well as their utilisation as probiotics in humans and slaughter animals. However, they are also important nosocomial pathogens that cause bacteraemia, endocarditis and other infections. Some strains are resistant to many antibiotics and possess virulence factors such as adhesins, invasins, pili and haemolysin. The role of enterococci in disease has raised questions on their safety for use in foods or as probiotics. Studies on the incidence of virulence traits among enterococcal strains isolated from food showed that some can harbour virulence traits, but it is also thought that virulence is not the result of the presence of specific virulence determinants alone, but is rather a more intricate process. Specific genetic lineages of hospital-adapted strains have emerged, such as E. faecium clonal complex (CC) 17 and E. faecalis CC2, CC9, CC28 and CC40, which are high risk enterococcal clonal complexes. These are characterised by the presence of antibiotic resistance determinants and/or virulence factors, often located on pathogenicity islands or plasmids. Mobile genetic elements thus are considered to play a major role in the establishment of problematic lineages. Although enterococci occur in high numbers in certain types of fermented cheeses and sausages, they are not deliberately added as starter cultures. Some E. faecium and E. faecalis strains are used as probiotics and are ingested in high numbers, generally in the form of pharmaceutical preparations. Such probiotics are administered to treat diarrhoea, antibiotic-associated diarrhoea or irritable bowel syndrome, to lower cholesterol levels or to improve host immunity. In animals, enterococcal probiotics are mainly used to treat or prevent diarrhoea, for immune stimulation or to improve growth. From a food microbiological point of view, the safety of the bacteria used as probiotics must be assured, and data on the major strains in use so far indicate that they are safe. The advantage of use of probiotics in slaughter animals, from a food microbiological point of view, lies in the reduction of zoonotic pathogens in the gastrointestinal tract of animals which prevents the transmission of these pathogens via food. The use of enterococcal probiotics should, in view of the development of problematic lineages and the potential for gene transfer in the gastrointestinal tract of both humans and animals, be carefully monitored, and the advantages of using these and new strains should be considered in a well contemplated risk/benefit analysis.