Fermented Dairy Research Articles

High-Fat Dairy Products May Decrease the Risk of Chronic Kidney Disease Incidence: A Long-Term Prospective Cohort Study

The association between consumption of dairy products and risk of chronic kidney disease (CKD) is under debate. We aimed to determine the potential effects of total and subtypes of dairy intake on the occurrence of CKD. This study was conducted within the Tehran Lipid and Glucose Study (TLGS) on 2416 CKD-free adults. At baseline, consumption of dairy products was estimated using a validated 168-items semiquantitative food frequency questionnaire. Adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) of CKD were calculated in tertile categories of dairy products. Also, the CKD risk was estimated with multivariable Cox regression to substitute total dairy with other dietary protein sources. During 8.4years of follow-up, the incidence rate of CKD was 21%. The participants' mean (±SD) age was 38 (±13) years and 46% were men. Dietary intakes of total dairy, low-fat dairy, and fermented dairy were not associated with CKD risk. There were significant lower risks of CKD in the highest compared to the lowest tertiles of high-fat dairy (HR=0.76, 95% CI=0.60-0.95) and high-fat milk (HR=0.75, 95% CI=0.59-0.96). However, no significant associations were found between other categories of dairy products and CKD incidence. Substitutions of total dairy with other dietary protein sources were not associated with CKD risk. In this study, higher intakes of high-fat dairy and high-fat milk were associated with lower risks of CKD. No significant associations were found between other dairy products and CKD. More prospective and clinical trials are needed to clarify the issue.

Comparative genomic analysis of Lacticaseibacillus paracasei SMN-LBK from koumiss.

Lacticaseibacillus paracasei SMN-LBK, which was isolated in Xinjiang, has been shown to be a probiotic strain and used as the auxiliary starter for dairy fermentation. Comparative genomic analysis was performed to investigate the metabolic preference and ethanol tolerance mechanisms of L. paracasei SMN-LBK. The results of comparative genomics showed that L. paracasei strains had high conservation and genetic diversity. SMN-LBK encoded various genes related to carbohydrate and amino acid metabolism pathways, which endow this strain with good fermentation potential. In addition, 6 CRISPR sequences and 8 cas proteins were found in SMN-LBK, and these could play vital roles in the immune system. Furthermore, a unique cluster of potential secondary metabolism genes related to bacteriocins was detected in the genome of SMN-LBK, and this could be important for the preservation of fermented foods. Multiple genes related to alcohol tolerance were also identified. In conclusion, our study explained the traits that were previously demonstrated for SMN-LBK as phenotypes and provided a theoretical basis for the application of SMN-LBK in the food industry.

Host-encoded, cell surface-associated exopolysaccharide required for adsorption and infection by lactococcal P335 phage subtypes.

Lactococcus lactis and Lactococcus cremoris compose commercial starter cultures widely used for industrial dairy fermentations. Some lactococcal strains may produce exopolysaccharides (EPS), which have technological applications, including texture production and phage resistance. Two distinct gene clusters associated with EPS production, designated 6073-like and 7127-like, were identified on plasmids in lactococcal strains. Infectivity of two subsets of P335 group phages, distinguished based on their single-component baseplate/receptor-binding protein nucleotide sequences, was correlated to the presence of a host-encoded 6073-like or 7127-like eps gene cluster. Furthermore, phages belonging to these subsets differentially adsorbed to lactococcal strains harboring the respective eps gene cluster. Loss of the respective EPS-encoding plasmid from a fully phage-sensitive strain resulted in loss of phage adsorption and resistance to the phage. Transmission electron microscopy (TEM) showed that the EPS produced by strains encoding the 6073-like or 7127-like eps gene clusters are cell-surface associated, which, coupled with phage plaquing and adsorption data, shows that specific capsular EPS are involved in host recognition by certain P335 phage subgroups. To our knowledge, this is the first description of the involvement of EPS produced via the Wzx/Wzy-dependent pathway in phage sensitivity of L. lactis or L. cremoris. This study also shows strains that do not appear to be phage-related based on plaque formation may still be related by phage adsorption and indicates that optimal formulation of phage-robust cultures should take into account the EPS type of individual strains.

Acquisition strategies for fermentation processes with a low-cost miniaturized NIR-spectrometer from scratch: Issues and challenges

In recent years, low-cost miniaturized NIR spectrometers have become extremely useful for quantification, discrimination and classification problems in many field and industrial application domains. The dairy industry is showing particular interest in using portable near-infrared spectroscopy as a quality assessment method or process analytical tool but, when coming to at-line, in/on-line possibilities there is no effective and explanatory literature that presents how to approach analytical method development, even though handheld spectroscopy is invaluable to evaluate fermentation as a crucial dairy operation.In this study the potential and limits of a handheld spectrometer (1350–2550 nm) in gaining information about a dairy fermentation process were investigated. Kefir is a fermented dairy product of rising interest, due to its health beneficial effects and the complexity of the process which involved chemicals and physical transformations that bring to the final product starting from milk by inoculating the so-called “kefir grains”; although the chemistry and physics involved are convoluted, the process itself can be easily conducted at home. Handheld spectrophotometers could be helpful to determine early stages of fermentation, before visual changes occur; being a helpful tool for the healthy citizen.Spectral characteristics and variability related to different experimental set-up were explored first, for the starting and ending products and then, during the fermentation. Semi-skimmed milk was used as fermentation media. After adding the kefir grains, spectra were acquired at interval times during the evolution of the process that was carried out under temperature control. To catch all the information included in the spectra and to investigate the possibilities of paving the way for process monitoring, different approaches were employed.

Associations between the timing of different foods' consumption with cardiovascular disease and all-cause mortality among adults with sleep disorders.

IntroductionPeople with sleep disorders are under disrupted biological rhythms. Whether changing the timing of specific food consumption contributes to decreasing cardiovascular and all-cause risk is unknown.MethodsA total of 8,005 participants with sleep disorders were selected from the U.S. National Health and Nutrition Examination Survey (NHANES) from 2005 to 2014. Cox proportional hazards regression models were used to analyze the relationship between the consumption time of foods and cardiovascular disease (CVD) and all-cause death. Moreover, equivalent food substitution models were carried out to evaluate the alterations in the risk of CVD mortality for the changed food intake time.ResultsAfter adjusting for multiple confounders, participants who consume red and orange vegetables, starchy vegetables, and fermented dairy in the morning (hazard ratio (HR)red and orange vegetables = 0.45, 95% CI: 0.26–0.81; HRstarchy vegetables = 0.47, 95% CI: 0.25–0.88; HRfermented dairy = 0.57, 95% CI: 0.36–0.89) and milk and eggs in the evening contribute to reducing the likelihood of death from CVD (HRmilk = 0.65, 95% CI: 0.43–0.96; HReggs = 0.72, 95% CI: 0.53–0.98). Iso-calorically switching 0.1 serving of starchy vegetable and fermented dairy and milk intake from one period to another does significantly reduce the mortality risk of CVD.ConclusionHigher intake of red and orange vegetables, starchy vegetables, and fermented dairy in the morning and milk and eggs in the evening confers a lower risk of CVD among individuals with sleep disorders.

Identification of Single and Combined Serum Metabolites Associated with Food Intake.

Assessment of dietary intake is challenging. Traditional methods suffer from both random and systematic errors; thus objective measures are important complements in monitoring dietary exposure. The study presented here aims to identify serum metabolites associated with reported food intake and to explore whether combinations of metabolites may improve predictive models. Fasting blood samples and a 4-day weighed food diary were collected from healthy Swedish subjects (n = 119) self-defined as having habitual vegan, vegetarian, vegetarian + fish, or omnivore diets. Serum was analyzed for metabolites by 1H-nuclear magnetic resonance spectroscopy. Associations between single and combined metabolites and 39 foods and food groups were explored. Area under the curve (AUC) was calculated for prediction models. In total, 24 foods or food groups associated with serum metabolites using the criteria of rho > 0.2, p < 0.01 and AUC ≥ 0.7 were identified. For the consumption of soybeans, citrus fruits and marmalade, nuts and almonds, green tea, red meat, poultry, total fish and shellfish, dairy, fermented dairy, cheese, eggs, and beer the final models included two or more metabolites. Our results indicate that a combination of metabolites improve the possibilities to use metabolites to identify several foods included in the current diet. Combined metabolite models should be confirmed in dose–response intervention studies.

Lactic acid bacteria: an essential probiotic and starter culture for the production of yoghurt

SummaryLactic acid bacteria (LAB) are ubiquitous and integral members of the heterogeneous class of bacteria employed for fermented food and dairy applications such as yoghurt products. LAB are gram‐positive, non‐spore‐forming, non‐respiring but aerotolerant microorganisms that are generally characterised by the production of lactic acid as a key fermentation product. LAB, specifically Lb. bulgaricus, are essential dairy starter cultures for the manufacture of several fermented dairy products such as yoghurt and cheese. In this review, we discuss the importance of LAB as starter cultures and a probiotic for yoghurt production, its mode of metabolism, acidification characteristic, synthesis of lactase (β‐galactosidase) and a perspective on LAB's growth medium for dairy fermentations.

Phenotype testing, genome analysis, and metabolic interactions of three lactic acid bacteria strains existing as a consortium in a naturally fermented milk.

This work reports the characterization of three lactic acid bacteria (LAB) strains –Lactococcus lactis LA1, Lactococcus cremoris LA10, and Lactiplantibacillus plantarum LA30– existing as a stable consortium in a backslopping-inoculated, naturally fermented milk (NFM). This study aimed at uncovering the biochemical and genetic basis of the stability of the consortium and the cooperativity among the strains during milk fermentation. All three strains were subjected to phenotyping, covering the utilization of carbohydrates, enzyme activity, and antibiotic resistance. The strains were grown in milk individually, as well as in all possible combinations, and the resulting fermented product was analyzed for sugars, organic acids, and volatile compounds. Finally, the genomes of the three strains were sequenced and analyzed for genes associated with technological and safety properties. As expected, wide phenotypic diversity was seen between the strains. Lactococcus cremoris LA10 was the only strain to reach high cell densities and coagulate milk alone after incubation at 22°C for 24 h; congruently, it possessed a gene coding for a PrtP type II caseinolytic protease. Compared to any other fermentation, acetaldehyde concentrations were greater by a factor of six when all three strains grew together in milk, suggesting that its production might be the result of an interaction between them. Lactococcus lactis LA1, which carried a plasmid-encoded citQRP operon, was able to utilize milk citrate producing diacetyl and acetoin. No genes encoding virulence traits or pathogenicity factors were identified in any of the strains, and none produced biogenic amines from amino acid precursors, suggesting them to be safe. Lactiplantibacillus plantarum LA30 was susceptible to tetracycline, although it harbors a disrupted antibiotic resistance gene belonging to the tetM/tetW/tetO/tetS family. All three strains contained large numbers of pseudogenes, suggesting that they are well adapted (“domesticated”) to the milk environment. The consortium as a whole or its individual strains might have a use as a starter or as starter components for dairy fermentations. The study of simple consortia, such as that existing in this NFM, can help reveal how microorganisms interact with one another, and what influence they may have on the sensorial properties of fermented products.

Antifungal cultures and metabolites of lactic acid bacteria for use in dairy fermentations

Fungal spoilage limits the shelf life of fermented dairy products. To address the problem, this study explores the potential of lactic acid bacteria as antifungal adjunct cultures in dairy matrices. Strains of lactic acid bacteria (113) representing 19 species were screened for their activity against Penicillium caseifulvum, Aspergillus clavatus and Mucor racemosus in modified MRS medium, milk, and yogurt. Strains of Lactiplantibacillus plantarum, Furfurilactobacillus milii, and Lentilactobacillus parabuchneri inhibited the growth of mycelial fungi. The inhibitory effects of lactic acid bacteria against yeasts were also determined in yogurt with Candida sake, Saccharomyces bayanus, and Torulaspora delbrueckii as challenge strains. The inhibition of yeasts by lactic acid bacteria was strain-specific and unrelated to the activity towards mycelial fungi. Organic acids and hydroxy fatty acids were quantified by liquid chromatograph coupled with refractive index detector and tandem mass spectrometry, respectively. Principal component analysis indicated 10-OH 18: 1 fatty acids and acetate are the main antifungal metabolites and explained over 50 % of the antifungal activity. The correlation analysis of metabolites and mold-free shelf life of milk and yogurt confirmed the role of these compounds. The genomic study analysed genes related to the production of major antifungal metabolites and predicted the formation of 1,2-propanediol and acetate but not of hydroxy unsaturated fatty acids. The findings provide new perspectives on the selection of antifungal strains, the characterization of antifungal metabolites and the exploration of antifungal mechanisms among different species.

Open pangenome of Lactococcus lactis generated by a combination of metagenome-assembled genomes and isolate genomes.

Lactococcus lactis (L. lactis) is a well isolated and cultured lactic acid bacterium, but if utilizing the isolate genomes alone, the genome-based analysis of this taxon would be incomplete, because there are still uncultured strains in some ecological niches. In this study, we recovered 93 high-quality metagenome-assembled genomes (MAGs) of L. lactis from food and human gut metagenomes with a culture-independent method. We then constructed a unified genome catalog of L. lactis by integrating these MAGs with 70 publicly available isolated genomes. Having this comprehensive resource, we assessed the genomic diversity and phylogenetic relationships to further explore the genetic and functional properties of L. lactis. An open pangenome of L. lactis was generated using our genome catalog, consisting of 13,066 genes in total, from which 5,448 genes were not identified in the isolate genomes. The core genome-based phylogenetic analysis showed that L. lactis strains we collected were separated into two main subclades corresponding to two subspecies, with some uncultured phylogenetic lineages discovered. The species disparity was also indicated in PCA analysis based on accessory genes of our pangenome. These various analyzes shed further light on unexpectedly high diversity within the taxon at both genome and gene levels and gave clues about its population structure and evolution. Lactococcus lactis has a long history of safe use in food fermentations and is considered as one of the important probiotic microorganisms. Obtaining the complete genetic information of L. lactis is important to the food and health industry. However, it can naturally inhabit many environments other than dairy products, including drain water and human gut samples. Here we presented an open pan-genome of L. lactis constructed from 163 high-quality genomes obtained from various environments, including MAGs recovered from environmental metagenomes and isolate genomes. This study expanded the genetic information of L. lactis about one third, including more than 5,000 novel genes found in uncultured strains. This more complete gene repertoire of L. lactis is crucial to further understanding the genetic and functional properties. These properties may be harnessed to impart additional value to dairy fermentation or other industries.

Whole genome sequence analysis of bacteriophage P1 that infects the Lactobacillus plantarum.

Phage P1 was isolated from the abnormal fermented liquid using Lactobacillus plantarum (L. plantarum) IMAU10120. To date, genetic knowledge regarding L. plantarum phage diversity is still limited, and further in-depth sequencing analysis of isolated L. plantarum phages can fill this gap. Here, we investigated the whole genome sequence of L. plantarum phage P1, sequenced by Illumina HiSeq platform, to decipher its genomic characteristics and putative DNA packaging mechanism. It was revealed that phage P1 was 73,787bp in length, which was composed of linear double-stranded DNA (dsDNA), and the GC content was 39.17%. Its genome contained 86 coding sequences for various functions, such as adsorption, injection, replication, assembly, and release. Moreover, it was observed that L. plantarum phage P1 utilized the 'cohesive ends' DNA packaging mechanism. This study furthered the genomic knowledge of L. plantarum phages and provided some basis for the control of L. plantarum phages in the dairy fermentation industry.

A structural discovery journey of streptococcal phages adhesion devices by AlphaFold2.

Successful bacteriophage infection starts with specific recognition and adhesion to the host cell surface. Adhesion devices of siphophages infecting Gram-positive bacteria are very diverse and remain, for the majority, poorly understood. These assemblies often comprise long, flexible, and multi-domain proteins, which limits their structural analyses by experimental approaches such as X-ray crystallography and electron microscopy. However, the protein structure prediction program AlphaFold2 is exquisitely adapted to unveil structural and functional details of such molecular machineries. Here, we present structure predictions of whole adhesion devices of five representative siphophages infecting Streptococcus thermophilus, one of the main lactic acid bacteria used in dairy fermentations. The predictions highlight the mosaic nature of these devices that share functional domains for which active sites and residues could be unambiguously identified. Such AlphaFold2 analyses of phage-encoded host adhesion devices should become a standard method to characterize phage-host interaction machineries and to reliably annotate phage genomes.

Orally Ingested Probiotics, Prebiotics, and Synbiotics as Countermeasures for Respiratory Tract Infections in Nonelderly Adults: A Systematic Review and Meta-Analysis.

The impact of gut microbiota-targeted interventions on the incidence, duration, and severity of respiratory tract infections (RTIs) in nonelderly adults, and factors moderating any such effects, are unclear. This systematic review and meta-analysis aimed to determine the effects of orally ingested probiotics, prebiotics, and synbiotics compared with placebo on RTI incidence, duration, and severity in nonelderly adults, and to identify potential sources of heterogeneity. Studies were identified by searching CENTRAL, PubMed, Scopus, and Web of Science up to December 2021. English-language, peer-reviewed publications of randomized, placebo-controlled studies that tested an orally ingested probiotic, prebiotic, or synbiotic intervention of any dose for ≥1 wk in adults aged 18-65y were included. Results were synthesized using intention-to-treat and per-protocol random-effects meta-analysis. Heterogeneity was explored by subgroup meta-analysis and meta-regression. Risk of bias was assessed using the Cochrane risk-of-bias assessment tool for randomized trials version 2 (RoB2). Forty-two manuscripts reporting effects of probiotics (n=38), prebiotics (n=2), synbiotics (n=1) or multiple -biotic types (n=1) were identified (n=9179 subjects). Probiotics reduced the risk of experiencing ≥1 RTI (relative risk=0.91; 95% CI: 0.84, 0.98; P=0.01), and total days (rate ratio=0.77; 95% CI: 0.71, 0.83; P<0.001), duration (Hedges' g = -0.23; 95% CI: -0.39, -0.08; P=0.004), and severity (Hedges' g = -0.16; 95% CI: -0.29, -0.03; P=0.02) of RTIs. Effects were relatively consistent across different strain combinations, doses, and durations, although reductions in RTI duration were larger with fermented dairy as the delivery matrix, and beneficial effects of probiotics were not observed in physically active populations. Overall risk of bias was rated as "some concerns" for most studies. In conclusion, orally ingested probiotics, relative to placebo, modestly reduce the incidence, duration, and severity of RTIs in nonelderly adults. Physical activity and delivery matrix may moderate some of these effects. Whether prebiotic and synbiotic interventions confer similar protection remains unclear due to few relevant studies. This trial was registered at https://www.crd.york.ac.uk/prospero/ as CRD42020220213.

Nonfermented Dairy Intake, but Not Fermented Dairy Intake, Associated with a Higher Risk of Depression in Middle-Age and Older Finnish Men

BackgroundDespite the putative health benefits of fermented dairy products, evidence on the association between fermented dairy and nonfermented dairy intake, and depression incidence is limited. ObjectivesThis study examined cross-sectional and prospective associations between total dairy, fermented dairy, and nonfermented dairy intake with 1) the presence of elevated depressive symptoms and 2) the risk of a future hospital discharge or outpatient diagnosis of depression. MethodsData from 2603 Finnish men (aged 42–60 y), recruited as part of the Kuopio Ischaemic Heart Disease Risk Factor Study, were included. Multivariable logistic regression models were used to examine ORs and 95% CIs for elevated depressive symptoms (Human Population Laboratory scale ≥5 points) at baseline. Cox proportional hazards regression models were used to estimate HRs and 95% CIs between dairy categories and risk of depression diagnoses. ResultsIn cross-sectional analyses, fermented dairy intake in the highest (compared with lowest) tertile was associated with lower odds of having elevated depressive symptoms (adjusted OR: 0.70; 95% CI: 0.52, 0.96). Each 100-g increase in nonfermented dairy intake was associated with higher odds of having elevated depressive symptoms (adjusted OR: 1.06; 95% CI: 1.01, 1.10). During a mean follow-up time of 24 y, 113 males received a diagnosis of depression. After excluding cheese intake, higher fermented dairy intake was associated with a lower risk of depression diagnosis (adjusted HR: 0.62; 95% CI: 0.38, 1.03), which was strengthened after excluding those with elevated depressive symptoms at baseline (adjusted HR: 0.55; 95% CI: 0.31, 0.99), whereas nonfermented dairy intake in the highest tertile was associated with a 2-fold higher risk of depression (adjusted HR: 2.02; 95% CI: 1.20, 3.42). ConclusionsFermented dairy and nonfermented dairy intake were differentially associated with depression outcomes when examined cross-sectionally and over a mean period of 24 y. These findings suggest that dairy fermentation status may influence the association between dairy intake and depression in Finnish men. The KIHD study was registered at clinicaltrials.gov as NCT03221127.

Semantics of Dairy Fermented Foods: A Microbiologist's Perspective.

Food ontologies are acquiring a central role in human nutrition, providing a standardized terminology for a proper description of intervention and observational trials. In addition to bioactive molecules, several fermented foods, particularly dairy products, provide the host with live microorganisms, thus carrying potential “genetic/functional” nutrients. To date, a proper ontology to structure and formalize the concepts used to describe fermented foods is lacking. Here we describe a semantic representation of concepts revolving around what consuming fermented foods entails, both from a technological and health point of view, focusing actions on kefir and Parmigiano Reggiano, as representatives of fresh and ripened dairy products. We included concepts related to the connection of specific microbial taxa to the dairy fermentation process, demonstrating the potential of ontologies to formalize the various gene pathways involved in raw ingredient transformation, connect them to resulting metabolites, and finally to their consequences on the fermented product, including technological, health and sensory aspects. Our work marks an improvement in the ambition of creating a harmonized semantic model for integrating different aspects of modern nutritional science. Such a model, besides formalizing a multifaceted knowledge, will be pivotal for a rich annotation of data in public repositories, as a prerequisite to generalized meta-analysis.

Long-term daily high-protein, drained yoghurt consumption alters abundance of selected functional groups of the human gut microbiota and fecal short-chain fatty acid profiles in a cohort of overweight and obese women

• A cohort of overweight and obese women consumed Skyr daily for 4 months. • This study combines longitudinal analysis, quantitative microbiota profiling, and in-depth fecal metabolite analysis. • Skyr consumption successfully transmitted both starter cultures to the gastrointestinal tract. • Intervention-dependent changes in fecal microbiota composition and short chain fatty acid profiles were linked to metabolites of dairy fermentations. • Skyr consumption had major impact on intestinal microbial cross-feeding. The consumption of fermented foods has gained considerable attention due to the ability to deliver live microbes with specific enzymatic activities, and fermentation metabolites, which might play a role in health promotion or disease prevention. The aim of this study was to determine the impact of long-term daily consumption of a high-protein drained yoghurt (Skyr) on intestinal microbial ecology and fermentation activity in a free-living cohort of overweight and obese women (n = 29). Longitudinal analysis and quantitative microbiota profiling identified time intervals with significantly differentially abundant taxa during intervention that differed in functional activity. Our results suggest that ingestion of Skyr persistently modified intestinal microbial cross-feeding activities which altered fecal short chain fatty acid profiles. This study provides a framework indicating the potential of fermented dairy containing starter cultures, lactose and lactate in individualized nutrition or microbiome engineering due to nutritive and microbial components.

Manganese Modulates Metabolic Activity and Redox Homeostasis in Translationally Blocked Lactococcus cremoris, Impacting Metabolic Persistence, Cell Culturability, and Flavor Formation.

ABSTRACTManganese (Mn) is an essential trace element that is supplemented in microbial media with varying benefits across species and growth conditions. We found that growth of Lactococcus cremoris was unaffected by manganese omission from the growth medium. The main proteome adaptation to manganese omission involved increased manganese transporter production (up to 2,000-fold), while the remaining 10 significant proteome changes were between 1.4- and 4-fold. Further investigation in translationally blocked (TB), nongrowing cells showed that Mn supplementation (20 μM) led to approximately 1.5 X faster acidification compared with Mn-free conditions. However, this faster acidification stagnated within 24 h, likely due to draining of intracellular NADH that coincides with substantial loss of culturability. Conversely, without manganese, nongrowing cells persisted to acidify for weeks, albeit at a reduced rate, but maintaining redox balance and culturability. Strikingly, despite being unculturable, α-keto acid-derived aldehydes continued to accumulate in cells incubated in the presence of manganese, whereas without manganese cells predominantly formed the corresponding alcohols. This is most likely reflecting NADH availability for the alcohol dehydrogenase-catalyzed conversion. Overall, manganese influences the lactococcal acidification rate, and flavor formation capacity in a redox dependent manner. These are important industrial traits especially during cheese ripening, where cells are in a non-growing, often unculturable state.IMPORTANCE In nature as well as in various biotechnology applications, microorganisms are often in a nongrowing state and their metabolic persistence determines cell survival and functionality. Industrial examples are dairy fermentations where bacteria remain active during the ripening phases that can take up to months and even years. Here we investigated environmental factors that can influence lactococcal metabolic persistence throughout such prolonged periods. We found that in the absence of manganese, acidification of nongrowing cells remained active for weeks while in the presence of manganese it stopped within 1 day. The latter coincided with the accumulation of amino acid derived volatile metabolites. Based on metabolic conversions, proteome analysis, and a reporter assay, we demonstrated that the manganese elicited effects were NADH dependent. Overall the results show the effect of environmental modulation on prolonged cell-based catalysis, which is highly relevant to non-growing cells in nature and biotechnological applications.

In Vitro Characterization and Identification of Potential Probiotic Yeasts Isolated from Fermented Dairy and Non-Dairy Food Products.

This study is about the isolation of yeast from fermented dairy and non-dairy products as well as the characterization of their survival in in vitro digestion conditions and tolerance to bile salts. Promising strains were selected to further investigate their probiotic properties, including cell surface properties (autoaggregation, hydrophobicity and coaggregation), physiological properties (adhesion to the HT-29 cell line and cholesterol lowering), antimicrobial activities, bile salt hydrolysis, exopolysaccharide (EPS) producing capability, heat resistance and resistance to six antibiotics. The selected yeast isolates demonstrated remarkable survivability in an acidic environment. The reduction caused by in vitro digestion conditions ranged from 0.7 to 2.1 Log10. Bile salt tolerance increased with the extension in the incubation period, which ranged from 69.2% to 91.1% after 24 h. The ability of the 12 selected isolates to remove cholesterol varied from 41.6% to 96.5%, and all yeast strains exhibited a capability to hydrolyse screened bile salts. All the selected isolates exhibited heat resistance, hydrophobicity, strong coaggregation, autoaggregation after 24 h, robust antimicrobial activity and EPS production. The ability to adhere to the HT-29 cell line was within an average of 6.3 Log10 CFU/mL after 2 h. Based on ITS/5.8S ribosomal DNA sequencing, 12 yeast isolates were identified as 1 strain for each Candida albicans and Saccharomyces cerevisiae and 10 strains for Pichia kudriavzevii.

Exploration of adaptation, evolution and domestication of fermentation microorganisms by applying ancient DNA technology.

Fermentation production is the most primitive application of microorganisms by humans, which is of great significance in human history. However, due to the lack of molecular evidence, the history of human fermentation production and the evolution and domestication of fermentation microorganisms remain to be further investigated. Taking wine and fermented dairy, the two most common types of fermented foods as examples, we introduce the archaeology evidence of fermented foods and the evolution and domestication of fermented microorganisms, introduce the research status of paleomicrobiology and fermented paleomicroorganisms, and explore the feasibility and challenges of the research of ancient fermented microorganisms applying microbial ancient DNA technology, as well as the application potential of ancient DNA capture technology in this field.

Streptococcus thermophilus Phages in Whey Derivatives: From Problem to Application in the Dairy Industry.

Fifteen samples of whey protein concentrate (WPC) were tested against 37 commercial Streptococcus thermophilus strains to detect infective bacteriophages. Seventy-three diverse phages were isolated from 12 samples, characterized by using DNA restriction patterns and host range analyses. Sixty-two of them were classified as cos, two as pac, and nine as 5093, according to PCR multiplex assays. Phage concentration was greater than 104 PFU/g for 25.3% of isolated phages. Seven phages showed an unusual wide host range, being able to infect a high number of the tested strains. Regarding thermal resistance, pac phages were the most sensitive, followed by cos phages, those classified as 5093 being the most resistant. Treatments at 85 °C for 5 min in TMG buffer were necessary to completely inactivate all phages. Results demonstrated that the use, without control, of these whey derivatives as additives in dairy fermentations could be a threat because of the potential phage infection of starter strains. In this sense, these phages constitute a pool of new isolates used to improve the phage resistance of starter cultures applied today in the fermentative industry.