Genotypic and technological characterization of Leuconostoc isolates to be used as adjunct starters in Manchego cheese manufacture

Onopordum platylepis (Murb.) Murb. as a novel source of thistle rennet: First application to the manufacture of traditional Italian raw ewe's milk cheese

In this study, for the very first time, aqueous extracts obtained from flowers of spontaneously grown or cultivated Onopordum platylepis (Murb.) Murb. thistles were used as coagulating agents for the pilot-scale manufacture of Caciofiore, a traditional Italian raw ewe's milk cheese. Cheese prototypes were compared to control cheeses curdled with a commercial thistle rennet obtained from flowers of Cynara cardunculus L. After 45 days of ripening under controlled conditions, both the experimental and control cheese prototypes were analyzed for: cheese yield, physico-chemical (pH, titratable acidity, aw, proximate composition), morpho-textural (color and texture), and microbiological parameters (viable cell counts and species composition assessed by Illumina sequencing), as well as volatile profile by SPME-GC-MS. Slight variations in titratable acidity, color, and texture were observed among samples. Based on the results overall collected, neither the yield nor the proximate composition was apparently affected by the type of thistle coagulant. However, the experimental cheese prototypes curdled with extracts from flowers of both spontaneous or cultivated thistles showed 10 % higher values of water-soluble nitrogen compared to the control prototypes. On the other hand, these latter showed slightly higher loads of presumptive lactococci, thermophilic cocci, coliforms, and eumycetes, but lower counts of Escherichia coli. No statistically significant differences were revealed by the metataxonomic analysis of the bacterial and fungal biota. Though most volatile organic compounds (VOCs) were consistent among the prototypes, significant variability was observed in the abundance of some key aroma compounds, such as butanoic, hexanoic, and octanoic acids, ethanol, propan-2-ol, isobutyl acetate, 2-methyl butanoic acid, and 3-methyl butanal. However, further investigations are required to attribute these differences to either the type of coagulant or the metabolic activity of the microorganisms occurring in the analyzed cheese samples. The results overall collected support the potential exploitation of O. platylepis as a novel source of thistle coagulant to produce ewe's milk cheeses.

The role of fermentation with lactic acid bacteria in quality and health effects of plant-based dairy analogues

The modern food industry is undergoing a rapid change with the trend of production of plant-based food products that are more sustainable and have less impact on nature. Plant-based dairy analogues have been increasingly popular due to their suitability for individuals with milk protein allergy or lactose intolerance and those preferring a plant-based diet. Nevertheless, plant-based products still have insufficient nutritional quality, undesirable structure, and earthy, green, and bean-like flavor compared to dairy products. In addition, most plant-based foods contain lesser amounts of essential nutrients, antinutrients limiting the bioavailability of some nutrients, and allergenic proteins. Novel processing technologies can be applied to have a homogeneous and stable structure. On the other hand, fermentation of plant-based matrix with lactic acid bacteria can provide a solution to most of these problems. Additional nutrients can be produced and antinutrients can be degraded by bacterial metabolism, thereby increasing nutritional value. Allergenic proteins can be hydrolyzed reducing their immunoreactivity. In addition, fermentation has been found to reduce undesired flavors and to enhance various bioactivities of plant foods. However, the main challenge in the production of fermented plant-based dairy analogues is to mimic familiar dairy-like flavors by producing the major flavor compounds other than organic acids, yielding a flavor profile similar to those of fermented dairy products. Further studies are required for the improvement of the flavor of fermented plant-based dairy analogues through the selection of special microbial cultures and formulations.

Progress and prospects of biopolymers production strategies

In recent decades, biopolymers have garnered significant attention owing to their aptitude as an environmentally approachable precursor for an extensive application. In addition, due to their alluring assets and widespread use, biopolymers have made significant strides in their production based on various sources and forms. This review focuses on the most recent improvements and breakthroughs that have been made in the manufacturing of biopolymers, via sections focusing the most frequented and preferred routes like micro-macro, algae apart from focusing on microbials routes with special attention to bacteria and the synthetic biology avenue of biopolymer production. For ensuring the continued growth of the global polymer industry, promising research trends must be pursued, as well as methods for overcoming obstacles that arise in exploiting the beneficial properties exhibited by a variety of biopolymers.

Analyzing the genetic diversity and biotechnological potential of Leuconostoc pseudomesenteroides by comparative genomics

Leuconostoc pseudomesenteroides is a lactic acid bacteria species widely exist in fermented dairy foods, cane juice, sourdough, kimchi, apple dumpster, caecum, and human adenoid. In the dairy industry, Ln. pseudomesenteroides strains are usually found in mesophilic starter cultures with lactococci. This species plays a crucial role in the production of aroma compounds such as acetoin, acetaldehyde, and diacetyl, thus beneficially affecting dairy technology. We performed genomic characterization of 38 Ln. pseudomesenteroides from diverse ecological niches to evaluate this species' genetic diversity and biotechnological potential. A mere ~12% of genes conserved across 38 Ln. pseudomesenteroides genomes indicate that accessory genes are the driving force for genotypic distinction in this species. Seven main clades were formed with variable content surrounding mobile genetic elements, namely plasmids, transposable elements, IS elements, prophages, and CRISPR-Cas. All but three genomes carried CRISPR-Cas system. Furthermore, a type IIA CRISPR-Cas system was found in 80% of the CRISPR-Cas positive strains. AMBR10, CBA3630, and MGBC116435 were predicted to encode bacteriocins. Genes responsible for citrate metabolism were found in all but five strains belonging to cane juice, sourdough, and unknown origin. On the contrary, arabinose metabolism genes were only available in nine strains isolated from plant-related systems. We found that Ln. pseudomesenteroides genomes show evolutionary adaptation to their ecological environment due to niche-specific carbon metabolism and forming closely related phylogenetic clades based on their isolation source. This species was found to be a reservoir of type IIA CRISPR-Cas system. The outcomes of this study provide a framework for uncovering the biotechnological potential of Ln. pseudomesenteroides and its future development as starter or adjunct culture for dairy industry.

Investigation of the Role of Leuconostoc mesenteroides subsp. cremoris in Periodontitis around Abutments of Fixed Prostheses

This study included the role of Leuconostoc mesenteroides subsp. cremoris in oral diseases such as periodontitis. Material and Method. Isolation and identification of Leuconostoc mesenteroides subsp. cremoris from a saliva sample of twenty patients wearing fixed dental prostheses suffering from periodontitis followed by estimating susceptibility generally to the most common antibiotics and specifically to chlorhexidine (CHX) to determine the MIC of CHX and also screening of the strength of biofilm production under aerobic and anaerobic conditions; here, the study included six groups: Group I: screening of biofilm formation under aerobic condition, Group II: screening the MIC of CHX effect on biofilm formation under aerobic condition, Group III: screening of the MIC of CHX effect on preformed biofilm under aerobic condition, Group IV: screening of biofilm formation under anaerobic condition, Group V: screening of MIC of CHX effect on biofilm formation under anaerobic condition, and Group VI: screening of MIC of CHX effect on preformed biofilm under anaerobic condition. Results. The results showed that about 5 (25%) isolates were identified as L. mesenteroides subsp. cremoris, while 75% are other isolates. Furthermore, susceptibility results to antibiotic showed the sensitivity to penicillin (100%), azithromycin (100%), ciprofloxacin (100%), tetracycline (100%), gentamicin (100%), doxycycline (100%), vancomycin (100%), ofloxacin (60%), chloramphenicol (80%), ampicillin (80%), and cefoxitin (60%). On the other side, the biofilm production assays revealed that all isolates were moderate biofilm former under the aerobic and anaerobic conditions but for the biofilm treated with MIC of CHX, the current study noticed that the strength of the biofilm became weaker in aerobic and anaerobic conditions; regardless, the strength of the biofilm under anaerobic conditions was higher than in that under aerobic conditions, with no significant differences at p ≤ 0.05 depending on the statistical analysis (T-test) before and after the treatment with MIC of CHX in aerobic and anaerobic conditions. Conclusions. The presence of mesenteroides subsp. cremoris in the oral cavity is due to eating foods and vegetables; based on the strength of the biofilm and sensitivity tests, the isolates have less pathogenicity in the oral cavity due to the weakness of the biofilm production and the lack of resistance to antibiotics.

Use of Autochthonous Lactic Acid Bacteria as Starter Culture of Pasteurized Milk Adobera Cheese

Adobera, a genuine, brick-shaped, lightly ripened, unstretched pasta filata-like cheese from Western México, is one of the most important market-share wise but is usually made with raw milk and prepared following artisanal procedures. A pasteurized milk cheese is needed to assess its safety and guarantee standardized quality features. However, no commercial Adobera cheese culture is available, as specific lactic acid bacteria relevant for its production have not been thoroughly identified. This study is aimed at comparing the technological and quality features of Adobera cheeses made with pasteurized milk inoculated with a mixture of autochthonous lactic acid bacteria (Lactobacillus and Leuconostoc strains) to those of traditional raw milk cheeses, hypothesizing that no significant differences would be found between them. Milk pasteurization promoted water retention into the cheese matrix, impacting its texture and color profiles. Raw milk cheeses were harder, more cohesive, and less elastic than pasteurized milk cheeses. Ripening markers were significantly higher in raw milk cheeses at all sampling times, although its evolution over time showed that the starter culture could exhibit similar proteolytic activity than that of native milk microbiota under favorable ripening conditions. The principal component analysis revealed apparent overall differences between raw Adobera cheeses and those made with pasteurized cheese milk.

The Impact of the Adjunct Heat-Treated Starter Culture and Lb. helveticus LH-B01 on the Proteolysis and ACE Inhibitory Activity in Dutch-Type Cheese Model during Ripening

Simple Summary

Adjunct cultures are used in cheesemaking to improve flavour characteristics and accelerating cheese ripening. Different adjunct cultures are capable of producing enzymes with the specificity to hydrolyze caseins, leading to the release of various bioactive compounds. We studied the effect of adjunct heat-treated starter XT–312 and a cheese culture Lb. helveticus LH-B01 on selected physicochemical, microbiological properties, and on proteolysis in cheese models. Additionally, the effect of adjunct cultures on ACE inhibitory activity during ripening was determined. The application of adjunct cultures may be used as functional ingredients in Dutch-type cheese to maintain sufficient bioactive properties and improve proteolysis.

Abstract

Adjunct cultures are used in cheesemaking to improve the sensory characteristics of the ripened cheeses. In addition, it is known that different adjunct cultures are capable of producing enzymes with the specificity to hydrolyze caseins, leading to the release of various bioactive compounds (bioactive peptides, amino acids, etc.). The objective of this study was to evaluate the effect of adjunct heat-treated starter XT–312 and a cheese culture Lb. helveticus LH-B01 on the proteolytic activity and angiotensin converting enzymes inhibitors (ACE) in cheese models during ripening. Seven different cheese models were evaluated for: proteolytic activity using the spectrophotometric method with ortho-phthaldialdehyde (OPA), soluble nitrogen (SN), trichloroacetic acid-soluble nitrogen (TCA-SN) phosphotungstic acid-soluble nitrogen (PTA-SN), total nitrogen (TN), pH, contents of water, fat, as well as for total bacteria count (TBC), count of Lactococcus genus bacteria, count of Lb. helveticus, and number of non-starter lactic acid bacteria (NSLAB). Presence of adjunct bacterial cultures both in the form of a cheese culture LH-B01 and heat-treated XT–312 starter promoted primary and secondary proteolysis, which resulted in acceleration of the ripening process. ACE inhibitory activity and proteolytic activity was the highest throughout of ripening for cheese model with LH-B01 culture. The cheese models with the adjunct heat-treated starter were characterized by lower TBC, NSLAB and lower count of Lactococcus genus bacteria during ripening, compared to control cheeses.

Safety, probiotic properties, antimicrobial activity, and technological performance of Lactobacillus strains isolated from Iranian raw milk cheeses

The objective of this study was to investigate probiotic, antimicrobial, technological and safety properties of lactobacillus strains isolated from local Iranian cheese made from raw milk. Six different samples were prepared, after serial dilution, culture was performed on MRS culture medium. The gram-positive and catalase-negative lactobacillus strains were subjected to grouping and identifying using biochemical tests, carbohydrates fermentation profiles, and 16S rDNA analysis. The results of sequence analysis showed the Lactobacillus spp. belonged to Lactobacillus brevis, Lactobacillus acidophilus, Lactobacillus plantarum, and Lactobacillus casei. After 3 hr incubation at pH=2, 3-6 log units of strains decreased which Lactobacillus acidophilus (B14) and Lactobacillus brevis (B2) showed highest resistance to low pH as well as simulated GIT juices. The highest and lowest hydrophobicity degree was belonged to L. acidophilus (B14) (65.9%) and L. casei (B22) (25.6%), respectively. Also, the highest auto-aggregation and coaggregation were observed in L. acidophilus (B14) (51.3%) and L. plantarum (B20) (43.6%). The adhered percentage of strains varied from 2.5% to 14.6%. L. plantarum (B20) showed highest proteolytic activity followed by L. acidophilus (B14). Also, the highest autolytic activity belonged to L. acidophilus (B14). All of the strains showed low acidifying potential, except for L. acidophilus (B17) which decreased 2.05 unit of pH after 24 hr. The isolates did not show lipolytic activity as well as biogenic amines production (except L. brevis B3). All of the strains were sensitive to chloramphenicol and erythromycin except L. acidophilus (B15) and L. casei (B22). All strains showed no hemolysis activity which make them safe for consumption. Based on the obtained results, L. acidophilus (B14) presented the best probiotic and technological characteristics and is proposed for using as coculture in the dairy industrial.

Technological characterization of indigenous lactic acid bacteria from Moroccan camel milk for their potential use as starter or adjunct culture

This study aimed to isolate lactic acid bacteria (LABs) of technological interest from Moroccan camel milk and select starter or adjunct culture for dairy product manufacturing. The phenotypic and biochemical identification of 47 isolates revealed the existence of ten Lactococcus lactis, eleven Lactobacillus plantarum, three Lactobacillus brevis, two Lactobacillus paracasei, eleven Enterococcus spp., seven Lactococcus spp. and two Lactobacillus spp. Our strains showed a fast acidifying ability (ΔpH ranged between 0.69 ± 0.01 and 1.22 ± 0.05 after 6 h), high proteolytic and autolytic activities (1.93 ± 0.02 to 9.9 ± 0.022 mM glycine and 15.21 ± 2.21% to 83.24 ± 1% respectively), and an important lipolytic and free radical scavenging capacity. Furthermore, they were able to use citrate, to produce exopolysaccharide, and they exhibited antibacterial activity against Gram-negative and Gram-positive pathogenic bacteria and had no hemolytic activity. This study has shown that Moroccan camel milk represents a rich biotope of interesting LABs for dairy products industry.

Impact of NSLAB on Kazakh cheese flavor

Xinjiang is a multiethnic region of China. Traditionally, most ethnic minorities are known to produce and consume cheese. Nomadic people have been reported to use lactic acid bacteria (LAB) for decades to produce fermented dairy products as part of a balanced diet. Non-starter LAB (NSLAB) contribute to different degrees of ripening, depending on the cheese variety. In the present study, we screened three types of NSLAB with good proteolysis and autolytic abilities from traditional Kazakh cheese: Pediococcus acidilactici R3-5, Staphylococcus epidermidis R4-2, and Lactobacillus rhamnosus R9-6. A control (no NSLAB) was also included, resulting in four distinct types of cheese samples. We used gas chromatography-mass spectrometry and the electronic nose system to identify volatile compounds and analyze the effect of NSLAB on cheese flavor at the ripening stage. The physicochemical indicators changed significantly during the ripening of Kazakh cheese. Compared with the control, the protein content, free fatty acid content, pH, flavor compounds, and odor profiles of the test cheeses were significantly different. The major chemical differences among cheeses were the synthesis of some key volatile components (ethyl caprylate, ethyl caprate, myristyl carbonate, capric acid, caprylic acid, nonanal, and benzyl alcohol). NSLAB can be used as an adjunct starter to make Kazakh cheese and the use of NSLAB affected the cheese flavor quality positively.

Microbial Interactions within the Cheese Ecosystem and Their Application to Improve Quality and Safety

The cheese microbiota comprises a consortium of prokaryotic, eukaryotic and viral populations, among which lactic acid bacteria (LAB) are majority components with a prominent role during manufacturing and ripening. The assortment, numbers and proportions of LAB and other microbial biotypes making up the microbiota of cheese are affected by a range of biotic and abiotic factors. Cooperative and competitive interactions between distinct members of the microbiota may occur, with rheological, organoleptic and safety implications for ripened cheese. However, the mechanistic details of these interactions, and their functional consequences, are largely unknown. Acquiring such knowledge is important if we are to predict when fermentations will be successful and understand the causes of technological failures. The experimental use of "synthetic" microbial communities might help throw light on the dynamics of different cheese microbiota components and the interplay between them. Although synthetic communities cannot reproduce entirely the natural microbial diversity in cheese, they could help reveal basic principles governing the interactions between microbial types and perhaps allow multi-species microbial communities to be developed as functional starters. By occupying the whole ecosystem taxonomically and functionally, microbiota-based cultures might be expected to be more resilient and efficient than conventional starters in the development of unique sensorial properties.

Diversity of non-starter lactic acid bacteria in autochthonous dairy products from Western Balkan Countries - Technological and probiotic properties

The aim of this review was to summarize the data regarding diversity of non-starter lactic acid bacteria (NSLAB) isolated from various artisanal dairy products manufactured in Western Balkan Countries. The dairy products examined were manufactured from raw cow's, sheep's or goat's milk or mixed milk, in the traditional way without the addition of commercial starter cultures. Dairy products such as white brined cheese, fresh cheese, hard cheese, yogurt, sour cream and kajmak were sampled in the households of Serbia, Croatia, Slovenia, Bosnia and Herzegovina, Montenegro, and North Macedonia. It has been established that the diversity of lactic acid bacteria (LAB) from raw milk artisanal dairy products is extensive. In the reviewed literature, 28 LAB species and a large number of strains belonging to the Lactobacillus, Lactococcus, Enterococcus, Streptococcus, Pediococcus, Leuconostoc and Weissella genera were isolated from various dairy products. Over 3000 LAB strains were obtained and characterized for their technological and probiotic properties including: acidification and coagulation of milk, production of aromatic compounds, proteolytic activity, bacteriocins production and competitive exclusion of pathogens, production of exopolysaccharides, aggregation ability and immunomodulatory effect. Results show that many of the isolated NSLAB strains had one, two or more of the properties mentioned. The data presented emphasize the importance of artisanal products as a valuable source of NSLAB with unique technological and probiotic features important both as a base for scientific research as well as for designing novel starter cultures for functional dairy food.

Piacentinu Ennese PDO Cheese as Reservoir of Promising Probiotic Bacteria

Piacentinu Ennese is a protected designation of origin (PDO) cheese produced in the surrounding area of Enna (Sicily, Italy), using raw ewe's milk without the addition of any starter cultures. In the present study, the Lactobacillus population of Piacentinu Ennese PDO cheese was in vitro screened in order to select promising probiotic strains to be further used in humans. One hundred and sixty-nine lactic acid bacteria (LAB) were isolated from 90 days ripened cheeses and identified by Rep-PCR genomic fingerprinting, using the (GTG)5-primer, and by MALDI-TOF MS. One hundred and thirteen (113) isolates belonging to QPS-list species were characterized for both safety and functional properties. All tested isolates were considered safe because none showed either gelatinase, DNase, mucinase, or hemolytic activity. Tolerance to lysozyme, bile salts, and acidic conditions, along with ability to survive under simulated gastrointestinal digestion, were observed. In addition, based on antimicrobial activity against pathogens, cell surface characteristics, Caco-2 adhesion abilities, and anti-inflammatory potential, it was possible to confirm the strain-dependent functional aptitude, suggesting that Piacentinu Ennese PDO cheese may be considered a precious source of probiotic candidates.

Improvement of the Sensory Characteristics of Goat Milk Yogurt

The sensory characteristics of goat yogurt could be greatly improved by integrating to a culture typical of yogurt starters, Streptococcus thermophilus, Lactobacillus delbrueckii spp. bulgaricus, with cultures of Leuconostoc lactis. The addition of L. lactis requires the use of the definition of  "fermented milk" to the product, although it is prepared according to the same technology. The experimental plan has designed the use of inoculation with a bacterial concentration of at least 109 , for each microbial species considered, with the aim of increasing the probiotic effect of yogurt and fermented milk. Descriptive analysis of the samples was conducted using the profile sheet obtained applying the consensus profiling method (UNI EN ISO 13299:2010) by a trained panel. The acceptability of our products was evaluated by 62 consumers through 7-points hedonic scale. The results of this study indicated that the addition of L. lactis to the traditional yogurt starter produced a noticeable improvement to the sensory characteristics of fermented goat milk. PRACTICAL APPLICATION: To improve the sensory characteristics of goat's yogurt to make it more acceptable to the consumer and increase market demand we tested the integration of Leuconostoc lactis to typical starter cultures. The experimentation carried out tested different combinations of fermenting microorganisms with the aim of developing a better flavor as compared to that of traditional yogurt, which is often unpleasant to consumers. The addition of L. lactis to the starter culture of the goat's milk results in less aggressive aromatic notes and greater appreciation as confirmed by consumers who tested the product.

Potential of lactic acid bacteria from Pico cheese for starter culture development

Autochthonous lactic acid bacteria may provide a means of promoting the quality and safety of traditional fermented food products, in particular, artisanal cheeses. Pico cheese is an artisanal, dairy specialty of the Azores in risk of disappearing. Efforts to maintain its quality to the requirements of the modern markets are, thus, necessary. Lactic acid bacteria were isolated from artisanal Pico cheese, identified by sequencing of the 16S rRNA gene, and their potential as starter cultures was evaluated by studying their acidification ability, enzymatic activities (caseinolysis, lipolysis and API-ZYM profile), diacetyl and expolysaccharide production, autolysis, antimicrobial activity against Listeria monocytogenes ATCC 7466, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 29523, Pseudomonas aeruginosa ATCC 27853 and Clostridium perfringens ATCC 8357, sensory evaluation of odour formation in milk, syneresis and firmness of the curd. Several of the studied lactic acid bacteria isolates showed interesting properties for practical application as starters in artisanal cheese production. The isolates with the highest number of positive traits and, therefore, the most promising for starter development were Lactococcus lactis ssp. lactis L1C21M1, Lactobacillus paracasei L1B1E3, Leuconostoc pseudomesenteroides L1C1E6, Lactobacillus casei L1A1E5 and L1C1E8.

Isolation and characterization of an exopolysaccharide-producing Leuconostoc citreum strain from artisanal cheese

High molar mass exopolysaccharides (EPS) produced from sucrose by lactic acid bacteria (LAB) are of great interest as natural additives to use in foods, medical and pharmaceutical industry. This study aimed to identify the EPS produced by Leuconostoc citreum L3C1E7 isolated from Pico cheese and characterize the strain for technological and probiotic potential. Purified EPS was isolated from the culture of L. citreum L3C1E7 by ethanol precipitation, with a yield of 520 mg ml^-1 . The EPS-producing strain had a mucoid phenotype and average molecular weight of 5·88 × 10⁶  Da. The structural characterization of the purified EPS was determined by ¹ H, ¹³ C and two-dimensional NMR spectroscopy. EPS was composed of alternating α-(1→6)-linked and α-(1→3)-linked D-glucopyranyl units, suggesting the existence of an alternan. The strain was slow acidifying, produced diacetyl and displayed high esterase/lipase and aminopeptidase activities, which promote the desirable flavours in dairy products. Moreover, L. citreum showed moderate resistance to the adverse conditions of the gastrointestinal (GI) tract and high adhesion to GI cells. This work provides a better understanding of EPS produced by L. citreum and the potential application of EPS-producing strain in food and/or as a probiotic culture. SIGNIFICANCE AND IMPACT OF THE STUDY: Some LAB strains are known to use extracellular glycoside-hydrolase enzymes for synthesizing a diversity of exopolysaccharides (EPS) with potential application as natural additives to foods. Previous studies have identified an EPS-producing Leuconostoc citreum strain with immunomodulatory properties. This work provides a better understanding of EPS produced by this strain and the potential application of the strain in food fermentation and/or as a probiotic culture.

Selection of Leuconostoc strains isolated from artisanal Serrano Catarinense cheese for use as adjuncts in cheese manufacture

BACKGROUND

Serrano Catarinense cheese is a raw bovine milk cheese produced in the region of Santa Catarina, Brazil. Twelve representative strains of Leuconostoc isolated from 20 samples of this artisanal cheese were selected and submitted for evaluation of the acidifying, proteolytic, autolytic, aminopeptidase and lipolytic activities, NaCl and acid resistance, production of dextran and biogenic amines and antimicrobial activity. The aim was to genetically and technologically characterize the Leuconostoc strains in order to use them in mixed starter cultures for cheese manufacture.

RESULTS

Leuconostoc mesenteroides subsp. mesenteroides was the species that accounted for the largest proportion of isolates of Leuconostoc genus. Two leuconostoc isolates stood out in the acidifying activity, with reduction in pH of 1.12 and 1.04 units. The isolates showed low proteolytic and autolytic activity. Most of the isolates were dextran producers, presented good resistance to the salt and pH conditions of the cheese and showed antimicrobial activity against cheese pathogen bacteria, and none of them produced biogenic amines.

CONCLUSION

These results allowed the selection of five strains (UEL 04, UEL 12, UEL 18, UEL 21 and UEL 28) as good candidates for use as adjunct cultures for cheese manufacture. © 2018 Society of Chemical Industry.

Bacterial Communities in Serpa Cheese by Culture Dependent Techniques, 16S rRNA Gene Sequencing and High-throughput Sequencing Analysis

Serpa cheese is one of the traditional regional Portuguese cheeses having the Protected Denomination of Origin (PDO) designation. This study investigated the bacterial community in the traditional Portuguese Serpa cheese. The microorganisms identified at the end of ripening (30 days) mainly were lactic acid bacteria (LAB). Lactobacillus paracasei/Lactobacillus casei was the main species in cheese from PDO registered industries, whereas in non-PDO registered industries Lactobacillus brevis was highlighted, among other LAB. Enterobacteriaceae species were detected at 20% to 40% of the total isolates. The results obtained by high-throughput sequencing analysis confirmed that LAB was the main microbial group, with Lactococcus genus contributing to approximately 40% to 60% of the population, followed by Leuconostoc and Lactobacillus. The Enterobacteriaceae family was also important. The differences between bacterial communities from PDO and non-PDO registered industries suggest that the lack of regulation of the cheese-making practices may influence unfavorably. The new knowledge about bacterial diversity in Serpa cheese could be useful to set up new ripening conditions, which favor the development of desirable microorganisms.

PRACTICAL APPLICATION

The control of the manufacturing process of traditional cheeses can be improved through the knowledge of the bacterial diversity that develops. Thus, the growth of desirable microorganisms can be promoted to homogenize the final product.

Genetic diversity analysis of Leuconostoc mesenteroides from Korean vegetables and food products by multilocus sequence typing

In the present study, 35 Leuconostoc mesenteroides strains isolated from vegetables and food products from South Korea were studied by multilocus sequence typing (MLST) of seven housekeeping genes (atpA, groEL, gyrB, pheS, pyrG, rpoA, and uvrC). The fragment sizes of the seven amplified housekeeping genes ranged in length from 366 to 1414 bp. Sequence analysis indicated 27 different sequence types (STs) with 25 of them being represented by a single strain indicating high genetic diversity, whereas the remaining 2 were characterized by five strains each. In total, 220 polymorphic nucleotide sites were detected among seven housekeeping genes. The phylogenetic analysis based on the STs of the seven loci indicated that the 35 strains belonged to two major groups, A (28 strains) and B (7 strains). Split decomposition analysis showed that intraspecies recombination played a role in generating diversity among strains. The minimum spanning tree showed that the evolution of the STs was not correlated with food source. This study signifies that the multilocus sequence typing is a valuable tool to access the genetic diversity among L. mesenteroides strains from South Korea and can be used further to monitor the evolutionary changes.

Response of Leuconostoc strains against technological stress factors: Growth performance and volatile profiles

The ability of twelve strains belonging to three Leuconostoc species (Leuconostoc mesenteroides, Leuconostoc lactis and Leuconostoc pseudomesenteroides) to grow under diverse sub-lethal technological stress conditions (cold, acidic, alkaline and osmotic) was evaluated in MRS broth. Two strains, Leuconostoc lactis Ln N6 and Leuconostoc mesenteroides Ln MB7, were selected based on their growth under sub-lethal conditions, and volatile profiles in RSM (reconstituted skim milk) at optimal and under stress conditions were analyzed. Growth rates under sub-lethal conditions were strain- and not species-dependent. Volatilomes obtained from the two strains studied were rather diverse. Particularly, Ln N6 (Ln. lactis) produced more ethanol and acetic acid than Ln MB7 (Ln. mesenteroides) and higher amounts and diversity of the rest of volatile compounds as well, at all times of incubation. For the two strains studied, most of stress conditions applied diminished the amounts of ethanol and acetic acid produced and the diversity and levels of the rest of volatile compounds. These results were consequence of the different capacity of the strains to grow under each stress condition tested.

Leuconostoc strains isolated from dairy products: Response against food stress conditions

A systematic study about the intrinsic resistance of 29 strains (26 autochthonous and 3 commercial ones), belonging to Leuconostoc genus, against diverse stress factors (thermal, acidic, alkaline, osmotic and oxidative) commonly present at industrial or conservation processes were evaluated. Exhaustive result processing was made by applying one-way ANOVA, Student's test (t), multivariate analysis by Principal Component Analysis (PCA) and Matrix Hierarchical Cluster Analysis. In addition, heat adaptation on 4 strains carefully selected based on previous data analysis was assayed. The strains revealed wide diversity of resistance to stress factors and, in general, a clear relationship between resistance and Leuconostoc species was established. In this sense, the highest resistance was shown by Leuconostoc lactis followed by Leuconostoc mesenteroides strains, while Leuconostoc pseudomesenteroides and Leuconostoc citreum strains revealed the lowest resistance to the stress factors applied. Heat adaptation improved thermal cell survival and resulted in a cross-resistance against the acidic factor. However, all adapted cells showed diminished their oxidative resistance. According to our knowledge, this is the first study regarding response of Leuconostoc strains against technological stress factors and could establish the basis for the selection of "more robust" strains and propose the possibility of improving their performance during industrial processes.

Genomic Characterization of Dairy Associated Leuconostoc Species and Diversity of Leuconostocs in Undefined Mixed Mesophilic Starter Cultures

Undefined mesophilic mixed (DL-type) starter cultures are composed of predominantly Lactococcus lactis subspecies and 1-10% Leuconostoc spp. The composition of the Leuconostoc population in the starter culture ultimately affects the characteristics and the quality of the final product. The scientific basis for the taxonomy of dairy relevant leuconostocs can be traced back 50 years, and no documentation on the genomic diversity of leuconostocs in starter cultures exists. We present data on the Leuconostoc population in five DL-type starter cultures commonly used by the dairy industry. The analyses were performed using traditional cultivation methods, and further augmented by next-generation DNA sequencing methods. Bacterial counts for starter cultures cultivated on two different media, MRS and MPCA, revealed large differences in the relative abundance of leuconostocs. Most of the leuconostocs in two of the starter cultures were unable to grow on MRS, emphasizing the limitations of culture-based methods and the importance of careful media selection or use of culture independent methods. Pan-genomic analysis of 59 Leuconostoc genomes enabled differentiation into twelve robust lineages. The genomic analyses show that the dairy-associated leuconostocs are highly adapted to their environment, characterized by the acquisition of genotype traits, such as the ability to metabolize citrate. In particular, Leuconostoc mesenteroides subsp. cremoris display telltale signs of a degenerative evolution, likely resulting from a long period of growth in milk in association with lactococci. Great differences in the metabolic potential between Leuconostoc species and subspecies were revealed. Using targeted amplicon sequencing, the composition of the Leuconostoc population in the five commercial starter cultures was shown to be significantly different. Three of the cultures were dominated by Ln. mesenteroides subspecies cremoris. Leuconostoc pseudomesenteroides dominated in two of the cultures while Leuconostoc lactis, reported to be a major constituent in fermented dairy products, was only present in low amounts in one of the cultures. This is the first in-depth study of Leuconostoc genomics and diversity in dairy starter cultures. The results and the techniques presented may be of great value for the dairy industry.

Technological Properties and Biogenic Amines Production by Bacteriocinogenic Lactococci and Enterococci Strains Isolated from Raw Goat's Milk

Technological properties and biogenic amine production were analyzed in 56 bacteriocinogenic lactococci and enterococci strains isolated from raw goat's milk. Fifteen lactococci strains were able to reduce milk pH to 5.3 or lower after 6 h, while enterococci strains were initially slow in producing acids. Lactococcus lactis subsp. lactis GLc06 and three strains of Enterococcus faecalis (GEn20, GEn22, and GEn23) presented high proteolytic activity. L. lactis subsp. lactis GLc06 and E. faecalis GEn22 also showed a high percentage of autolysis after only 4 h, reaching 71.11 and 97.67%, respectively, after 24 h. No strain was able to secrete exopolysaccharides, and L. lactis subsp. lactis GLc22 and 25 of the Enterococcus strains were able to produce diacetyl. L. lactis subsp. lactis GLc05 and 23 of the Enterococcus strains presented a high tolerance to NaCl at 10% (wt/vol). Regarding biogenic amine production, 12 strains (5 lactococci and 7 enterococci) were capable of forming tyramine and 4 strains (1 lactococcus and 3 enterococci) were capable of forming 2-phenylethylamine, but in very low amounts. GLc06 presented great acidifying, proteolytic, and autolytic activities, and GLc05 was capable of growing at high NaCl concentrations (10%, wt/vol), possessing medium autolytic and proteolytic activities. Some enterococci strains produced diacetyl and high autolytic and extracellular proteolytic activities and also presented resistance to high NaCl concentrations. The interesting technological properties presented by some bacteriocinogenic strains can justify their use by the dairy industry, with the aim of ensuring both safety due to bacteriocin production and technological transformations in fermented products.

Genetic diversity, safety and technological characterization of lactic acid bacteria isolated from artisanal Pico cheese

A total of 114 lactic acid bacteria were isolated at one and 21 days of ripening from a traditional raw cow's milk cheese without the addition of starter culture, produced by three artisanal cheese-makers in Azores Island (Pico, Portugal). Identification to species and strain level was accomplished by16S rRNA gene and PFGE analysis. Carbohydrate utilization profiles were obtained with the relevant API kits. Isolates were evaluated according to safety and technological criteria. The most frequently observed genus identified by 16S rRNA sequencing analysis was Enterococcus, whereas API system mostly identified Lactobacillus. The highest percentages of antibiotic resistance were to nalidixic acid (95%), and aminoglycosides (64-87%). All isolates were sensitive to several beta-lactam antibiotics and negative for histamine and DNase production. Gelatinase activity was detected in 49.1% of isolates, 43% were able to degrade casein and 93% were α-hemolytic. Most enterococci presented virulence genes, such as gelE, asaI, ace. Diacetyl production was found to be species dependent and one strain (Leu. citreum) produced exopolysaccharides. Selected strains were further studied for technological application and were found to be slow acid producers in milk and experimental cheeses, a desirable trait for adjunct cultures. Two strains were selected on the basis of technological and safety application as adjunct cultures in cheese production and presented the best cheese aroma and flavor in consumer preference tests. This is the first effort to characterize Pico cheese LAB isolates for potential application as adjunct cultures; the results suggest the potential of two strains to improve the quality of this traditional raw milk product.

Lactic acid microbiota identification in water, raw milk, endogenous starter culture, and fresh Minas artisanal cheese from the Campo das Vertentes region of Brazil during the dry and rainy seasons

Minas artisanal cheese, produced in the Campo das Vertentes region of Brazil, is made from raw milk and endogenous starter cultures. Although this cheese is of great historical and socioeconomic importance, little information is available about its microbiological and physical-chemical qualities, or about its beneficial microbiota. This work was aimed at evaluating the qualities of the cheese and the components used for its production, comparing samples collected during the dry and rainy seasons. We also conducted molecular identification and isolated 50 samples of lactic acid bacteria from cheese (n=21), water (n=3), raw milk (n=9), and endogenous starter culture (n=17). The microbiological quality of the cheese, water, raw milk, and endogenous starter culture was lower during the rainy period, given the higher counts of coagulase-positive Staphylococcus and total and thermotolerant coliforms. Enterococcus faecalis was the lactic acid bacteria isolated most frequently (42.86%) in cheese samples, followed by Lactococcus lactis (28.57%) and Lactobacillus plantarum (14.29%). Lactobacillus brevis (5.88%), Enterococcus pseudoavium (5.88%), Enterococcus durans (5.88%), and Aerococcus viridans (5.88%) were isolated from endogenous starter cultures and are described for the first time in the literature. The lactic acid bacteria identified in the analyzed cheeses may inhibit undesirable microbiota and contribute to the safety and flavor of the cheese, but this needs to be evaluated in future research.

Antibiotic Susceptibility Profiles of Dairy Leuconostoc, Analysis of the Genetic Basis of Atypical Resistances and Transfer of Genes In Vitro and in a Food Matrix

In spite of a global concern on the transfer of antibiotic resistances (AR) via the food chain, limited information exists on this issue in species of Leuconostoc and Weissella, adjunct cultures used as aroma producers in fermented foods. In this work, the minimum inhibitory concentration was determined for 16 antibiotics in 34 strains of dairy origin, belonging to Leuconostoc mesenteroides (18), Leuconostoc citreum (11), Leuconostoc lactis (2), Weissella hellenica (2), and Leuconostoc carnosum (1). Atypical resistances were found for kanamycin (17 strains), tetracycline and chloramphenicol (two strains each), and erythromycin, clindamycin, virginiamycin, ciprofloxacin, and rifampicin (one strain each). Surprisingly, L. mesenteroides subsp. mesenteroides LbE16, showed resistance to four antibiotics, kanamycin, streptomycin, tetracycline and virginiamycin. PCR analysis identified tet(S) as responsible for tetracycline resistance in LbE16, but no gene was detected in a second tetracycline-resistant strain, L. mesenteroides subsp. cremoris LbT16. In Leuconostoc mesenteroides subsp. dextranicum LbE15, erythromycin and clindamycin resistant, an erm(B) gene was amplified. Hybridization experiments proved erm(B) and tet(S) to be associated to a plasmid of ≈35 kbp and to the chromosome of LbE15 and LbE16, respectively. The complete genome sequence of LbE15 and LbE16 was used to get further insights on the makeup and genetic organization of AR genes. Genome analysis confirmed the presence and location of erm(B) and tet(S), but genes providing tetracycline resistance in LbT16 were again not identified. In the genome of the multi-resistant strain LbE16, genes that might be involved in aminoglycoside (aadE, aphA-3, sat4) and virginiamycin [vat(E)] resistance were further found. The erm(B) gene but not tet(S) was transferred from Leuconostoc to Enterococcus faecalis both under laboratory conditions and in cheese. This study contributes to the characterization of AR in the Leuconostoc-Weissella group, provides evidence of the genetic basis of atypical resistances, and demonstrates the inter-species transfer of erythromycin resistance.

Pulsed-field gel electrophoresis for Leuconostoc mesenteroides and L. pseudomesenteroides

Pulsed-field gel electrophoresis (PFGE) is a technique using alternating electric fields to help the separation of high molecular weight DNA fragments with a high resolution. This method consists of the digestion of bacterial chromosomal DNA with rare-cutting restriction enzymes and of applying an alternating electrical current between spatially distinct pairs of electrodes. DNA molecules migrate at different speeds according to the size of the fragment. This method is considered as the "gold standard" for genotyping, genetic fingerprinting, epidemiological studies, genome size estimation, and studying radiation-induced DNA damage and repair.

Draft Genome Sequence of Three Antibiotic-Resistant Leuconostoc mesenteroides Strains of Dairy Origin

Leuconostoc mesenteroides is a lactic acid bacterium (LAB) commonly associated with fermented foods. Here, we report the genome sequence of three selected dairy strains, showing atypical antibiotic resistances (AR). Genome analysis provided a better understanding of the genetic bases of AR in Leuconostoc and its potential transferability among foodborne bacteria.

The Good, the Bad, and the Ugly: Tales of Mold-Ripened Cheese

The history of cheese manufacture is a "natural history" in which animals, microorganisms, and the environment interact to yield human food. Part of the fascination with cheese, both scientifically and culturally, stems from its ability to assume amazingly diverse flavors as a result of seemingly small details in preparation. In this review, we trace the roots of cheesemaking and its development by a variety of human cultures over centuries. Traditional cheesemakers observed empirically that certain environments and processes produced the best cheeses, unwittingly selecting for microorganisms with the best biochemical properties for developing desirable aromas and textures. The focus of this review is on the role of fungi in cheese ripening, with a particular emphasis on the yeast-like fungus Geotrichum candidum. Conditions that encourage the growth of problematic fungi such as Mucor and Scopulariopsis as well as Arachnida (cheese mites), and how such contaminants might be avoided, are discussed. Bethlehem cheese, a pressed, uncooked, semihard, Saint-Nectaire-type cheese manufactured in the United Sates without commercial strains of bacteria or fungi, was used as a model for the study of stable microbial succession during ripening in a natural environment. The appearance of fungi during a 60-day ripening period was documented using light and scanning electron microscopy, and it was shown to be remarkably reproducible and parallel to the course of ripening of authentic Saint-Nectaire cheese in the Auvergne region of France. Geotrichum candidum, Mucor, and Trichothecium roseum predominate the microbiotas of both cheese types. Geotrichum in particular was shown to have high diversity in different traditional cheese ripening environments, suggesting that traditional manufacturing techniques selected for particular fungi. This and other studies suggest that strain diversity arises in relation to the lore and history of the regions from which these types of cheeses arose.

Genotypic and technological diversity of Brevibacterium linens strains for use as adjunct starter cultures in 'Pecorino di Filiano' cheese ripened in two different environments

Twenty-two Brevibacterium linens strains isolated from 'Pecorino di Filiano' cheese ripened in two different environments (natural cave and storeroom) were characterized and differentiated for features of technological interest and by genotypic methods, in order to select strains with specific features to be used as surface starter cultures. Results showed significant differences among strains on the basis of physiological and technological features, indicating heterogeneity within the species. A middle-low level of proteolytic activity was observed in 27.3 % of strains, while a small group (9.1 %) showed a high ability. Lipolytic activity was observed at three different temperatures and the highest value was detected at 20 °C with 13.6 % of strains, while an increase in temperature produced a slightly lower lipolysis in all strains. The evaluation of diacetyl production revealed that only 22.8 % of strains showed this ability, and most of them were isolated from product ripened in the natural cave. All strains exhibited only leu-aminopeptidase activity, with values more elevated in strains coming from the natural cave product. The combined analysis of genotypic results with the data obtained by the features of technological interest study established that the random amplified polymorphic DNA (RAPD) clusters obtained were composed not only of different genotypes but of different profiles based on technological properties too. This study demonstrated the importance of the ripening environment that affects the typical features of the artisanal product, leading to the selection of a specific surface microflora. Characterized strains could be associated within surface starters to standardize the production process of cheese, but preserving its typical organoleptic and sensory characteristics and improving the quality of the final product.

A novel multi-locus sequence typing (MLST) protocol for Leuconostoc lactis isolates from traditional dairy products in China and Mongolia

BACKGROUND

Economically, Leuconostoc lactis is one of the most important species in the genus Leuconostoc. It plays an important role in the food industry including the production of dextrans and bacteriocins. Currently, traditional molecular typing approaches for characterisation of this species at the isolate level are either unavailable or are not sufficiently reliable for practical use. Multilocus sequence typing (MLST) is a robust and reliable method for characterising bacterial and fungal species at the molecular level. In this study, a novel MLST protocol was developed for 50 L. lactis isolates from Mongolia and China.

RESULTS

Sequences from eight targeted genes (groEL, carB, recA, pheS, murC, pyrG, rpoB and uvrC) were obtained. Sequence analysis indicated 20 different sequence types (STs), with 13 of them being represented by a single isolate. Phylogenetic analysis based on the sequences of eight MLST loci indicated that the isolates belonged to two major groups, A (34 isolates) and B (16 isolates). Linkage disequilibrium analyses indicated that recombination occurred at a low frequency in L. lactis, indicating a clonal population structure. Split-decomposition analysis indicated that intraspecies recombination played a role in generating genotypic diversity amongst isolates.

CONCLUSIONS

Our results indicated that MLST is a valuable tool for typing L. lactis isolates that can be used for further monitoring of evolutionary changes and population genetics.