Safety and technological application of autochthonous Streptococcus thermophilus cultures in the buffalo Mozzarella cheese

An integrated approach to explore the microbial biodiversity of natural milk cultures for cheesemaking

The use of natural milk culture (NMC) represents a key factor in Protected Designation of Origin (PDO) Montasio cheese, contributing to its distinctive sensory profile. The complex microbial ecosystem of NMC is the result of heat treatment and incubation conditions, which can vary considerably among different production plants. In this study, the microbiota of NMC collected from 10 PDO Montasio cheese dairies was investigated by employing colony counts and metagenomic analysis. Furthermore, residual sugars, organic acids, and volatile profiles were quantitatively investigated. Results showed that Streptococcus thermophilus was the dominant species in all NMC, and a subdominant population made of other streptococci and Ligilactobacillus salivarius was also present. The incubation temperature appeared to be the main driver of biodiversity in NMC. Metagenomics allowed us to evidence the presence of minor species involving safety (e.g., Staphylococcus aureus) as well as possible functional aspects (Next Generation Probiotics). Statistical analysis based on residual sugars, organic acids, and volatiles' content allowed to correlate the presence of specific microbial groups with metabolites of great technological and sensory relevance, which can contribute to giving value to the artisanal production procedures of NMC and clarify their role in the creation of the characteristics of PDO Montasio cheese.

Potential of Cheese-Associated Lactic Acid Bacteria to Metabolize Citrate and Produce Organic Acids and Acetoin

Lactic acid bacteria (LAB) are pivotal in shaping the technological, sensory, and safety aspects of dairy products. The evaluation of proteolytic activity, citrate utilization, milk pH reduction, and the production of organic compounds, acetoin, and diacetyl by cheese associated LAB strains was carried out, followed by Principal Component Analysis (PCA). Citrate utilization was observed in all Leuconostoc (Le.) mesenteroides, Le. citreum, Lactococcus (Lc.) lactis, Lc. garvieae, and Limosilactobacillus (Lm.) fermentum strains, and in some Lacticaseibacillus (Lact.) casei strains. Most strains exhibited proteolytic activity, reduced pH, and generated organic compounds. Multivariate PCA revealed Le. mesenteroides as a prolific producer of acetic, lactic, formic, and pyruvic acids and acetoin at 30 °C. Enterococcus sp. was distinguished from Lact. casei based on acetic, formic, and pyruvic acid production, while Lact. casei primarily produced lactic acid at 37 °C. At 42 °C, Lactobacillus (L.) helveticus and some L. delbrueckii subsp. bulgaricus strains excelled in acetoin production, whereas L. delbrueckii subsp. bulgaricus and Streptococcus (S.) thermophilus strains primarily produced lactic acid. Lm. fermentum stood out with its production of acetic, formic, and pyruvic acids. Overall, cheese-associated LAB strains exhibited diverse metabolic capabilities which contribute to desirable aroma, flavor, and safety of dairy products.

The microbiota of Mozzarella di Bufala Campana PDO cheese: a study across the manufacturing process

Introduction

Mozzarella di Bufala Campana PDO cheese (MBC) is a globally esteemed Italian cheese. The traditional cheesemaking process of MBC relies on natural whey starter culture, water buffalo's milk, and the local agroecosystem.

Methods

In this study, the microbial ecology of intermediate samples of MBC production, coming from two dairies with slightly different cheesemaking technology (dairy M large producer, and dairy C medium-small), was investigated using 16S rRNA amplicon sequencing. This research aimed to provide insights into the dynamics of microbial consortia involved in various cheesemaking steps.

Results and discussion

All samples, except for raw buffalo milk, exhibited a core microbiome predominantly composed of Streptococcus spp. and Lactobacillus spp., albeit with different ratios between the two genera across the two MBC producers. Notably, the microbiota of the brine from both dairies, analyzed using 16S amplicon sequencing for the first time, was dominated by the Lactobacillus and Streptococcus genera, while only dairy C showed the presence of minor genera such as Pediococcus and Lentilactobacillus. Intriguingly, the final mozzarella samples from both producers displayed an inversion in the dominance of Lactobacillus spp. over Streptococcus spp. in the microbiota compared to curd samples, possibly attributable to the alleviation of thermal stress following the curd stretching step. In conclusion, the different samples from the two production facilities did not exhibit significant differences in terms of the species involved in MBC cheesemaking. This finding confirms that the key role in the MBC cheesemaking process lies with a small-sized microbiome primarily composed of Streptococcus and Lactobacillus spp.

Foodborne Microbial Communities as Potential Reservoirs of Antimicrobial Resistance Genes for Pathogens: A Critical Review of the Recent Literature

Antimicrobial resistance (AMR) is a global and increasing threat to human health. Several genetic determinants of AMR are found in environmental reservoirs, including bacteria naturally associated with widely consumed fermented foods. Through the food chain, these bacteria can reach the gut, where horizontal gene transfer (HGT) can occur within the complex and populated microbial environment. Numerous studies on this topic have been published over the past decades, but a conclusive picture of the potential impact of the non-pathogenic foodborne microbial reservoir on the spread of AMR to human pathogens has not yet emerged. This review critically evaluates a comprehensive list of recent experimental studies reporting the isolation of AMR bacteria associated with fermented foods, focusing on those reporting HGT events, which represent the main driver of AMR spread within and between different bacterial communities. Overall, our analysis points to the methodological heterogeneity as a major weakness impairing determination or a causal relation between the presence of AMR determinants within the foodborne microbial reservoir and their transmission to human pathogens. The aim is therefore to highlight the main gaps and needs to better standardize future studies addressing the potential role of non-pathogenic bacteria in the spread of AMR.

Yogurt-like product from lupine (Lupinus albus L.) milk as an alternative to dairy products

Recently, the number of people suffering from allergy to caw’s milk has increased. Lupine, a plant rich in protein, can be a good alternative product for non-dairy products production. We aimed to obtain a yogurt-like product based on lupine milk and evaluate its properties. Lupine milk was obtained from lupine seeds, egg white protein powder, disaccharides, and starter cultures were added to the milk to obtain yogurt-like products: samples with maltose, samples with lactose, and samples without sugars. Physico-chemical and microbiological characteristics of the products were determined by the standard techniques. Sensory attributes were evaluated by trained panelists. In the study, the effects of egg white protein powder and disaccharides on the activities of starter cultures and the properties of the yogurt-like products obtained were investigated. The relationship between the addition of sugar and the growth of starter cultures was found to be significant (P < 0.05). In terms of physico-chemical, rheological, and microbiological properties, the yogurt-like products obtained from lupine milk with disaccharides demonstrated good results, especially the sample with maltose. Sensory analysis revealed high sensory properties of the yogurt-like products. Yogurt-like products from lupine milk can be used as an alternative to cow’s milk fermented products, but more detailed studies should be conducted on their formulations.

Advantages and disadvantages of non-starter lactic acid bacteria from traditional fermented foods: Potential use as starters or probiotics

Traditional fermented foods are a significant source of starter and/or non-starter lactic acid bacteria (nsLAB). Moreover, these microorganisms are also known for their role as probiotics. The potential of nsLAB is huge; however, there are still challenges to be overcome with respect to characterization and application. In the present review, the most important steps that autochthonous lactic acid bacteria isolated from fermented foods need to overcome, to qualify as novel starter cultures, or as probiotics, in food technology and biotechnology, are considered. These different characterization steps include precise identification, detection of health-promoting properties, and safety evaluation. Each of these features is strain specific and needs to be accurately determined. This review highlights the advantages and disadvantages of nsLAB, isolated from traditional fermented foods, discussing safety aspects and sensory impact.

Biodiversity and succession of lactic microbiota involved in Brazilian buffalo mozzarella cheese production

The biodiversity and succession of lactic acid bacteria (LAB) involved in the production and storage of Brazilian buffalo mozzarella cheese were evaluated. The isolates were characterized by Gram staining and catalase test, by the ability to grow at different conditions: temperatures, pH, concentrations of NaCl, and production of CO₂ from glucose. The biodiversity and succession of 152 LAB isolated during cheese production were evaluated by 16S rRNA gene sequencing, Random Amplified Polymorphic DNA (RAPD-PCR), and Restriction Fragment Length Polymorphism (RFLP-PCR) techniques. Most of the strains grow well at 30 °C and are tolerant to 6.5% of NaCl, and in general, the best pH for growing was 9.6. Leuconostoc mesenteroides, Lacticaseibacillus casei, Limosilactobacillus fermentum, and Enterococcus sp. were prevalent and present in almost all steps of production. The LAB strains are typically found in the traditional Italian cheese, except the Leuconostoc citreum species. Sixty clusters were obtained by RAPD-PCR with 85% of similarity (114 isolates) while most of the LAB was clustered with 100% of similarity by the RFLP-PCR technique. The applied techniques enabled a valuable elucidation of the LAB biodiversity and succession, contributing to a better understanding of the specific microbial cultures with a technological aptitude of this cheese.

The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on fermented foods

An expert panel was convened in September 2019 by The International Scientific Association for Probiotics and Prebiotics (ISAPP) to develop a definition for fermented foods and to describe their role in the human diet. Although these foods have been consumed for thousands of years, they are receiving increased attention among biologists, nutritionists, technologists, clinicians and consumers. Despite this interest, inconsistencies related to the use of the term 'fermented' led the panel to define fermented foods and beverages as "foods made through desired microbial growth and enzymatic conversions of food components". This definition, encompassing the many varieties of fermented foods, is intended to clarify what is (and is not) a fermented food. The distinction between fermented foods and probiotics is further clarified. The panel also addressed the current state of knowledge on the safety, risks and health benefits, including an assessment of the nutritional attributes and a mechanistic rationale for how fermented foods could improve gastrointestinal and general health. The latest advancements in our understanding of the microbial ecology and systems biology of these foods were discussed. Finally, the panel reviewed how fermented foods are regulated and discussed efforts to include them as a separate category in national dietary guidelines.

Application of qPCR for multicopper oxidase gene (MCO) in biogenic amines degradation by Lactobacillus casei

Degradation of undesirable biogenic amines (BAs) in foodstuffs by microorganisms is considered one of the most effective ways of eliminating their toxicity. In this study, we designed two sets of primers for the detection and quantification of the multicopper oxidase gene (MCO), which encodes an enzyme involved in BAs degradation, and endogenous (glyceraldehyde-3-phosphate dehydrogenase) gene (GAPDH) in Lactobacillus casei group by real-time PCR (qPCR). We tested 15 Lactobacillus strains in the screening assays (thus, MCO gene possessing assay (PCR) and monitoring of BAs degradation by HPLC-UV), in which Lactobacillus casei CCDM 198 exhibited the best degradation abilities. For this strain, we monitored the expression of the target gene (MCO) in time (qPCR), the effect of redox treatments (cysteine, ascorbic acid) on the expression of the gene, and the ability to degrade BAs not only in a modified MRS medium (MRS/2) but also in a real food sample (milk). Moreover, decarboxylase activity (ability to form BAs) of this strain was excluded. According to the results, CCDM 198 significantly (P < 0.05) reduced BAs (putrescine, histamine, tyramine, cadaverine), up to 25% decline in 48 h. The highest level of relative expression of MCO (5.21 ± 0.14) was achieved in MRS/2 media with cysteine.