Study of Lactococcus lactis during advanced ripening stages of model cheeses characterized by GC-MS

Natural creaming significantly modulates the metabolomic profile and bacterial community of raw milk: A case study on organic milk for Parmigiano Reggiano PDO

This study analyzed raw milk's microbial community and chemical profile during the natural creaming process of Parmigiano Reggiano production by comparing milk from farms following two different organic certifications. Specifically, the natural creaming process underlined the positive accumulation of potentially pro-dairy bacteria, particularly those of the genera Lactococcus and Streptococcus, and a significant reduction of negative bacterial genera, such as Acinetobacter and Rothia, in the final mix milk. Meanwhile, untargeted metabolomic analysis confirmed the representativeness of lipids and lipid-derivatives as chemical markers involved in the overnight creaming process, with fatty acid esters and long fatty acids enriched in the evening samples. Finally, by using a multi-omics approach, we integrated microbial and metabolomic datasets and identified correlations between specific microbial populations and metabolite changes. This integrative analysis revealed microbial-metabolite interactions that may be a starting point to better understand the pivotal role exerted by milk creaming on the final cheese quality.

Lactic acid fermentation of a novel Sea buckthorn-monk fruit beverage: Phenolic profile, volatile compounds, and antidiabetic and antihypertensive potential

Functional foods offer health benefits that extend beyond basic nutrition, addressing critical public health challenges such as diabetes and hypertension. This study developed a novel lactic acid bacteria (LAB)-fermented beverage integrating sea buckthorn and monk fruit, two bioactive-rich ingredients with complementary properties. Sea buckthorn provides a robust profile of antioxidants, while monk fruit's natural sweetness and low glycemic index make it an ideal ingredient for health-conscious consumers. Three LAB strains (Lactiplantibacillus plantarum (LP), Lacticaseibacillus paracasei (LPC), and Lactobacillus acidophilus (LA) were utilized individually and in combination to evaluate their impact on the beverage's bioactive and functional properties. Phenolic profiling (HPLC) revealed 13 phenolic compounds, with LPC fermentation achieving the highest total polyphenol content (232.50 ± 2.37a). Quinic acid and neochlorogenic acids were most abundant in all samples, with significantly elevated concentrations observed in fermented samples. Remarkably, LAB fermentation induced the formation of kaempferol, a phenolic compound with well-documented therapeutic properties, which was absent in the control. Volatile compound analysis (HS-SPME-GC-MS) and aroma profiling (E-nose) demonstrated that LP and LPC + LA fermentations enhanced key volatile compounds and improved sensory complexity, as corroborated by aroma profiling. The functional properties of the beverage were assessed through α-amylase, α-glucosidase, and angiotensin-converting enzyme (ACE) inhibitory assays. LP and LP + LPC demonstrated superior antidiabetic and antihypertensive potential. A Mantel test confirmed strong correlations between phenolic profiles and bioactivities, substantiating the role of LAB fermentation in enhancing therapeutic potential.

Comparative transcriptomic analysis of the flavor production mechanism in yogurt by traditional starter strains

The synergistic fermentation of milk by Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus is one of the key factors that determines the quality of yogurt. In this study, the mechanism whereby yogurt flavor compounds are produced by a mixture of S. thermophilus SIT-20.S and L. delbrueckii ssp. bulgaricus SIT-17.B were investigated by examining the flavor production, growth, and gene transcription of these strains. The results showed that yogurt produced by a 10:1 mixture of the aforementioned strains had the highest abundance of acetoin, whereas yogurt produced by a 1:1 mixture had the highest abundance of diacetyl and acetaldehyde. In addition, the growth of S. thermophilus SIT-20.S was enhanced in the 10:1 mixture. Transcriptomic analysis revealed differentially expressed genes in the flavor-compound-related pathways of S. thermophilus SIT-20.S and L. delbrueckii ssp. bulgaricus SIT-17.B in yogurts produced by 10:1 and 1:1 mixtures compared with those produced by either strain alone. Mixed fermentations regulated the expression of genes related to glycolysis, resulting in an increase of pyruvate, which is an important precursor for diacetyl and acetoin synthesis. The gene encoding the acetoin reductase (SIT-20S_orf01454) was decreased in S. thermophilus SIT-20.S, which ensured the accumulation of acetoin. In addition, the gene encoding the acetaldehyde dehydrogenase (SIT-20S_orf00949) was upregulated in S. thermophilus SIT-20.S, and the expression of alcohol dehydrogenase (SIT-20S_orf01479; SIT-17B_orf00943) was downregulated in both strains, maintaining the abundance of acetaldehyde. In addition, the gene encoding the NADH oxidase (SIT-17B_orf00860) in L. delbrueckii ssp. bulgaricus SIT-17.B were upregulated, which promoted the accumulation of diacetyl and acetoin. Overall, we characterized the mechanism by which S. thermophilus and L. delbrueckii ssp. bulgaricus synergistically generated yogurt flavor compounds during their production of yogurt and highlighted the importance of appropriate proportions of fermentation starters for improving the flavor of yogurts.

Study of the Microbiome of the Cretan Sour Cream Staka Using Amplicon Sequencing and Shotgun Metagenomics and Isolation of Novel Strains with an Important Antimicrobial Potential

Staka is a traditional Greek sour cream made mostly from spontaneously fermented sheep milk or a mixture of sheep and goat milk. At the industrial scale, cream separators and starter cultures may also be used. Staka is sometimes cooked with flour to absorb most of the fat. In this study, we employed culture-based techniques, amplicon sequencing, and shotgun metagenomics to analyze the Staka microbiome for the first time. The samples were dominated by Lactococcus or Leuconostoc spp. Most other bacteria were lactic acid bacteria (LAB) from the Streptococcus and Enterococcus genera or Gram-negative bacteria from the Buttiauxella, Pseudomonas, Enterobacter, Escherichia-Shigella, and Hafnia genera. Debaryomyces, Kluyveromyces, or Alternaria were the most prevalent genera in the samples, followed by other yeasts and molds like Saccharomyces, Penicillium, Aspergillus, Stemphylium, Coniospotium, or Cladosporium spp. Shotgun metagenomics allowed the species-level identification of Lactococcus lactis, Lactococcus raffinolactis, Streptococcus thermophilus, Streptococcus gallolyticus, Escherichia coli, Hafnia alvei, Streptococcus parauberis, and Enterococcus durans. Binning of assembled shotgun reads followed by recruitment plot analysis of single reads could determine near-complete metagenome assembled genomes (MAGs). Culture-dependent and culture-independent analyses were in overall agreement with some distinct differences. For example, lactococci could not be isolated, presumably because they had entered a viable but not culturable (VBNC) state or because they were dead. Finally, several LAB, Hafnia paralvei, and Pseudomonas spp. isolates exhibited antimicrobial activities against oral or other pathogenic streptococci, and certain spoilage and pathogenic bacteria establishing their potential role in food bio-protection or new biomedical applications. Our study may pave the way for additional studies concerning artisanal sour creams to better understand the factors affecting their production and the quality.

Investigation of the Microbiome of Industrial PDO Sfela Cheese and Its Artisanal Variants Using 16S rDNA Amplicon Sequencing and Shotgun Metagenomics

Sfela is a white brined Greek cheese of protected designation of origin (PDO) produced in the Peloponnese region from ovine, caprine milk, or a mixture of the two. Despite the PDO status of Sfela, very few studies have addressed its properties, including its microbiology. For this reason, we decided to investigate the microbiome of two PDO industrial Sfela cheese samples along with two non-PDO variants, namely Sfela touloumotiri and Xerosfeli. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), 16S rDNA amplicon sequencing and shotgun metagenomics analysis were used to identify the microbiome of these traditional cheeses. Cultured-based analysis showed that the most frequent species that could be isolated from Sfela cheese were Enterococcus faecium, Lactiplantibacillus plantarum, Levilactobacillus brevis, Pediococcus pentosaceus and Streptococcus thermophilus. Shotgun analysis suggested that in industrial Sfela 1, Str. thermophilus dominated, while industrial Sfela 2 contained high levels of Lactococcus lactis. The two artisanal samples, Sfela touloumotiri and Xerosfeli, were dominated by Tetragenococcus halophilus and Str. thermophilus, respectively. Debaryomyces hansenii was the only yeast species with abundance > 1% present exclusively in the Sfela touloumotiri sample. Identifying additional yeast species in the shotgun data was challenging, possibly due to their low abundance. Sfela cheese appears to contain a rather complex microbial ecosystem and thus needs to be further studied and understood. This might be crucial for improving and standardizing both its production and safety measures.

Design and Volatile Compound Profiling of Starter Cultures for Yogurt Preparation

Stable symbiotic starter cultures were created using selected strains of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus with antimicrobial activity against pathogens and necessary antibiotic sensitivity, growth kinetic parameters, and metabolic profiles. The volatile compound profiles of the obtained starter cultures were determined and their specificity was proven depending on the ratio of monocultures in each combination. The influence of the freeze-drying process on the starter cultures in relation to the production of aromatic components was investigated and it was demonstrated that this process had a significant effect on the content of the aroma-forming substances in the fermented milk. However, the influence of the pre-cooling process and crude fat content from 1.5 to 3.0% did not notably affect the levels of volatile compounds synthesized by the selected starter cultures. Comprehensive data for all volatile aromatic metabolites in the fermented milk were also obtained. These designed symbiotic starter cultures can be used to produce traditional Bulgarian yogurt with increased functional and probiotic properties.

Advances in fermented foods revealed by multi-omics: A new direction toward precisely clarifying the roles of microorganisms

Fermented foods generally comprise a complex micro-ecosystem with beneficial microbiota, functional products, and special flavors and qualities that are welcomed globally. Single-omics analysis allows for a comprehensive characterization of the main microbial factors influencing the function, flavor, and quality of fermented foods. However, the species, relative abundance, viability, growth patterns, and metabolic processes of microorganisms vary with changes in processing and environmental conditions during fermentation. Furthermore, the mechanisms underlying the complex interaction among microorganisms are still difficult to completely understand and analyze. Recently, multi-omics analysis and the integration of multiple types of omics data allowed researchers to more comprehensively explore microbial communities and understand the precise relationship between fermented foods and their functions, flavors, and qualities. Multi-omics approaches might help clarify the mechanisms underpinning the fermentation processes, metabolites, and functional components of these communities. This review clarified the recent advances in the roles of microorganisms in fermented foods based on multi-omics data. Current research achievements may allow for the precise control of the whole industrial processing technology of fermented foods, meeting consumers' expectations of healthy products.

Further culture-independent characterization of the lactic microbiota of Serro artisanal cheese

This study aimed to provide a further characterization of the lactic microbiota present in Minas artisanal cheese (MAC) from the Serro region by using culture-independent methods, as a complementary analysis of a previous study. The total DNA extracted from MAC samples (n = 55) was subjected to repetitive extragenic palindromic-PCR (rep-PCR) and PCR-denaturing gradient gel electrophoresis (PCR-DGGE). Rep-PCR analysis showed that core microbiota of Serro MAC was closely related, independent of the production town, farm size, or time of production. The sequencing of PCR-DGGE bands identified the prevalence of Lactococcus lactis in all samples, and Streptococcus salivarius was also identified. Thus, we conclude that when more accurate methods are unavailable, rep-PCR can be used as a culture-independent method to demonstrate if the microbiota is closely related or not among the samples. PCR-DGGE results also matched to the main findings of high-throughput sequencing, previously presented, confirming its confidence to detect the main microbial groups present in the raw milk cheeses.

The Bacterial and Fungal Microbiota of “Robiola di Roccaverano” Protected Designation of Origin Raw Milk Cheese

Robiola di Roccaverano is an artisanal Protected Designation of Origin (PDO) soft cheese made with raw goat’s milk and by the addition of Natural Milk Culture (NMC) to drive the fermentation process. Cheeses collected from five different dairy plants were analyzed for their bacterial and fungal microbiota diversity. Lactococcus lactis and Leuconostoc mesenteroides were the main bacterial population, while Galactomyces candidum and Kluyveromyces marxianus constituted the core mycobiota but many other minor taxa were observed, suggesting a high level of complexity in fungal composition by these cheeses compared to bacteria population.

Omics Approaches to Assess Flavor Development in Cheese

Cheese is characterized by a rich and complex microbiota that plays a vital role during both production and ripening, contributing significantly to the safety, quality, and sensory characteristics of the final product. In this context, it is vital to explore the microbiota composition and understand its dynamics and evolution during cheese manufacturing and ripening. Application of high-throughput DNA sequencing technologies have facilitated the more accurate identification of the cheese microbiome, detailed study of its potential functionality, and its contribution to the development of specific organoleptic properties. These technologies include amplicon sequencing, whole-metagenome shotgun sequencing, metatranscriptomics, and, most recently, metabolomics. In recent years, however, the application of multiple meta-omics approaches along with data integration analysis, which was enabled by advanced computational and bioinformatics tools, paved the way to better comprehension of the cheese ripening process, revealing significant associations between the cheese microbiota and metabolites, as well as their impact on cheese flavor and quality.

Evaluation of the Relationships Between Microbiota and Metabolites in Soft-Type Ripened Cheese Using an Integrated Omics Approach

Cheese ripening is effected by various microorganisms and results in the characteristic flavors of cheese. Owing to the complexity of the microbiota involved, the relationship between microorganisms and components during ripening remains unclear. In this study, metagenomics and metabolomics were integrated to reveal these relationships in three kinds of surface mold-ripened cheeses and two kinds of bacterial smear-ripened cheeses. The microbiota is broadly divided into two groups to correspond with different cheese types. Furthermore, surface mold-ripened cheese showed similar microbiota regardless of the cheese variety, whereas bacterial smear-ripened cheese showed specific microbiota characterized by marine bacteria (MB) and halophilic and alkaliphilic lactic acid bacteria for each cheese variety. In the metabolite analysis, volatile compounds suggested differences in cheese types, although organic acids and free amino acids could not determine the cheese characteristics. On the other hand, Spearman correlation analysis revealed that the abundance of specific bacteria was related to the formation of specific organic acids, free amino acids, and volatile compounds. In particular, MB was positively correlated with esters and pyrazines, indicating their contribution to cheese quality. These methodologies and results further our understanding of microorganisms and allow us to select useful strains for cheese ripening.

Combined proteomics and transcriptomics analysis of Lactococcus lactis under different culture conditions

During industrial handling, Lactococcus lactis needs to adapt to different culture conditions by regulating its metabolic pathways. Modifying culture conditions may be an important way to control the biomass and functional metabolites of lactic acid bacteria. In this study, we identified the differentially expressed genes and proteins of L. lactis under different culture conditions by integrating transcriptomics and proteomics. We also analyzed the data using a bioinformatic approach to reveal the regulatory mechanisms affected by culture conditions. The transcriptome and proteome studies indicated that different culture conditions (fructose, calcium ion, palmitic acid, low pH) affected gene and protein expressions. The levels of differentially expressed proteins did not significantly correlate with the expression levels of their corresponding genes. Our results highlight the importance of comparative transcriptomics and proteomics analyses. In this study, fructose and pH significantly affected sugar metabolism of L. lactis. When lactose was replaced by fructose, fructokinase expression was promoted, and fructose metabolism was accelerated, whereas starch and sucrose metabolism and galactose metabolism system were inhibited. Low pH may be beneficial to homofermentation of L. lactis, which may also metabolize galactose through the tagatose pathway and the Leloir pathway. Fatty acid metabolism and fatty acid biosynthesis were significantly downregulated under calcium ion and palmitic acid. The purine metabolism was upregulated under fructose treatment and downregulated under palmitic acid treatment.

GC-MS analysis of e-cigarette refill solutions: A comparison of flavoring composition between flavor categories

OBJECTIVES

Electronic cigarette refill solutions (e-liquids) are available in various flavor descriptions that can be categorized as fruit, tobacco, and more. Flavors increase sensory appeal, thereby stimulating e-cigarette use, and flavoring ingredients can contribute to e-cigarette toxicity. We aim to inform toxicologists, sensory scientists, and regulators by determining flavoring compounds in e-liquids with various flavors, and compare results between flavor categories.

METHODS

Gas chromatography - mass spectrometry (GC-MS) was used to identify 79 flavorings in 320 e-liquids, classified in 15 flavor categories. Ten flavorings highly prevalent in e-liquids according to information from manufacturers were quantified. Flavoring prevalence was defined as the number of e-liquids with the flavoring as percentage of the total number of e-liquids. The method was validated in terms of specificity, linearity, repeatability, recovery, and sensitivity.

RESULTS

The mean number of flavorings per e-liquid was 6 ± 4. Flavoring prevalence was highest for vanillin (creamy/vanilla flavor), ethyl butyrate (ethereal/fruity), and cis-3-hexenol (fresh/green). Based on similarities in flavoring prevalence, four clusters of categories were distinguished: (1) fruit, candy, alcohol, beverages; (2) dessert, coffee/tea, nuts, sweets; (3) menthol/mint; and (4) spices, tobacco, and unflavored. Categories from cluster 4 generally had less flavorings per e-liquid than fruit, candy, alcohol, beverages (cluster 1) and dessert (cluster 2) (p < 0.05). Flavoring concentrations varied between e-liquids within the categories.

CONCLUSIONS

We evaluated flavoring compositions of 320 e-liquids using a simple GC-MS method. Flavoring prevalence was similar within four clusters of typically fresh/sweet, warm/sweet, fresh/cooling, and non-sweet flavor categories. To compare flavoring concentrations between individual flavor categories, additional research is needed.

Integrated metabonomic-proteomic analysis reveals the effect of glucose stress on metabolic adaptation of Lactococcus lactis ssp. lactis CICC23200

A combined proteomic and metabonomic approach was used to investigate the metabolism of Lactococcus lactis ssp. lactis subjected to glucose stress treatment. A proteomic method was used to determine 1,427 altered proteins, including 278 proteins with increased expression and 255 proteins with decreased expression. A metabonomic approach was adopted to identify 98 altered metabolites, including 62 metabolites with increased expression and 26 metabolites with decreased expression. The integrated analysis indicated that the RNA and DNA mismatch repair process and energy metabolism were enhanced in response to high-glucose stress in L. lactis. Lactococcus lactis responded to glucose stress by up-regulating oxidoreductase activity, which acted on glycosyl bonds, hydrolase activity, and organic acid transmembrane transporter activity. This led to an improvement in the metabolic flux from glucose to pyruvate, lactate, acetate, and maltose. Down-regulation of amino acid transmembrane transporter, aminoacyl-transfer RNA ligase, hydroxymethyl-, formyl-, and related transferase activities resulted in a decrease in the nitrogen metabolism-associated metabolic pathway, which might be related to inhibition of the production of biogenic amines. Overall, we highlight the response of metabolism to glucose stress and provide potential possibilities for the reduced formation of biogenic amines in improved level of sugar in the dairy fermentation industry. Moreover, according to the demand for industrial production, sugar concentration in fermented foods should be higher, or lower, than a set value that is dependent on bacterial strain and biogenic amine yield.

A Double-Blind, Randomized, Placebo-Controlled Trial of Heat-Killed Pediococcus acidilactici K15 for Prevention of Respiratory Tract Infections among Preschool Children

Although some probiotic bacteria have been reported to prevent infections in children, there are few well-designed double-blind studies. Here we evaluated the effects of a probiotic strain of lactic acid bacteria (LAB), Pediococcus acidilactici K15, on viral respiratory tract infections in preschool children. A four-month, randomized, double-blind, placebo-controlled study was performed in 172 healthy children aged 3 to 6 years. Subjects were administered dextrin alone or dextrin including heat-killed K15 (5 × 10¹⁰ bacteria). The number of febrile days was the primary outcome. The number of absent days from preschools and the influenza incidence were secondary outcomes. Secretory IgA (sIgA) concentrations in saliva were measured as an exploratory outcome. The primary and secondary outcomes were not significantly different between both groups. Analyses in children with little intake of fermented foods including LAB showed that the duration of a fever significantly decreased by K15 intake. The salivary sIgA level in the K15 group was maintained significantly higher than it was in the placebo group. The effects of K15 on preventing viral respiratory tract infections were not observed without the restriction of fermented foods intake. However, K15 supported anti-infectious immune systems in children who took less fermented foods and the maintenance of salivary sIgA levels in all subjects.

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.

Short communication: Sensory characteristics and volatile organic compound profile of high-moisture mozzarella made by traditional and direct acidification technology

In the present study, the sensory characteristics and the volatile organic compound (VOC) profiles of high-moisture mozzarella made by different acidification techniques were compared. The cheeses were manufactured at the same dairy by fermentation by autochthonous natural whey starter (traditional backslopping method) and direct acidification with citric acid (the most used industrial technology). Three cheesemaking trials were performed from February to June using raw milk from a single farm. The mozzarella samples were subjected to assessment of the chemical, microbiological, and sensory characteristics and to VOC analysis by headspace solid-phase microextraction coupled to gas chromatography-mass spectrometry. The relevant microbiological differences found between the 2 types of products were reflected in different sensory and VOC profiles. The cheeses were clearly discriminated by the panel, and traditional mozzarella had higher intensity attributes. The most discriminating descriptors were elasticity, overall odor and taste intensity, sour milk and fruity/vegetable odors, sour taste, and aftertaste. Even though some variability was observed among the trials, the VOC profile of traditional product was always much more complex than that obtained by direct acidification. In both products the carbonyl compounds were the most abundant chemical class, accounting for about 50% of the total. In detail, 51 compounds were identified in the entire set of samples, and their contribution to cheese aroma was roughly estimated by calculating the odor activity values on the basis of the odor thresholds available in the literature. The results allowed hypothesizing that only 12 of them could play a primary role. The most important among the odor-active compounds was 3-methyl-butanal that can both derive from metabolism of lactic acid bacteria and yeasts. The results of the study may be very useful in view of European Union PDO labeling of the traditional product, in terms of protecting it from imitations.

High Throughput Sequencing Technologies as a New Toolbox for Deep Analysis, Characterization and Potentially Authentication of Protection Designation of Origin Cheeses?

Protected Designation of Origin (PDO) labeling of cheeses has been established by the European Union (EU) as a quality policy that assures the authenticity of a cheese produced in a specific region by applying traditional production methods. However, currently used scientific methods for differentiating and establishing PDO are limited in terms of time, cost, accuracy and their ability to identify through quantifiable methods PDO fraud. Cheese microbiome is a dynamic community that progressively changes throughout ripening, contributing via its metabolism to unique qualitative and sensorial characteristics that differentiate each cheese. High Throughput Sequencing (HTS) methodologies have enabled the more precise identification of the microbial communities developed in fermented cheeses, characterization of their population dynamics during the cheese ripening process, as well as their contribution to the development of specific organoleptic and physio-chemical characteristics. Therefore, their application may provide an additional tool to identify the key microbial species that contribute to PDO cheeses unique sensorial characteristics and to assist to define their typicityin order to distinguish them from various fraudulent products. Additionally, they may assist the cheese-makers to better evaluate the quality, as well as the safety of their products. In this structured literature review indications are provided on the potential for defining PDO enabling differentiating factors based on distinguishable microbial communities shaped throughout the ripening procedures associated to cheese sensorial characteristics, as revealed through metagenomic and metatranscriptomic studies. Conclusively, HTS applications, even though still underexploited, have the potential to demonstrate how the cheese microbiome can affect the ripening process and sensorial characteristics formation via the catabolism of the available nutrients and interplay with other compounds of the matrix and/or production of microbial origin metabolites and thus their further quality enhancement.

1H NMR Metabolic Profile to Discriminate Pasture Based Alpine Asiago PDO Cheeses

Simple Summary

Nowadays, alpine cheese from grazing dairy herds has a premium market value because consumers perceive its higher degree of healthiness and sustainability. The authenticity of pasture-based cheese should be safeguarded from local hay-based milk analogues. The study aimed at assessing the reliability of proton nuclear magnetic resonance (¹H NMR) to discriminate pasture-based alpine Asiago PDO cheeses of different ripening time from similar hay-based samples processed in the same dairy plant. Cheeses were produced from raw milk collected from grazing or hay-fed alpine dairy herds and they were ripened for 2 (Pressato), 4 (Allevo_4), and 6 (Allevo_6) months. Samples of the cheeses were submitted to wet chemistry and nuclear magnetic resonance analysis. The outcomes of the ¹H NMR spectroscopy were used in a multivariate discriminant procedure. Choline, 2,3-butanediol, lysine, and tyrosine and some residual sugar-like compounds were water-soluble biomarkers of cows’ feeding system. However, the application of ¹H NMR based metabolomics was an effective fingerprinting method to correctly identify only cheese samples with the shortest ripening period. The classification of more aged cheese samples according to the cows’ feeding system was less accurate likely due to the chemical and biochemical changes induced by a prolonged maturation process.

Abstract

The study was carried out in an alpine area of North-Eastern Italy to assess the reliability of proton nuclear magnetic resonance ¹H NMR to fingerprint and discriminate Asiago PDO cheeses processed in the same dairy plant from upland pasture-based milk or from upland hay-based milk. Six experimental types of Asiago cheese were made from raw milk considering 2 cows’ feeding systems (pasture- vs. hay-based milk) and 3 ripening times (2 months, Pressato vs. 4 months, Allevo_4 vs. 6 months, Allevo_6). Samples (n = 55) were submitted to chemical analysis and to ¹H NMR coupled with multivariate canonical discriminant analysis. Choline, 2,3-butanediol, lysine, tyrosine, and some signals of sugar-like compounds were suggested as the main water-soluble metabolites useful to discriminate cheese according to cows’ feeding system. A wider pool of polar biomarkers explained the variation due to ripening time. The validation procedure based on a predictive set suggested that ¹H NMR based metabolomics was an effective fingerprinting tool to identify pasture-based cheese samples with the shortest ripening period (Pressato). The classification to the actual feeding system of more aged cheese samples was less accurate likely due to their chemical and biochemical changes induced by a prolonged maturation process.

Volatile Flavor Compounds Profile and Fermentation Characteristics of Milk Fermented by Lactobacillus delbrueckii subsp. bulgaricus

Lactobacillus delbrueckii subsp. bulgaricus is one of the predominant lactic acid bacterial species used as starter cultures in industrial fermented dairy manufacturing, as it strongly affects the quality of the products. Volatile flavor compound profiles and fermentation characteristics are considered to be the most important indicators for starter culture screening. In the present study, volatile compounds in milk fermented by 17 test strains of L. delbrueckii subsp. bulgaricus and a commercial strain used as a control were identified using solid-phase microextraction (SPME) methods coupled with gas chromatography mass spectrometry (GC-MS). In total, 86 volatile flavor compounds were identified in the fermented milk upon completion of fermentation, including 17 carboxylic acids, 14 aldehydes, 13 ketones, 29 alcohols, 8 esters, and 5 aromatic hydrocarbon compounds. Various volatile flavor compounds (acetaldehyde, 3-methyl-butanal, (E)-2-pentenal, hexanal, (E)-2-octenal, nonanal, 2,3-butanedione, acetoin, 2-heptanone, 2-non-anone, formic acid ethenyl ester) were identified due to their higher odor activity values (>1). In addition, of the 17 test strains of L. delbrueckii subsp. bulgaricus, IMAU20312 (B14) and IMAU62081 (B16) strains exhibited good fermentation characteristics in milk compared with the control strain. The combination of the volatile flavor compound profile and fermentation characteristics in this work could be useful when selecting lactic acid bacteria that may serve as important resources in the development of novel fermented milk products.

Hepatoprotective effects of Lactococcus chungangensis CAU 1447 in alcoholic liver disease

Alcoholic liver disease (ALD) is correlated with alcohol consumption, and ALD progression depends on various factors. Some lactic acid bacteria (LAB) are beneficial for mitigating ALD. However, the valuable effects of LAB-derived dairy products remain unclear. Here, we evaluated the effects of Lactococcus chungangensis CAU 1447 dry cells (CAU 1447) and cream cheese derived from CAU 1447 on ALD progression following long-term alcohol consumption in rats. Oral administration of CAU 1447 and CAU 1447 cream cheese significantly reduced alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, and triglyceride levels. We found that CAU 1447 and CAU 1447 cream cheese downregulated mRNA encoding various cytokines and antioxidative factors in the liver. Oral CAU 1447 cream cheese administration increased short-chain fatty acid, butyrate, and acetate levels in feces. Thus, administration of CAU 1447 and CAU 1447 cream cheese induced hepatoprotective effects, indicating potential applications as a supplement for ALD mitigation.

Shortening Fermentation Period and Quality Improvement of Fermented Fish, Chouguiyu, by Co-inoculation of Lactococcus lactis M10 and Weissella cibaria M3

Chouguiyu, a Chinese traditional fermented fish, is famous for its uniquely strong odor and desirable taste. However, traditional spontaneous fermentation often resulted in contamination and unstable quality of products. In this study, individual or conjunctive inoculation of two indigenous lactic acid bacteria (LAB), Lactococcus lactis M10 and Weissella cibaria M3, was tested for their effect on improving Chouguiyu's quality. It was shown that inoculation would not affect the system's pH, while increased the total bacteria count and lactic acid bacteria amounts. Matrix-assisted laser desorption/ionization time-of-flight mass (MALDI-TOF) analysis results revealed that Lactoc. lactis M10 and W. cibaria M3 could quickly occupy a dominant position in the ecosystem, and Lactoc. lactis M10 played an important role in the control of spoilage bacteria. Volatile basic nitrogen (TVB-N), thiobarbituric acid reactive substances (TBARS), and biogenic amines results also showed that Lactoc. lactis M10 had a positive effect on improving the product's quality. Co-inoculation of Lactoc. lactis M10 and W. cibaria M3 could promote the formation of flavor according to the E-nose and gas chromatography-mass spectrometer (GC-MS) analyses, especially for the aroma-active and key volatile compounds. PCA plots of E-nose and hierarchical clustering analysis of GC-MS profiles revealed that the co-inoculation sample at the fifth day (LW5) was the most similar to the natural fermentation sample at the seventh day (C7). The overall acceptance of LW5 was also the closest to that of C7 in sensory evaluation. In conclusion, mixed starter culture was shown to have a good effect on improving product quality and enhancing flavor with fermentation time shortened by 29%.