Year: 2026
Type: article
Abstract: Background and Objective: The metabolomic profile represents the totality of all low-molecular-weight metabolites. It reflects the physiological state of micro-organisms and their potential for biotechnological uses. The aim of this study was to analyze the metabolomic profile of Lactococcus strains, which allowed the researchers to study the characteristics of these microorganisms. As a result, principles for designing lactic acid bacteria consortia with pronounced production-significant chara-cteristics for the creation of next-generation fermented milk products can be developed. Material and Methods: The study microbes were Lactococcus strains. The content of organic and amino acids in the experimental samples was assessed by capillary electrophoresis. The contents of vitamins, mono- and disaccharides were assessed using high-performance liquid chromatography. Results and Conclusion: The metabolomic profiles of 16 industrially associated Lactococcus strains were analyzed. All strains produced lactic acid, with the highest content observed in Strain Ll1, at 8677.8 mg·kg-1. The experimental samples showed a significant increase in methionine content, with the highest value of 311.2 mg·(100 g)-1 in Strain Ll3 and cystine content, with the highest value of 45.6 mg·(100 g)-1 in Strain Ld1. Strain Lc8 showed the ability to synthesize methionine and cystine, which might be promising in cheese production, since these sulfur-containing amino acids contribute to the aroma and flavor of fermented milk products. This strain produced formic, succinic and acetic acids and could catabolize citric acid and galactose. The Strains Ld1, Ld2 and Ld3 showed galactose accumulation, indicating a lack of enzymatic activity for the oxidation of this monosaccharide. Literature data on variability in vitamin synthesis levels between the strains have been verified. Thus, only Strain Ld2 synthesized vitamin B2, the content of which significantly exceeded the control and reached 103.18 ±2.06 μg·(100 g)-1. Five strains were capable of synthesizing vitamin B6 up to 247.69 ±5.45 μg·(100 g)-1. The vitamin B9 content increased, compared to the control, in eight samples, with maximum values of 69.59 ±1.46 μg·(100 g)-1 for Strains Ll3. The dataset on lactococci metabolomic profiles can serve as a basis for the further development of methodological systems, mathematical models and algorithms for selecting strains for the creation of consortia and the production of products, including those with functional characteristics. The results can serve as a basis for the design of consortia of lactic acid bacteria in biotechnological approaches to produce novel fermented milk products with specific characteristics, including functional ones, which include positive effects on human organs when consumed regularly. Keywords: Lactic acid bacteria, Lactococcus, Functional characteristics, Metabolomic profiles, Metabolites Introduction Fermented dairy products contain various metabolites produced by starter cultures that offer health benefits to the human body. These include organic acids, exopolysacchar-ides, vitamins and nitrogenous compounds such as peptides and amino acids. Metabolites are formed as a result of the vital activity of lactic acid bacteria (LAB), which ferment lactose into lactic acid, hydrolyze proteins and lipids to peptides, amino acids and free fatty acids. Some metabolites can regulate human metabolism, decrease inflammation or include antimicrobial effects [1]. Lactococcus bacteria (Streptococcaceae family) are among industrially asso-ciated bacteria in the dairy industry. They are Gram-positive, facultative anaerobic catalase-negative cocci [2]. Their primary role in fermentation processes includes efficient conversion of lactose into lactic acid, thereby increasing medium acidity, which enhances antimicrobial characteristics and extends the shelf life of the final product [3]. Lactose metabolism occurs via the pentose phosphate pathway and/or the Embden-Meyerhof-Parnas pathway (glycolysis) through the action of the enzyme β-galactosidase, which hydrolyzes lactose into glucose and galactose. Glucose enters glycolysis, forming pyruvate, which is subsequently reduced to L-lactic acid by lactate dehydrogenase. Another major route of lactose catabolism is the pentose phosphate pathway, in which lactose is phosphorylated to lactose-6-phosphate during transport and then cleaved into glucose and galactose-6-phosphate by phospho-β-galactosidase. Then, galactose-6-phosphate is converted into tagetose-6-phosphate by isomerase, which turns into glyceraldehyde-3-phosphate and dihydroxyace-tone phosphate. Glyceraldehyde-3-phosphate enters glycol-ysis and leads to pyruvate and L-lactic acid formation [4]. The accumulation of L-lactic acid leads to a decrease in the pH of the medium, which determines the intensity and pathway of lactic acid fermentation. Other key factors affecting this process are the acidification rate and the presence of oxygen and carbon dioxide in the medium. Within the Genus Lactococcus, L. lactis subsp. lactis stands out for its higher rate of lactose utilization and the ability to ferment maltose and trehalose [2]. Moreover, acid production is indirectly linked to exopolysaccharide (EPS) production. The EPS are high-molecular-weight carbohydrate polymers (either homo or heteropolysaccharides) secreted by microorganisms into the extracellular environment. Their precursors are intermediate metabolites of glycolysis and the pentose phosphate pathway glucose-6-phosphate, fructose-6-phosphate, uridine diphosphate glucose and other nucleotide sugars. Since these intermediates serve as precursors for lactic acid, a competitive relationship for carbohydrate substrates occurs [5]. The highest activity of the enzymatic complex of EPS synthesis is achieved at lower acidity levels during lactate biosynthesis (pH 5.0–5.5) [6, 7]. The production of EPS leads to the formation of a slimy layer surrounding the cell, which forms a colloidal aggregate in the form of an amorphous substance with little or no cell adhesion or a cohesive capsule [8]. Acid formation and then EPS production by Lactococcus spp. contribute to the texture of dairy fermented products, resulting in a smooth, creamy, homogeneous consistency with possibly slight ropiness. Cow milk contains 0.4–0.5 mg·(100 g)-1 of potassium and sodium citrates. Among Lactococcus species, only L. lactis subsp. lactis var. Diacetylactis is capable of citrate metabolism. End products of citrate metabolism include diacetyl, acetoin, 2,3-butanediol, acetaldehyde, ethanol and lactic acid. The induction of the citrate permease catalytic enzyme is caused by the presence of lactic acid rather than citrate, which is synthesized from glucose and citrate under acidic pH conditions [9]. Thus, acid formation affects citrate metabolism. The most valuable metabolic products in this biosynthesis are diacetyl and carbon dioxide, as they improve the texture and flavor of fermented dairy products. Lactococcus species include a limited ability to synthesize amino acids de novo from inorganic carbon sources and are therefore auxotrophic. However, fermented dairy products can be enriched with amino acids through the proteolysis of milk caseins [10]. Extracellular proteinases of Lactococcus hydrolyze caseins into oligopeptides, which are then transported into the cell and cleaved by intracellular peptidases into amino acids [11]. The activity of proteolytic enzymes and transport systems depends on the availability of nitrogen, acidity and the content of free amino acids and is controlled by regulatory systems. Particularly, L. lactis subsp. cremoris cleaves β-casein with the similar protease specificity as L. lactis subsp. lactis, but has less active proteolysis [12]. Amino acids are used for cellular biosynthesis and as precursors of biologically active compounds. Several amino acids are degraded to volatile compounds (aldehydes, ketones and alcohols), which can affect the sensory characteristics of fermented dairy products [12, 13]. Partial hydrolysis of milk proteins by lactococci, with lactose reduction, enhances digestibility in the human gastrointestinal tract (GIT) and may decrease the risk of intolerance, compared to raw milk. Amino acids play a critical role in the synthesis of the bacteriocin of nisin (a polycyclic peptide composed of 34 amino acid residues, including the non-proteinogenic amino acid lanthionine) which is active against a broad spectrum of Gram-positive bacteria [14]. Studies have shown that the presence of amino acids such as alanine, isoleucine, serine, glutamic acid, tyrosine and tryptophan in the culture medium enhances bactericidal activity against strains of Escherichia coli and Staphylococcus aureus [14, 15]. Regarding vitamin biosynthesis, Lactococcus species are largely auxotrophic due to their adaptation to nutrient-rich environments such as milk, where several vitamins are readily available. Nevertheless, certain strains have the ability to synthesize B-group vitamins, such as folates (B9) and riboflavin (B2) [16]. Folate production levels vary significantly between the strains. Efforts to enhance B9 biosynthesis in LAB have involved optimized cultivation conditions and genetic modification through strain selection and metabolic engineering [17]. The ability of Lactococcus strains to produce riboflavin is limited and highly strain-dependent. Some strains function as “riboflavin producers” and are used to enrich dairy products with improved nutritional value, as well as imparting a yellowish color to whey and cheeses [18, 19]. The metabolomic profile reflects the key characteristics of the microorganism that determine its technological potential in dairy production. Industrially associated characteristics of strains include technological significance in the production of dairy products (e.g., fermentation time and viscosity) Understanding the genetic and regulatory mechan
Source: Applied food biotechnology
Language: English
Subfield: Food Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: gold
Estimated APC paid: $200
OpenAlex ID: W7214952016