In vitro Bi-Directional Metabolism of Lactic Acid Bacteria and Finger Millet Polyphenols

It can be expected that extracellular electron transfer to regenerate NAD+ changes the glucose metabolism of the homofermentative lactic acid bacteria. In this work, the glucose metabolism of Lactobacillusplantarum and Lactococcus lactis was examined in resting cells with 2-amino-3-carboxy-1,4-naphthoquinone (ACNQ) as the electron transfer mediator and ferricyanide (Fe(CN)6(3-)) as the extracellular electron acceptor. NADH in the cells was oxidized by ACNQ with the aid of diaphorase, and the reduced ACNQ was reoxidized with Fe(CN)6(3-). The extracellular electron transfer system promoted the generation of pyruvate, acetate, and acetoin from glucose, and restricted lactate production. Diaphorase activity increased when cultivation was aerobic, and this increased the concentrations of pyruvate, acetate, and acetoin relative to the concentration of lactate to increase in the presence of ACNQ and Fe(CN)6(3-)

Abiotic factors modulating metabolic pathways of lactic acid in solid-state fermentation of cereal vinegar

A genomic view on lactic metabolism.

This comprehensive review explores the development of food-grade selection markers in lactic acid bacteria and yeast; some of their strains are precisely defined as safe microorganisms and are crucial in the food industry. Lactic acid bacteria, known for their ability to ferment carbohydrates into lactic acid, provide essential nutrients and contribute to immune responses. With its strong fermentation capabilities and rich nutritional profile, yeast finds use in various food products. Genetic engineering in these microorganisms has grown rapidly, enabling the expression of enzymes and secondary products for food production. However, the focus is on ensuring safety, necessitating food-grade selection markers. Traditional antibiotic and heavy metal resistance selection markers pose environmental and health risks, prompting the search for safer alternatives. Complementary selection markers, such as sugar utilization markers, offer a promising solution. These markers use carbohydrates as carbon sources for growth and are associated with the natural metabolism of lactic acid bacteria and yeast. This review discusses the use of specific sugars, such as lactose, melibiose, sucrose, D-xylose, glucosamine, and N-acetylglucosamine, as selection markers, highlighting their advantages and limitations. In summary, this review underscores the importance of food-grade selection markers in genetic engineering and offers insights into their applications, benefits, and challenges, providing valuable information for researchers in the field of food microbiology and biotechnology.

14 - Enzymatic Activities and Fermentation Products of Lactic Acid Bacteria From Fruits and Fermented Beverages. Incidence on Food Quality

Pyruvate kinase (PYK) is a critical allosterically regulated enzyme that links glycolysis, the primary energy metabolism, to cellular metabolism. Lactic acid bacteria rely almost exclusively on glycolysis for their energy production under anaerobic conditions, which reinforces the key role of PYK in their metabolism. These organisms are closely related, but have adapted to a huge variety of native environments. They include food-fermenting organisms, important symbionts in the human gut, and antibiotic-resistant pathogens. In contrast to the rather conserved inhibition of PYK by inorganic phosphate, the activation of PYK shows high variability in the type of activating compound between different lactic acid bacteria. System-wide comparative studies of the metabolism of lactic acid bacteria are required to understand the reasons for the diversity of these closely related microorganisms. These require knowledge of the identities of the enzyme modifiers. Here, we predict potential allosteric activators of PYKs from three lactic acid bacteria which are adapted to different native environments. We used protein structure-based molecular modeling and enzyme kinetic modeling to predict and validate potential activators of PYK. Specifically, we compared the electrostatic potential and the binding of phosphate moieties at the allosteric binding sites, and predicted potential allosteric activators by docking. We then made a kinetic model of Lactococcus lactis PYK to relate the activator predictions to the intracellular sugar-phosphate conditions in lactic acid bacteria. This strategy enabled us to predict fructose 1,6-bisphosphate as the sole activator of the Enterococcus faecalis PYK, and to predict that the PYKs from Streptococcus pyogenes and Lactobacillus plantarum show weaker specificity for their allosteric activators, while still having fructose 1,6-bisphosphate play the main activator role in vivo. These differences in the specificity of allosteric activation may reflect adaptation to different environments with different concentrations of activating compounds. The combined computational approach employed can readily be applied to other enzymes.

Lactic acid bacteria exopolysaccharide (EPS) is a large molecular polymer produced during the growth and metabolism of lactic acid bacteria. EPS has multiple biological functions and is widely used in fields such as food and medicine. However, the low yield and high production cost of EPS derived from lactic acid bacteria limit its widespread application. In this study, we used beet waste residue as a substrate to produce EPS by fermentation with Leuconostoc pseudomesenteroides to improve the utilization rate of agricultural waste and reduce the production cost of lactic acid bacterial EPS. After purification, the molecular weight (Mw) of EPS was determined to be 417 kDa using high-performance size exclusion chromatography (HPSEC). High-performance liquid chromatography (HPLC), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy revealed that the EPS was composed of glucose subunits with α-1,6 glycosidic linkages. The thermal analysis and heavy metal adsorption capacity revealed a relatively high degradation temperature of 315.54 °C and that the material could effectively adsorb Cu2+. Additionally, the findings indicated that the EPS exhibited a significant ability to neutralize free radicals, a property that was found to be concentration dependent. Furthermore, the results of the intracellular study showed the protective effect of freshly isolated EPS on tBHP-induced cellular oxidative stress at a concentration of 50 µg/mL. These results suggest that the EPS from L. pseudomesenteroides may be developed as antioxidant agents for functional food products and pharmaceutical applications due to its capacity to scavenge free radicals.

Lactic acid fermentation is one of the oldest and most commonly used methods of bioconservation. This process is widely used for food preservation and also for a production technique that relies on the metabolism of lactic acid bacteria (LAB) to convert carbohydrates into lactic acid. This fermentation imparts unique flavors and texture of foods, extends their shelf life, and can offer health benefits. There are both traditional and new microorganisms involved in the lactic acid fermentation of food. The current review outlines the issues of fermented foods. Based on traditional fermentation methods, a broad panorama of various food products is presented, with the microorganisms involved. The methods of both traditional fermentation (spontaneous and back-slopping) as well as the importance and application of starter cultures in mass food production are presented. Currently, based on the results of scientific research, the health-promoting effect of fermented foods is becoming more and more important. This is due to the presence of probiotic microorganisms that are naturally presented or may be added to them, as starter cultures or additives, and from the presence of prebiotics and postbiotics. New innovative methods of using probiotic microorganisms open up new and broad perspectives for fermented functional foods.

Nonstarter lactic acid bacteria volatilomes produced using cheese components

The objects of the study were lactic acid bacteria Lactobacillus lactis and Lactobacillus casei used in the food industry. It is proposed to use an extremely high frequency electromagnetic field (EMF EHF) with a wavelength of 4.9 mm for 5 minutes to activate the metabolism of lactic acid bacteria. The stimulating effect of EMF EHF on the growth of biomass and excretion of lactic acid during the growth was found. Physiological constants characterizing the development of microorganisms have been determined. It was found that the maximum yield from the consumed substrate Ymax increased by 40% and the maximum specific growth rate rmax by 70% when exposed to radiation, the consumption rate for maintenance ms decreased by 10% and the substrate saturation constant Ks by 23%. A change in the activity of key enzymes of metabolic pathways of lactose utilization immediately after the action of EMF of the EHF was revealed. The preservation of the achieved effect during the entire fermentation was observed. The activity of β-galactosidase and hexokinase after exposure to EMF EHF increases from 134% to 290%, depending on the strain and fermentation conditions. The increase in the activity of fumarate hydratase is 6-9%.

Lactic acid fermentation offers a processing alternative for preservation of watermelon juice, which is sensitive to heat, oxygen, and light. In this study, 8.8 × 107 CFU/mL of Lactobacillus plantarum DSM 9843 in MRS broth was inoculated in 9.9 mL of sterilized watermelon juice. Nanosecond-pulsed electric field was applied during the log growth phase of the bacteria. An 19% increase in L-lactic acid, 6.8% increase in D-lactic acid and 15% increase in acetic acid were observed over control. The final pH was 3.8. These increased levels of metabolites were dependent on the applied voltages (L-lactic acid: 5.0 kV 700 pulses, D-lactic acid: 4.5 kV 700 pulses and acetic acid: 4.5 kV 1000 pulses). The nsPEF treatment did not affect the viability of the cells and sufficient numbers remained in the product after fermentation (1.6 × 109 CFU/mL in average). These results suggest that the metabolism of lactic acid bacteria was stimulated by the PEF treatment.

This study investigated the impact of Lactobacillus acidophilus NCFM, Oenococcus oeni Viniflora® Oenos and Lactobacillus brevis CICC 6239 on bog bilberry juice with a considerably low pH and rich in anthocyanins content. Moreover, the effects of the strains on the composition of phenolic compounds, amino acids, ammonium ion, biogenic amines, reduced sugars, organic acids, and color parameters of the juice were studied. All three bacteria consumed sugars and amino acids but exhibited different growth patterns. Lactic acid was detected only in L. acidophilus inoculated juice. The content of the phenolic compounds, especially anthocyanins, decreased in juice after inoculation. The CIELa*b* analysis indicated that the juice inoculated with L. acidophilus and O. oeni showed a decrease on a* and b* (less red and yellow) but an increase on L (more lightness), whereas the color attributes of L. brevis inoculated juice did not significantly change. Based on this study, L. brevis showed the most optimal performance in the juice due to its better adaptability and fewer effects on the appearance of juice. This study provided a useful reference on the metabolism of lactic acid bacteria in low pH juice and the evolution of primary and secondary nutrients in juice after inoculated with lactic acid bacteria.

The application of lactic acid bacteria in medicine mainly originates from the efficacy of food. In 1906 Metchnikoff suggested that bacteria in yogurt are good for human health. Later, according to the phenomenon that yogurt can inhibit the growth of acid-tolerant bacteria, he assumed that similar phenomena will appear in the human intestine. The bacteria in the yogurt protect human health from spoilage bacteria by making some spoilage bacteria fail to proliferate and cannot produce toxic substances. This argument became a popular medical topic in Western Europe at the time. Following the first successful use of bacteria to treat diseases, Daviel Newman applied lactic acid bacteria to treat bladder infections and pointed out that the reason for the cure is that the lactic acid produced by the metabolism of lactic acid bacteria has anti-infective properties. However, because of the exhaustive information provided, the simple sample, and the lacking basic characteristics of the strain, the mechanism cannot be clarified. However, this finding laid the foundation for the clinical application of lactic acid bacteria. Subsequently, Rettger et al. made a lot of research on the role and application of Lactobacillus acidophilus in 1935, which made people to have a strong interest in yogurt once again. They agreed that yogurt has a mitigating effect on constipation, inflammatory bowel disease (IBD), bacterial dysentery, obesity, and other diseases. So far, yogurt has prevailed in Europe and other places.

SummaryWe proposed a novel phenomic approach to track the effect of short‐term exposures of Lactiplantibacillus plantarum and Leuconostoc pseudomesenteroides to environmental pressure induced by brewers' spent grain (BSG)‐derived saccharides. Water‐soluble BSG‐based medium (WS‐BSG) was chosen as model system. The environmental pressure exerted by WS‐BSG shifted the phenotypes of bacteria in species‐ and strains‐dependent way. The metabolic drift was growth phase‐dependent and likely underlay the diauxic profile of organic acids production by bacteria in response to the low availability of energy sources. Among pentosans, metabolism of arabinose was preferred by L. plantarum and xylose by Leuc. pseudomesenteroides as confirmed by the overexpression of related genes. Bayesian variance analysis showed that phenotype switching towards galactose metabolism suffered the greatest fluctuation in L. plantarum. All lactic acid bacteria strains utilized more intensively sucrose and its plant‐derived isomers. Sucrose‐6‐phosphate activity in Leuc. pseudomesenteroides likely mediated the increased consumption of raffinose. The increased levels of some phenolic compounds suggested the involvement of 6‐phospho‐β‐glucosidases in β‐glucosides degradation. Expression of genes encoding β‐glucoside/cellobiose‐specific EII complexes and phenotyping highlighted an increased metabolism for cellobiose. Our reconstructed metabolic network will improve the understanding of how lactic acid bacteria may transform BSG into suitable food ingredients.

Enzymatic and bacterial conversions during sourdough fermentation