Food phenolics and lactic acid bacteria

A multistrategic approach in the development of sourdough bread targeted towards blood pressure reduction

Rising prevalence of hypertension is pushing food industry towards the development of innovative food products with antihypertensive effects. The aim was to study the effect of reduced sodium content and 21% addition of wholemeal wheat sourdough (produced by Lactobacillus brevis CECT 8183 and protease) on proximate composition, γ-aminobutyric acid (GABA) and peptide content of wheat bread. Angiotensin converting enzyme I (ACE) inhibitory and antioxidant activities were also evaluated. Sodium replacement by potassium salt did not affect chemical composition and biological activities of bread. In contrast, GABA and peptides <3 kDa contents in sourdough bread (SDB) were 7 and 3 times higher, respectively, than the observed in control. ACE inhibitory and antioxidant activities of the peptide fraction < 3 kDa from SDB was 1.7 and 2.6-3.0 times higher than control. Therefore, the combination of reduced sodium content with enriched concentrations of bioactive compounds in bread making may provide interesting perspectives for development of innovative breads towards blood pressure reduction.

Organic cultivation of Triticum turgidum subsp. durum is reflected in the flour-sourdough fermentation-bread axis

Triticum turgidum subsp. durum was grown according to four farming systems: conventional (CONV), organic with cow manure (OMAN) or green manure (OLEG), and without inputs (NOINPUT). Some chemical and technological characteristics differed between CONV and organic flours. As shown by two-dimensional electrophoresis (2-DE) analysis, OMAN and OLEG flours showed the highest number of gliadins, and OMAN flour also had the highest number of high-molecular-mass glutenins. Type I sourdoughs were prepared at the laboratory level through a back-slopping procedure, and the bacterial ecology during sourdough preparation was described by 16S rRNA gene pyrosequencing. Before fermentation, the dough made with CONV flour showed the highest bacterial diversity. Flours were variously contaminated by genera belonging to the Proteobacteria, Firmicutes, and Actinobacteria. Mature sourdoughs were completely and stably dominated by lactic acid bacteria. The diversity of Firmicutes was the highest for mature sourdoughs made with organic and, especially, NOINPUT flours. Beta diversity analysis based on the weighted UniFrac distance showed differences between doughs and sourdoughs. Those made with CONV flour were separated from the other with organic flours. Lactic acid bacterium microbiota structure was qualitatively confirmed through the culturing method. As shown by PCR-denaturing gradient gel electrophoresis (DGGE) analysis, yeasts belonging to the genera Saccharomyces, Candida, Kazachstania, and Rhodotorula occurred in all sourdoughs. Levels of bound phenolic acids and phytase and antioxidant activities differed depending on the farming system. Mature sourdoughs were used for bread making. Technological characteristics were superior in the breads made with organic sourdoughs. The farming system is another determinant affecting the sourdough microbiota. The organic cultivation of durum wheat was reflected along the flour-sourdough fermentation-bread axis.

Fermentation Characteristics and Microbial Diversity of Tropical Grass-legumes Silages

Calliandra calothyrsus preserved in silage is an alternative method for improving the crude protein content of feeds for sustainable ruminant production. The aim of this research was to evaluate the quality of silage which contained different levels of C. calothyrsus by examining the fermentation characteristics and microbial diversity. Silage was made in a completely randomized design consisting of five treatments with three replications i.e.: R0, Pennisetum purpureum 100%; R1, P. purpureum 75%+C. calothyrsus 25%;, R2, P. purpureum 50%+C. calothyrsus 50%; R3, P. purpureum 25%+C. calothyrsus 75%; and R4, C. calothyrsus 100%. All silages were prepared using plastic jar silos (600 g) and incubated at room temperature for 30 days. Silages were analyzed for fermentation characteristics and microbial diversity. Increased levels of C. calothyrsus in silage had a significant effect (p<0.01) on the fermentation characteristics. The microbial diversity index decreased and activity was inhibited with increasing levels of C. calothyrsus. The microbial community indicated that there was a population of Lactobacillus plantarum, L. casei, L. brevis, Lactococcus lactis, Chryseobacterium sp., and uncultured bacteria. The result confirmed that silage with a combination of grass and C. calothyrsus had good fermentation characteristics and microbial communities were dominated by L. plantarum.

LC-MS(n) characterization of steroidal saponins in Helleborus niger L. roots and their conversion products during fermentation

Steroidal saponins comprise a substantial part of the secondary metabolite spectrum in the medicinal plant Helleborus niger L. (black hellebore). The saponin fraction from the roots was investigated by LC-MS(n) resulting in 38 saponins and β-ecdysone. Nine diosgenyl-type glycosides, mainly furostanols consisting of the aglycones diosgenin, macranthogenin, sceptrumgenin, and sarsasapogenin were accompanied by 5 diosgenyl-type saponins exhibiting an aglycone with an additional OH group. However, the most relevant compounds were 24 acetylated polyhydroxy saponins including hellebosaponins A and D. The enzymes glucuronidase, β-glucosidase, and pectinase were used to obtain an idea on potential fermentative transformation reactions by incubation of the isolated model saponins macranthosid I and hellebosaponin A. In a second step, aqueous H. niger extracts containing a much greater range of saponins were monitored during fermentation and 12months of storage. The metabolites were examined and assigned by LC-MS(n) and targeted extracted ion current (EIC) scan analyses. Good agreement was found among the results from the model compounds and the whole aqueous fermented extracts. The native diosgenyl-type furostanol saponins were converted to spirostanols under scission of hexoses. Alteration of the acetylated polyhydroxy saponins, exclusively spirostanols, took place following cleavage of acetyl groups and terminal deoxyhexoses. Most interestingly, the pentoses of the sugar chain at C(1) were not affected. Conversion of acetylated polyhydroxy saponins resulted in a final structure type which was stable and detectable, even after 12months of fermentation and storage.

Antibacterial activity of carob (Ceratonia siliqua L.) extracts against phytopathogenic bacteria Pectobacterium atrosepticum

Acetone and ethanol extracts of carob (Ceratonia siliqua L.) leaf and pods were evaluated for their in vitro inhibitory ability against the pectinolytic Gram negative Pectobacterium atrosepticum (Pca, CFBP-5384) bacteria, the causal agent of potato soft rot. Potato (Solanum tuberosum, var nicola) tuber rot tissues obtained after 5 day bacterial inoculation was analyzed by LC-MS and GC-MS to study Pca pathogenicity. Trans/cis N-feruloylputrescine was identified in potato tuber after 5-day inoculation with Pca in a dark moist chamber. Although glycoalkoloid (α-chaconine and α-solanine) production increased due to Pca soft rot infection, it was not a resistance-determining factor. Many secondary metabolites were identified including the phytoalexins solavetivone and fatty acids responsible for plant defence responses. Acetone extract of carob leaf (FCA) exhibited the strongest inhibitory effect (IC50 = 1.5 mg/ml) and displayed synergistic antimicrobial effect in the presence of infected potato tuber extract (Pdt-Pca extract) against Pca. This synergy could be used in an integrated control program against potato soft rot pathogens, thereby reducing chemical treatments.

Eruca sativa might influence the growth, survival under simulated gastrointestinal conditions and some biological features of Lactobacillus acidophilus, Lactobacillus plantarum and Lactobacillus rhamnosus strains

The growth and viability of three Lactobacillus strains, Lactobacillus acidophilus, Lactobacillus plantarum and Lactobacillus rhamnosus, after their passage through simulated gastric and pancreatic juices were studied as a function of their presence in the growth medium of rocket salad (Eruca sativa). The presence of E. sativa affected some of the biological properties of the strains. For example, L. acidophilus and L. plantarum worked more efficiently in the presence of E. sativa, increasing not only the antioxidant activity of the medium, but also their own antioxidant power and antimicrobial activity; L. rhamnosus was not affected in the same manner. Overall, the presence of vegetables might help to boost, in specific cases, some of the characteristics of lactobacilli, including antioxidant and antimicrobial power.

Hydroxycinnamic acids used as external acceptors of electrons: an energetic advantage for strictly heterofermentative lactic acid bacteria

The metabolism of hydroxycinnamic acids by strictly heterofermentative lactic acid bacteria (19 strains) was investigated as a potential alternative energy route. Lactobacillus curvatus PE5 was the most tolerant to hydroxycinnamic acids, followed by strains of Weissella spp., Lactobacillus brevis, Lactobacillus fermentum, and Leuconostoc mesenteroides, for which the MIC values were the same. The highest sensitivity was found for Lactobacillus rossiae strains. During growth in MRS broth, lactic acid bacteria reduced caffeic, p-coumaric, and ferulic acids into dihydrocaffeic, phloretic, and dihydroferulic acids, respectively, or decarboxylated hydroxycinnamic acids into the corresponding vinyl derivatives and then reduced the latter compounds to ethyl compounds. Reductase activities mainly emerged, and the activities of selected strains were further investigated in chemically defined basal medium (CDM) under anaerobic conditions. The end products of carbon metabolism were quantified, as were the levels of intracellular ATP and the NAD(+)/NADH ratio. Electron and carbon balances and theoretical ATP/glucose yields were also estimated. When CDM was supplemented with hydroxycinnamic acids, the synthesis of ethanol decreased and the concentration of acetic acid increased. The levels of these metabolites reflected on the alcohol dehydrogenase and acetate kinase activities. Overall, some biochemical traits distinguished the common metabolism of strictly heterofermentative strains: main reductase activity toward hydroxycinnamic acids, a shift from alcohol dehydrogenase to acetate kinase activities, an increase in the NAD(+)/NADH ratio, and the accumulation of supplementary intracellular ATP. Taken together, the above-described metabolic responses suggest that strictly heterofermentative lactic acid bacteria mainly use hydroxycinnamic acids as external acceptors of electrons.

Metabolism of phenolic compounds by Lactobacillus spp. during fermentation of cherry juice and broccoli puree

This study aimed to investigate the metabolism of phenolic acids and flavonoids during lactic acid fermentation of cherry juice and broccoli puree for potential food and pharmaceutical purposes. When fermenting cherry juice and broccoli puree, Lactobacillus spp. exhibited strain-specific metabolism of phenolic acid derivatives. The metabolism of protocatechuic, caffeic and p-coumaric acids through phenolic acid decarboxylases and reductases differed between mMRS and cherry juice and broccoli puree. The synthesis of reduced compounds was the highest during food fermentations and the substrate seemed to modulate the metabolism of phenolic compounds. The reduction of phenolic acids involves a hydrogen donor and the re-oxidation of the reduced co-factor NADH, which may provide a metabolic advantage through NAD(+) regeneration. Quinic acid reduction may replace fructose and pyruvate as hydrogen acceptors, and it may provide an energetic advantage to heterofermentative bacteria when growing in broccoli puree lacking of fructose. This study demonstrated that phenolics metabolism may confer a selective advantage for lactobacilli in vegetable and fruit fermentation, and the metabolic routes are strongly dependent on the intrinsic factors of substrate. Fermented cherry juice and broccoli puree, due to the selected bacterial bioconversion pathways, are enriched in phenolic derivative with high human bioavailability and biological activity.

Exploitation of Albanian wheat cultivars: characterization of the flours and lactic acid bacteria microbiota, and selection of starters for sourdough fermentation

Six Albanian soft and durum wheat cultivars were characterized based on chemical and technological features, showing different attitudes for bread making. Gliadin and glutenin fractions were selectively extracted from flours, and subjected to two-dimensional electrophoresis. Linja 7 and LVS flours showed the best characteristics, and abundance of high molecular weight (HMW)-glutenins. Type I sourdoughs were prepared through back slopping procedure, and the lactic acid bacteria were typed and identified. Lactobacillus plantarum and Leuconostoc mesenteroides were the predominant species. Thirty-eight representative isolates were singly used for sourdough fermentation of soft and durum wheat Albanian flours and their selection was carried out based on growth and acidification, quotient of fermentation, and proteolytic activity. Two different pools of lactic acid bacteria were designed to ferment soft or durum wheat flours. Sourdough fermentation with mixed and selected starters positively affected the quotient of fermentation, concentration of free amino acids, profile of phenolic acids, and antioxidant and phytase activities. This study provided the basis to exploit the potential of wheat Albanian flours based on an integrated approach, which considered the characterization of the flours and the processing conditions.

Polyphenols from olive mill waste affect biofilm formation and motility in Escherichia coli K-12

Olive mill wastes are sources of phenolic compounds with a wide array of biological activities, including antimicrobial effects. A potential option for bioremediation to overcome ecological problems is the reutilization of these natural compounds in food production. The aim of this work was to gain a better understanding of the antimicrobial mode of action of a phenols extract from olive vegetation water (PEOVW) at molecular level by studying Escherichia coli as a model microorganism. Genome-wide transcriptional analysis was performed on E. coli K-12 exposed to PEOVW. The repression of genes for flagellar synthesis and the involvement of genes linked to biofilm formation and stress response were observed. Sub-inhibitory concentrations of PEOVW significantly decreased biofilm formation, swarming and swimming motility, thus confirming the gene expression data. This study provides interesting insights on the molecular action of PEOVW on E. coli K-12. Given these anti-biofilm properties and considering that biofilm formation is a serious problem for the food industry and human health, PEOVW has proved to be a high-value natural product.

Metabolic fate of depsides and alkaloid constituents in aqueous extracts from Mercurialis perennis L. during fermentation

Dog's mercury (Mercurialis perennis L.) is an old medicinal plant, nowadays used in complementary medicine. Aqueous fermented extracts of the plant are being mainly applied in remedies to treat external inflammations, but a thorough phytochemical characterization is still lacking. Therefore, the conversion of characteristic compound classes from M. perennis extracts during fermentation and storage was investigated. The microbial transformation of the two main depsides phaselic acid (=(2R)-O-[(E)-caffeoyl]malic acid; 1) and mercurialis acid (=(2R)-[(E)-caffeoyloxy]glutaric acid; 2) was monitored by HPLC-DAD. The degradation followed a second-order kinetic, and the calculated half-life periods of both constituents were 67 and 30 months, respectively. Several depside metabolites were detected by GC/MS in AcOEt extracts as (t) BuMe2 Si (TBDMS) derivatives after derivatization, mainly dihydrocinnamic acids. Moreover, numerous α-hydroxy acids were found, allegedly as degradation products from amino acids or peptides. The microbial alteration of the main alkaloid hermidin was also examined. After three days of fermentation, three novel N-metabolites were formed and thoroughly assigned in CH2 Cl2 extracts as a mixture of 3-ethylhermidin, 3-ethylhermidin quinone, and (E/Z)-3-ethylidenehermidin by GC/MS and NMR methods, as well as by means of total synthesis. A mechanism for the formation of these N-metabolites starting from dimeric hermidin oxidation products is proposed. The obtained results reveal the complex pathways plant constituents may undergo during the fermentation of the extracts.

Effect of fermentation on the antioxidant activity in plant-based foods

This study provides an overview of the factors that influence the effect of fermentation on the antioxidant activity and the mechanisms that augment antioxidative activities in fermented plant-based foods. The ability of fermentation to improve antioxidant activity is primarily due to an increase in the amount of phenolic compounds and flavonoids during fermentation, which is the result of a microbial hydrolysis reaction. Moreover, fermentation induces the structural breakdown of plant cell walls, leading to the liberation or synthesis of various antioxidant compounds. These antioxidant compounds can act as free radical terminators, metal chelators, singlet oxygen quenchers, or hydrogen donors to radicals. The production of protease, α-amylase and some other enzymes can be influenced by fermentation that may have metal ion chelation activity. Because the mechanisms that affect antioxidant activity during fermentation are extremely varied, further investigation is needed to establish the precise mechanisms for these processes.

Effect of green tea supplementation on the microbiological, antioxidant, and sensory properties of probiotic milks

Green tea and its constituents are known for a wide range of health-promoting properties. They may exert antimicrobial action but without altering lactic acid bacteria. The aim of the present study was to estimate the effect of green tea addition on the selected properties of probiotic milks. Bioyogurts (fermented with ABT-1 coculture of Streptococcus thermophilus, Lactobacillus acidophilus LA-5, Bifidobacterium animalis subsp. lactis BB-12) and acidophilus milks (fermented with pure L. acidophilus LA-5 culture) with addition of 0, 5, 10, or 15% (v/v) green tea infusion (GTI) were produced and analyzed for the antioxidant capacity by the “diphenyl picrylhydrazyl” (DPPH) and “ferric-reducing antioxidant power” (FRAP) methods, acidity, the count of starter bacteria, and sensory properties at the 1st, 7th, 14th, and 21st day of cold storage. The 15% addition of GTI to the acidophilus milk significantly reduced the lactic acid production during the whole study. The GTI had no impact on the level of S. thermophilus and B. lactis BB-12 in bioyogurts, and its effect on the count of L. acidophilus LA-5 depended on the concentration and probiotic milk type. GTI similarly and in a dose-dependent manner enhanced the antioxidant capacity of both milk types. There were no significant differences between the sensory notes received for bioyogurts, whereas acidophilus milks with tea were less appreciated by the panelists. In conclusion, green tea could be successfully used as a functional additive for selected probiotic milks enhancing their health benefits, but the proper selection of tea additive and starter culture is recommended.

Influence of fresh date palm co-products on the ripening of a paprika added dry-cured sausage model system

Date palm co-products are a source of bioactive compounds that could be used as a new ingredient for the meat industry. An intermediate food product (IFP) from date palm co-products (5%) was incorporated into a paprika added dry-cured sausage (PADS) model system and was analysed for physicochemical parameters, lipid oxidation and sensory attributes during ripening. Addition of 5% IFP yielded a product with physicochemical properties similar to the traditional one. Instrumental colour differences were found, but were not detected visually by panellists, who also evaluated positively the sensory properties of the PADS with IFP. Therefore, the IFP from date palm co-products could be used as a natural ingredient in the formulation of PADS.

Metabolic responses of Lactobacillus plantarum strains during fermentation and storage of vegetable and fruit juices

Strains of Lactobacillus plantarum were grown and stored in cherry (ChJ), pineapple (PJ), carrot (CJ), and tomato (TJ) juices to mimic the chemical composition of the respective matrices. Wheat flour hydrolysate (WFH), whey milk (W), and MRS broth were also used as representatives of other ecosystems. The growth rates and cell densities of L. plantarum strains during fermentation (24 h at 30°C) and storage (21 days at 4°C) differed only in part, being mainly influenced by the matrix. ChJ and PJ were the most stressful juices for growth and survival. Overall, the growth in juices was negatively correlated with the initial concentration of malic acid and carbohydrates. The consumption of malic acid was noticeable for all juices, but mainly during fermentation and storage of ChJ. Decreases of branched-chain amino acids (BCAA)-with the concomitant increase of their respective branched alcohols-and His and increases of Glu and gamma-aminobutyric acid (GABA) were the main traits of the catabolism of free amino acids (FAA), which were mainly evident under less acidic conditions (CJ and TJ). The increase of Tyr was found only during storage of ChJ. Some aldehydes (e.g., 3-methyl-butanal) were reduced to the corresponding alcohols (e.g., 3-methyl-1-butanol). After both fermentation and storage, acetic acid increased in all fermented juices, which implied the activation of the acetate kinase route. Diacetyl was the ketone found at the highest level, and butyric acid increased in almost all fermented juices. Data were processed through multidimensional statistical analyses. Except for CJ, the juices (mainly ChJ) seemed to induce specific metabolic traits, which differed in part among the strains. This study provided more in-depth knowledge on the metabolic mechanisms of growth and maintenance of L. plantarum in vegetable and fruit habitats, which also provided helpful information to select the most suitable starters for fermentation of targeted matrices.

The role of oxygen in the liquid fermentation of wheat bran

The extensive use of wheat bran as a food ingredient is limited due to its bitter taste and hard texture. To overcome these, some preprocessing methods, such as fermentation with yeast and lactic acid bacteria or enzymatic treatments have been proposed. The current work studied microbial communities, acidification, ethanol formation and metabolite profile of wheat bran fermented in either aerated or anaerobic conditions. In aerated conditions, yeasts grew better and the production of organic acids was smaller, and hence pH was higher. In anaerobic conditions, lactic acid bacteria and endogenous heterotrophic bacteria grew better. Aeration had a large effect on the sourdough metabolite profile, as analyzed by UPLC-qTOF-MS. Anaerobic conditions induced degradation of ferulic and caffeic acids, whereas the amount of sinapic acid increased. Aeration caused degradation of amino acids and hydroxycinnamic acid derivatives of polyamines. The results suggest that the control of oxygen could be used for tailoring the properties of bran sourdough.

β-Glucosidase activities of lactic acid bacteria: mechanisms, impact on fermented food and human health

Through the hydrolysis of plant metabolite glucoconjugates, β-glucosidase activities of lactic acid bacteria (LAB) make a significant contribution to the dietary and sensory attributes of fermented food. Deglucosylation can release attractive flavour compounds from glucosylated precursors and increases the bioavailability of health-promoting plant metabolites as well as that of dietary toxins. This review brings the current literature on LAB β-glucosidases into context by providing an overview of the nutritional implications of LAB β-glucosidase activities. Based on biochemical and genomic information, the mechanisms that are currently considered to be critical for the hydrolysis of β-glucosides by intestinal and food-fermenting LAB will also be reviewed.

Phenolic acid composition, antioxidant activity and phenolic content of tarhana supplemented with oat flour

In this study, oat flour (OF) was used to replace wheat flour in tarhana formulation at the levels of 10, 20, 30 and 40% (w/w). Control sample did not contain OF. The results showed that addition of OF caused increases in levels of phenolic acids within tarhana samples. The most abundant phenolic acids were vanillic and ferulic acids, and they were followed by gallic acid. Tarhana samples with OF also showed higher antioxidant activities than control sample did. Compared with the control sample, the total phenolic content level increased with the increase in the amount of OF. The results of sensory analysis showed that OF addition neither caused any undesirable taste nor an odor and panelists emphasised a sweet taste as the OF amounts were increased. Therefore, tarhana supplemented with OF can be claimed to be a good source of minerals, phenolics and antioxidants as compared to tarhana without OF.

Structure, biochemical characterization and analysis of the pleomorphism of carboxylesterase Cest-2923 from Lactobacillus plantarum WCFS1

The hydrolase fold is one of the most versatile structures in the protein realm according to the diversity of sequences adopting such a three-dimensional architecture. In the present study, we clarified the crystal structure of the carboxylesterase Cest-2923 from the lactic acid bacterium Lactobacillus plantarum WCFS1 refined to 2.1 Å resolution, determined its main biochemical characteristics and also carried out an analysis of its associative behaviour in solution. We found that the versatility of a canonical α/β hydrolase fold, the basic framework of the crystal structure of Cest-2923, also extends to its oligomeric behaviour in solution. Thus, we discovered that Cest-2923 exhibits a pH-dependent pleomorphic behaviour in solution involving monomers, canonical dimers and tetramers. Although, at neutral pH, the system is mainly shifted to dimeric species, under acidic conditions, tetrameric species predominate. Despite these tetramers resulting from the association of canonical dimers, as is commonly found in many other carboxylesterases from the hormone-sensitive lipase family, they can be defined as 'noncanonical' because they represent a different association mode. We identified this same type of tetramer in the closest relative of Cest-2923 that has been structurally characterized: the sugar hydrolase YeeB from Lactococcus lactis. The observed associative behaviour is consistent with the different crystallographic results for Cest-2923 from structural genomics consortia. Finally, the presence of sulfate or acetate molecules (depending on the crystal form analysed) in the close vicinity of the nucleophile Ser116 allows us to identify interactions with the putative oxyanion hole and deduce the existence of hydrolytic activity within Cest-2923 crystals.

Enzymatic activity of Lactobacillus reuteri grown in a sweet potato based medium with the addition of metal ions

The effect of metal ions on the enzymatic activity of Lactobacillus reuteri was studied. The enzymatic activity was determined spectrophotometrically using the corresponding substrate. In the control group, L. reuteri MF14-C, MM2-3, SD2112, and DSM20016 produced the highest α-glucosidase (40.06 ± 2.80 Glu U/mL), β-glucosidase (17.82 ± 1.45 Glu U/mL), acid phosphatase (20.55 ± 0.74 Ph U/mL), and phytase (0.90 ± 0.05 Ph U/mL) respectively. The addition of Mg(2+) and Mn(2+) led to enhance α-glucosidase produced by L. reuteri MM2-3 by 113.6% and 100.6% respectively. α-Glucosidase produced by MF14-C and CF2-7F was decrease in the presence of K(+) by 65.8 and 69.4% respectively. β-Glucosidase activity of MM7 and SD2112 increased in the presence of Ca(2+) (by 121.8 and 129.8%) and Fe(2+) (by 143.9 and 126.7%) respectively. Acid phosphatase produced by L. reuteri CF2-7F and MM2-3 was enhanced in the presence of Mg(2+), Ca(2+) or Mn(2+) by (94.7, 43.2, and 70.1%) and (63.1, 67.8, and 45.6%) respectively. On the other hand, Fe(2+), K(+), and Na(+) caused only slight increase or decrease in acid phosphatase activity. Phytase produced by L. reuteri MM2-3 was increase in the presence of Mg(2+) and Mn(2+) by 51.0 and 74.5% respectively. Ca(2+) enhanced phytase activity of MM2-3 and DSM20016 by 27.5 and 28.9% respectively. The addition of Na(+) or Fe(2+) decreased phytase activity of L. reuteri. On average, Mg(2+) and Mn(2+) followed by Ca(2+) led to the highest enhancement of the tested enzymes. However, the effect of each metal ion on the enzymatic activity of L. reuteri was found to be a strain dependent. Therefore, a maximized level of a target enzyme could be achieved by selecting a combination of specific strain and specific metal ion.

Characterization of a feruloyl esterase from Lactobacillus plantarum

Lactobacillus plantarum is frequently found in the fermentation of plant-derived food products, where hydroxycinnamoyl esters are abundant. L. plantarum WCFS1 cultures were unable to hydrolyze hydroxycinnamoyl esters; however, cell extracts from the strain partially hydrolyze methyl ferulate and methyl p-coumarate. In order to discover whether the protein Lp_0796 is the enzyme responsible for this hydrolytic activity, it was recombinantly overproduced and enzymatically characterized. Lp_0796 is an esterase that, among other substrates, is able to efficiently hydrolyze the four model substrates for feruloyl esterases (methyl ferulate, methyl caffeate, methyl p-coumarate, and methyl sinapinate). A screening test for the detection of the gene encoding feruloyl esterase Lp_0796 revealed that it is generally present among L. plantarum strains. The present study constitutes the description of feruloyl esterase activity in L. plantarum and provides new insights into the metabolism of hydroxycinnamic compounds in this bacterial species.

Identification of critical genes for growth in olive brine by transposon mutagenesis of Lactobacillus pentosus C11

Olive brine represents a stressful environment due to the high NaCl concentration, presence of phenolic compounds known as antimicrobials, and low availability of nutrients. Thus, only a few strains of lactic acid bacteria (LAB) are adapted to grow in and ferment table olives. To identify the mechanisms by which these few strains are able to grow in olive brine, Lactobacillus pentosus C11, a particularly resistant strain isolated from naturally fermented table olives, was mutagenized by random transposition using the P(junc)-TpaseIS1223 system (H. Licandro-Seraut, S. Brinster, M. van de Guchte, H. Scornec, E. Maguin, P. Sansonetti, J. F. Cavin, and P. Serror, Appl. Environ. Microbiol. 78:5417-5423, 2012). A library of 6,000 mutants was generated and screened for adaptation and subsequent growth in a medium, named BSM (brine screening medium), which presents the stressful conditions encountered in olive brine. Five transposition mutants impaired in growth on BSM were identified. Transposition occurred in two open reading frames and in three transcription terminators affecting stability of transcripts. Thus, several essential genes for adaptation and growth of L. pentosus C11 in olive brine were identified.

Enzymatic and bacterial conversions during sourdough fermentation

Enzymatic and microbial conversion of flour components during bread making determines bread quality. Metabolism of sourdough microbiota and the activity of cereal enzymes are interdependent. Acidification, oxygen consumption, and thiols accumulation by microbial metabolism modulate the activity of cereal enzymes. In turn, cereal enzymes provide substrates for bacterial growth. This review highlights the role of cereal enzymes and the metabolism of lactic acid bacteria in conversion of carbohydrates, proteins, phenolic compounds and lipids. Heterofermentative lactic acid bacteria prevailing in wheat and rye sourdoughs preferentially metabolise sucrose and maltose; the latter is released by cereal enzymes during fermentation. Sucrose supports formation of acetate by heterofermentative lactobacilli, and the formation of exopolysaccharides. The release of maltose and glucose by cereal enzymes during fermentation determines the exopolysaccharide yield in sourdough fermentations. Proteolysis is dependent on cereal proteases. Peptidase activities of sourdough lactic acid bacteria determine the accumulation of (bioactive) peptides, amino acids, and amino acid metabolites in dough and bread. Enzymatic conversion and microbial metabolism of phenolic compounds is relevant in sorghum and millet containing high levels of phenolic compounds. The presence of phenolic compounds with antimicrobial activity in sorghum selects for fermentation microbiota that are resistant to the phenolic compounds.

Effects of bilberry (Vaccinium myrtillus) in combination with lactic acid bacteria on intestinal oxidative stress induced by ischemia-reperfusion in mouse

Intestinal ischemia-reperfusion (I/R) results in oxidative stress, inflammation, and tissue injuries. The present study investigates the antioxidative and anti-inflammatory effects of a dietary supplement of bilberry, either alone or in combination with Lactobacillus plantarum RESO56, L. plantarum HEAL19, or Pediococcus acidilactici JAM046, in an I/R-induced model for oxidative stress in mice. A bilberry diet without addition of bacteria significantly decreased both lipid peroxidation (p = 0.001) and mucosal injury in the ileum. Of 14 anthocyanins identified in bilberry, anthocyanin arabinosides were the most resistant to absorption and microbial degradation in the intestines. Cyanidin-3-glucoside and delphinidin-3-glucoside seemed to be mostly absorbed in the stomach and upper part of the small intestine, while malvidin-3-galactoside, peonidin-3-glucoside, peonidin-3-galactoside, and petunidin-3-galactoside seemed to be digested by the microbiota in the cecum. Bilberry strongly influenced the composition of the cecal microbiota. In conclusion, a food supplement of bilberry protected small intestine against oxidative stress and inflammation induced by ischemia-reperfusion.