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Graphical abstract Highlights • Immunotherapy with peptides positively modulates the microbiota of allergic mice. • Therapy with peptides improves intestinal barrier function. • The expression of genes that take part in vitamin A metabolism is upregulated. • Protection is associated with Foxp3+ cells that simultaneously express RORγt. Abstract This study investigates the mechanism by which food peptides are more effective than intact allergens in providing desensitization against food allergy. BALB/c mice sensitized to egg white (EW) were subjected to oral immunotherapy (OIT) with intact and pepsin-hydrolysed EW (EP). Treatment with EP was superior to that with EW in terms of reduction of anaphylaxis and levels of specific antibodies. OIT with EP, but not with EW, modulated the microbiota by restoring the levels of some members of the order Clostridiales (clusters IV and XIVa) that were affected by sensitization. Mice treated with EP exhibited upregulated intestinal expression of Il22 and Muc2 , which encode for factors that contribute to reinforce the epithelial barrier function, as well as Aldh1a1 , Aldh1a2 , Csf2 and Tfgb1 , that take part in the conversion of vitamin A into retinoic acid. Tolerance induced by EP paralleled the development of Foxp3+ cells that simultaneously expressed RORγt. [ABSTRACT FROM AUTHOR]

The aim of the study was to evaluate the potential use of Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) for fast and reliable detection of strains producing the lantibiotics nisin, lacticin 481 and lacticin 3147 in a large collection of lactococci. A total of one hundred lactococcal isolates from traditional ewe's and goat's raw milk cheeses were identified to the species level as Lactococcus lactis by MALDI-TOF MS based on comparison with lactococcal entries in the BioTyper database. Mass spectra in the range 2000–4000 Da of the identified isolates were compared to reference spectra of three lactococcal strains producing lacticin 481 (IFPL 330), lacticin 3147 (IFPL 105) and nisin (IFPL 503). Only eight isolates had mass spectra with peaks that could be unequivocally identified as lacticin 481 (2900.47 Da) or nisin (3330.31 Da). None of the assayed isolates matched the mass spectra corresponding to the two-peptide lacticin 3147 (2847.97 and 3306.29 Da). The results obtained by MALDI-TOF MS were genetically validated by amplification of the corresponding structural gene coding for lacticin 481, nisin and lacticin 3147. MALDI-TOF MS can be used as a fast and reliable technique to screen a large number of lactococcal isolates for the ability to produce the lantibiotics nisin, lacticin 481 and lacticin 3147. [ABSTRACT FROM AUTHOR]

[Display omitted] • People with obesity (OB) showed decreased retronasal and taste perception. • OB presented an impaired liking for specific flavor attributes. • Differences in salivary biochemical parameters between BMI groups were observed. • A relation between salivary bacterial community and obesity was found. • Specific salivary parameters associated with BMI were linked to flavor intensity. Understanding the individual factors that modulate flavor perception is a central issue for the development of personalized diets strategies to fight obesity. This study aimed to investigate differences in flavor perception between adults with normal weight and those with obesity, as well as some potential biological factors related to these differences. To do that, liking and flavor perception intensity were measured against retronasal olfactory (pineapple, butter, tropical and chocolate) and taste attributes (sweetness, umami and bitter) in 77 individuals grouped as normalweight or obese, according to their body mass index (BMI). Unstimulated saliva was collected from all participants and characterized in terms of salivary flow, total protein content, total antioxidant capacity, total esterase activity and bacterial composition through 16S rDNA amplicon sequencing. The results showed that participants displayed differences in flavor perception according to their BMI group. Thus, the group with obesity showed significant lower liking and intensity scores for low calorie related food aroma (pineapple and tropical), lower taste intensity scores for sweet and umami, and a higher acceptability for umami than the group with normal weight. Significant differences between BMI groups were observed for salivary biochemical variables and specific bacterial taxa, some of which were significantly correlated to flavor intensity. This work suggests for the first time the existence of an oral-brain axis that might contribute to the development or perpetuation of obesity, which opens new and interesting avenues of research. [ABSTRACT FROM AUTHOR]

The recent research focus on the human microbiota has provided data which suggests that the composition of the gut microbiota can play an important role in the modulation of body weight and of related mucosal and systemic immune responses. However, recent results from human and animal studies have raised the debate about whether specific microbial groups play a causative role in obesity or if the gut microbiota is modulated in response to diet or the obese state itself. Studies targeting selective alterations in the gut microbiota to control weight gain through the intake of probiotics and/or prebiotics or modulating undesirable populations through the use of antimicrobials or transplantation of faecal microbiota have provided promising results. Nonetheless, further placebo-controlled, double blind human studies are still required. Likewise, while it is now well accepted that obesity is followed by a low grade inflammatory response, more research studies are needed to unravel the mechanisms that would explain how different microbiota profiles affect the mucosal and systemic immune responsiveness, the intestinal barrier function and the development of adiposity. [Copyright &y& Elsevier]

Abstract: This study investigated the potential use of lacticin 3147 to control growth of wine lactic acid bacteria (LAB) aiming to develop new approaches for reducing the content of sulphites in wine. Lacticin 3147, potassium metabisulphite and eucalyptus extract interactions were also evaluated. Inhibitory activity of the bacteriocin demonstrated to be strain-dependent and the highest antimicrobial effect was established at the exponential growth phase. Low lacticin 3147 IC50 values (10.46–57.97UA/mL) were measured for most of the strains, except for Lactobacillus casei CIAL-51 which were remarkably resistant (IC50 = 141.70UA/mL); Oenococcus oeni CIAL-117 were the most sensitive strain (IC50 = 10.46UA/mL). A synergistic effect of either lacticin 3147 or eucalyptus extract in combination with metabisulphite in inhibiting LAB growth was measured. Addition of lacticin 3147 to growing cultures of Lactobacillus plantarum CIAL-92 caused effective cell lysis, decrease of cell viability and extensive membrane damage, differing from the effects detected after addition of eucalyptus extract. To our knowledge, this is the first study that reports the inhibitory activity of this bacteriocin against oenological LAB and its potential role in the wine industry. The potential of eucalyptus extract as antimicrobial agent in winemaking is also highlighted. A combination of these two antimicrobials with metabisulphite could represent a promising approach to preserve LAB spoilage in wine and, consequently, eliminate or reduce the addition of SO2. [Copyright &y& Elsevier]

Abstract: Amino acid catabolism is mainly initiated in Lactococcus lactis by a transamination reaction that leads to the formation of α-keto acids. In addition, a novel α-keto acid decarboxylase enzyme, rare in lactic acid bacteria, responsible for the conversion of α-keto acids into aldehydes has been reported in L. lactis IFPL730. The effect of lacticin 3147-induced cell damage on both amino acid transamination and α-keto acid decarboxylation by L. lactis IFPL730 leading to the formation of aldehydes from amino acids was investigated. Cell membrane permeabilization induced by lacticin 3147 facilitated the diffusion of amino acids into the cells and thus, enhanced amino acid transamination and formation of α-keto acids. However, α-keto acid decarboxylation was not affected by cell membrane permeabilization since decarboxylation of α-keto acids in both control and lacticin 3147-treated cells were similar, suggesting that these substrates could freely diffuse inside the cells. Nevertheless, the formation of 2-methylbutyraldehyde from isoleucine was enhanced in lacticin 3147-treated cells. The increase in α-keto acids formation rate by L. lactis IFPL730 due to lacticin 3147-induced cell damage, led to a concomitant increase in the subsequent decarboxylation reaction that complete the metabolic pathway to aldehyde production from amino acids. The present study points out to the use of the food grade lacticin 3147 along with L. lactis IFPL730 as a valuable tool in the development of cheese flavour. [Copyright &y& Elsevier]

The gut microbiota should be included in the scientific processes of risk assessment of food additives. Xylitol is a sweetener that shows low digestibility and intestinal absorption, implying that a high proportion of consumed xylitol could reach the colonic microbiota. The present study has evaluated the dose-dependent effects of xylitol intake on the composition and the metabolic activity of the child gut-microbiota. The study was conducted in a dynamic simulator of the colonic microbiota (BFBL Gut Simulator) inoculated with a child pooled faecal sample and supplemented three times per day, for 7 days, with increasing xylitol concentrations (1 g/L, 3 g/L and 5 g/L). Sequencing of 16S rRNA gene amplicons and group-specific quantitative PCR indicated a xylitol dose-response effect on the abundance of Lachnospiraceae , particularly the genera Blautia , Anaerostipes and Roseburia. The microbial changes observed with xylitol corresponded with a dose-dependant effect on the butyrate concentration that, in parallel, favoured an increase in epithelial integrity of Caco-2 cells. The study represents a detailed observation of the bacterial taxa that are the main contributors to the metabolism of xylitol by the child gut microbiota and the results could be relevant in the risk assessment re-evaluation of xylitol as a sweetener. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dairy products have a potential positive impact on the management of T2DM. • Anti-diabetic properties of probiotics and prebiotics are based on multiple mechanisms. • Synbiotic products have better anti-diabetic properties than conventional dairy fermented foods. • New proposed prebiotics (non-carbohydrates and minerals) inside dairy matrices should be explored. • More clinical trials must be conducted to develop practice guidelines to control T2DM. Diabetes mellitus type 2 (T2DM) is associated with hyperglycemia, insulin resistance, and gut dysbiosis. Probiotics and prebiotics can ameliorate T2DM through different mechanisms of action, such as reducing oxidative stress, or the inhibition of pro-inflammatory markers, among others. Multiple studies in vitro and in vivo have demonstrated the reduction of hyperglycemia, depressive behaviors, obesity, oxidative stress, and insulin resistance in diabetic patients through the consumption of dairy products, such as yogurt, fermented milk, and cheese, enriched with potential probiotic strains, prebiotic ingredients, and synbiotics (understood as a combination of both). Therefore, this review aims to provide an updated overview about the impact of dairy foods with probiotics, prebiotics, or synbiotics to prevent and manage T2DM, the mechanism of action related to the host health, and the future tendencies for developing new dairy foods. Despite the addition of probiotics, prebiotics, and synbiotics to dairy products could be highly beneficial, more evidence, especially from clinical trials, is needed to develop evidence-based T2DM prevention guidelines. [ABSTRACT FROM AUTHOR]

Lactococcus lactis contains a large number of key enzymes responsible for the formation of volatile compounds characteristic of cheese flavour. In the present work we have investigated the expression of genes codifying amino acid converting enzymes (AACE) and the formation of volatile compounds by L. lactis IFPL953 and its mutant lacking the hydroxy acid dehydrogenase PanE (L. lactis IFPL953Δ panE). The growth in absence of isoleucine was the main induction factor in the expression of araT , bcaT , panE , and kivD. The expression of the gdh gene of L. lactis IFPL953Δ panE increased remarkably during the stationary growth phase, particularly under isoleucine and valine starvation conditions. L. lactis IFPL953Δ panE showed an enhanced formation of 2- and 3-methylbutanal and their corresponding alcohols and an increase in the formation of ketones. These findings contribute to a better knowledge of L. lactis AACE regulation and its potential application in cheese flavour formation. [ABSTRACT FROM AUTHOR]

The microbiological and metabolic changes of an overweight-associated colonic microbiota after reducing in vitro the carbohydrate supply and its supplementation with oligosaccharides derived from lactulose (OsLu) were evaluated using a dynamic simulator of the gastrointestinal tract. The differentiation and stability of the microbial communities within each colon compartment were reached after two weeks of feeding the system with a high energy (HE) medium based on fructose and readily fermentable starches. The effect of reducing the energy content (low-energy medium, LE) and the supplementation with OsLu caused minor variations in bacterial counts, except for Enterobacteriaceae. The LE medium caused an effect on the microbial metabolic activity that was characterized by an absence of net butyrate production and an increase in ammonium content. This shift from fermentative to proteolytic metabolism was not observed when the LE medium was supplemented with OsLu. This oligosaccharide mixture was mainly metabolized in the proximal colonic compartment. The results obtained in this study indicate that the substitution in the diet of easily digestible carbohydrates by OsLu maintains the fermentative functionality of the intestinal microbiota, allowing the net production of butyric acid with potential beneficial effects on health, and avoiding a full transition to proteolytic metabolism profiles. [ABSTRACT FROM AUTHOR]

Objective This study has evaluated the effect of regular and moderate red wine consumption on the diversity and occurrence of different groups of bacteria that are representative in human saliva. Methods Saliva from twenty-two healthy volunteers (age range 20–48 years) was analyzed in this study. Fourteen individuals consumed red wine (250 mL/day) during 4 weeks, whereas 8 volunteers were included in the control group. The evolution and composition of the microbial community in saliva was evaluated by PCR–DGGE and quantitative PCR. Results The microbial inter-individual variability observed in the PCR–DGGE band patterns was higher than the differences observed after the 4-weeks period of red wine intake. Bifidobacterium dentium , Bifidobacterium spp. and Alloscardovia omnicolens were the most representative bifidobacterial species, whereas the Streptococcus mitis – Streptococcus oralis group predominated within Streptococcus . This genus was the most numerous of the bacterial groups assayed, reaching average counts above 8 log copy numbers/mL. On the other hand, the lowest counts were recorded for Actinomyces , Fusobacterium , Haemophilus , Neisseria and Veillonella , which showed average values of 5 log copy numbers/mL. The results showed no significant differences ( P > 0.5) in bacterial counts after the period of red wine intake. Conclusion The overall diversity and stability of representative bacterial groups of the human saliva is not disturbed due to regular-moderate red wine consumption. [ABSTRACT FROM AUTHOR]

Abstract: The growth of potential probiotic strains from the genera Lactobacillus, Bifidobacterium and Streptococcus was evaluated with the novel lactose-derived trisaccharides 4′-galactosyl-kojibiose and lactulosucrose and the potential prebiotics lactosucrose and kojibiose. The novel oligosaccharides were synthesised from equimolar sucrose:lactose and sucrose:lactulose mixtures, respectively, using a Leuconostoc mesenteroides dextransucrase and purified by liquid chromatography. The growth of the strains using the purified carbohydrates as the sole carbon source was evaluated by recording the culture optical density and calculating maximum growth rates and lag phase parameters. The results revealed an apparent bifidogenic effect of lactulosucrose, being a moderate substrate for streptococci and not utilised by lactobacilli. In addition, 4′-galactosyl-kojibiose was selectively fermented by Bifidobacterium breve, which was the only tested bifidobacterial species able to ferment kojibiose. The described fermentation properties of the specific probiotic strains on the lactose-derived oligosaccharides would enable the design of prebiotics with a high degree of selectivity. [Copyright &y& Elsevier]

Abstract: Bacterial aggregation phenotype and cell surface hydrophobicity of dairy Lactobacillus plantarum strains were screened in order to assess a correlation with their adhesion and pathogen competitive exclusion abilities. Lactobacilli strains showing an aggregation phenotype, L. plantarum IFPL33, IFPL81, IFPL150, IFPL156 and IFPL162, also exhibited the highest percentages of autoaggregation (>50%) at 24h. In addition, autoaggregation abilities of the lactobacilli were highly correlated with their percentages of co-aggregation with all the pathogens tested, although co-aggregation properties were pathogen specific. Nevertheless, none of the autoaggregation and co-aggregation abilities correlated with the affinity to xylene (hydrophobicity) and the ability of adhesion to Caco-2 cells. Furthermore, these properties are not fully correlated with the ability of the lactobacilli strains for inhibiting pathogen adhesion. Aggregation abilities and cell surface hydrophobicity may not be the only components responsible for adhesion but some of the criteria to bear in mind of a complex mechanism that enables microorganisms to interact with the host and exert its beneficial effect. Further research is needed to identify remaining attributes related to adhesion and pathogen exclusion properties of potential probiotic strains. [Copyright &y& Elsevier]

Abstract: Formation of cheese aroma compounds by Lactococcus lactis from amino acid catabolism depends on a complex network of reactions, which involve enzymes such as aminotransferases, dehydrogenases, lyases, and decarboxylases, among others. Based on the ability of some L. lactis strains to grow with low requirements of amino acids, we have studied in L. lactis IFPL730 the effect of the branched chain amino acid (BCAA) content on the expression of functional genes related to amino acid catabolism and aroma compound formation (araT, bcaT, kivD, ytjE and panE). L. lactis IFPL730 growth rate decreased under leucine, valine or isoleucine starvation but the strain reached similar viable counts at the stationary phase in all culture conditions studied. The level of expression of some genes encoding enzymes involved in amino acid catabolism changed significantly (P <0.05) when those conditions were compared. Specially, α-ketoisovalerate decarboxylase (kivD), BCAA-specific aminotransferase (bcaT) and C-S lyase (yjtE) gene expressions increased markedly by both isoleucine and valine starvation. In addition to gene expression, formation of volatile compounds was determined in all growth conditions. The results showed that BCAA starvation conditions caused a significant increase (P <0.05) in the formation of metabolic end products related to cheese aroma, such as 3-methylbutanal and 3-methylbutanol. [Copyright &y& Elsevier]

Abstract: In this paper, β-lactoglobulin (β-Lg) and sodium caseinate (SC) have been glycated via Maillard reaction with galactose and lactose and, subsequently, the effect of glycoconjugates hydrolyzed under simulated gastrointestinal digestion on the growth of pure culture of Lactobacillus, Streptococcus and Bifidobacterium has been investigated. Glycopeptides were added to the growth media as the sole carbon source. None of the bacterial strains was able to grow in hydrolysates of native and control heated β-Lg and SC. However, glycopeptides were fermented, in different degree, by Lactobacillus and Bifidobacterium and hardly any effect was detected on the growth of Streptococcus. Digested β-Lg glycoconjugates showed a strain-dependent effect whereas growth profiles of bacteria when hydrolysates of SC glycoconjugates were used as substrates were very similar, regardless of the strain. A general preference towards peptides from β-Lg/SC glycated with galactose, particularly at the state of the reaction in which the highest content in the Amadori compound tagatosyl-lysine is present, was observed. SC glycoconjugates were quickly fermented by some strains, promoting their growth in a greater extent than β-Lg complexes or even glucose. Therefore, from the results obtained in this work it can be concluded that conjugation of both milk proteins with galactose and lactose via the Maillard reaction could be an efficient method to obtain novel food ingredients with a potential prebiotic character. [Copyright &y& Elsevier]

Abstract: The effect of structure on the fermentative properties of potential prebiotic trisaccharides derived from lactulose like 6′-galactosyl-lactulose (β-d-galactopyranosyl-(1→6)-β-d-galactopyranosyl-(1→4)-β-d-fructopyranose), 4′-galactosyl-lactulose (β-d-galactopyranosyl-(1→4)-β-d-galactopyranosyl-(1→4)-β-d-fructopyranose), and 1-galactosyl-lactulose (β-d-galactopyranosyl-(1→4)-β-d-fructopyranosyl-(1→1)-β-d-galactopyranose); and from lactose like 4′-galactosyl-lactose (β-d-galactopyranosyl-(1→4)-β-d-galactopyranosyl-(1→4)-β-d-glucopyranose) and 6′-galactosyl-lactose (β-d-galactopyranosyl-(1→6)-β-d-galactopyranosyl-(1→4)-β-d-glucopyranose), has been assessed in vitro. Fermentations with twelve pure strains of Lactobacillus, Streptococcus and Bifidobacterium were carried out using the purified trisaccharides as the sole carbon source, and bacteria growth was evaluated at 600nm by means of a microplate reader during 48h. Maximum growth rates (μmax) and lag phase were calculated. In general, all the strains tested were able to utilize lactulose and pure trisaccharides derived from lactulose and lactose when they were used as sole carbon source. Nonetheless, glycosidic linkage and/or the monosaccharide composition of the trisaccharides affected the individual strains lag phase, cell densities and growth rates. A general preference towards β-galactosyl residues β(1-6) and β(1-1) linked over those β(1-4) linked was observed, and some strains showed higher cell densities and speed of growth on 6′-galactosyl-lactulose than on 6′-galactosyl-lactose. This is the first study of the effect of lactulose-derived oligosaccharides on pure culture growth which shows that transglycosylation of lactulose allows for obtaining galactooligosaccharides with new glycosidic structures and would open new routes to the synthesis of compounds with potential prebiotic effects. [Copyright &y& Elsevier]

Abstract: Volatile sulphur compounds (VSCs) are of prime importance in the overall aroma of cheese and make a significant contribution to their typical flavours. Thus, the control of VSCs formation offers considerable potential for industrial applications. Here, lactic acid bacteria (LAB) from different ecological origins were screened for their abilities to produce VSCs from L-methionine. From the data presented, VSC-forming abilities were shown to be strain-specific and were correlated with the C-S lyase enzymatic activities determined using different approaches. High VSCs formation were detected for those strains that were also shown to possess high thiol-producing abilities (determined either by agar plate or spectrophotometry assays). Moreover, differences in C-S lyase activities were shown to correspond with the enzymatic potential of the strains as determined by in situ gel visualization. Therefore, the assessment of the C-S lyase enzymatic potential, by means of either of these techniques, could be used as a valuable approach for the selection of LAB strains with high VSC-producing abilities thus, representing an effective way to enhance cheese sulphur aroma compounds synthesis. In this regard, this study highlights the flavour forming potential of the Streptococcus thermophilus STY-31, that therefore could be used as a starter culture in cheese manufacture. Furthermore, although C-S lyases are involved in both biosynthetic and catabolic pathways, an association between methionine and cysteine auxotrophy of the selected strains and their VSCs-producing abilities could not be found. [Copyright &y& Elsevier]

Abstract: Phenolic acids (benzoic, phenylacetic and phenylpropionic acids) are the most abundant phenolic structures found in fecal water. As an approach towards the exploration of their action in the gut, this paper reports the antimicrobial activity of thirteen phenolic acids towards Escherichia coli, Lactobacillus spp., Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans. The growth of E. coli ATCC 25922 was inhibited by only four of the phenolic acids tested at a concentration of 1000 μg/mL, whereas pathogenic E. coli O157:H7 (CECT 5947) was susceptible to ten of them. The genetically manipulated E. coli lpxC/tolC strain was highly susceptible to phenolic acids. The growth of lactobacilli (Lactobacillus paraplantarum LCH7, Lactobacillus plantarum LCH17, Lactobacillus fermentum LPH1, L. fermentum CECT 5716, Lactobacillus brevis LCH23, and Lactobacillus coryniformis CECT 5711) and pathogens (S. aureus EP167 and C. albicans MY1055) was also inhibited by phenolic acids, but to varying extents. Only P. aeruginosa PAO1 was not susceptible to any of the phenolic compounds tested. Structure–activity relationships of phenolic acids and some of their diet precursors [(+)-catechin and (−)-epicatechin] were established, based on multivariate analysis of microbial activities. The antimicrobial properties of phenolic acids reported in this paper might be relevant in vivo. [Copyright &y& Elsevier]

Abstract: Bacteriocins produced by lactic acid bacteria offer potential as tools for ensuring food safety and quality. Lacticin 3147 is a two-peptide lantibiotic previously shown to inhibit a broad range of food spoilage and pathogenic bacteria. Lacticin 3147-producing Lactococcus lactis IFPL 3593 was investigated for its ability to inhibit the growth of clostridia as a means to prevent late blowing in cheese. L. lactis IFPL 3593 was shown to inhibit germination of clostridia spores and prevent late blowing in semi-hard cheeses, with a 5 log g−1 reduction in the numbers of spores when compared to control cheeses. Furthermore, this bacteriocin-producing strain demonstrated considerable potential as a biopreservative agent against heterofermentative lactobacilli and their associated blowing defects. The use of this strain to prevent late blowing in cheese thereby represents a promising alternative to the addition of lysozyme particularly given the increasing concerns regarding the potential allergenicity of this additive. [Copyright &y& Elsevier]

Abstract: Eight strains of Lactobacillus plantarum, 6 strains of Lactobacillus casei, Lactobacillus acidophilus LA-5, and Bifidobacterium lactis BB-12 were screened for β-glucosidase activity. We then proceeded to investigate the enzymatic potential of selected strains for bioconversion of delphinidin and malvidin glycosides to their metabolites. L. plantarum and L. casei strains showed the highest cell-envelope associated β-glucosidase activity. Intracellular β-glucosidase activity from B. lactis BB-12 was up to 287-fold higher than that of the other strains. The L. acidophilus strain showed low β-glucosidase activity, both, intra and extracellularly. No aglycons were detected in bacterial extract reactions with anthocyanin glycosides. Delphinidin-3-glucoside underwent chemical degradation to form mainly gallic acid, although delphinidin-3-glucoside degradation due to B. lactis BB-12 and enzymatic activity towards chemically-formed metabolites due to L. casei LC-01 were observed. Incubation of malvidin-3-glucoside with B. lactis BB-12, L. plantarum IFPL722, and L. casei LC-01 cell-free extracts led to different patterns of gallic, homogentisic and syringic acid formation. [Copyright &y& Elsevier]

Abstract: Lactobacillus acidophilus La-5 is a probiotic strain used in dairy products. Production of bacteriocin by L. acidophilus La-5 was achieved when it was grown in co-cultures with the yogurt starter species Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. However, bacteriocin induction was not observed when heat-killed cells were used as inducers. This study demonstrates that L. acidophilus La-5 produces lactacin B and that the bacteriocin expression is controlled by an auto-induction mechanism involving the secreted peptide IP_1800. The transcript level of the lactacin B gene cluster expression was investigated in co-cultures between L. acidophilus La-5 and S. thermophilus STY-31 and a remarkable increase of the bacteriocin structural gene (lbaB) transcription was observed. However, lbaB was transcribed constitutively in uninduced L. acidophilus La-5 cells, but the levels of the secreted bacteriocin were not enough to be detected by the agar diffusion assay. A new method for bacteriocin detection was formulated based on the monitoring on real time of Lactobacillus sakei subsp. sakei growth in presence of the supernatant and the cell wall extracts of pure and induced L. acidophilus La-5. These results showed that part of lactacin B secreted remains adhered to cell envelope. [Copyright &y& Elsevier]

Abstract: This study describes a procedure that allows specific detection and enumeration of viable bacteria in four species of lactic acid bacteria (Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus casei subsp. casei and Lactobacillus acidophilus) and of Bifidobacterium lactis, mixed in fermented milk products. The procedure is based on the combined use of propidium monoazide (PMA), able to distinguish between viable and irreversibly damaged cells, with species-specific quantitative real-time PCR (RTi-PCR). Loss of viability of the species in a fermented milk through storage at 4°C was similarly (P <0.05) detected by PMA–RTi-PCR and selective plate counts. Furthermore, comparison of results obtained by both methods showed a Pearson linear correlation of 0.995. The enumeration of viable bacteria by PMA–RTi-PCR could be performed in 3h, whereas enumeration by selective plate counts required three days. The procedure developed is a fast method for the identification, enumeration and discrimination of viability of lactic acid bacteria and bifidobacteria mixed in fermented milk products. [Copyright &y& Elsevier]

Abstract: Eight dairies, located in two distant geographic regions of Portugal, were screened along the production cycle in order to evaluate the presence and distribution of Listeria spp. in their environment. Three dairies in each region were positive for the presence of listeriae and 213 isolates were obtained. Based on an integrated analysis of RAPD fingerprints with three primers, molecular identification and genomic typing of isolates was performed followed by spatial and temporal mapping on dairy plants. The occurrence of Listeria species by region was noticeable different. Listeria monocytogenes prevailed in South Portugal dairies and L. innocua presented the highest occurrence in Azores, whereas L. seeligeri and L. ivanovii were detected in distinct regions. Dairies were at risk of contamination, from more than one source, whatever the stage in the production cycle and the surface materials used. For the three prevalent species, most of the genomic types were dairy and sampling time specific. Nonetheless, more than one type could be found in each dairy at a particular site and, in a few cases, even for different species. Some dairies also shared types, mainly for L. innocua and usually at the same stage of the production cycle. For L. monocytogenes, PCR serotyping was applied and 52% of genomic types were serotype 4b. An equal frequency of genomic types (24%) was found for serotypes 1/2b or 3b and 1/2a or 3a. The global pattern of types within a dairy is not constant, suggesting cycles of elimination and recontamination along the production cycle. [Copyright &y& Elsevier]

The amino acid conversion to volatile compounds by lactic acid bacteria is important for aroma formation in cheese. In this work, we analyzed the effect of the lytic bacteriocin Lacticin 3147 on transamination of isoleucine and further formation of the volatile compound 2-methylbutanal in cheese. The Lacticin 3147 producing strain Lactococcus lactis IFPL3593 was fluorescently tagged (IFPL3593-GFP) by conjugative transfer of the plasmid pMV158GFP from Streptococcus pneumoniae, and used as starter in cheese manufacture. Starter adjuncts were the bacteriocin-sensitive strains L. lactis T1 and L. lactis IFPL730, showing branched chain amino acid aminotransferase and α-keto acid decarboxylase activity, respectively. Adjunct strains were selected to complete the isoleucine conversion pathway and, hence, increase formation of 2-methylbutanal conferring aroma to the cheese. The non-bacteriocin-producing strain L. lactis IFPL359-GFP was included as starter in the control batch. Fluorescent tagging of the starter strains allowed their tracing in cheese during ripening by fluorescence microscopy and confocal scanning laser microscopy. The bacteriocin produced by L. lactis IFPL3593-GFP enhanced lysis of the adjuncts with a concomitant increase in isoleucine transamination and about a two-fold increase of the derived volatile compound 2-methylbutanal. This led to an enhancement of the cheese aroma detected by a sensory panel. The improvement of cheese flavour and aroma may be of significant importance for the dairy industry. [Copyright &y& Elsevier]