Optimization of asymmetric bioreduction conditions of 1-indanone by Leuconostoc mesenteroides N6 using a face-centered design-based multi-objective optimization model.

There has been an increasing interest in biocatalysts over the past few decades in order to obtain high efficiency, high yield, and environmentally benign procedures aiming at the manufacture of pharmacologically relevant chemicals. Lactic Acid Bacteria (LAB), a microbial group, can be employed as biocatalysts while performing asymmetric reduction of prochiral ketones. In this study, Leuconostoc mesenteroides N6 was used for the asymmetric bioreduction 1-indanone. And then, a novel and innovative face-centered design-based multi-objective optimization model was used to optimize experimental conditions. Also, the experimental design factors were defined as agitation speed, incubation period, pH, and temperature for optimization to acquire the maximum enantiomeric excess (ee) and conversion rate (cr) values. When using the face-centered design-based multi-objective optimization model, the optimum culture conditions corresponded to 96.34 and 99.42%, ee and cr responses, respectively, were pH = 5.87, incubation temperature = 35 °C, incubation period = 50.88 h, and agitation speed = 152.60 rpm. Notably, the validation experiment under the optimum model conditions confirmed the model results. This study demonstrated the importance of the optimization and the efficiency of the face-centered design-based multi-objective model.

Effects of acidification by traditional Jiaozi starter and neutralization with alkali (Na2CO3) on whole wheat dough properties.

BACKGROUND: Whole wheat steamed bread has been recommended for its potential nutritional benefits to human health. Given the positive role of both organic acid and alkali in improving dough development and product quality, the present study investigated the effects of neutralization by addition of alkali (Na2CO3) after dough acidification with traditional Jiaozi starter on the properties of whole wheat dough. RESULTS: The population of yeast and lactic acid bacteria and the acidification level of the dough increased significantly after fermentation with Jiaozi. Incorporation of alkali greatly improved the leavening capacity of the remixed dough and the quality of steamed bread. Jiaozi fermentation and alkali addition changed the water distribution patterns (T2) and affected the secondary structures of gluten protein, starch crystallinity and pasting properties. The storage modulus (G') of the dough increased significantly with the alkali addition, which could be attributed to the promoted cross-linking of the gluten structure and the altered hydration state of the macromolecules. CONCLUSION: The results of the present study indicate that a combination of Jiaozi fermentation and alkali addition could improve the technological properties of whole wheat dough and the quality of steamed bread. The results will help us to further explore the potential application of moderate acidification and alkali addition in the production of leavened whole wheat products. © 2024 Society of Chemical Industry.

Effect of transglutaminase crosslinking combined with lactic fermentation on the potential allergenicity and conformational structure of soy protein.

BACKGROUND: Food allergies are a growing concern worldwide, with soy proteins being important allergens that are widely used in various food products. This study investigated the potential of transglutaminase (TGase) and lactic acid bacteria (LAB) treatments to modify the allergenicity and structural properties of soy protein isolate (SPI), aiming to develop safer soy-based food products. RESULTS: Treatment with TGase, LAB or their combination significantly reduced the antibody reactivity of ß-conglycinin and the immunoglobulin E (IgE) binding capacity of soy protein, indicating a decrease in allergenicity. TGase treatment led to the formation of high-molecular-weight aggregates, suggesting protein crosslinking, while LAB treatment resulted in partial protein hydrolysis. These structural changes were confirmed by Fourier transform infrared spectroscopy, which showed a decrease in ß-sheet content and an increase in random coil and ß-turn contents. In addition, changes in intrinsic fluorescence and ultraviolet spectroscopy were also observed. The alterations in protein interaction and the reduction in free sulfhydryl groups highlighted the extensive structural modifications induced by these treatments. CONCLUSION: The synergistic application of TGase and LAB treatments effectively reduced the allergenicity of SPI through significant structural modifications. This approach not only diminished antibody reactivity of ß-conglycinin and IgE binding capacity of soy protein but also altered the protein's primary, secondary and tertiary structures, suggesting a comprehensive alteration of SPI's allergenic potential. These findings provide a promising strategy for mitigating food allergy concerns and lay the foundation for future research on food-processing techniques aimed at allergen reduction. © 2024 Society of Chemical Industry.

Biological activities and applications of exopolysaccharides produced by lactic acid bacteria: a mini-review.

Exopolysaccharides (EPSs) are naturally occurring high-molecular-weight carbohydrates that have been widely studied for their biological activities, including antioxidant, immunomodulatory, anticancer and gut microbiota regulation activities. Polysaccharides are abundant in nature and can be derived from animals, plants, algae, and microorganisms, but among polysaccharides with potential uses, EPSs from microorganisms have the advantages of a short production cycle, high yield, and independence of production from season and climate and thus have broad prospects. While the safety of the producing microorganism can represent a problem in application of microbial EPSs, lactic acid bacteria (LAB) have been used by humans for thousands of years, and they and their products are generally recognized as safe. This makes LAB excellent sources for exopolysaccharides. EPS-producing LAB are readily found in nature. Through screening of strains, optimization of culture conditions, and improvement of the growth medium, the yield of EPSs from LAB can be increased and the scope of application broadened. This review summarizes EPSs from LAB in terms of structure, function and applications, as well as yield optimization, and introduces recent research on the biological activities and practical applications of LAB EPSs, aiming to provide references for researchers in related areas.

Insights into lactic acid bacteria cryoresistance using FTIR microspectroscopy.

Freezing is widely used for bacterial cell preservation. However, resistance to freezing can greatly vary depending on bacterial species or growth conditions. Our study aims at identifying cellular markers of cryoresistance based on the comparison of three lactic acid bacteria (LAB) exhibiting different tolerance to freezing: Carnobacterium maltaromaticum CNCM I-3298, Lactobacillus delbrueckii subsp. bulgaricus ATCC 11842, and Lactobacillus delbrueckii subsp. bulgaricus CFL1. A thorough characterization of their cytoplasmic membrane properties was carried out by measuring their fatty acid composition, membrane fluidity, and lipid phase transition upon cooling from 50 to -50 °C. Vitrification temperatures of the intra- and extra-cellular compartments were also quantified by differential scanning calorimetry. Additionally, the cell biochemical characterization was carried out using a recently developed Fourier transform infrared (FTIR) micro-spectroscopic approach allowing the analysis of live bacteria in an aqueous environment. The multivariate analysis of the FTIR spectra of fresh and thawed cells enabled the discrimination of the three bacteria according to their lipid, protein, and cell wall peptidoglycan components. It also revealed freezing-induced modifications of these three cellular components and an increase in bacteria heterogeneity for the two strains of L. bulgaricus, the freeze-sensitive bacteria. No cellular damage was observed for C. maltaromaticum, the freeze-resistant bacteria. Comparison of the results obtained from the different analytical methods confirmed previously reported cryoresistance markers and suggested new ones, such as changes in the absorbance of specific infrared spectral bands. FTIR microspectroscopy could be used as a rapid and non-invasive technique to evaluate the freeze-sensitivity of LAB.

Lactic acid bacterial exopolysaccharides strongly bind histamine and can potentially be used to remove histamine contamination in food.

The symptoms of foodborne histamine poisoning are similar to those of IgE-mediated food allergies. In this study, we investigated the histamine-binding capacity of lactic acid bacteria (LAB) strains as potential preventive agents against histamine poisoning. Histamine biosorption capacity was determined for 16 LAB strains. Leuconostoc mesenteroides TOKAI 51 m, Lactobacillus paracasei TOKAI 65 m, Lactobacillus plantarum TOKAI 111 m and Pediococcus pentosaceus TOKAI 759 m showed especially high biosorption rates and reached saturation within 30 min. Adsorption isotherms showed better conformance to the Freundlich model than to the Langmuir model. Analyses after heat, periodic acid and guanidine hydrochloride treatments suggested that histamine was bound to the bacterial cell surface. HPLC analysis revealed that exopolysaccharides produced by Lact. paracasei TOKAI 65 m strongly bound to histamine. In the detachment test with 1 mol l-1 HCl solution, the dissociation rate of histamine for Lact. paracasei TOKAI 65 m was <10 %. This strain is presumably a suitable candidate for use against histamine poisoning.

Suitability of lactic acid bacteria and deriving antibacterial preparations to enhance shelf-life and consumer safety of emulsion type sausages.

Ready-to-eat (RTE) sliced emulsion type sausages are sensitive to recontamination with Listeria (L.) monocytogenes during processing and packaging steps. Since Listeria spp. are able to grow on those products under cold storage conditions, taking steps to reduce the recontamination risk and implementing antibacterial hurdles contribute to consumer safety and increase the product quality. With this study data about the suitability of culture broth, cell-free supernatant (CFS) or concentrated bacteriocin preparations (CFSconc) of bacteriocin-producing lactic acid bacteria (LAB) obtained from fermented sausages from Germany as protective culture or antibacterial additive were provided. In different challenge tests, the potential of selected LAB or their preparations were investigated for their potential to reduce growth of L. monocytogenes and/or Brochothrix (B.) thermosphacta on sliced RTE emulsion type sausages under modified atmosphere or vacuum during refrigerated storage for a 21-day period. Applied LAB culture broth and CFS could not reduce the growth of L. monocytogenes or B. thermosphacta. On the other hand, samples treated with CFSconc obtained from Pediococcus spp. strains showed a significant inhibition (p < 0.05) of more than 1.5 log10 of the applied L. monocytogenes strains during the storage period. The growth of B. thermosphacta could not be influenced. Thereby, the need for concentrating preparations was shown to be important to obtain a suitable antibacterial preparation that would contribute to consumer safety and food quality when applied as a protective additive.

Co-Microencapsulated Black Rice Anthocyanins and Lactic Acid Bacteria: Evidence on Powders Profile and In Vitro Digestion.

Two multi-functional powders, in terms of anthocyanins from black rice (Oryza sativa L.) and lactic acid bacteria (Lactobacillus paracasei, L. casei 431®) were obtained through co-microencapsulation into a biopolymer matrix composed of milk proteins and inulin. Two extracts were obtained using black rice flour as a raw material and hot water and ethanol as solvents. Both powders (called P1 for aqueous extract and P2 for ethanolic extract) proved to be rich sources of valuable bioactives, with microencapsulation efficiency up to 80%, both for anthocyanins and lactic acid bacteria. A higher content of anthocyanins was found in P1, of 102.91 ± 1.83 mg cyanindin-3-O-glucoside (C3G)/g dry weight (DW) when compared with only 27.60 ± 17.36 mg C3G/g DW in P2. The morphological analysis revealed the presence of large, thin, and fragile structures, with different sizes. A different pattern of gastric digestion was observed, with a highly protective effect of the matrix in P1 and a maximum decrease in anthocyanins of approximatively 44% in P2. In intestinal juice, the anthocyanins decreased significantly in P2, reaching a maximum of 97% at the end of digestion; whereas in P1, more than 45% from the initial anthocyanins content remained in the microparticles. Overall, the short-term storage stability test revealed a release of bioactive from P2 and a decrease in P1. The viable cells of lactic acid bacteria after 21 days of storage reached 7 log colony forming units (CFU)/g DW.

Profiling of Potential Antibacterial Compounds of Lactic Acid Bacteria against Extremely Drug Resistant (XDR) Acinetobacter baumannii.

A total of 20 of isolates of lactic acid bacteria (LAB) were selected and screened for antagonistic activity against clinical strains of 30 clinical isolates of extremely drug-resistant (XDR) Acinetobacter baumannii using the well diffusion assay method. Results showed that 50% of the highly LAB strains possessed inhibitory activity against (up to 66%) of the XDR A. baumannii strains tested. The supernatant of the twenty LAB strains was subjected to gas chromatography mass spectrometry (GCMS) revealed that the common compound found in the active isolates against XDR A. baumannii was 3-Isobutyl-2,3,6,7,8,8a-hexahydropyrrolo[1,2-a]pyrazine-1,4-dione, a known potential diketopiperazine group. The molecular docking study against potential antibacterial targets with selected ligands was performed to predict the binding mode of interactions, which is responsible for antibacterial activity. The docking analysis of the potent compounds supported the potential antibacterial activity exhibiting high inhibition constant and binding affinity in silico.

Dairy associations for the targeted control of opportunistic Candida.

Antifungal and antibacterial activities of twenty-six combinations of lactic acid bacteria, propionibacteria, acetic acid bacteria and dairy yeasts inoculated in whey and milk were investigated. Associations including acetic acid bacteria were shown to suppress growth of the opportunistic yeast Candida albicans in well-diffusion assays. The protective effect of milk fermented with the two most promising consortia was confirmed in Caco-2 cell culture infected with C. albicans. Indeed, these fermented milks, after heat-treatment or not, suppressed lactate dehydrogenase release after 48 h while significant increase in LDH release was observed in the positive control (C. albicans alone) and with fermented milk obtained using commercial yogurt starter cultures. The analysis of volatile compounds in the cell-free supernatant using solid phase microextraction (SPME) coupled to gas chromatography-mass spectrometry (GC-MS) showed accumulation of significant amount of acetic acid by the consortium composed of Lactobacillus delbrueckii 5, Lactobacillus gallinarum 1, Lentilactobacillus parabuchneri 3, Lacticaseibacillus paracasei 33-4, Acetobacter syzygii 2 and Kluyveromyces marxianus 19, which corresponded to the zone of partial inhibition of C. albicans growth during well-diffusion assays. Interestingly, another part of anti-Candida activity, yielding small and transparent inhibition zones, was linked with the consortium cell fraction. This study showed a correlation between anti-Candida activity and the presence of acetic acid bacteria in dairy associations as well as a significant effect of two dairy associations against C. albicans in a Caco-2 cell model. These two associations may be promising consortia for developing functional dairy products with antagonistic action against candidiasis agents.

Feeding Honeybee Colonies with Honeybee-Specific Lactic Acid Bacteria (Hbs-LAB) Does Not Affect Colony-Level Hbs-LAB Composition or Paenibacillus larvae Spore Levels, Although American Foulbrood Affected Colonies Harbor a More Diverse Hbs-LAB Community.

The main current methods for controlling American Foulbrood (AFB) in honeybees, caused by the bacterial pathogen Paenibacillus larvae, are enforced incineration or prophylactic antibiotic treatment, neither of which is fully satisfactory. This has led to an increased interest in the natural relationships between the pathogenic and mutualistic microorganisms of the honeybee microbiome, in particular, the antagonistic effects of Honeybee-Specific Lactic Acid Bacteria (hbs-LAB) against P. larvae. We investigated whether supplemental administration of these bacteria affected P. larvae infection at colony level over an entire flowering season. Over the season, the supplements affected neither colony-level hbs-LAB composition nor naturally subclinical or clinical P. larvae spore levels. The composition of hbs-LAB in colonies was, however, more diverse in apiaries with a history of clinical AFB, although this was also unrelated to P. larvae spore levels. During the experiments, we also showed that qPCR could detect a wider range of hbs-LAB, with higher specificity and sensitivity than mass spectrometry. Honeybee colonies are complex super-organisms where social immune defenses, natural homeostatic mechanisms, and microbiome diversity and function play a major role in disease resistance. This means that observations made at the individual bee level cannot be simply extrapolated to infer similar effects at colony level. Although individual laboratory larval assays have clearly demonstrated the antagonistic effects of hbs-LAB on P. larvae infection, the results from the experiments presented here indicate that direct conversion of such practice to colony-level administration of live hbs-LAB is not effective.

Lipidomic analysis of lactic acid bacteria strains by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Analysis by MALDI-TOF mass spectrometry and gas chromatography-mass spectrometry was used to characterize the lipid profile of 3 lactic acid bacteria strains. By gas chromatography coupled with mass spectrometry, 23 fatty acids were identified. Dominant acids were palmitic (C16:0), oleic (C18:1), and α-linoleic acid (C18:3n-3) for Lactobacillus paracasei; for Lactococcus lactis they were palmitic (C16:0), gondoic (C20:1), myristoleic (C14:1), and eicosadienoic acid (C20:2), respectively; and in the case of Lactobacillus curvatus were C18:1, C18:2n-6, and C16:0, respectively. The effect of the medium on fatty acid composition was also determined. In addition, the fatty acid profile was also compared using MALDI MS analysis. The MALDI-TOF MS was used for qualitative analysis and identification of bacterial lipids. Phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylcholine, triacylglycerols, and ceramides were the most abundant species in lactic acid bacteria. One hundred different combinations of fatty acids in polar and nonpolar lipids have been identified, including 11 phospholipids (18 phosphatidylglycerol, 16 phosphatidylethanolamine, 10 phosphatidylinositol, 8 phosphatidylcholine, 4 lyso-phosphatidylethanolamine, 3 lyso-phosphatidylcholine, 3 phosphatidylserine, 1 lyso-phosphatidic acid, 1 lyso-phosphatidylglycerol, 1 lyso-phoshatidylinositol, and 1 phosphatidic acid), 23 triacylglycerols, 9 ceramides, and 2 sphingomyelin. The most abundant fatty acids identified were C16:0, C16:1, C18:0, and C18:3. Obtained lipid profiles allowed to distinguish the tested bacterial strains.

Freeze-dried immobilized kefir culture in cider-making.

BACKGROUND: The aim of the present study was to evaluate the fermentation efficiency of freeze-dried immobilized kefir culture on natural supports (apple pieces, delignified cellulosic material) in cider making at various temperatures (5-45 °C) in comparison with freeze-dried free cells. Freeze-dried cells were initially tested in apple juice fermentations at 30 °C, and then the freeze-dried cultures produced with no cryoprotectants were assessed in repeated batch fermentations. RESULTS: Repeated batch fermentations lasted for longer than 5 months. High malic acid conversion rates (up to 78.5%) and ethanol productivity values (up to 37.9 g L-1 day-1 ) were recorded for freeze-dried immobilized cells. Polymerase chain reaction - denaturing gradient gel electrophoresis (PCR-DGGE) analysis showed that freeze-drying had no effect on the microbial diversity of kefir culture. Higher alcohols were significantly reduced at low fermentation temperatures. Application of principal component analysis (PCA) revealed that both the fermentation temperature and the nature of the freeze-dried kefir culture affected significantly the minor volatiles determined by gas chromatography/mass spectrometry (GC/MS). Notably, all ciders produced were of high quality and were accepted by the tasting panel. CONCLUSIONS: Freeze-dried immobilized kefir culture on natural supports with no cryoprotectants was found to be suitable for simultaneous alcoholic and malolactic cider fermentation at various temperatures (5-45 °C). The high operational stability of the systems was confirmed and the results obtained are of great interest for the industrial sector as they could be exploited for cider, low-alcohol cider, or 'soft' cider production. © 2020 Society of Chemical Industry.

Postbiotics produced by lactic acid bacteria: The next frontier in food safety.

There are many critical challenges in the use of primary and secondary cultures and their biological compounds in food commodities. An alternative is the application of postbiotics from the starter and protective lactic acid bacteria (LAB). The concept of postbiotics is relatively new and there is still not a recognized definition for this term. The word "postbiotics" is currently used to refer to bioactive compounds, which did not fit to the traditional definitions of probiotics, prebiotics, and paraprobiotics. Therefore, the postbiotics may be presently defined as bioactive soluble factors (products or metabolic byproducts), produced by some food-grade microorganisms during the growth and fermentation in complex microbiological culture (in this case named cell-free supernatant), food, or gut, which exert some benefits to the food or the consumer. Many LAB are considered probiotic and their postbiotic compounds present similar or additional health benefits to the consumer; however, this review aimed to address the most recent applications of the postbiotics with food safety purposes. The potential applications of postbiotics in food biopreservation, food packaging, and biofilm control were reviewed. The current uses of postbiotics in the reduction and biodegradation of some food safety-related chemical contaminants (e.g., biogenic amines) were considered. We also discussed the safety aspects, the obstacles, and future perspectives of using postbiotics in the food industry. This work will open up new insights for food applications of postbiotics prepared from LAB.

Genome, transcriptome and fermentation analyses of Lactobacillus plantarum LY-78 provide new insights into the mechanism of phenyllactate biosynthesis in lactic acid bacteria.

Phenyllactate (PLA) is found in a variety of fermented foods and is a promising antibacterial agent, drug and plastic synthetic precursor. Previous studies have shown that PLA is a product of Phe catabolism in lactic acid bacteria (LAB), and PLA biosynthesis is mainly related to lactate dehydrogenases (LDHs). Here, the genome, transcriptome and fermentation characteristics of PLA-producing Lactobacillus plantarum LY-78 were studied. The fermentation experiments demonstrated that L. plantarum LY-78 possesses the ability to synthesize PLA de novo. Secondly, the genome and transcriptome analyses revealed candidate pathways, operons and key genes for PLA biosynthesis in the strain. Finally, genome-wide transcriptome analysis revealed significant changes in the expression profile of strain LY-78 in the absence and presence of PPA. Overall, this work demonstrates for the first time that PLA can be a by-product of Phe anabolism in LAB, provides new insights and evidence for elucidating the mechanism of PLA biosynthesis in LAB, and may provide new candidate genes and research strategies for future PLA biosynthesis applications.

Lactobacillus curvatus UFV-NPAC1 and other lactic acid bacteria isolated from calabresa, a fermented meat product, present high bacteriocinogenic activity against Listeria monocytogenes.

BACKGROUND: Bacteriocins produced by lactic acid bacteria (LAB) can be considered as viable alternatives for food safety and quality, once these peptides present antimicrobial activity against foodborne pathogens and spoilage bacteria. Fermented foods, such as artisanal sausages and cured meats, are relevant sources of LAB strains capable of producing novel bacteriocins, with particular interest by the food industry. RESULTS: Three LAB strains (firstly named as Lactobacillus curvatus 12, L. curvatus 36 and Weissella viridescens 23) were obtained from calabresa by presenting promising bacteriocinogenic activity, distinct genetic profiles (rep-PCR, RAPD, bacteriocin-related genes) and wide inhibitory spectrum. Among these strains, L. curvatus 12 presented higher bacteriocin production, reaching 25,000 AU/mL after incubation at 25, 30 and 37 °C and 6, 9 and 12 h. Partially purified bacteriocins from L. curvatus 12 kept their inhibitory activity after elution with isopropanol at 60% (v/v). Bacteriocins produced by this strain were purified by HPLC and sequenced, resulting in four peptides with 3102.79, 2631.40, 1967.06 and 2588.31 Da, without homology to known bacteriocins. CONCLUSIONS: LAB isolates obtained from calabresa presented high inhibitory activity. Among these isolates, bacteriocins produced by L. curvatus 12, now named as L. curvatus UFV-NPAC1, presented the highest inhibitory performance and the purification procedures revealed four peptides with sequences not described for bacteriocins to date.

In vitro removal of polycyclic aromatic hydrocarbons by lactic acid bacteria.

AIMS: The current study aimed to investigate the ability of lactic acid bacteria (LABs) in removing four polycyclic aromatic hydrocarbons (PAHs) namely, benzo(a)pyrene (BaP), benz(a)anthracene (BaA), chrysene (Chr) and benzo(b)fluoranthene (BbF) from contaminated phosphate buffer saline (PBS). METHOD AND RESULTS: The effect of initial PAH concentrations (5, 10, 15, 20 µg ml-1 ), bacterial population (107 , 108 , 109 , 1010 CFU per ml) and pH (3, 5, 7) was studied to evaluate bacterial binding ability. All the tested bacteria could remove BaA, Chr, BbF and BaP from phosphate buffer solution and in almost all assays, removing of PAHs was as follows: BaP>Chr>BaA>BaF. Bifidobacterium lactis BB-12 had the lowest binding rate for all four PAHs, while the highest binding ability was related to Lactobacillus acidophilus LA-5. Moreover, cell viability was not required for the binding ability and even acid-treated, heat-treated and ultrasonic-treated bacterial cells showed more binding ability. The results showed that the bacteria-PAH complex was irreversible after washing with PBS. CONCLUSIONS: The removal of PAHs was significantly related to pH of media, strains of bacteria, type and concentration of PAHs SIGNIFICANCE AND IMPACT OF THE STUDY: This study has been focused on the reduction of polycyclic aromatic hydrocarbons using LABs and probiotics. Our results showed that not only live strains but also inactivated tested strains are able to remove PAHs from aqueous media, presenting new methods to diminish the amount of these contaminants in foods. Furthermore, the results of this study can be used in future research on evaluating the effects of oral administration of probiotic supplements and even dead probiotic strains on reducing PAHs in humans.

Factors influencing the membrane fluidity and the impact on production of lactic acid bacteria starters.

Production of lactic acid bacteria starters for manufacturing food, probiotic, and chemical products requires the application of successive steps: fermentation, concentration, stabilization, and storage. Despite process optimization, losses of bacterial viability and functional activities are observed after stabilization and storage steps due to cell exposure to environmental stresses (thermal, osmotic, mechanical, and oxidative). Bacterial membrane is the primary target for injury and its damage is highly dependent on its physical properties and lipid organization. Membrane fluidity is a key property for maintaining cell functionality, and depends on lipid composition and cell environment. Extensive evidence has been reported on changes in membrane fatty acyl chains when modifying fermentation conditions. However, a deep characterization of membrane physical properties and their evolution following production processes is scarcely reported. Therefore, the aims of this mini-review are (i) to define the membrane fluidity and the methods used to assess it and (ii) to summarize the effect of environmental conditions on membrane fluidity and the resulting impact on the resistance of lactic acid bacteria to the stabilization processes. This will make it possible to highlight existing gaps of knowledge and opens up novel approaches for future investigations.

A comparison of dynamic tertiary and competition models for describing the fate of Listeria monocytogenes in Minas fresh cheese during refrigerated storage.

This study compares dynamic tertiary and competition models for L. monocytogenes growth as a function of intrinsic properties of a traditional Brazilian soft cheese and the inhibitory effect of lactic acid bacteria (LAB) during refrigerated storage. Cheeses were prepared from raw or pasteurized milk with or without the addition of selected LAB with known anti-listerial activity. Cheeses were analyzed for LAB and L. monocytogenes counts, pH and water activity (aw) throughout cold storage. Two approaches were used to describe the effect of LAB on L. monocytogenes: a Huang-Cardinal model that considers the effect of pH and aw variation in a dynamic kinetic analysis framework; and microbial competition models, including Lotka-Volterra and Jameson-effect variants, describing the simultaneous growth of L. monocytogenes and LAB. The Jameson-effect with γ and the Lotka-Volterra models produced models with statistically significant coefficients that characterized the inhibitory effect of selected LAB on L. monocytogenes in Minas fresh cheese. The Huang-Cardinal model [pH] outperformed both competition models. Taking aw change into account did not improve the fit quality of the Huang-Cardinal [pH] model. These models for Minas soft cheese should be valuable for future microbial risk assessments for this culturally important traditional cheese.

Dietary effects of commercial probiotics on growth performance, digestibility, and intestinal morphometry of broiler chickens.

This study compared five commercially available probiotics vis-à-vis antibiotic growth promotant (AGP) supplementation and absence of feed additive based on efficiency, intestinal morphometry, and energy digestibility in improving broiler chicken production. A total of 630 straight run (Cobb) day-old broiler chicks were distributed to seven treatments following a completely randomized design, with ten replicates per treatment and nine birds per replicate per cage. Dietary treatments consisted of basal diet in combination with the following: without probiotics and AGP supplementation (treatment 1); 75 ppm each of chlorotetracycline (CTC) and Zn bacitracin (treatment 2); probiotic A, Bacillus subtilis (treatment 3); probiotic B, Bacillus subtilis (treatment 4); probiotic C, Enterococcus faecium (treatment 5); and probiotic D, Bacillus subtilis (treatment 6); probiotic E, Enterococcus faecium, Bifidobacterium spp., Pediococcus spp., and Lactobacillus spp. (treatment 7). At day 42, energy digestibility was determined by fasting three randomly selected birds from each treatment for 12 h and then subjecting them to their corresponding dietary treatments. Excreta were collected and pooled after 24 h of feeding. Pooled excreta were weighed, oven-dried, and subjected to energy analyses after 3-day collection. Apparent total tract metabolizable energy was then computed. At day 47, three birds were randomly selected per treatment for intestinal morphometry (villi height and crypt depth) of the duodenum, jejunum, and ileum. Dietary supplementation using probiotics showed no significant effect on overall body weight, weight gain, feed consumption, feed efficiency, dressing percentage, mortality, harvest recovery, carcass quality parameters (e.g., meat to bone ratio and abdominal fat content), intestinal morphometry, and energy digestibility. Birds under treatment 7 (basal feed + probiotic E) generated the highest income over feed and chick cost.