Expression of the catalase gene katA in starter culture Lactobacillus plantarum TISTR850 tolerates oxidative stress and reduces lipid oxidation in fermented meat product

Catalase immobilization: Current knowledge, key insights, applications, and future prospects - A review

Catalase (CAT), a ubiquitous enzyme in all oxygen-exposed organisms, effectively decomposes hydrogen peroxide (H2O2), a harmful by-product, into water and oxygen, mitigating oxidative stress and cellular damage, safeguarding cellular organelles and tissues. Therefore, CAT plays a crucial role in maintaining cellular homeostasis and function. Owing to its pivotal role, CAT has garnered considerable interest. However, many challenges arise when used, especially in multiple practical processes. "Immobilization", a widely-used technique, can help improve enzyme properties. CAT immobilization offers numerous advantages, including enhanced stability, reusability, and facilitated downstream processing. This review presents a comprehensive overview of CAT immobilization. It starts with discussing various immobilization mechanisms, support materials, advantages, drawbacks, and factors influencing the performance of immobilized CAT. Moreover, the review explores the application of the immobilized CAT in various industries and its prospects, highlighting its essential role in diverse fields and stimulating further research and investigation. Furthermore, the review highlights some of the world's leading companies in the field of the CAT industry and their substantial potential for economic contribution. This review aims to serve as a discerning, source of information for researchers seeking a comprehensive cutting-edge overview of this rapidly evolving field and have been overwhelmed by the size of publications.

Expanding the genetic programmability of Lactiplantibacillus plantarum

Lactobacilli are ubiquitous in nature and symbiotically provide health benefits for countless organisms including humans, animals and plants. They are vital for the fermented food industry and are being extensively explored for healthcare applications. For all these reasons, there is considerable interest in enhancing and controlling their capabilities through the engineering of genetic modules and circuits. One of the most robust and reliable microbial chassis for these synthetic biology applications is the widely used Lactiplantibacillus plantarum species. However, the genetic toolkit needed to advance its applicability remains poorly equipped. This mini-review highlights the genetic parts that have been discovered to achieve food-grade recombinant protein production and speculates on lessons learned from these studies for L. plantarum engineering. Furthermore, strategies to identify, create and optimize genetic parts for real-time regulation of gene expression and enhancement of biosafety are also suggested.

Evaluation of the Effect of Plectranthus amboinicus L. Leaf Extracts on the Bacterial Antioxidant System and Cell Membrane Integrity of Pseudomonas aeruginosa PA01 and Staphylococcus aureus NCTC8325

Plectranthus amboinicus (Indian borage) has been extensively studied for its medicinal properties, which can be exploited to develop new antimicrobial therapeutics. The current study investigated the effect of Plectranthus amboinicus leaf extracts on the catalase activity, reactive oxygen species, lipid peroxidation, cytoplasmic membrane permeability, and efflux pump activity in S. aureus NCTC8325 and P. aeruginosa PA01. As the enzyme catalase protects bacteria against oxidative stress, disruption of its activity creates an imbalance in reactive oxygen species (ROS) levels, which subsequently oxidizes lipid chains, leading to lipid peroxidation. In addition, bacterial cell membranes are a potential target for new antibacterial agents, as efflux pump systems play a crucial role in antimicrobial resistance. Upon exposure of the microorganisms to Indian borage leaf extracts, the observed catalase activity decreased by 60% and 20% in P. aeruginosa and S. aureus, respectively. The generation of ROS can cause oxidation reactions to occur within the polyunsaturated fatty acids of the lipid membranes and induce lipid peroxidation. To investigate these phenomena, the increase in ROS activity in P. aeruginosa and S. aureus was studied using H₂DCFDA, which is oxidized to 2',7'-dichlorofluorescein (DCF) by ROS. Furthermore, the concentration of lipid peroxidation product (malondialdehyde) was assessed using the Thiobarbituric acid assay and was shown to increase by 42.4% and 42.5% in P. aeruginosa and S. aureus, respectively. The effect of the extracts on the cell membrane permeability was monitored using diSC3-5 dye and it was observed that the cell membrane permeability of P. aeruginosa increased by 58% and of S. aureus by 83%. The effect on efflux pump activity was investigated using Rhodamine-6-uptake assay, which displayed a decrease in efflux activity of 25.5% in P. aeruginosa and 24.2% in S. aureus after treatment with the extracts. This combination of different methods to study various bacterial virulence factors provides a more robust, mechanistic understanding of the effect of P. amboinicus extracts on P. aeruginosa and S. aureus. This study thus represents the first report of the assessment of the effect of Indian borage leaf extracts on bacterial antioxidant systems and bacterial cell membranes, and can facilitate the future development of bacterial resistance modifying agents derived from P. amboinicus.

Role of the Mn-Catalase in Aerobic Growth of Lactobacillus plantarum ATCC 14431

Lactobacilli are Gram-positive aerotolerant organisms that comprise the largest genus of Lactic Acid Bacteria (LAB). Most lactobacilli are devoid of the antioxidant enzymes, superoxide dismutases, and catalases, required for protection against superoxide radicals and hydrogen peroxide (H2O2), respectively. However, some lactobacilli can accumulate millimolar concentrations of intracellular manganese and spare the need for superoxide dismutase, while others possess non-heme catalases. L. plantarum is associated with plant materials and plays an important role in fermented foods and gut microbiomes. Therefore, understanding the effects of the environment on the growth and survival of this organism is essential for its success in relevant industrial applications. In this report, we investigated the physiological role of Mn-catalase (MnKat) in Lactobacillus plantarum ATCC 14431. To this end, we compared the physiological and morphological properties of a ΔMnkat mutant strain and its isogenic parental strain L. plantarum ATCC 14431. Our data showed that the MnKat is critical for the growth of L. plantarum ATCC 14431 in the presence of oxygen and resistance to H2O2. The aerobic growth of the mutant in presence or absence of H2O2 was improved in the Mn-rich medium (APT) as compared to the growth in MRS medium. Furthermore, under aerobic conditions the mutant strain possessed atypical cellular morphology (i.e., shorter, and fatter). In conclusion, the MnKat of L. plantarum ATCC 14431 is important for aerobic growth, protection against H2O2, and maintenance of the rod-shaped cell morphology under aerobic conditions.

Exploring the antioxidant effect of Lactobacillus plantarum SCS2 on mice with type 2 diabetes

This study aimed to evaluate the antioxidant effect of Lactobacillus plantarum SCS2 (L. plantarum SCS2). After 1 week of acclimation, 120 male KM mice were divided into normal group (NG), model group (MG), solvent control group (KG), and different test groups (TG1, TG2, TG3) (n = 20/group) randomly. In the second week, except NG mice, other mice were given 0.2 ml 50 mg/kg (body weight) streptozocin (STZ) through intraperitoneal injection for 5 days. After successful modeling, NG and MG mice were fed normally, KG mice was given 0.5 ml 0.1 mol/L phosphate buffer saline (PBS) per day, TG1, TG2, and TG3 mice were given 0.5 ml suspension, intracellular content and heat-killed intracellular content of L. plantarum SCS2 per day for 9 weeks. Body weight and blood glucose were observed and recorded during intragastric administration. Glucose tolerance levels were measured at the twelfth week, then mice were sacrificed and the serum was collected to measure insulin (INS), glycosylated hemoglobin (HbA1c), malondialdehyde (MDA), reactive oxygen species (ROS) and antioxidant enzymes. The results showed that the reduction of weight loss in TG1 and TG2 mice was observed, which was consistent with the blood glucose. At the same time, the INS level of TG1, TG2, and TG3 mice were increased and the HbA1c levels were decreased. Otherwise, the MDA and ROS content in the serum of TG1, TG2, and TG3 mice were decreased and the level of antioxidant enzymes was increased. Interestingly, the activity and content of antioxidant enzymes in TG2 group was the highest in the three test groups. PRACTICAL APPLICATIONS: The results of this study showed that L. plantarum SCS2 could effectively reduce blood glucose, relieve weight loss, improve INS deficiency, and also improve oxidative stress by increasing the activity of antioxidant enzymes. The findings suggest that L. plantarum SCS2 could improve diabetes-related symptoms by alleviating oxidative stress. In the future, people could promote the application of lactic acid bacteria (LAB) which is found in traditional foods with the ability of improving oxidative damage in food nutrition and related fields, so as to guide residents to form good dietary habits, and effectively prevent type 2 diabetes. Meanwhile, it also can enhance the edible value of traditional foods.

Effects of Hemin and Heating Temperature on the Mutagenicity and Lipid Oxidation of Pork Batter during In Vitro Human Digestion with Enterobacteria

The objective of this study was to determine the effects of hemin and heating temperature on the mutagenicity and lipid oxidation of pork batter during in vitro human digestion with enterobacteria. The mutagenicity and lipid oxidation of pork batter increased in the presence of hemin and with increasing temperatures from 60 to 80°C by 17.9 and 23.0% and by 54.6 and 21.2%, respectively. However, the pork batter mutagenicity decreased by 6.09% during in vitro human digestion, whereas lipid oxidation increased by 19.4%. The antioxidant activities of pork batter decreased with hemin and increasing temperature but gradually increased during in vitro human digestion, especially in the large intestine, regardless of the type of enterobacteria ( Escherichia coli and/or Lactobacillus sakei). These results indicate that hemin and temperature are closely related to mutagenicity in pork batter, and in vitro human digestion with enterobacteria could reduce mutagenicity possibly owing to the increase in antioxidant activity by antioxidative enzymes released by enterobacteria.

Effect of Glutathione Dehydrogenase of Lactobacillus sanfranciscensis on Gluten Properties and Bread Volume in Type I Wheat Sourdough Bread

Disulfide exchange reactions in wheat dough impact the polymerization of gluten and the volume of bread. In wheat sourdoughs fermented with Lactobacillus sanfranciscensis, glutathione reductase activity accumulates thiols. This study investigated the role of glutathione reductase and NADH oxidase of L. sanfranciscensis on disulfide exchange reactions, peroxide levels, and gluten polymerization in type I wheat sourdoughs. Fermentation with L. sanfranciscensis DSM20451 Δ gshR lacking glutathione reductase activity reduced the thiol levels in dough when compared to the wild type strain L. sanfranciscensis DSM20451. Fermentation with any strain reduced peroxides in wheat doughs when compared to a chemically acidified control. The impact of baker's yeast on thiol and peroxide levels was greater than the impact of lactobacilli. The depolymerization of gluten proteins was dependent on the free thiol content and dough acidification. Bread produced with the glutathione reductase deficient mutant strain had the highest specific volume compared with all the other groups.

Antimicrobial and antioxidant activities of Enterococcus species isolated from meat and dairy products

Lactic acid bacteria (LAB) have an important role in a great variety of fermented foods. In addition to their contribution to sensory characteristics, they enhance food preservation and can be used as probiotics. In this study, the antimicrobial and antioxidant activities of culture supernatants and cell free extracts of 16 LAB isolated from meat and dairy products were investigated. The bacterial were identified by 16S rRNA sequencing. GenBank BLAST analysis revealed that all the isolates belong to Enterococcus faecium species. Antimicrobial activity against the indicator microorganism (Listeria monocytogenes) was observed at 11 culture supernatants and 4 cell free extracts. The sensibility of culture supernatant was evaluated by proteinase K and trypsin and it was observed that activity of antimicrobial substance was completely lost after the treatment. All of the isolates showed antioxidant activity as determined by the Thiobarbituric Acid Reactive Substances (TBARS) method with both types of extracts. When the antioxidant capacity was investigated using ABTS•+ method (2,2 azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)) and DPPH method (2,2-diphenyl-1-picrylhydrazyl) it was observed that only culture supernatants showed antioxidant capacity. These bacteria could particularly help to reduce or inhibit pathogenic microorganisms as well as oxidative spoilage in foods and feed.

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.

Genomic analysis by deep sequencing of the probiotic Lactobacillus brevis KB290 harboring nine plasmids reveals genomic stability

We determined the complete genome sequence of Lactobacillus brevis KB290, a probiotic lactic acid bacterium isolated from a traditional Japanese fermented vegetable. The genome contained a 2,395,134-bp chromosome that housed 2,391 protein-coding genes and nine plasmids that together accounted for 191 protein-coding genes. KB290 contained no virulence factor genes, and several genes related to presumptive cell wall-associated polysaccharide biosynthesis and the stress response were present in L. brevis KB290 but not in the closely related L. brevis ATCC 367. Plasmid-curing experiments revealed that the presence of plasmid pKB290-1 was essential for the strain's gastrointestinal tract tolerance and tendency to aggregate. Using next-generation deep sequencing of current and 18-year-old stock strains to detect low frequency variants, we evaluated genome stability. Deep sequencing of four periodic KB290 culture stocks with more than 1,000-fold coverage revealed 3 mutation sites and 37 minority variation sites, indicating long-term stability and providing a useful method for assessing the stability of industrial bacteria at the nucleotide level.

Heme proteins in lactic acid bacteria

Lactic acid bacteria (LAB) are of profound importance in food production and infection medicine. LAB do not rely on heme (protoheme IX) for growth and are unable to synthesize this cofactor but are generally able to assemble a small repertoire of heme-containing proteins if heme is provided from an exogenous source. These features are in contrast to other bacteria, which synthesize their heme or depend on heme for growth. We here present the cellular function of heme proteins so far identified in LAB and discuss their biogenesis as well as applications of the extraordinary heme physiology of LAB.

Enhancing the stress responses of probiotics for a lifestyle from gut to product and back again

Before a probiotic bacterium can even begin to fulfill its biological role, it must survive a battery of environmental stresses imposed during food processing and passage through the gastrointestinal tract (GIT). Food processing stresses include extremes in temperature, as well as osmotic, oxidative and food matrix stresses. Passage through the GIT is a hazardous journey for any bacteria with deleterious lows in pH encountered in the stomach to the detergent-like properties of bile in the duodenum. However, bacteria are equipped with an array of defense mechanisms to counteract intracellular damage or to enhance the robustness of the cell to withstand lethal external environments. Understanding these mechanisms in probiotic bacteria and indeed other bacterial groups has resulted in the development of a molecular toolbox to augment the technological and gastrointestinal performance of probiotics. This has been greatly aided by studies which examine the global cellular responses to stress highlighting distinct regulatory networks and which also identify novel mechanisms used by cells to cope with hazardous environments. This review highlights the latest studies which have exploited the bacterial stress response with a view to producing next-generation probiotic cultures and highlights the significance of studies which view the global bacterial stress response from an integrative systems biology perspective.

Coexpression of the superoxide dismutase and the catalase provides remarkable oxidative stress resistance in Lactobacillus rhamnosus

Lactic acid bacteria (LAB) are generally sensitive to oxidative stress caused by reactive oxygen species (ROS). Antioxidant enzymes, especially superoxide dismutase (SOD) and catalase (CAT), can protect against ROS by eliminating superoxide and H(2)O(2), respectively. Lactobacillus rhamnosus is a valuable probiotic starter culture but is deficient in both SOD and CAT, and is thus likely to suffer from oxidative stress in industrial fermentation. To confer high level of oxidative resistance on L. rhamnosus , the SOD gene sodA from Streptococcus thermophilus and CAT gene katA from L. sakei were coexpressed in L. rhamnosus AS 1.2466. The enzyme activities of SOD and CAT were 147.80 ± 1.08 U/mg protein and 2.53 μmol of H(2)O(2) /min/10(8) cfu, respectively, in the recombinant L. rhamnosus CS. After incubation with 10 mM H(2)O(2), the survival ratio of L. rhamnosus CS was 400-fold higher than that of L. rhamnosus CAT. In long-term aerated conditions, viable cells of L. rhamnosus CS remained ∼10(6) cfu/mL after incubation for 7 days, while no living cells of the control were detected. These results showed that the cooperation between SOD and CAT could significantly enhance oxidative resistance in L. rhamnosus . To our best knowledge, this is the first report of two synergistic antioxidant genes being coexpressed in the same Lactobacilli.

Coexpression of bile salt hydrolase gene and catalase gene remarkably improves oxidative stress and bile salt resistance in Lactobacillus casei

Lactic acid bacteria (LAB) encounter various types of stress during industrial processes and gastrointestinal transit. Catalase (CAT) and bile salt hydrolase (BSH) can protect bacteria from oxidative stress or damage caused by bile salts by decomposing hydrogen peroxide (H(2)O(2)) or deconjugating the bile salts, respectively. Lactobacillus casei is a valuable probiotic strain and is often deficient in both CAT and BSH. In order to improve the resistance of L. casei to both oxidative and bile salts stress, the catalase gene katA from L. sakei and the bile salt hydrolase gene bsh1 from L. plantarum were coexpressed in L. casei HX01. The enzyme activities of CAT and BSH were 2.41 μmol H(2)O(2)/min/10(8) colony-forming units (CFU) and 2.11 μmol glycine/min/ml in the recombinant L. casei CB, respectively. After incubation with 8 mM H(2)O(2), survival ratio of L. casei CB was 40-fold higher than that of L. casei CK. Treatment of L. casei CB with various concentrations of sodium glycodeoxycholate (GDCA) showed that ~10(5) CFU/ml cells survived after incubation with 0.5% GDCA, whereas almost all the L. casei CK cells were killed when treaded with 0.4% GDCA. These results indicate that the coexpression of CAT and BSH confers high-level resistance to both oxidative and bile salts stress conditions in L. casei HX01.

Phenotypic and genomic diversity of Lactobacillus plantarum strains isolated from various environmental niches

Lactobacillus plantarum is a ubiquitous microorganism that is able to colonize several ecological niches, including vegetables, meat, dairy substrates and the gastro-intestinal tract. An extensive phenotypic and genomic diversity analysis was conducted to elucidate the molecular basis of the high flexibility and versatility of this species. First, 185 isolates from diverse environments were phenotypically characterized by evaluating their fermentation and growth characteristics. Strains clustered largely together within their particular food niche, but human fecal isolates were scattered throughout the food clusters, suggesting that they originate from the food eaten by the individuals. Based on distinct phenotypic profiles, 24 strains were selected and, together with a further 18 strains from an earlier low-resolution study, their genomic diversity was evaluated by comparative genome hybridization against the reference genome of L. plantarum WCFS1. Over 2000 genes were identified that constitute the core genome of the L. plantarum species, including 121 unique L. plantarum-marker genes that have not been found in other lactic acid bacteria. Over 50 genes unique for the reference strain WCFS1 were identified that were absent in the other L. plantarum strains. Strains of the L. plantarum subspecies argentoratensis were found to lack a common set of 24 genes, organized in seven gene clusters/operons, supporting their classification as a separate subspecies. The results provide a detailed view on phenotypic and genomic diversity of L. plantarum and lead to a better comprehension of niche adaptation and functionality of the organism.

Nisin inducible production of listeriolysin O in Lactococcus lactis NZ9000

Background

Listeria monocytogenes is a well-characterized food-borne pathogen that infects pregnant women and immunocompromised individuals. Listeriolysin O (LLO) is the major virulence factor of the pathogen and is often used as a diagnostic marker for detection of L. monocytogenes. In addition, LLO represents a potent antigen driving T cell-mediated immunity during infection. In the present work, Lactococcus lactis NZ9000 was used as an expression host to hyper-produce LLO under inducible conditions using the NICE (NIsin Controlled Expression) system. We created a modified pNZ8048 vector encoding a six-His-tagged LLO downstream of the strong inducible PnisA promoter.

Results

The constructed vector (pNZPnisA:CYTO-LLO) was expressed in L. lactis NZ9000 and was best induced at mid-log phase with 0.2% v/v nisin for 4 h statically at 30°C. Purification of the His-tagged LLO was accomplished by Ni-NTA affinity chromatography and functionality was confirmed through haemolytic assays. Total LLO yield (measured as total protein content) was 4.43–5.9 mg per litre culture and the haemolytic activity was still detectable after 8 months of storage at 4°C.

Conclusion

The LLO production method described in this work provides an approach to efficient LLO production in the Gram-positive Lactococcus bacterium to yield a significant source of the protein for research and diagnostic applications. Expression of LLO in L. lactis has a number of benefits over E. coli which may facilitate both in vivo and in vitro applications of this system.

Oral administration of a catalase-producing Lactococcus lactis can prevent a chemically induced colon cancer in mice

Reactive oxygen species, such as hydrogen peroxide (H2O2), are involved in various aspects of tumour development. Decreasing their levels can therefore be a promising approach for colon cancer prevention. The objective of this study was to evaluate the effect of catalase-producing Lactococcus lactis on the prevention of an experimental murine 1,2-dimethylhydrazine (DMH)-induced colon cancer. DMH-treated BALB/c mice received either a catalase-producing L. lactis strain or the isogenic non-catalase-producing strain as a control, whereas other untreated mice did not receive bacterial supplementation. Catalase activity and H2O2 levels in intestinal fluids and blood samples were measured, and changes in the histology of the large intestines during tumour progression were evaluated. The catalase-producing L. lactis strain used in this study was able to slightly increase catalase activities in DMH-treated mice (1.19+/-0.08 U ml(-1)) and reduce H2O2 levels (3.4+/-1.1 microM) compared to (i) animals that received the non-catalase-producing strain (1.00+/-0.09 U ml(-1), 9.0+/-0.8 microM), and (ii) those that did not receive bacterial supplementation (1.06+/-0.07 U ml(-1), 10.0+/-1.1 microM). Using the histopathological grading scale of chemically induced colorectal cancer, animals that received the catalase-producing L. lactis had a significantly lesser extent of colonic damage and inflammation (2.0+/-0.4) compared to animals that received the non-catalase-producing L. lactis (4.0+/-0.3) or those that did not receive bacterial supplementation (4.7+/-0.5). The catalase-producing L. lactis strain used in this study was able to prevent tumour appearance in an experimental DMH-induced colon cancer model.

Proteomic analysis of log to stationary growth phase Lactobacillus plantarum cells and a 2-DE database

Lactobacillus plantarum is part of the natural microbiota of many food fermentations as well as the human gastro-intestinal tract. The cytosolic fraction of the proteome of L. plantarum WCFS1, whose genome has been sequenced, was studied. 2-DE was used to investigate the proteins from the cytosolic fraction isolated from mid- and late-log, early- and late-stationary phase cells to generate reference maps of different growth conditions offering more knowledge of the metabolic behavior of this bacterium. From this fraction, a total of 200 protein spots were identified by MALDI-MS and a proteome production map was constructed to facilitate further studies such as detection of suitable biomarkers for specific growth conditions. More than half (57%) of the identified proteins were predicted to be involved in metabolic pathways of the bacterium. The protein profile changed during the growth of the bacteria such that 29% of the identified proteins involved in anabolic pathways were at least twofold up-regulated throughout the mid- and late-exponential and early-stationary phases. In the late-stationary phase, six proteins involved in stress or with a potential role for survival during starvation were up-regulated significantly.

Selection criteria for lactic acid bacteria to be used as functional starter cultures in dry sausage production: An update

Lactic acid bacteria (LAB) have long been used as starter cultures in the production of fermented dry sausages and other meat-derived commodities. These cultures are generally designed to meet food safety, shelf-life, technological effectiveness and economic feasibility criteria. Besides all these traditional properties, novel starter cultures should take into account the risks posed by the formation of biogenic amines in food, and the development and spreading of bacterial resistance to antibiotics. Further, 'functional starters' could protect consumers from harmful bacteria either by a rapid acidification or by the production of antimicrobials (bacteriocins). Specially-selected cultures may also provide probiotic benefits, and, if properly modified, they may even be endorsed with nutraceutical traits. The present review discusses the technological and new selection criteria that should be taken into account when selecting LAB starter cultures for the production of fermented dry sausages.

Production of a heterologous nonheme catalase by Lactobacillus casei: an efficient tool for removal of H2O2 and protection of Lactobacillus bulgaricus from oxidative stress in milk

Lactic acid bacteria (LAB) are generally sensitive to H2O2, a compound that they can paradoxically produce themselves, as is the case for Lactobacillus bulgaricus. Lactobacillus plantarum ATCC 14431 is one of the very few LAB strains able to degrade H2O2 through the action of a nonheme, manganese-dependent catalase (hereafter called MnKat). The MnKat gene was expressed in three catalase-deficient LAB species: L. bulgaricus ATCC 11842, Lactobacillus casei BL23, and Lactococcus lactis MG1363. While the protein could be detected in all heterologous hosts, enzyme activity was observed only in L. casei. This is probably due to the differences in the Mn contents of the cells, which are reportedly similar in L. plantarum and L. casei but at least 10- and 100-fold lower in Lactococcus lactis and L. bulgaricus, respectively. The expression of the MnKat gene in L. casei conferred enhanced oxidative stress resistance, as measured by an increase in the survival rate after exposure to H2O2, and improved long-term survival in aerated cultures. In mixtures of L. casei producing MnKat and L. bulgaricus, L. casei can eliminate H2O2 from the culture medium, thereby protecting both L. casei and L. bulgaricus from its deleterious effects.

High-level resistance to oxidative stress in Lactococcus lactis conferred by Bacillus subtilis catalase KatE

Lactococcus lactis, a lactic acid bacterium widely used for food fermentations, is often exposed to damaging stress conditions. In particular, oxidative stress leads to DNA, protein and membrane damages that can be lethal. As L. lactis has no catalase, the impact of production of the Bacillus subtilis haem catalase KatE on its oxidative stress resistance was tested. This cytoplasmic catalase was engineered for extracellular expression in L. lactis with an optimization strategy based on fusion to the nisin-inducible promoter and a lactococcal signal peptide (SP(Usp45)). The production of KatE by L. lactis conferred an 800-fold increase in survival after 1 h exposure to 4 mM hydrogen peroxide, and a 160-fold greater survival in long-term (3 days) survival of aerated cultures in a cydA mutant, which is unable to respire. The presence of KatE protected DNA from oxidative damage and limited its degradation after long-term aeration in a cydA/recA mutant, defective in DNA repair. L. lactis is thus able to produce active catalase that can provide efficient antioxidant activity.

Effect of Lactobacillus-protective cultures with bacteriocin-like inhibitory substances' producing ability on microbiological, chemical and sensory changes during storage of refrigerated vacuum-packaged sliced beef

AIMS

To investigate the effect of applying two different Lactobacillus-protective cultures, with bacteriocin-like inhibitory substances' (BLIS) producing ability, individually or in combination, on microbiological, chemical and sensory changes during storage of refrigerated vacuum-packaged sliced beef meat.

METHODS AND RESULTS

Lactobacillus sakei CECT 4808 and Lactobacillus curvatus CECT 904(T), which were shown to be producers of BLIS, were inoculated individually or in combination on slices of beef M. semitendinosus. The samples were vacuum packaged and stored at 4 +/- 1 degrees C and were assessed during a 28-day storage period for microbiological [Enterobacteriaceae, Pseudomonas spp., lactic acid bacteria (LAB), Brochothrix thermosphacta and yeasts and moulds], chemical (pH, protein hydrolysis degree, lipid oxidation), sensory (abnormal odour) parameters and instrumental colour. Samples inoculated with the Lact. sakei strain and samples inoculated with the combination of the two strains had significantly (P < 0.05) lower spoilage microbial counts than those inoculated with the Lact. curvatus strain alone or the controls, while both chemical parameters (including lipid oxidation) and abnormal odour scores were also significantly (P < 0.05) improved by the former. Moreover, Lact. sakei alone showed a better preserving effect (P < 0.05) than the combination of both strains in the majority of the parameters tested. Instrumental colour measurements changed with storage time, but no treatment effects (P >or= 0.05) were observed during the whole 28-day storage period.

CONCLUSIONS

The BLIS producer Lact. sakei CECT 4808 strain may be used for improving preservation of vacuum-packaged beef slices, as regards spoilage microbial counts and the chemical parameters tested in this study.

SIGNIFICANCE AND IMPACT OF THE STUDY

Inoculation with the BLIS producer Lact. sakei CECT 4808 strain would provide an additional hurdle to improve storage life of refrigerated vacuum-packaged sliced beef. Furthermore, this strain demonstrated limited antioxidative ability, which could make a contribution to the prevention of lipid oxidation in meat and meat products.