Combined effects of heat, nisin and acidification on the inactivation of Clostridium sporogenes spores in carrot-alginate particles: From kinetics to process validation

Bacteriostasis of nisin against planktonic and biofilm bacteria: Its mechanism and application

Food safety incidents caused by bacterial contamination have always been one of the public safety issues of social concern. Planktonic cells, viable but non-culturable (VBNC) cells, and biofilm cells of bacteria can coexist in food or food processing, posing more serious challenges to public health and safety by increasing bacterial survival and difficulty in detection. As a non-toxic, no side effect, and highly effective bacteriostatic substance, nisin has received wide attention from researchers. In this review, we summarized the species and biosynthesis of nisin, the effects of nisin alone or in combination with other treatments on planktonic and biofilm cells, and its applications in the fields of food, feed, and medicine by consulting numerous studies. Meanwhile, the mechanism of nisin on planktonic and biofilm cells was proposed based on existing researches. Nisin not only has antibacterial activity against most G+ bacteria but also exhibits a bacteriostatic effect on G- bacteria when combined with other antibacterial treatments. In addition to planktonic cells, nisin also has significant effects on bacterial cells in biofilms by changing the thickness, density, and composition of biofilms. Based on the three action processes of nisin on biofilms, we summarized the changes of bacteria in biofilms, including the causes of bacterial death and the formation of the VBNC state. We consider that research on the relationship between nisin and VBNC state should be strengthened.

Recent Advances in the Application of the Antimicrobial Peptide Nisin in the Inactivation of Spore-Forming Bacteria in Foods

Conventional thermal and chemical treatments used in food preservation have come under scrutiny by consumers who demand minimally processed foods free from chemical agents but microbiologically safe. As a result, antimicrobial peptides (AMPs) such as bacteriocins and nisin that are ribosomally synthesised by bacteria, more prominently by the lactic acid bacteria (LAB) have appeared as a potent alternative due to their multiple biological activities. They represent a powerful strategy to prevent the development of spore-forming microorganisms in foods. Unlike thermal methods, they are natural without an adverse impact on food organoleptic and nutritional attributes. AMPs such as nisin and bacteriocins are generally effective in eliminating the vegetative forms of spore-forming bacteria compared to the more resilient spore forms. However, in combination with other non-thermal treatments, such as high pressure, supercritical carbon dioxide, electric pulses, a synergistic effect with AMPs such as nisin exists and has been proven to be effective in the inactivation of microbial spores through the disruption of the spore structure and prevention of spore outgrowth. The control of microbial spores in foods is essential in maintaining food safety and extension of shelf-life. Thus, exploration of the mechanisms of action of AMPs such as nisin is critical for their design and effective application in the food industry. This review harmonises information on the mechanisms of bacteria inactivation from published literature and the utilisation of AMPs in the control of microbial spores in food. It highlights future perspectives in research and application in food processing.

Identification of Clostridium spp. derived from a sheep and cattle slaughterhouse by matrix-assisted laser desorption and ionization-time of flight mass spectrometry (MALDI-TOF MS) and 16S rDNA sequencing

Clostridia are widespread and some of them are serious human pathogens. Identification of Clostridium spp. is important for managing microbiological risks in the food industry. Samples derived from sheep and cattle carcasses from a slaughterhouse in Iran were analyzed by MALDI-TOF MS using direct transfer and extended direct transfer sample preparation methods and 16S rDNA sequencing. MALDI-TOF MS could identify ten species in 224 out of 240 Clostridium isolates. In comparison to the 16S rDNA sequencing, correct identification rate of the Clostridium spp. at the species level by MALDI-TOF MS technique was 93.3%. 16 isolates were not identified by MALDI-TOF MS but 16s rDNA sequencing identified them as C. estertheticum, C. frigidicarnis, and C. gasigenes species. The most frequently identified Clostridium species were: C. sporogenes (13%), C. cadaveris (12.5%), C. cochlearium (12%) and C. perfringens (10%). Extended direct transfer method [2.26 ± 0.18 log (score)] in comparison to direct transfer method [2.15 ± 0.23 log (score)] improved Clostridium spp.

IDENTIFICATION

Using a cut-off score of 1.7 was sufficient for accurate identification of Clostridium species. MALDI-TOF MS identification scores for Clostridium spp. decreased with longer incubation time. Clostridium species predominantly were isolated from carcasses after skinning and evisceration steps in the slaughterhouse. MALDI-TOF MS could be an accurate way to identify Clostridium species. Moreover, continuous improvement of the database and MALDI-TOF MS instrument enhance its performance in food control laboratories.

Inhibitory activity of Lactobacillus plantarum TF711 against Clostridium sporogenes when used as adjunct culture in cheese manufacture

Bacteriocins produced by lactic acid bacteria are of great interest to the food-processing industry as natural preservatives. This work aimed to investigate the efficacy of bacteriocin-producing Lactobacillus plantarum TF711, isolated from artisanal Tenerife cheese, in controlling Clostridium sporogenes during cheese ripening. Cheeses were made from pasteurised milk artificially contaminated with 10(4) spores m/l C. sporogenes. Experimental cheeses were manufactured with Lb. plantarum TF711 added at 1% as adjunct to commercial starter culture. Cheeses made under the same conditions but without Lb. plantarum TF711 served as controls. Evolution of microbiological parameters, pH and NaCl content, as well as bacteriocin production was studied throughout 45 d of ripening. Addition of Lb. plantarum TF711 did not bring about any significant change in starter culture counts, NaCl content and pH, compared with control cheese. In contrast, clostridial spore count in experimental cheeses were significantly lower than in control cheeses from 7 d onwards, reaching a maximum reduction of 2·2 log units on day 21. Inhibition of clostridia found in experimental cheeses was mainly attributed to plantaricin activity, which in fact was recovered from these cheeses.

Mathematical modeling and microbiological verification of ohmic heating of a multicomponent mixture of particles in a continuous flow ohmic heater system with electric field parallel to flow

To accomplish continuous flow ohmic heating of a low-acid food product, sufficient heat treatment needs to be delivered to the slowest-heating particle at the outlet of the holding section. This research was aimed at developing mathematical models for sterilization of a multicomponent food in a pilot-scale ohmic heater with electric-field-oriented parallel to the flow and validating microbial inactivation by inoculated particle methods. The model involved 2 sets of simulations, one for determination of fluid temperatures, and a second for evaluating the worst-case scenario. A residence time distribution study was conducted using radio frequency identification methodology to determine the residence time of the fastest-moving particle from a sample of at least 300 particles. Thermal verification of the mathematical model showed good agreement between calculated and experimental fluid temperatures (P > 0.05) at heater and holding tube exits, with a maximum error of 0.6 °C. To achieve a specified target lethal effect at the cold spot of the slowest-heating particle, the length of holding tube required was predicted to be 22 m for a 139.6 °C process temperature with volumetric flow rate of 1.0 × 10(-4) m3/s and 0.05 m in diameter. To verify the model, a microbiological validation test was conducted using at least 299 chicken-alginate particles inoculated with Clostridium sporogenes spores per run. The inoculated pack study indicated the absence of viable microorganisms at the target treatment and its presence for a subtarget treatment, thereby verifying model predictions.

Probiotics and its functionally valuable products-a review

During the past two decades probiotic bacteria have been increasingly proposed as health promoting bacteria in variety of food system, because of its safety, functional, and technological characteristics. Commonly, Lactobacillus spp., Bifidobacterium spp., Saccharomyces boulardii, and some other microorganisms have been considered as probiotic strains. Possibly these bacterial strains exerted several beneficial effects into gastrointestinal tract of host while administered with variety of food system. Lactic acid bacteria (LAB) usually produce antimicrobial substances like bacteriocin which have broad spectrum of antagonist effect against closely related Gram positive and Gram negative pathogens. LAB strains often produce polymeric substances such as exopolysaccharides (EPS) which increase the colonization of probiotic bacteria by cell-cell interactions in gastrointestinal tract. LAB also produces biosurfactant which showed that the wide range of antimicrobial activity against bacterial pathogen as well as its antiadhesive properties reduces the adhesion of pathogens into gastric wall membrane. Furthermore, LAB strains have also been reported for production of antioxidants which are ability to scavenge the free radicals such as superoxide anions and hydroxyl radicals. For this sense, this review article is mainly focused on the ecology, biosynthesis, genetics, target sites, and applications of bacteriocins and EPS from LAB strains. Moreover, this review discusses about the production and functions of nutritive essential element folate and iron chelating agent such as siderophores from LAB.

Clostridium sporogenes PA 3679 and its uses in the derivation of thermal processing schedules for low-acid shelf-stable foods and as a research model for proteolytic Clostridium botulinum

The putrefactive anaerobe Clostridium sporogenes PA 3679 has been widely used as a nontoxigenic surrogate for proteolytic Clostridium botulinum in the validation of thermal processes for low-acid shelf-stable foods, as a target organism in the derivation of thermal processes that reduce the risk of spoilage of such foods to an acceptable level, and as a research model for proteolytic strains of C. botulinum. Despite the importance of this organism, our knowledge of it has remained fragmented. In this article we draw together the literature associated with PA 3679 and discuss the identity of this organism, the phylogenetic relationships that exist between PA 3679 and various strains of C. sporogenes and proteolytic C. botulinum, the heat resistance characteristics of PA 3679, the advantages and limitations associated with its use in the derivation of thermal processing schedules, and the knowledge gaps and opportunities that exist with regard to its use as a research model for proteolytic C. botulinum. Phylogenetic analysis reviewed here suggests that PA 3679 is more closely related to various strains of proteolytic C. botulinum than to selected strains, including the type strain, of C. sporogenes. Even though PA 3679 is demonstrably nontoxigenic, the genetic basis of this nontoxigenic status remains to be elucidated, and the genetic sequence of this microorganism appears to be the key knowledge gap remaining to be filled. Our comprehensive review of comparative heat resistance data gathered for PA 3679 and proteolytic strains of C. botulinum over the past 100 years supports the practice of using PA 3679 as a (typically fail-safe) thermal processing surrogate for proteolytic C. botulinum.

Genomic sequence of bacteriophage ATCC 8074-B1 and activity of its endolysin and engineered variants against Clostridium sporogenes

Lytic bacteriophage ATCC 8074-B1 produces large plaques on its host Clostridium sporogenes. Sequencing of the 47,595-bp genome allowed the identification of 82 putative open reading frames, including those encoding proteins for head and tail morphogenesis and lysis. However, sequences commonly associated with lysogeny were absent. ORF 22 encodes an endolysin, CS74L, that shows homology to N-acetylmuramoyl-L-alanine amidases, and when expressed in Escherichia coli, the protein causes effective lysis of C. sporogenes cells when added externally. CS74L was also active on Clostridium tyrobutyricum and Clostridium acetobutylicum. The catalytic domain expressed alone (CS74L(1-177)) exhibited a similar activity and the same host range as the full-length endolysin. A chimeric endolysin consisting of the CS74L catalytic domain fused to the C-terminal domain of endolysin CD27L, derived from Clostridium difficile bacteriophage ΦCD27, was produced. This chimera (CSCD) lysed C. sporogenes cells with an activity equivalent to that of the catalytic domain alone. In contrast, the CD27L C-terminal domain reduced the efficacy of the CS74L catalytic domain when tested against C. tyrobutyricum. The addition of the CD27L C-terminal domain did not enable the lysin to target C. difficile or other CD27L-sensitive bacteria.

Influence of pH and sodium chloride on kinetics of thermal inactivation of the bacteriocin-like substance P34

AIMS

To investigate the kinetics of thermal inactivation of the bacteriocin-like substance P34 at different pH and sodium chloride concentration.

METHODS AND RESULTS

Samples of bacteriocin were treated at different time-temperature combinations in the range of 0-300 min and 90-120°C and the kinetic parameters for bacteriocin inactivation were calculated. For all treatments, the thermal inactivation reaction fitted adequately to first-order model. D- and k-values were smaller and higher, respectively, for pH 4·5 than for 6·0 or 7·0, indicating that bacteriocin P34 was less thermostable at lower pH. At 120, 115 and 100°C, the addition of sodium chloride decreased thermal stability. For other temperatures, addition of NaCl increased stability of the peptide. The presence of greater amount of the salt (50 g l(-1) ) resulted in a higher thermal stability of bacteriocin P34, suggesting that the reduction in water activity of the solution interfered on the stability of the peptide.

CONCLUSIONS

Based on an isothermal experiment in the temperature range of 90-120°C, and by thermal death time models, bacteriocin P34 is less heat stable at low pH and has increased thermal stability in the presence of NaCl. Addition of NaCl improved the stability of the peptide P34 at high temperatures.

SIGNIFICANCE AND IMPACT OF THE STUDY

Studies on kinetics of thermal inactivation of bacteriocins are essential to allow their proper utilization in the food industry.

Kinetic modeling of the thermal inactivation of bacteriocin-like inhibitory substance p34

Optimization of thermal processes relies on adequate degradation kinetic models to warrant food safety and quality. The knowledge on thermal inactivation kinetics of antimicrobial peptides is necessary to allow for their adequate use as natural biopreservatives in the food industry. In this work, thermal inactivation of the previously characterized bacteriocin-like inhibitory substance (BLIS) P34 was kinetically investigated within the temperature range of 90-120 degrees C. Listeria monocytogenes ATCC 7644 was used as the indicator microorganism for antimicrobial activity. Applicability of various inactivation models available in the literature was critically evaluated. The first-order model provided the best description of the kinetics of inactivation over the selected temperatures, with k values between 0.059 and 0.010 min(-1). D and k values decreased and increased, respectively, with increasing temperature, indicating a faster inactivation at higher temperatures. Results suggest that BLIS P34 is thermostable, with a z value of 37.74 degrees C and E(a) of 72 kJ mol(-1).