Bacteria In Food Industry Research Articles

Inactivation mechanism of phenyllactic acid against Bacillus cereus spores and its application in milk beverage

Phenyllactic acid (PLA) as a natural phenolic acid exhibits antibacterial activity against non-spore-forming bacteria, while the inhibitory effect against bacterial spore remained unknown. Herein, this study investigated the inactivation effect of PLA against Bacillus cereus spores. The results revealed that the minimum inhibitory concentration of PLA was 1.25 mg/mL. PLA inhibited the outgrowth of germinated spores into vegetative cells rather than germination of spores. PLA disrupted the spore coat, and damaged the permeability and integrity of inner membrane. Moreover, PLA disturbed the establishment of membrane potential due to the inhibition of oxidative metabolism. SEM observations further visualized the morphological changes and structural disruption caused by PLA. Besides, PLA caused the degradation of DNA of germinated spores. Finally, PLA was applied in milk beverage, and showed promising inhibitory effect against B. cereus spores. This finding could provide scientific basis for the application of PLA against spore-forming bacteria in food industry.

Isolation, characterization, and application of bacteriophage cocktails for the biocontrol of Pseudomonas fluorescens group strains in whole and skimmed milk.

Pseudomonas fluorescens group strains can lead to spoilage of milk as well as loss of quality in dairy products through their heat-resistant enzymes. Phages are important alternatives for combating spoilage bacteria in food industry and used successfully in many applications. The aim of this study was the isolation and characterization of phages and to assess the efficiency of a phage cocktail in whole and skimmed milk. For this purpose, phages effective against Pseudomonas fluorescens (L23.2), Pseudomonas tolaasii (P22.1), and Pseudomonas rhodesiae (A11.1) were isolated. Their host range was found to be highly specific, and the transmission electron micrographs indicates that they belonged to Tectiviridae family. Their genome sizes were found to be vary between 38.3 and 53.5 kb. The latent periods and burst sizes were determined as 15, 10, 15 min and 91, 20, 80 PFU/infected cell for L23.2, P22.1, and A11.1, respectively. All three phages were found to be sensitive to low pH and high temperature. The effect of the phage cocktail was monitored in milk with different fat contents during storage at 4 °C for 5 days. As a result, bacterial reductions up to 4.09 and 5.29 log-units were observed for the whole and skimmed milk, respectively. Thus, the efficacy of a phage cocktail against a bacterial mixture of different P. fluorescens strains was tested in milk samples with different fat contents in accordance with real-life scenarios for the first time.

Antibacterial and antibiofilm potential of Lacticaseibacillus rhamnosus YT and its cell-surface extract

BackgroundFoodborne pathogens and spoilage bacteria survived in the biofilm pose a serious threat to food safety and human health. It is urgent to find safe and effective methods to control the planktonic bacteria as well as the biofilm formation. Substances with antibacterial and antibiofilm activity found in lactic acid bacteria were mainly metabolites secreted in the cell-free supernatant. Previously, Lacticaseibacillus rhamnosus YT was isolated because its cell pellets displayed distinguished antibacterial activity under neutral conditions. This study aimed to investigate the antibacterial and antibiofilm properties of the L. rhamnosus YT cells and its crude cell-surface extract.ResultsThe antibacterial activity of the L. rhamnosus YT cells constantly increased with cells growth and reached the peak value after the cells grew into stationary phase. After cocultivation with the L. rhamnosus YT cells, the biofilm formation of B. subtilis and S. enterica was reduced. The antibacterial activity of the L. rhamnosus YT cells was varied along with various culture conditions (carbon sources, nitrogen sources, medium pH and cultural temperatures) and the antibacterial intensity (antibacterial activity per cell) was disproportional to the biomass. Furthermore, the cell-surface extract was isolated and displayed broad antimicrobial spectrum with a bacteriostatic mode of action. The antibiofilm activity of the extract was concentration-dependent. In addition, the extract was stable to physicochemical treatments (heat, pH and protease). The extract performed favorable emulsifying property which could reduce the water surface tension from 72.708 mN/m to 51.011 mN/m and the critical micelle concentration (CMC) value was 6.88 mg/mL. Besides, the extract was also able to emulsify hydrocarbon substrates with the emulsification, index (E24) ranged from 38.55% (for n-hexane) to 53.78% (for xylene). The E24 for xylene/extract emulsion was merely decreased by 5.77% after standing for 120 h. The main components of the extract were polysaccharide (684.63 μg/mL) and protein (120.79 μg/mL).ConclusionThe properties of the extract indicated that it might be a kind of biosurfactant. These data suggested that L. rhamnosus YT and the cell-surface extract could be used as an alternative antimicrobial and antibiofilm agent against foodborne pathogens and spoilage bacteria in food industry.

Natural sources and encapsulating materials for probiotics delivery systems: Recent applications and challenges in functional food development.

Probiotics are known as the live microorganisms which upon adequate administration elicit a health beneficial response inside the host by decreasing the luminal pH, eliminating the pathogenic bacteria in the gut as well as producing short chain fatty acids (SCFA). With advancements in research; probiotics have been explored as potential ingredients in foods. However, their use and applications in food industry have been limited due to restrictions of maintaining the viability of probiotic cells and targeting the successful delivery to gut. Encapsulation techniques have significant influence on increasing the viability rates of probiotic cells with the successful delivery of cells to the target site. Moreover, encapsulating techniques also prevent the live cells from harsh physiological conditions of gut. This review discusses several encapsulating techniques as well as materials derived from natural sources and nutraceutical compounds. In addition to this, this paper also comprehensively discusses the factors affecting the probiotics viability and evaluation of successful release and survival of probiotics under simulated gastric, intestinal conditions as well as bile, acid tolerant conditions. Lastly applications and challenges of using encapsulated bacteria in food industry for the development of novel functional foods have also been discussed in detail too. Future studies must include investigating the use of encapsulated bacterial formulations in in-vivo models for effective health beneficial properties as well as exploring the mechanisms behind the successful release of these formulations in gut, hence helping us to understand the encapsulation of probiotic cells in a meticulous manner.

Research Progress of Seaweed Fermentation with Lactic Acid Bacteria

Edible seaweed is one of the most important marine food stuffs. Many nutrient elements such as proteins, carbohydrates, vitamins, minerals, and bioactive substances such as polysaccharides, phenols, etc. have been found in the tissue of seaweed. More and more researchers have revealed that seaweed is fermentable to lactic acid bacteria (LAB) due to its nutritional facts. It has been shown that LAB fermentation can improve the quality or safety of seaweed products, and promote the release or production of some bioactive compounds. Thus, seaweed fermentation by using LAB can provide a wide array of fermented seaweed-based foods with excellent health benefits. In this paper, according to the relevant research reports of seaweed fermentation by lactic acid bacteria at home and abroad in recent years, the types of fermentation by lactic acid bacteria, the feasibility of seaweed fermentation by lactic acid bacteria and the main types of lactic acid bacteria, as well as the effect and role of lactic acid bacteria in seaweed fermentation are described, and the development and application status of seaweed fermentation by lactic acid bacteria in food industry is summarized. Finally, the future trends and prospects in this research field are analyzed to provide a certain reference for the further development of more healthy LAB fermented seaweed foods.

Eradication of planktonic Vibrio parahaemolyticus and its sessile biofilm by curcumin-mediated photodynamic inactivation

Vibrio parahaemolyticus is the leading pathogen in seafoods. This study established the efficient blue light-emitting diode (LED) photodynamic inactivation (PDI) to eradicate Vibrio parahaemolyticus and its biofilm with photosensitizer curcumin, and the antibacterial and antibiofilm mechanisms were elucidated by determining the DNA integrity, protein changes, morphological alteration, gene expression levels, chemical composition and structural parameters of biofilm, etc. Results showed that the planktonic V. parahaemolyticus could not be visibly detectable on the medium after the curcumin-mediated PDI treatment with 1.0 μM curcumin within 5 min (1.14 J/cm2), and its biofilm was almost completely eradiated with 20.0 μM curcumin within 60 min (13.68 J/cm2). The cellular wall and proteins of V. parahaemolyticus were the vulnerable target for the PDI treatment. Meanwhile, the PDI efficiently inactivated the living cells, reduced the key chemical composition of extracellular polymeric substance and negatively altered the architectures of biofilm. Furthermore, the PDI treatment down-regulated the expression of virulence genes (tdh and toxR) and biofilm formation genes (oxyR, aphA, luxR and opaR) of V. parahaemolyticus, which would impede the bacterial infection, colonization and biofilm formation. The study will enrich our knowledge of the PDI-induced inactivation of V. parahaemolyticus, hence unlock the design of novel PDI technology to eradicate bacteria in food industry.

The fingerprint mapping and genotyping systems application on methicillin-resistant Staphylococcus aureus

As a typical Gram-positive microorganism, S. aureus was recognized as common foodborne pathogenic bacteria in food industry. To study their individuality and pathogenicity mechanism, thirty-three Staphylococci strains were applied to the investigation with the identification of MRSA by PCR targeting on S. aureus specific 16S rRNA and femA genes as well as methicillin-resistant mecA and orfX elements by multiplex-PCR assay. Fingerprinting mapping was then employed using three typing systems (KZ/M13, IS256 and ERIC2) to genotype 33 MRSA strains. As the result indicated, all 33 Staphylococci strains were identified as MRSA. However, diversity occurred among different fingerprinting system results. KZ/M13 system and IS256 system both typed 10 genotypes while ERIC2 system had 8 genotypes. Based on the genotyping results, a discussion was performed in typing ability, discriminatory ability and accordance ratio. Given the above studies, a novel rapid detection method for MRSA was conducted with multiplex-PCR, which possessed rapidity and accuracy. Meanwhile, three fingerprinting systems showed high sensitivity, resolution and classification ratio in MRSA typing. These methods have a broad application prospect in food safety and epidemiology in the future.

A Study on Biofilms Inhibition and Preservative Activity of Pomegranate Peel Methanol Extract (PPME)

Objectives: Microorganisms with biofilms are associated with chronic human infections (highly resistant to antimicrobial agents). Pomegranate is used in treatment of several diseases, as its peels contain phenolic compounds and hydrolysable tannins. We aimed to study the effect of PPME on inhibition of biofilms and as a natural preservative in food industrial application. Methods: Pomegranate peel was extracted with methanol. E. coli clinical isolates were identified by standard microbiological procedures. Antibiotic susceptibility testing was performed using disc diffusion method. Antibacterial activity of PPME was tested using agar well diffusion assay. Minimum Inhibitory Concentration (MIC) was evaluated according to The European Committee on Antimicrobial Susceptibility Testing (EUCAST) agar dilution method. Biofilms detection was done by Tube method. Total phenolic content (TPC) in PPME was determined using spectrophotometric method. PPME ability to scavenge (1, 1diphenyl-2-picryl hydrazyl) DPPH free radicals was assessed by the standard method. Total antioxidant capacity of PPME was evaluated by phosphormolybdenum method. Total Phenolic Content (TPC) for cooked patties was freshly analyzed at different concentrations (1-0.25mg/ml). Results: Tested isolates were multidrug resistant. High antibacterial activity of PPME was found. MIC of PPME was found to be 10mg/ml. Tested isolates were biofilms producers, PPME largely affected on biofilm forming ability. TPC for treated group was (2785.19-349.22 µg/kg): for untreated group was 1251-226 µg/kg). DPPH radical scavenging activity was 38.12-5.45%. Thiobarbituric Acid Reactive Substances (TBARS) values were measured for samples from (0 -9 days) of storage period which was 0.522-1.3,0.859-1.816mg malonladehyde/kg meat for treated, untreated group respectively. AOA% was 31.49-66.92 from (0 – 9) days of storage. Conclusions: PPME was able to inhibit biofilm formation in tested isolates and can be promising in inhibiting contamination caused by biofilm forming bacteria in food industry.

Strain‐level characterization of cold‐stressed Listeria monocytogenes using maldi‐tof mass fingerprinting

AbstractListeria monocytogenes, a common food borne bacterial pathogen, could survive in stress conditions applied in food production such as cold environments. Twenty‐eight strains of L. monocytogenes under cold stress were subjected to MALDI‐TOF MS analysis and compared with control strains under normal growth conditions. The resulting protein mass finger printings were visualized by phyloproteomic cluster and self‐organized map (SOM). It was observed that after cold‐stressed treatment, all strains exhibited change of mass finger printings. In most strains, the variations of the fingerprinting profiles were significant. The diversity in protein fingerprinting of L. monocytogenes after cold stress was also improved. The strain‐level differentiation of the stressed L. monocytogenes would not only improve the understanding of bacterial responses to cold stress but also facilitate classification and detection of stressed bacteria in food industry.Practical applicationsListeria monocytogenes that causes lethal listeriosis could survive in cold‐stressed treatment and pose high risk to food safety. However, the entire picture of the physiology of stress response adaptation of this strain is still unknown. The protein fingerprinting analysis of the cold‐stressed L. monocytogenes provided an entire picture of phenotypic stress response adaptation at strain level and helped to understand bacterial resistance to cold stress. Additionally, the study on the peptide fingerprints changes, covering 28 strains of L. monocytogenes from different sources would be particularly valuable for the strain‐level differentiation and detection of stressed bacteria in food industry.

Study Bacteriocin Production and Optimization Using New Isolates of <i>Lactobacillus</i> spp. Isolated from Some Dairy Products under Different Culture Conditions

Lactobacilli belong to the group of lactic acid bacteria (LAB), that have several distinguished abilities such as production of lactic acid, enzymes such as β-Galactosidase and natural antimicrobial substances called bacteriocins. Bacteriocin is a biopreservative agent potential of suppressing growth of some contaminant bacteria in food industry but its commercial availability is limited and costly. The study aimed to select isolates of Lactobacillus spp. potential for producing bacteriocins to suppress the growth of Escherichia coli ATCC 25922 and Bacillus subtilis NCIB3610, and to optimize the process of bacteriocin production. Results obtained in this study showed that L. acidophilus isolate CH1 was selected as the best candidate for bacteriocin among the four isolates that tested. The largest amounts of the bacteriocins were synthesized only in MRS medium was supplemented with K2HPO4 (1.0%), Tween 80 (1%), Beef extract (1%), glucose, cyctein and peptone extract (1%). The optimization of culture conditions for bacteriocin production areas showed that corn steep liquor medium was the best medium for all isolates against Bacillus subtilis while no effect was observed on Escherichia coli ATCC 25922 except when used MRS medium. The optimum conditions for bacteriocin production were pH 6.0, temperature 34?C with 4% Phenyl acetamide showing the greatest growth inhibition areas.