Reduction of Escherichia coli O157:H7 in Biofilms Using Bacteriophage BPECO 19

Biofilm formation is a growing concern in the food industry. Escherichia coli O157:H7 is one of the most important foodborne pathogens that can persists in food and food‐related environments and subsequently produce biofilms. The efficacy of bacteriophage BPECO 19 was evaluated against three E. coli O157:H7 strains in biofilms. Biofilms of the three E. coli O157:H7 strains were grown on abiotic (stainless steel, rubber, and minimum biofilm eradication concentration [MBEC^TM] device) and biotic (lettuce) surfaces at different temperatures. The effectiveness of bacteriophage BPECO 19 in reducing preformed biofilms on these surfaces was further evaluated by treating the surfaces with a phage suspension (10⁸ PFU/mL) for 2 h. The results indicated that the phage treatment significantly reduced (P  < 0.05) the number of adhered cells in all the surfaces. Following phage treatment, the viability of adhered cells was reduced by ≥3 log CFU/cm², 2.4 log CFU/cm², and 3.1 log CFU/peg in biofilms grown on stainless steel, rubber, and the MBEC^TM device, respectively. Likewise, the phage treatment reduced cell viability by ≥2 log CFU/cm² in biofilms grown on lettuce. Overall, these results suggested that bacteriophages such as BPECO 19 could be effective in reducing the viability of biofilm‐adhered cells.     

Reduction of Listeria monocytogenes in cold‐smoked salmon by bacteriophage P100, nisin and lauric arginate,singly or in combinations

Three GRAS antimicrobials including, lauric arginate (LAE), bacteriophage P100 (phage P100) and bacteriocin nisin, were evaluated either singly or in combinations for the reduction of initial load of Listeria monocytogenes in cold‐smoked salmon (CSS). The stability of phage P100 in the presence of LAE (200 ppm) and nisin (500 ppm) or at 10× and 100× of these concentrations was determined at 4 °C or 30 °C for 24 h in a broth model. Phage P100 was found to be highly stable in the presence of these antimicrobial agents as plaque‐forming units (PFU) did not vary between control and antimicrobial‐treated phage. The survival of L. monocytogenes in the presence of phage P100, nisin and LAE showed remarkable reduction within 24 h both at 4 °C or 30 °C in broth. Treatment of CSS containing 3.5 log CFU cm^?2 L. monocytogenes with phage P100 (10⁸ PFU mL^?1), nisin (500 ppm) and LAE (200 ppm) showed strong listericidal action and reduced the L. monocytogenes by 2–3 log CFU cm^?2 after 24 h. Among the combined treatments, phage P100 + LAE or nisin + LAE exhibited the most listericidal action in which L. monocytogenes cells were reduced to undetectable level within 24 h in CSS.     

Bactericidal Effect of Calcium Oxide (Scallop‐Shell Powder) Against Pseudomonas aeruginosa Biofilm on Quail Egg Shell,Stainless Steel,Plastic, and Rubber

The aim of this study was to evaluate the bactericidal effect of calcium oxide (CaO) against Pseudomonas aeruginosa biofilms on quail eggshells and major egg contacting surfaces (stainless steel, plastic, and rubber). The samples were subjected to CaO treatments (0%, 0.01%, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, and 0.30%) for 1 min. All the CaO treatments significantly reduced P. aeruginosa biofilms on all tested surfaces as compared to controls. In comparison of biofilm stability, the strongest and most resistant biofilm was formed on eggshell against the CaO treatment, followed by rubber, stainless steel, and plastic. In evaluation of bactericidal effect, the largest reduction (3.16 log CFU) was observed in plastic even at the lowest concentration of CaO (0.01%), whereas the least reduction was found in eggshells, regardless of CaO concentration. In addition, stainless steel showed a significant reduction in biofilm formation at all concentrations except 0.10% to 0.15% CaO. At 0.30% CaO, the reduction of P. aeruginosa in biofilms on stainless steel, plastic, rubber, and eggshell were 5.48, 6.37, 4.87, and 3.14 log CFU/cm² (CFU/egg), respectively. Biofilm reduction after CaO treatment was also observed by field emission scanning electron microscopy (FE‐SEM). Based on the FE‐SEM images, we observed that P. aeruginosa biofilms formed compact aggregations on eggshell surfaces with CaO treatments up to 0.30%. More specifically, a 0.20% CaO treatment resulted in the reductions of 3 to 6 log CFU in all materials.     

Bacterial inactivation and quality changes of fresh‐cut avocados as affected by intense light pulses of specific spectra

Intense light pulses (ILP) treatments have good prospects for becoming an alternative to traditional thermal methods for decontamination of food surfaces. The aim of this work was to evaluate which ranges of the light spectrum are responsible for bacterial inactivation and their effect on the quality of fresh‐cut avocado. Results show that the effectiveness of ILP treatment decreases when the ultraviolet (UV) spectral region is blocked (particularly UV‐C). ILP treatments without UV‐C light (305–1100 nm) and an overall fluence of 10.68 J cm^?2 caused reductions of 2.47 and 1.35 log CFU g^?1 in the initial counts of inoculated Escherichia coli and Listeria innocua, respectively, in comparison with those treated using only VIS–NIR light (0.83 and 0.68 log CFU g^?1, respectively). Treatments applying light of a wavelength between 305 and 1100 nm had a more pronounced impact on colour, texture and headspace gas composition than treatments that did not contain UV light (400–1100 nm).     

Fate of biofilm cells of Cronobacter sakazakii under modified atmosphere conditions

Survival of biofilm cells of Cronobacter sakazakii formed on stainless steel and polyvinyl chloride (PVC) on exposure to different atmosphere conditions was studied. Biofilms were formed on stainless steel and PVC coupons by using three strains of C. sakazakii. Six day old biofilms on stainless steel and PVC coupons were stored under N₂ gas, CO₂ gas, and air for up to 20 days. N₂ and CO₂ gases resulted in significant (p < 0.05) further reductions of 1.79 and 2.47 log CFU/cm² after 20 days of storage, respectively, compared to air storage. N₂ and CO₂ gases led to less reduction of biofilm cells on PVC compared to those on stainless steel. N₂ and CO₂ gases resulted in significant (p < 0.05) further reductions of 0.98 and 1.20 log CFU/cm² after 20 days of storage, respectively, compared to air storage.     

Effects of electron beam irradiation on microbial inactivation and quality of kimchi paste during storage

The effects of electron beam irradiation on microbial inactivation and quality of noninoculated and inoculated (Listeria monocytogenes) kimchi pastes were examined. Kimchi paste samples were irradiated at doses of 2, 4, 6, 8 and 10 kGy and stored for 21 days at 4 °C. Irradiation (10 kGy) reduced the populations of total aerobic bacteria, lactic acid bacteria, and yeast and moulds in the samples by 1.72, 2.24 and 0.86 log CFU g^?1, respectively, compared to the control. In particular, coliforms were not detected at 8 and 10 kGy, and the population of L. monocytogenes in inoculated samples was significantly decreased by 2.67 log CFU g^?1. Electron beam irradiation delayed the changes in O₂ and CO₂ concentrations, pH, acidity and reducing sugar content observed in kimchi paste during storage. These results suggest that electron beam irradiation can be used to improve the microbiological safety and shelf life of kimchi paste.     

Effects of Pseudomonas chlororaphis and gaseous chlorine dioxide on the survival of Salmonella enterica on tomatoes

Control of Salmonella enterica on tomatoes is important for food safety. The aim of this research was to evaluate the survival of Salmonella enterica serovars Montevideo (SM) and Typhimurium (ST) on tomatoes exposed to gaseous chlorine dioxide and Pseudomonas chlororaphis (Pc). Pc was applied to stem scars of tomatoes prior to inoculations with SM and ST. Tomatoes were treated with gaseous ClO₂ at 0.4 mg L^?1 for 2 and 4 h (90% R.H. 13 °C), respectively. At 4 h of ClO₂ treatment, SM and ST populations were reduced to 0.82 and <0.30 log CFU g^?1, respectively. Tomatoes treated with SM and ST had 5.42 and 5.37 log CFU g^?1 of Salmonella. Tomatoes treated with Pc + Salmonella count was 2.59 (treated) and 5.83 log CFU g^?1 (control). Salmonella survival was similar at 2 and 4 h of ClO₂ treatment. Application of ClO₂ and Pc may reduce contamination of tomatoes by Salmonella serovars.     

Biofilm formation of Pectobacterium carotovorum subsp. carotovorum on polypropylene surface during multiple cycles of vacuum cooling

During vacuum cooling, polypropylene turnover boxes are repeatedly used for containing vegetables for cooling, while Pectobacterium carotovorum subsp. carotovora (Pcc) can form a biofilm on polypropylene adhesion surface. This study evaluated the effects of multiple cycles of vacuum cooling on the morphology and composition of Pcc biofilm formed on polypropylene turnover boxes. Results showed that Pcc biofilm in different growth stages including adhesion, development and mature phases displayed different responses to vacuum cooling. Pcc biofilm in adhesion stage decreased from 10⁶ to 10⁵ CFU cm⁻², indicating the positive interference of vacuum cooling on biofilm formation in the initial developmental stage. However, with the increasing of the number of vacuum cooling cycles from 0 to 3, the biomass of Pcc biofilm in the development stage increased from 10⁷ to 10⁸ CFU cm⁻² and the polysaccharide secretion increased from 7.96 to 16.7 mg cm⁻², showing the promotion of biofilm formation and the secretion of extracellular polymeric substances. Therefore, regular cleansing and sterilisation of turnover boxes are necessary to prevent cross-contamination during vacuum cooling.     

Microbial inactivation and quality improvement of tomatoes treated by package film with allyl isothiocyanate vapour

In‐package sanitisation was developed using polylactic acid (PLA) films with allyl isothiocyanate (AIT) vapour. Tomatoes were artificially inoculated with Escherichia coli, Geotrichum candidum and Fusarium oxysporum and stored in clamshell boxes with the film fixed to the underside of the lid. The changes in bacterial and fungal populations and the quality of tomatoes during storage at 4 and 10 °C were evaluated. The results revealed that the film treatment (4 × 8 cm² film in 1 L box) reduced the populations of inoculated bacteria and fungi on tomatoes by 2–3 log CFU g^?1, and then significantly (P < 0.05) inhibited their growth during the 21‐day storage period at both temperatures. Tomatoes subject to film treatment had fewer changes in quality (colour, firmness, contents of total soluble solid, titratable acids and vitamin C) than the control samples during storage. The antimicrobial PLA film can be used for in‐package sanitisation to extend the shelf‐life of packaged tomatoes or similar perishable vegetables.     

Combination of vaporized ethyl pyruvate and non-thermal atmospheric pressure plasma for the inactivation of bacteria on lettuce surfaces

The effect of vaporized ethyl pyruvate (EP) and atmospheric pressure plasma (APP) treatments on the inactivation of total viable counts of bacteria on fresh lettuce leaves samples after treatment and during storage (1 and 3 days) at 6 and 25 °C was studied. For this purpose, freshly grown B. cereus and Escherichia coli were inoculated on the lettuce leaves prior to treatments. Combination of EP (at a concentration of around 10 μL dm⁻³) with APP was more effective on inactivation of bacteria when compared to EP and APP treatments separately, reducing the total viable counts nearly 5 CFU cm⁻² compared to control. The use of EP and APP together led to around 2.5 more log (CFU cm⁻²) reductions when compared to the sole use of EP and APP separately. B. cereus cells were almost three times more susceptible to APP treatment than E. coli. Growth inhibition increased after storing the treated samples at 25 °C by around 2.5 and 1.5 logs for E. coli and B. cereus, respectively, compared to 6 °C. APP treatment time (30 and 60 s) and storage time (1 and 3 days) did not significantly affect the inactivation levels. E. coli was more effectively inactivated after EP + O₂ treatment followed by storage at 25 °C. The highest level of inactivation was noted as nearly 5 log reductions. Slight differences in the peak intensities of FTIR spectra of treated lettuce samples were observed compared to control, indicating slight modifications on the chemical structure on the lettuce leaves.Industrial relevanceThe microbial load influences the quality, safety, and shelf-life of fresh produce such as lettuce. Current decontamination techniques may cause some unwanted effects such as odor, discoloration, and decreased nutritional value. This study shows that the use of the APP-EP hurdle represents a promising strategy to improve the decontamination efficiency and hence, enhance the shelf-life of freshly cut vegetables. The data obtained contribute to a better understanding of APP-EP-induced effects on the quality and shelf-life of fresh-cut lettuce and provide a scientific basis for industrial implementation.     

Removal of Salmonella enterica serovar Typhimurium and Cronobacter sakazakii biofilms from food contact surfaces through enzymatic catalysis

Bacterial biofilms are highly difficult to control, hence significant economic resources have been allocated to develop strategies to eradicate them. This study evaluated the effect of an enzymatic treatment to be used as a cleaning product to control the presence of biofilms. Two different materials used in the food industry, polystyrene and stainless steel, were tested using Salmonella Typhimuirum and Cronobacter sakazakii. Biofilm formation was carried out by inoculating the surfaces with a standardized concentration of 4 log (CFU cm⁻²) and incubated for 48 hr with renewal of nutrients. The biofilm formation and subsequent enzymatic treatment were quantified using fluorescence microscopy and the conventional culture method. The enzymatic treatment showed significant reductions of 2–3 log (CFU cm⁻²) in biofilm cells, which was attributed to the degradation of the extracellular matrix and the further detachment of both microorganisms. The maximum biofilm detachment obtained with the preventive formula was 46.67%; however, this percentage could be increased by applying an aggressive treatment or by adding a subsequent disinfection step that would eliminate adhered microbial cells. Further, the enzymatic cleaning treatment could be exploited as a potent technology to control bacterial adherence and biofilm formation in the food industry.     

Development of a predictive model for the reduction of Escherichia coli on the surface of materials as a function of concentration and treatment time with ethanol

The purpose of this study was to develop a model that could predict the reduction of Escherichia coli on different surfaces treated with ethanol as a function of concentration and treatment time. The reduction in E. coli on the surfaces of stainless steel, plastic, wood, rubber, glass, and ceramic at various ethanol concentrations (0–70%) after 0–5 min treatment times were evaluated. The contamination levels of E. coli were reduced to 6.73, 5.49, 4.68, 6.38, 5.40, and 6.30 log CFU/cm² on the surface of stainless steel, plastic, wood, rubber, glass, and ceramic, respectively, when treated with a maximum concentration (70%) of ethanol for 5 min. Each predictive model was significant (p<0.05) and the fitness was defined by the lack of fit and probability of normal residuals. Therefore, these models could be used to determine the minimum required ethanol concentrations and treatment times to control E. coli on the surface of various materials.     

Inactivation and removal of Klebsiella michiganensis biofilm attached to the inner surfaces of piping by plasma-activated microbubble water (PMBW)

Plasma-activated microbubble water (PMBW) is an environmentally friendly sanitizer that possesses potent antimicrobial activities and imparts substantial shear stress to food contact surfaces. In this study, PMBW, plasma-activated water (PAW), microbubble water (MBW), and chlorine water (100 mg/L) were used to clean PVC tubing inoculated by Klebsiella michiganensis. The sanitizer flow with microbubble was numerically simulated by COMSOL Multiphysics® and the shear stress imparted to the bacteria was calculated. The presence of microbubbles in the flow increased the shear stress imparted to the bacteria. The number of K. michiganensis on the inner surfaces of the pipes was ∼7.4 log CFU/cm² before washing. PMBW showed the most potent antimicrobial effect, which reduced the number of bacteria by 3.1 log CFU/cm² at a flow velocity of 1 m/s. PAW, MBW, and chlorine water reduced a similar number of bacteria (2.4 log CFU/ cm² to 2.6 log CFU/ cm²) at all the selected flow velocities. DI water only reduced the number of K. michiganensis by 0.7 log CFU/ cm² at 1 m/s flow velocity.Industrial relevancePMBW can potentially be an environmentally friendly sanitizer, which can be employed by food processors to clean their food processing equipment with minimized usage of chemical sanitizers. The technology developed in this study will benefit the food industry by mitigating potential risks of foodborne pathogens without generating environmental hazards.     

Production of biofilm and quorum sensing by Escherichia coli O157:H7 and its transfer from contact surfaces to meat,poultry, ready-to-eat deli,and produce products

Multistate outbreaks of Escherichia coli O157:H7 infections through consumption of contaminated foods including produce products have brought a great safety concern. The objectives of this study were to determine the effect of biofilm and quorum sensing production on the attachment of E. coli O157:H7 on food contact surfaces and to evaluate the transfer of the pathogen from the food contact to various food products. E. coli O157:H7 produced maximum levels of AI-2 signals in 12 h of incubation in tested meat, poultry, and produce broths and subsequently formed strong biofilm in 24 h of incubation. In general, E. coli O157:H7 formed stronger biofilm on stainless steel than glass. Furthermore, E. coli O157:H7 that had attached on the surface of stainless steel was able to transfer to meat, poultry, ready-to-eat deli, and produce products. Strong attachment of the transferred pathogen on produce products (cantaloupe, lettuce, carrot, and spinach) was detected (>10³ CFU/cm²) even after washing these products with water. Our findings suggest that biofilm formation by E. coli O157:H7 on food contact surfaces can be a concern for efficient control of the pathogen particularly in produce products that require no heating or cooking prior to consumption.     

Modelling Bacillus cereus adhesion on stainless steel surface as affected by temperature,pH and time

The adhesion of Bacillus cereus to stainless steel was modelled as a function of pH (4.0–8.0), time (2–24 h) and temperature (4.0–36.0 °C) using response surface methodology. Based on the initial inoculum (3 or 6 log cfu mL⁻¹), two equations describing B. cereus adhesion to stainless steel were obtained. The results indicated that B. cereus was able to reach up to 5.5 cfu cm⁻² and 6.4 cfu cm⁻² when the initial inocula were 3 log cfu mL⁻¹ and 6 log cfu mL⁻¹, respectively. The significance of the factors varied with the model; i.e., inoculum of 3 or 6 log cfu mL⁻¹. Bias and accuracy factors showed that the models are adequate to predict B. cereus adhesion to stainless steel surface under conditions assessed and to assess the adhesion of B. cereus under a range of conditions to which this microorganism can be exposed during either milk processing or cleaning procedures.     

Competitive interactions inside mixed-culture biofilms of Salmonella Typhimurium and cultivable indigenous microorganisms on lettuce enhance microbial resistance of their sessile cells to ultraviolet C (UV-C) irradiation

Salmonella Typhimurium (ST) is one of the leading causes of foodborne diseases in fresh produce, such as lettuce. Despite this, the role of the possible interactions between lettuce indigenous microorganisms and ST on their ability to form biofilm on lettuce and subsequently on the sensitivity of their sessile cells to ultraviolet C (UV-C) irradiation, remains relatively unexplored. Here, the interaction of a mixed-culture of ST and cultivable indigenous microorganisms (CIMs) was examined, as well as the efficacy of UV-C. Initially, the CIMs were isolated and cultured with ST at 15 °C either planktonically or left to form biofilms on stainless steel (SS) and lettuce leaves. Microbial growth, biofilm formation, and survival following UV-C treatment were monitored using traditional plate count methods while biofilm formation, production of extracellular polymeric substance (EPS), and stomatal colonization were also observed by field emission scanning electron microscopy (FESEM). Internalization strength, color, and texture were analyzed by standard methods. Results revealed that the mixed-culture of ST and CIMs presented significantly (p < 0.05) decreased biofilm formation on lettuce leaves compared to mono-cultures (i.e. ST or CIMs alone), which indicated competitive interaction between them, while no interactions were observed for biofilms on SS and for the planktonic cultures. It was also demonstrated that a mixed-culture biofilm on lettuce presented significantly higher resistance (p < 0.05) to UV-C treatment compared to mono-culture biofilms, but such an effect was not observed for biofilms formed on SS and for the planktonic cultures. The Weibull model fitted well to microbial inactivation curves with R² values that ranged from 0.90 to 0.97. Regarding the mixed-culture conditions, a UV-C fluency of 35 mJ/cm² was required to achieve a 5.0 log CFU/mL or cm² reduction in planktonic and biofilms on the SS for the mixed-culture, while 360 mJ/cm² was required to reduce biofilm cell number by approximately 2.0 log CFU/cm² on lettuce. Furthermore, FESEM analysis indicated higher EPS production, and greater stomatal colonization on lettuce mixed-cultures compared to mono-cultures. Finally, internalization strength was significantly higher (p < 0.05) for the mixed-culture on lettuce, thus supporting the notion that internalization in lettuce is a factor that contributes to microbial UV-C resistance. The absence of adverse effects of UV-C on the color and texture of the lettuce suggests it as an alternative means of eliminating ST.     

Encapsulation of probiotic Lactobacillus acidophilus by ionic gelation with electrostatic extrusion for enhancement of survival under simulated gastric conditions and during refrigerated storage

The probiotic Lactobacillus acidophilus was encapsulated in biodegradable and biocompatible capsules prepared by ionic gelation between phytic acid (PA) and chitosan (CS) with an electrostatic extrusion method. Calcium carbonate (CaCO₃) and starch were used as co‐encapsulants for improvement of capsule stability. Capsules were characterised and evaluated for survival of encapsulated L. acidophilus cells in simulated gastric fluid (SGF) and during refrigerated storage. Loading capacity values of PA‐CS capsules, PA‐CS‐starch capsules and PA‐CS‐CaCO₃ capsules were 8.20, 8.12 and 7.81 log CFU g^?1 of wet capsule, respectively. Capsules showed particle sizes of 1.3–1.5 mm and a uniform spherical shape. PA‐CS‐CaCO₃ capsules were the most stable vehicles for the protection of probiotic cells against acidic damage, particularly at pH 1.5 and pH 2. L. acidophilus cells from PA‐CS‐CaCO₃ capsules showed only a 0.64 log CFU reduction in numbers after 2 h in pH 1.5 SGF conditions. The numbers of L. acidophilus encapsulated in PA‐CS‐CaCO₃ capsules were decreased by only 0.69 log CFU g^?1, while PA‐CS capsules and PA‐CS‐starch capsule numbers were reduced by more than 1.45 log CFU g^?1 after 4 weeks at 4 °C. Addition of calcium carbonate to PA‐CS capsules provided protection against acid injury via antacid and buffering effects for encapsulation of L. acidophilus.     

Effect of grape dietary fibre on the storage stability of innovative functional seafood products made from farmed meagre (Argyrosomus regius)

Two groups of farmed meagre (Argyrosomus regius) sausages were studied regarding quality changes and antioxidant capacity during a 98‐day storage experiment at 2 ± 2 °C. Control sausages contained 3.9% (w/w) of inner pea dietary fibre (IPDF) and the other group contained 0.9% (w/w) IPDF plus 3.0% (w/w) of antioxidant grape dietary fibre (AGDF). The control and AGDF meagre sausages presented a high nutritional value, given their low caloric content, fatty acid profile, amino acid composition and high DF content. Both products were remarkably stable over storage time. The AGDF had an effective antioxidant capacity, proven not only by the radical scavenging activity (90.0–91.0% vs. 82.1–85.4%) and reducing power (8.13–9.10 mg ascorbic acid equivalent g^‐1 vs. 4.16–4.24 mg ascorbic acid equivalent g^?1) measurements, but also by the lower thiobarbituric acid reactive species (TBARS) values (0.78–1.10 vs. 1.50–2.08 mg malonaldehyde kg^?1) over storage time. AGDF seemed to present antimicrobial effect, since on the 63rd day (beginning of significant microbial growth), the control sausages had more than 3 log CFU g^?1 and AGDF sausages much <3 log CFU g^?1. The sensory assessment pointed to some loss of textural quality, more accentuated in the AGDF sausages.     

Effectiveness of ozone,heat and chlorine for destroying common food spoilage bacteria in synthetic media and biofilms†

Ozone, chlorine and heat applications were compared for killing effectiveness against food spoilage bacteria in synthetic broth. Fresh 24‐h bacterial cultures of Pseudomonas fluorescens (ATCC 948), Pseudomonas fragi (ATCC 4973), Pseudomonas putida (ATCC 795), Enterobacter aerogenes (ATCC 35028), Enterobacter cloacae (ATCC 35030) and Bacillus licheniformis (ATCC 14580) were exposed to ozone (0.6 ppm for 1 min and 10 min), chlorine (100 ppm for 2 min) or heat (77 ± 1°C for 5 min). One‐minute ozonation had little effect against the bacteria. There were significant differences (P < 0.05) among 10‐min ozonation, chlorine or heat inactivation of all bacteria exceptB. licheniformis. Ten‐minute ozonation caused the highest bacterial population reduction, with a mean reduction over all species of 7.3 log units followed by heat (5.4 log reduction) and chlorine (3.07 log reduction). Clean, passivated, sterile stainless steel (SS) metal coupons [2.54 × 2.54 cm², American Society for Testing Materials (ASTM) number 304] were incubated in ultra‐high temperature (UHT) sterile milk inoculated with P. fluorescens (ATCC 948), P. fragi (ATCC 4973) and P. putida (ATCC 795) for 24–72 h. After biofilm formation, the SS metal coupons were rinsed with phosphate‐buffered saline (1 min) and exposed to ozone (0.6 ppm for 10 min) and chlorine (100 ppm for 2 min). Results indicated that both ozone and chlorine significantly reduced the biofilm bacteria adhered to the SS metal coupons as compared to the control (P < 0.05). However, there was no significant difference (P > 0.05) between ozone and chlorine inactivation of the bacteria with the exception of P. putida. Ozone killed P. putida more effectively than chlorine.     

Enzymatic grafting of gallate ester onto chitosan: evaluation of antioxidant and antibacterial activities

The antioxidant octyl gallate (OG) has been successfully grafted onto chitosan by means of horseradish peroxidase biocatalyst. The maximum gallate incorporation onto chitosan determined by ¹H NMR spectroscopy was up to 16 molar%. The resulting materials displayed antioxidant capacities with DPPH radical inhibition percentage up to 23% upon the assay conditions. The grafting of the antioxidant on chitosan enhanced its antimicrobial activity. Minimal inhibitory concentration (MIC) for Escherichia coli was 0.5 g L^?1. The native medium molecular weight chitosan alone or grafted with the lowest OG incorporation (ca. 11 molar%) attained 100% inhibition of E. coli, whereas lower inhibition was observed for all other materials 50.7–68.9% corresponding a reduction in the counts from 10.6 to 5.23–3.30 Log CFU mL^?1. The inhibition of Listeria monocytogenes was significantly higher (59.8–100%) than that with the Gram negative bacterium reaching the MIC at 0.25 g L^?1 with a reduction in the counts from 12.6 Log CFU mL^?1 to 5.06–0 Log CFU mL^?1.