Combination of ultraviolet light-C and clove essential oil to inactivate Salmonella Typhimurium biofilms on stainless steel

Salmonella typhimurium is able to form biofilms as a resistance mechanism against antimicrobials; therefore, it represents a problem for assuring food safety and highlights the importance of research on anti-biofilm technologies. In this study, S. typhimurium biofilms were inactivated with the combination of clove essential oil (CEO) and ultraviolet light (UV-C). The volatile composition of the CEO determined by gas chromatography showed eugenol as the major constituent (82%). A combination of CEO with UV-C achieved a complete bacterial reduction (6.8 log/cm²) on biofilms with doses of 1.2 mg/ml and 76.41 mJ/cm², respectively. Individually, the CEO at 1.2 mg/ml caused a reduction of 1.8 log CFU/cm² of attached bacteria cells on stainless steel, while UV-C individually used at 620.4 mJ/cm² caused a 2.9 log CFU/cm² reduction compared to control biofilms. In conclusion, this study demonstrated a synergistic effect of combining CEO and UV-C irradiation to inactivate biofilms of S. typhimurium.     

Enhancing the bactericidal effect of electrolyzed water on Listeria monocytogenes biofilms formed on stainless steel

Biofilms are potential sources of contamination to food in processing plants, because they frequently survive sanitizer treatments during cleaning. The objective of this research was to investigate the combined use of alkaline and acidic electrolyzed (EO) water in the inactivation of Listeria monocytogenes biofilms on stainless steel surfaces. Biofilms were grown on rectangular stainless steel (type 304, no. 4 finish) coupons (2 by 5 cm) in a 1:10 dilution of tryptic soy broth that contained a five-strain mixture of L. monocytogenes for 48 h at 25 degrees C. The coupons with biofilms were then treated with acidic EO water or alkaline EO water or with alkaline EO water followed by acidic EO water produced at 14 and 20 A for 30, 60, and 120 s. Alkaline EO water alone did not produce significant reductions in L. monocytogenes biofilms when compared with the control. Treatment with acidic EO water only for 30 to 120 s, on the other hand, reduced the viable bacterial populations in the biofilms by 4.3 to 5.2 log CFU per coupon, whereas the combined treatment of alkaline EO water followed by acidic EO water produced an additional 0.3- to 1.2-log CFU per coupon reduction. The population of L. monocytogenes reduced by treatments with acidic EO water increased significantly with increasing time of exposure. However, no significant differences occurred between treatments with EO water produced at 14 and 20 A. Results suggest that alkaline and acidic EO water can be used together to achieve a better inactivation of biofilms than when applied individually.     

Atmospheric pressure plasma jet inactivation of Pseudomonas aeruginosa biofilms on stainless steel surfaces

This study established the efficacy of atmospheric pressure plasma jet on Pseudomonas aeruginosa on stainless steel types 316 and 304; with different finishes namely, mirror (MR), hairline (HL) and 2B surfaces. A cocktail of four strains of P. aeruginosa in the mid-stationary growth phase were allowed to attach on the test surfaces, and subjected to atmospheric pressure plasma jet treatment with an air injection rate of 5 l/min, output power of 360 W at 4.22 cm source-to-surface distance. Attachment rates were significantly affected by surface finish, rather than by stainless steel type. The D-values on the 316 stainless steel type ranged from 2.53 s (MR) to 3.16 s (2B); while those on the 304 type ranged from 1.95 s (HL) to 3.27 s (2B). Variations in D-values were observed between surface finishes within a specific stainless steel type. However, significant variations were not observed between the same surface finish of different steel types. The observed antimicrobial efficacy was attributed to the generation of reactive oxygen species, ultraviolet-C rays, and rapid temperature increase (final temperature of 143.42 °C to 174.05 °C) within 15 s of treatment. In the absence of heating, the D-value increased to 16.45 s, but a 5-log (99.999%) reduction in the population was observed in a relatively short treatment time of 90 s.Industrial relevanceThe results obtained in this work demonstrated the potential of using atmospheric pressure plasma jet technology as a non-chemical, non-thermal, and thermal stainless steel food contact surface decontamination against Pseudomonas aeruginosa, a common biofilm-producing bacterium. Such a technology shall help the industry address the challenge of cross contamination in the food manufacturing and food service settings.     

Antimicrobial effects of silver nanoparticles against bacterial cells adhered to stainless steel surfaces

Given the increasing number of antibiotic-resistant bacteria and the need to synthesize new antimicrobials, silver has attracted interest in the scientific community because of its recognized antimicrobial activity. This study aimed to evaluate the antimicrobial effects of silver nanoparticles (NP) obtained by a new method and tested at concentrations of 6 μg/ml and 60 μg/ml against the species Staphylococcus aureus, Listeria innocua, Salmonella Choleraesuis, Pseudomonas aeruginosa, Escherichia coli, and Bacillus cereus. The ability of these nanoparticles to remove or kill vegetative cells adhered to stainless steel surfaces was also evaluated. We observed that the NP obtained with the new method, concentrated silver nanoparticles (CNP), and silver nanoparticles with added sodium chloride (NPNaCl) had high antimicrobial activities (P < 0.05). We also verified that the most effective condition for the removal of P. aeruginosa cells on stainless steel coupons (10 by 10 mm) was immersion of the surfaces in CNP. The CNP treatment produced a 5-log reduction of the microbial population after 30 to 60 min of immersion. The CNP treatment also performed better than water and sodium carbonate, a compound commonly applied in clean-in-place procedures in the food industry, in removing adherent B. cereus cells from stainless steel cylinders. Therefore, these results suggest that NP synthesized by a new procedure may be used as antimicrobials in the food industry, for example, for the sanitization of utensils that come into contact with foods.     

Temperature and nutrient effects on Campylobacter jejuni attachment on multispecies biofilms on stainless steel

Campylobacterjejuni is a thermophilic microaerophilic pathogen that is commonly found in the intestinal tract of chickens. In this study, attachment of C. jejuni 1221gfp in biofilms on stainless steel was assessed at various temperatures and with reduced nutrients. Bacteria collected from a saline rinse of processed broiler chicken carcasses were used to form initial biofilms. The whole carcass rinse (WCR) biofilms were formed by incubation of the bacteria for 16 h at 13, 20, 37, and 42 degrees C on stainless steel coupons in tryptic soy broth (TSB). The resulting biofilms were stained with Hoechst 33258 stain and visualized by epifluorescence microscopy. WCR biofilms formed at 13 degrees C yielded the highest surface area coverage (47.6%), and the lowest coverage (2.1%) was attained at 42 degrees C. C. jejuni transformed to produce green fluorescent protein (gfp) was allowed to attach to the preexisting biofilms (from WCR incubated for 16 h) at each of the four temperatures, and attached cells were enumerated by visualization with an epifluorescence microscope. Attachment of C. jejuni 1221gfp did not significantly differ (P > 0.05) among the four temperatures. C. jejuni 1221gfp was cultured only from coupons with biofilms formed at 13 and 20 degrees C. For nutrient limitation experiments, WCR biofilms were allowed to grow in 10- and 50-fold diluted TSB at 20 and 37 degrees C for 48 h. The WCR biofilm surface area coverage (approximately 2%) was greater at 37 degrees C than at 20 degrees C for both TSB concentrations. C. jejuni 1221gfp was incubated with the WCR biofilm for 48 h at 20 and 37 degrees C, and attached cells were enumerated. Attachment was significantly higher (P < 0.05) only for the treatments with 1:10 TSB at 20 degrees C and 1:50 TSB at 37 degrees C. Under reduced-nutrient conditions, C. jejuni 1221gfp was cultured only from biofilms formed at 20 degrees C. Under the conditions tested, the attachment of C. jejuni 1221gfp on stainless steel and biofilms was affected by a combination of temperature and nutrient availability, but C. jejuni culturability was affected solely by temperature.     

Inclusion reactions of β-cyclodextrin and its derivatives with cinnamaldehyde in Cinnamomum loureirii essential oil

The inclusion reactions of β-cyclodextrin (β-CD), heptakis (2,6-di-O-methyl)-β-CD (DM-β-CD), and mono[2-O-(2-hydroxy-propyl)]-β-CD (HP-β-CD) with cinnamaldehyde (CA) in Cinnamomum loureirii essential oil were investigated using spectrofluorimetry. The results revealed that the best inclusion time was 30 min and the neutral pH conditions were more advantageous to the process. The stoichiometry of β-CD including CA complex was 1:1 (molar ratio). The inclusion constants decreased with the increase of temperature, and the inclusion abilities of β-CD were according to the following order: β-CD > DM-β-CD > HP-β-CD. At the same time, the inclusion constants and the thermodynamic parameters such as ΔG, ΔH, and ΔS were determined in the ranges of 25–55 °C. The thermodynamic measurements showed that the inclusion process was an exothermic and enthalpy-driven process accompanied with a negative entropic contribution. Molecular modeling was performed by molecular mechanics using MM2 in CS Chem 3D, determined by model calculation performance parameter, and the result was identical with the ultimate result of the thermodynamic measurements.     

Culture and detection of Campylobacter jejuni within mixed microbial populations of biofilms on stainless steel

Campylobacter jejuni is the most frequently reported cause of foodborne illness in the United States, but its survival outside the host is poor. The objective of this research was to examine the formation and composition of biofilms by C. jejuni alone and within mixed bacterial populations from the poultry-processing environment. C. jejuni growth was assessed with four media, two temperatures, and two atmospheric conditions to develop culture methods for liquid media that would allow growth within the biofilms. Growth kinetics was followed at four cell densities to determine temporal compatibility within biofilm mixtures. Analysis of the biofilms by confocal laser scanning microscopy showed that C. jejuni formed a biofilm when incubated without other bacteria. The average surface area of stainless steel covered by C. jejuni increased by 50% from 24 to 48 h, remained level to 96 h, and then decreased by 88% by 168 h. C. jejuni and mixed bacterial populations formed biofilms during incubation periods of up to 7 days. The area of the mixture was significantly greater than for C. jejuni alone at 24 h, was approximately the same at 48 h, and was significantly less by 168 h. When incubated with either of two initial inoculum densities of other bacteria, the number of C. jejuni was enhanced after 24 h. The intensity of fluorescence and cell viability were monitored by epifluorescence microscopy. This study provides the basis for studying interactions of Campylobacter spp. with other bacteria in the environment, which will aid in the design of effective intervention strategies.     

Survival of foodborne pathogens on stainless steel surfaces and cross-contamination to foods

The retention of bacteria on food contact surfaces increases the risk of cross-contamination of these microorganisms to food. The risk has been considered to be lowered when the surfaces are dry, partly because bacterial growth and survival would be reduced. However, some non-spore-forming bacteria might be able to withstand dry conditions on surfaces for an extensive period of time. In this study the survival of Salmonella enteritidis, Staphylococcus aureus and Campylobacter jejuni on stainless steel surfaces at different initial levels was determined at room temperature. The transfer rates of these pathogens from kitchen sponges to stainless steel surfaces and from these surfaces to foods were also investigated. Staph. aureus was recovered from the surfaces for at least 4 days when the contamination level was high (10(5) CFU/cm2) or moderate (10(3) CFU/cm2). At low levels (10 CFU/cm2), the surviving numbers decreased below the detection limit (4 CFU/100 cm2) within 2 days. S. enteritidis was recovered from surfaces for at least 4 days at high contamination levels, but at moderate level, the numbers decreased to the detection limit within 24 h and at low level within 1 h. C. jejuni was the most susceptible to slow-air-drying on surfaces; at high contamination levels, the numbers decreased below the detection limit within 4 h. The test microorganisms were readily transmitted from the wet sponges to the stainless steel surfaces and from these surfaces to the cucumber and chicken fillet slices, with the transfer rates varied from 20% to 100%. This study has highlighted the fact that pathogens remain viable on dry stainless steel surfaces and present a contamination hazard for considerable periods of time, dependent on the contamination levels and type of pathogen. Systematic studies on the risks of pathogen transfer associated with surface cleaning using contaminated sponges provide quantitative data from which a model of risks assessment in domestic setting could lead.     

Synergistic effect between Helichrysum italicum essential oil and cold nitrogen plasma against Staphylococcus aureus biofilms on different food‐contact surfaces

Staphylococcus aureus is the most common pathogen in human, and the most diseases produced by S. aureus are associated with biofilms. Helichrysum italicum essential oil (EO), as a natural and safe spice, was employed to disperse S. aureus biofilm by cold nitrogen plasma (CNP) assist. After S. aureus biofilm formation on food container surfaces, they were exposed to CNP and then treated with Helichrysum italicumEO for biofilm dispersion. The population of S. aureus biofilm was approximately reduced by 2 logs after individual treatment of 0.5 mg mL^?1 Helichrysum italicumEO or 400 W CNP. Interestingly, the combined treatment of Helichrysum italicumEO (0.5 mg mL^?1, 40 min) and CNP (400 W, 1 min) reduced the S. aureus viable count in biofilm below 2 logs CFU per cm² after 1‐day storage. Therefore, the synergetic treatment holds great promise to improve the current treatment systems of bacterial contamination on different food‐contact surfaces.     

无机膜过滤食品煎炸用油的研究

以不锈钢膜为过滤介质对食品煎炸用油进行过滤,对过 滤效率进行了研究。在膜过滤时,压力差、温度、滤饼厚度 等是影响膜通透性的关键因素,分别作出各个因素对流 速的影响关系曲线来分析它们对过滤效率的影响,其中 温度、压力与过滤速度有较好的正相关关系。滤饼在最初 形成时对流速的影响较大,当达到一定的厚度时,流速基 本稳定。     

Assessment of bacterial biofilm on stainless steel by hyperspectral fluorescence imaging

Hyperspectral fluorescence imaging techniques were investigated for detection of two genera of microbial biofilms on stainless steel material which is commonly used to manufacture food processing equipment. Stainless steel coupons were deposited in nonpathogenic E. coli O157:H7 and Salmonella cultures, prepared using M9 minimal medium with casamino acids (M9C), for 6 days at 37 °C. Hyperspectral fluorescence emission images of the biofilm formations on the stainless coupons were acquired from 416 to 700 nm with the use of ultraviolet-A (320–400 nm) excitation. In general, emission peaks for both bacteria were observed in the blue region at approximately 480 nm and thus provided the highest contrast between the biofilms and background stainless steel coupons. A simple thresholding of the 480 nm image showed significantly larger biofilm regions for E. coli O157:H7 than for Salmonella. Viable cell counts suggested that Salmonella formed significantly higher density biofilm regions than E. coli O157:H7 in M9C medium. On the basis of principal component analysis (PCA) of the hyperspectral fluorescence images, the second principal component image exhibited the most distinguishable morphological differences for the concentrated biofilm formations between E. coli and Salmonella. E. coli formed granular aggregates of biofilms above the medium on stainless steel while Salmonella formed dense biofilm in the medium-air interface region (pellicle). This investigation demonstrated the feasibility of implementing fluorescence imaging techniques to rapidly screen large surface areas of food processing equipment for bacterial contamination. Company and product names are used for clarity and do not imply any endorsement by USDA to the exclusion of other comparable products.     

Antibiofilm activity of the essential oil of citronella (Cymbopogon nardus) and its major component,geraniol, on the bacterial biofilms of Staphylococcus aureus

Food Science and Biotechnology - Medicinal plants with antimicrobial action have been investigated for uses against biofilms, among which, Cymbopogon nardus, citronella, stands out as a promising...     

Association of uranium with iron oxides typically formed on corroding steel surfaces

Decontamination of metal surfaces contaminated with low levels of radionuclides is a major concern at Department of Energy facilities. The development of an environmentally friendly and cost-effective decontamination process requires an understanding of their association with the corroding surfaces. We investigated the association of uranium with the amorphous and crystalline forms of iron oxides commonly formed on corroding steel surfaces. Uranium was incorporated with the oxide by addition during the formation of ferrihydrite, goethite, green rust II, lepidocrocite, maghemite, and magnetite. X-ray diffraction confirmed the mineralogical form of the oxide. EXAFS analysis at the U L(III) edge showed that uranium was present in hexavalent form as a uranyl oxyhydroxide species with goethite, maghemite, and magnetite and as a bidentate inner-sphere complex with ferrihydrite and lepidocrocite. Iron was present in the ferric form with ferrihydrite, goethite, lepidocrocite, and maghemite; whereas with magnetite and green rust II, both ferrous and ferric forms were present with characteristic ferrous:total iron ratios of 0.65 and 0.73, respectively. In the presence of the uranyl ion, green rust II was converted to magnetite with concomitantreduction of uranium to its tetravalent form. The rate and extent of uranium dissolution in dilute HCl depended on its association with the oxide: uranium present as oxyhydroxide species underwent rapid dissolution followed by a slow dissolution of iron; whereas uranium present as an inner-sphere complex with iron resulted in concomitant dissolution of the uranium and iron.     

Effect of biofilm dryness on the transfer of Listeria monocytogenes biofilms grown on stainless steel to bologna and hard salami

Listeria monocytogenes continues to be a major cause of class I food recalls in the United States. Very little is known about its transfer and cross-contamination in processing scenarios. The objective of this study was to evaluate the effect of hydration level on L. monocytogenes biofilms grown on stainless steel and its effect on the biofilm transfer to foods. Biofilms were grown on stainless steel in diluted tryptic soy broth 1:20 for 48 h at 32 degrees C. After this, biofilms were equilibrated over saturated salt solutions at 20 degrees C for 24 h (94, 75, 58, and 33% relative humidity; % RH) prior to transferring. Transfer experiments were conducted from inoculated stainless steel to bologna and hard salami at a constant pressure (45 kPa) and time (30 s) with a universal testing machine. The experiment was designed with a factorial design 4 x 2 (biofilms equilibrated at 4% RH and two foods) and duplicated every day, and the whole experiment was repeated nine times. The results were analyzed with an analysis of variance by SAS Statistical Analysis Software. Our results showed that more bacteria were transferred to bologna (mean efficiency of transfer [EOT] = 3.0) than to hard salami (mean EOT = 0.35, P < 0.01). As biofilms became drier, the transfer of Listeria from stainless steel to both foods increased (P < 0.05). The EOT increased from 2 to 3.8 and from 0.2 to 0.51 upon transfer when drying the biofilm for bologna and hard salami, respectively. This study may be an indication that as biofilms were dried, the cell-cell and cell-surface interactions became weaker, and bacterial transfer increased. This phenomenon was enhanced in foods containing higher water activity levels. We hypothesize that this increased in transfer was due to the presence of capillary forces in the food.     

Evaluation of growth/no growth interface of Listeria monocytogenes growing on stainless steel surfaces, detached from biofilms or in suspension, in response to pH and NaCl

The present study aimed to describe the growth/no growth interface of Listeria monocytogenes at three potential states of growth in industrial environments, namely attached, (Att), detached (Det) from a biofilm, or in a planktonic state (suspended; Plan). A 3-strain composite of L. monocytogenes cells was left to colonize stainless steel (SS) surfaces in tryptic soy broth supplemented with 0.6% yeast extract (TSBYE) at 20 °C for 72 h and then transferred to TSBYE at 30 different pH and NaCl concentrations, which were renewed every two days during incubation at 10 °C. Survival of attached population was observed at optimal conditions (pH 7.2, a(w) 0.996), whereas at 4.5-8.0% salt and/or pH<6.0, reduction of attached population on SS surfaces was observed. PFGE patterns showed that 91% of the cells colonizing the SS coupons after 30 days, at any pH and a(w) conditions, belonged to a single strain. Furthermore, the change in the probability of a single cell to initiate growth (P(in)) over time, as well as the number of cells needed (CN) for growth initiation of planktonically growing Plan and Det L. monocytogenes cells were evaluated based on MPN Tables. An ordinary logistic regression model was also used to describe the growth/no growth interface of varying inoculation levels (from <10 to 10(4)CFU/ml) of Plan and Det cells in response to pH and a(w). Although both cell types demonstrated similar growth limits at populations of 10(2)-10(4)CFU/ml, higher numbers of Det than Plan cells were needed (CN) in order to initiate growth at low a(w) and pH. Individual Plan cells reached higher maximum levels of probability of growth initiation (P(max)) and had shorter times to reach P(max)/2 (t(au)), compared to their Det counterparts. Data on growth potential of cells in suspension, attached or detached status, may assist in ranking the risk from different sources of contamination. In addition, they may establish the link between the behavior of L. monocytogenes in foods and its origin from the processing plant. The latter link is important component of biotraceability.     

Study of heat-denatured whey protein removal from stainless steel surfaces in clean-in-place systems

The build-up of protein deposits over the inner surfaces of process equipment, particularly heat exchangers, is a common phenomenon in dairy factories, which hinders the normal functioning of such equipment. In this work, we have studied the washing process of stainless steel surfaces stained with heat-denatured whey protein. To do that we have used the bath-substrate-flow (BSF) device, a bench-scale apparatus that simulates clean-in-place systems. Screening tests were performed at low temperature (30 °C) to investigate the effect of the presence of protease, NaOH, ozone and surfactants on cleaning efficiency. The best results were obtained with NaOH (0.5%, w/w), proteases (1 g L⁻¹) and ozone (40 NL h⁻¹, 80 g Nm⁻³). On the other hand, the use of surfactants (either anionic or nonionic) did not improve the washing efficiency significantly. Therefore, ozone and proteases can be used as environmentally friendly cleaning agents to remove protein deposits in the food industry.     

孜然精油及其熟制精油的研究

利用超临界CO₂萃取技术提取孜然精油,通过研究原料粒度、萃取压力、萃取温度、萃取时间等因素对孜然油萃取率及品值的影响,确定超临界CO₂萃取最佳工艺参数。另外,采用熟化工艺对孜然原料进行前处理再利用超临界CO₂萃取技术提取,获得具有熟香风味的熟制孜然精油。研究结果表明,超临界CO₂萃取孜然油的最佳工艺参数为:原料粒度30目,萃取压力30MPa,萃取温度60℃,萃取时间2.5h,精油得率约为13.97%,精油中枯茗醛质量分数高达32.75%。熟制孜然精油熟化工艺中最佳焙烤温度为180℃,超临界CO₂最佳萃取条件为原料粒度30目,萃取压力25MPa,萃取温度60℃,萃取时间2.5h,精油得率约为11.38%,精油中枯茗醛质量分数高达31.95%。     

Liquid ‘hold-up’ on stainless steel surfaces: I — Effect of surface finish

The effect of stainless steel surface finish on the ‘hold-up’ of a representative food liquid (sucrose solution) was studied for drainage angles between 0·46° and 3·7°. Surface finish was found to have a significant effect on ‘hold-up’, but no correlation was found between the Ra value and ‘hold-up’.An explanation of the results is proposed based on the effect of the nature of surface roughness rather than its magnitude (as measured by the Ra value) on wetting and contact angle.The orientation of grain direction had only a small effect on ‘hold-up’ and was dependent on the surface finish.It is suggested that electro-polishing may give the most cost-effective finish for stainless steel food contact surfaces. Drainage angle was found to have a considerable effect on ‘hold-up’ and it is recommended that the minimum drainage angle for food plant should be 2°.