Modeling the pulsed light inactivation of microorganisms naturally occurring on vegetable substrates

Pulsed light (PL) is a fast non-thermal method for microbial inactivation. This research studied the kinetics of PL inactivation of microorganisms naturally occurring in some vegetables. Iceberg lettuce, white cabbage and Julienne-style cut carrots were subjected to increasing PL fluences up to 12 J/cm² in order to study its effect on aerobic mesophilic bacteria determined by plate count. Also, sample temperature increase was determined by infrared thermometry. Survivors’ curves were adjusted to several models. No shoulder but tail was observed. The Weibull model showed good fitting performance of data. Results for lettuce were: goodness-of-fit parameter RMSE = 0.2289, fluence for the first decimal reduction δ = 0.98 ± 0.80 J/cm² and concavity parameter p = 0.33 ± 0.08. Results for cabbage were: RMSE = 0.0725, δ = 0.81 ± 0.23 J/cm² and p = 0.30 ± 0.02; and for carrot: RMSE = 0.1235, δ = 0.39 ± 0.24 J/cm² and p = 0.23 ± 0.03. For lettuce, a log-linear and tail model was also suitable. Validation of the Weibull model produced determination coefficients of 0.88-0.96 and slopes of 0.78-0.99. Heating was too low to contribute to inactivation. A single low-energy pulse was enough to achieve one log reduction, with an ultrafast treatment time of 0.5 ms. While PL efficacy was found to be limited to high residual counts, the achievable inactivation level may be considered useful for shelf-life extension.     

Modeling non-isothermal heat inactivation of microorganisms having biphasic isothermal survival curves

Biphasic isothermal inactivation constitutes a special case of non-linear mortality kinetics. It can be modeled with a primary model that contains an 'If' statement and three temperature dependent survival parameters: the first and second logarithmic inactivation rate constants and the time of the transition from one phase to the other. The temperature dependence of the two inactivation rates of Salmonella enteritidis and that of the transition time determined from published data could be described by empirical logistic terms. These were used to construct an inactivation rate equation for non-isothermal heating and cooling regimes. The resulting differential equation, despite having an 'If' statement in its formulation, could be easily solved numerically for simple as well elaborate temperature profiles. The solutions for a variety of realistic heat treatment histories indicated that when the heating or cooling rate is high enough, the biphasic character of the inactivation disappears. This is true regardless of whether the rate at the first phase is higher than at the second, the most common scenario, or vice versa. Theoretically, the same will happen with inactivation caused by a non thermal agent whose intensity increases or diminishes, in biphasic growth under rapidly varying conditions and in enzymatic activity or inactivation.     

Effect of dissolved carbon dioxide on thermal inactivation of microorganisms in milk

Postpasteurization addition of CO2 inhibits growth of certain microorganisms in dairy products, but few workers have investigated the effect of CO2 on the thermal inactivation of microorganisms during pasteurization. Concentrations of CO2 ranging from 44 to 58 mM added to raw whole milk significantly (P < 0.05) reduced the number of surviving standard plate count (SPC) organisms in milk heated over the range of 67 to 93 degrees C. A decrease in thermal survival rates (D-values) for Pseudomonas fluorescens R1-232 and Bacillus cereus ATCC 14579 spores in milk was positively correlated with CO2 concentrations (1 to 36 mM). D(50 degrees C)-values for P. fluorescens significantly decreased (P < 0.05) in a linear fashion from 14.4 to 7.2 min. D(89 degrees C)-values for B. cereus spores were significantly (P < 0.05) decreased from 5.56 min in control milk to 5.29 min in milk containing 33 mM CO2. The Weibull function was used as a model to describe the thermal inactivation of P. fluorescens, B. cereus spores, and SPC organisms in raw milk. Nonlinear parameters for the Weibull function were estimated, and survival data fitted to this model had higher R2 values than when fitted to the linear model, further providing support that the thermal inactivation of bacteria does not always follow first-order reaction rate kinetics. These results suggest that CO2 could be used as a processing aid to enhance microbial inactivation during pasteurization.     

超高压诱导食品中微生物失活的研究进展

超高压处理(high pressure processing,HPP)作为一种新型的非热杀菌技术,具有最大限度保留食品中营养物质的优势,已在食品工业中广泛应用。但由于加工环境以及食品基质的复杂性,不同微生物在HPP下敏感度不同,且会形成部分亚致死微生物,引发食品安全的潜在隐患。基于HPP设备原理及其应用于食品加工中的杀菌效果,该文对影响超高压杀菌效果的内外因子以及导致细菌失活(致死或亚致死效应)的作用机制进行了综述,并分析了超高压与其他技术联用可能是抑制微生物亚致死效应的有效途径。     

超高压处理对泡豇豆杀菌效果的影响

为了探求超高压杀菌在四川泡菜工业中的应用,提高其微生物安全,以泡豇豆为供试材料,研究了泡豇豆含盐量、处理压力、处理时间对超高压杀菌效果的影响,并考察了超高压处理对泡豇豆保藏性能的影响。实验结果表明:含盐量为4.2%的泡豇豆超高压杀菌效果优于含盐量6.7%,超高压技术更适用于低盐泡菜的杀菌;压力越大、处理时间越长,微生物致死率越高,但压力较时间对杀菌效果的影响更大;对样品分别采用300、400MPa处理30min,菌落总数降低的对数为5.45、5.52,且均无霉菌和酵母菌检出;300～400MPa处理可以使大肠菌群数有效得到降低,且能有效提高泡豇豆的保藏性能。     

Atmospheric plasma inactivation of foodborne pathogens on fresh produce surfaces

A study was conducted to determine the effect of one atmosphere uniform glow discharge plasma (OAUGDP) on inactivation of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes on apples, cantaloupe, and lettuce, respectively. A five-strain mixture of cultured test organisms was washed, suspended in phosphate buffer, and spot inoculated onto produce (7 log CFU per sample). Samples were exposed inside a chamber affixed to the OAUGDP blower unit operated at a power of 9 kV and frequency of 6 kHz. This configuration allows the sample to be placed outside of the plasma generation unit while allowing airflow to carry the antimicrobial active species, including ozone and nitric oxide, onto the food sample. Cantaloupe and lettuce samples were exposed for 1, 3, and 5 min, while apple samples were exposed for 30 s, 1 min, and 2 min. After exposure, samples were pummeled in 0.1% peptone water-2% Tween 80, diluted, and plated in duplicate onto selective media and tryptic soy agar and incubated as follows: E. coli O157:H7 (modified eosin methylene blue) and Salmonella (xylose lysine tergitol-4) for 48 h at 37 degrees C, and L. monocytogenes (modified Oxford medium) at 48 h for 32 degrees C. E. coli O157:H7 populations were reduced by >1 log after 30-s and 1-min exposures and >2 log after a 2-min exposure. Salmonella populations were reduced by >2 log after 1 min. Three- and 5-min exposure times resulted in >3-log reduction. L. monocytogenes populations were reduced by 1 log after 1 min of exposure. Three- and 5-min exposure times resulted in >3- and >5-log reductions, respectively. This process has the capability of serving as a novel, nonthermal processing technology to be used for reducing microbial populations on produce surfaces.     

Effect of superheated steam inactivation on naturally existent microorganisms and enzymes of highland barley

Superheated steam (SS) processing displayed noticeable effects on both microbial inactivation, including total bacterial count, Bacillus spp. and molds, and enzyme inactivation. Moisture content affected decontamination efficiency and recommendable moisture was 20%. Moisture adjusting method of spraying just before SS treatment was better than tempering. Molds were totally decontaminated by SS processing at 200 °C for 90 s and 120 °C for 180 s respectively. At 200 °C for 180 s, 99.98% of bacteria and 95.21% of Bacillus spp. were inactivated by spraying, while 99.95% of bacteria and 92.59% of Bacillus spp. were inactivated by tempering. The enzyme activity in highland barley processed with SS was decreased as processing time and temperature increased. Lipase showed better thermal resistance than peroxidase. Tempering was better in enzyme inactivation. SS treatment was effective in inactivating microorganisms and enzymes of highland barley, and could bring significant economic benefits to the highland barley industry.     

UV inactivation of milk-related microorganisms with a novel electrodeless lamp apparatus

A novel UV apparatus based on Dean vortex technology is designed for inactivating bacteria in milk. In this apparatus, the milk flows through a helical quartz tube coiling around an electrodeless UV lamp (EUL) with a radio frequency of 2.65 MHz. Flow rate, inner diameter of quartz tube, different UV sources, and different types of bacteria have been found as the key factors for the valuable effects on bacterial inactivation. The EUL apparatus worked more efficiently in the UV inactivation of the predetermined populations of milk-related bacteria than the conventional low-pressure high-intensity mercury lamp. When the UV dose of 21.3 mJ/cm² was applied, the numbers of all the bacteria were reduced by more than 6 log₁₀ with a flow rate of 28.8 L/h and a tube’s inner diameter of 1.5 mm. Dean vortices were formed in the milk flow during the UV processing and played an important role in the UV inactivation of the bacteria. Another inactivation test with the apparatus applying the UV dose of 21.3 mJ/cm² was also done with raw cow’s milk containing indigenous microorganisms, including Salmonella and Shigella spp., Listeria monocytogenes, Staphylococcus spp., Enterobacteriaceae, lactic acid bacteria, pseudomonads, and the total aerobic bacteria were reduced by approximately 3–4 log₁₀. In short, the EUL apparatus requires smaller energy, occupies less space, and has simpler operating procedures than thermal pasteurization. Thus, the novel method provides a viable alternative to thermal pasteurization of milk for improving the microbial safety of milk and extending its shelf life.     

The role of reactive oxygen species in the electrochemical inactivation of microorganisms

Electrochemical disinfection has emerged as one of the most promising alternatives to the conventional disinfection of water in many applications. Although the mechanism of electrochemical disinfection has been largely attributed to the action of electro-generated active chlorine, the role of other oxidants, such as the reactive oxygen species (ROS) *OH, O3, H2O2, and *O2- remains unclear. In this study, we examined the role of ROS in the electrochemical disinfection using a boron-doped diamond (BDD) electrode in a chloride-free phosphate buffer medium, in order to avoid any confusion caused by the generation of chlorine. To determine which species of ROS plays the major role in the inactivation, the effects of several operating factors, such as the presence of *OH scavenger, pH, temperature, and the initial population of microorganisms, were systematically investigated. This study clearly showed that the *OH is the major lethal species responsible for the E. coli inactivation in the chloride-free electrochemical disinfection process, and that the E. coli inactivation was highly promoted at a lower temperature, which was ascribed to the enhanced generation of O3.     

Determination of thermal inactivation kinetics of microorganisms with a continuous microflow apparatus

Use of a continuous microflow submerged microcoil (CSMC) apparatus was compared with the capillary tube (CT) method for measuring the thermal inactivation kinetics of Pseudomonas fluorescens at 61 degrees C for 3 to 29 s. Inocula were continuously pumped through a microbore (< or = 0.0762 cm inside diameter) thin-walled stainless steel capillary tube submerged in a heated oil bath. The heating time was set by changing the flow rate, tube dimensions, or both. With the use of microthermo-couples, the time for the inocula to reach within 1 degree C of the set temperature was <3 s, and shorter than that with capillary tubes or vials. Inactivation curves (61 degrees C) for P. fluorescens prepared by the CSMC method were not different from curves prepared by the CT method, as determined by analysis of variance (P > 0.05). Inactivation of Bacillus cereus spores (105 degrees C) and native microflora found in raw milk (72 degrees C) over heating times of 3 to 42 s were determined by CSMC. CSMC can measure thermal inactivation kinetics of microorganisms efficiently and simply at high temperatures and in short times. Survivors can be enumerated in 1-ml volumes of heat-treated samples, making it useful for determining inactivation kinetics of low numbers of microorganisms, such as those found in high-quality raw milk. Inactivation kinetics were generally more accurately described by the Weibull function (R2 > or = 0.97) than the linear kinetic model.     

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.     

High pressure inactivation of microorganisms inoculated into ovine milk of different fat contents

High hydrostatic pressure inactivation of Escherichia coli, Pseudomonas fluorescens, Listeria innocua, Staphylococcus aureus, and Lactobacillus helveticus were studied. These microorganisms were inoculated at a concentration between 10(7) and 10(8) cfu/ml in Ringer solution and in ovine milk adjusted to 0, 6, and 50% fat content to evaluate the baroprotective effect of fat content on inactivation of microorganisms. Treatments of pressurization consisted of combinations of pressure (100 to 500 MPa) and temperature (4, 25, and 50 degrees C) for 15 min. Gram-negative microorganisms were more sensitive than were Gram-positive ones (more destruction P. fluorescens > E. coli > or = List. innocua > Lb. helveticus > S. aureus). Pressurizations at low temperature (4 degrees C) produced greater inactivation on P. fluorescens, List. innocua, and Lb. helveticus than at room temperature (25 degrees C), whereas for E. coli and S. aureus the results were opposite. Ovine milk per se (0% fat) showed a baroprotective effect on all microorganisms, but percentage of fat (6 and 50%) did not show a progressive baroprotective effect in all pressurization conditions or for all microorganisms.     

Feedstock optimization of in-vessel food waste composting systems for inactivation of pathogenic microorganisms

An optimum composting recipe was investigated to reduce pathogenic microorganisms in a forced-aerated in-vessel system (55 liters). The feedstocks used for in-vessel composting were food waste, cow manure, and bulking materials (wood shavings and mulch hay). A statistical extreme vertices mixture design method was used to design the composting experiments and analyze the collected data. Each mixture (nine total) was replicated randomly three times. Temperature was monitored as an indicator of the efficiency of the composting experiments. The maximum temperature values of the mixtures were used as a response for both extreme vertices mixture design and statistical analyses. Chemical changes (moisture content, carbon/nitrogen ratio, volatile solids, and pH) and reductions of indicator (fecal coliforms and fecal streptococci) and pathogenic microorganisms (Salmonella and Escherichia coli O157:H7) were measured by the most-probable-number method before and after a 12-day composting period. Maximum temperatures for the tested compost mixtures were in the range of 37.0 to 54.7 degrees C. Extreme vertices mixture design analysis of the surface plot suggested an optimum mixture containing 50% food waste, 40% manure, and 10% bulking agents. This optimum mixture achieved maximum temperatures of 54.7 to 56.6 degrees C for about 3.3 days. The total reduction of Salmonella and E. coli O157:H7 were 92.3%, whereas fecal coliforms and fecal streptococci reductions were lower (59.3 and 27.1%, respectively). Future study is neededto evaluate the extreme vertices mixture design method for optimization of large-scale composting.     

Combination of levulinic acid and sodium dodecyl sulfate on inactivation of foodborne microorganisms: A review

Abstract

The combination of levulinic acid and sodium dodecyl sulfate (SDS) in recent years has shown considerable promise as an antimicrobial intervention. Both ingredients have been designated by the U.S. Food and Drug Administration (FDA) as Generally Recognized as Safe (GRAS) for being used as a flavoring agent and multipurpose food additive, respectively. The use of levulinic acid and SDS alone has limited antimicrobial efficacy on tested microorganisms, and synergism between levulinic acid and SDS has been observed. The postulated mechanism of action of the synergistic effect is presented. The antimicrobial efficacy of levulinic acid plus SDS remains high even when organic materials are present. The other features, including penetration, foamability, and being readily soluble, extend its potential applications to disinfection of difficult-to-access areas and control of foodborne pathogens both in a planktonic state and in a biofilm. These features indicate that the levulinic acid plus SDS combination may have the potential to be applied within the food processing environment on a large scale.     

High-throughput method for a kinetics analysis of the high-pressure inactivation of microorganisms using microplates

Using microplates as pressure and cultivation vessels, a high-throughput method was developed for analyzing the high-pressure inactivation kinetics of microorganisms. The loss of viability from a high-pressure treatment, measured based on the growth delay during microplate cultivation, showed reproducibility with the conventional agar plate method and was applicable for the kinetics analysis.     

Cold atmospheric plasma disinfection of cut fruit surfaces contaminated with migrating microorganisms

The efficacy of cold atmospheric gas plasmas against Escherichia coli type 1, Saccharomyces cerevisiae, Gluconobacter liquefaciens, and Listeria monocytogenes Scott A was examined on inoculated membrane filters and inoculated fruit surfaces. Inoculated samples were exposed to a cold atmospheric plasma plume generated by an AC voltage of 8 kV at 30 kHz. The cold atmospheric plasma used in this study was very efficient in reducing the microbial load on the surfaces of filter membranes. However, its efficacy was markedly reduced for microorganisms on the cut surfaces. This lack of effect was not the result of quenching of reactive plasma species responsible for microbial inactivation but principally the result of the migration of microorganisms from the exterior of the fruit tissue to its interior. The velocity of migration through melon tissues was estimated to be around 300 microm min(-1) for E. coli and S. cerevisiae and through mango tissues to be 75 to 150 microm min(-1). These data can serve as operational targets for optimizing the performance of gas plasma inactivation processes. The current capabilities of cold atmospheric plasmas are reviewed and ways to improve their bactericidal efficacy are identified and discussed. Considerable scope exists to enhance significantly the efficacy of cold atmospheric plasmas for decontaminating fresh cut fruits.     

Ultraviolet radiation as a non-thermal treatment for the inactivation of microorganisms in fruit juice

Fruit juices can be processed using ultraviolet (UV-C) light to reduce the number of microorganisms. The UV-C wavelength of 254 nm is used for the disinfection and has a germicidal effect against microorganisms. A novel turbulent flow system was used for the treatment of apple juice, guava-and-pineapple juice, mango nectar, strawberry nectar and two different orange and tropical juices. In comparison to heat pasteurization, juices treated with UV did not change taste and color profiles. Ultraviolet dosage levels (J L^− 1) of 0, 230, 459, 689, 918, 1 148, 1 377, 1 607 and 2 066 were applied to the different juice products in order to reduce the microbial load to acceptable levels. UV-C radiation was successfully applied to reduce the microbial load in the different single strength fruit juices and nectars but optimization is essential for each juice treated. This novel UV technology could be an alternative technology, instead of thermal treatment or application of antimicrobial compounds.

Industrial relevance

This novel UV-C system can be applied successfully to the Food Industry. UV-C can be effectively used to reduce the number of spoilage and pathogenic bacteria, as well as yeasts and moulds in different kinds of fruit juices.     

高密度CO2对生鲜调理鸡肉杀菌动力学模型构建

研究不同压力、温度和时间的高密度CO2对生鲜调理鸡肉中细菌的杀菌效果,并采用Weibull、Modified Gompertz、Logistic模型来拟合高密度CO2杀菌的动力学过程,以精确因子(Af),偏差因子(Bf),根平方和(SS),根平方方差(RMSE)和决定系数(R2)作为模型拟合度优劣的评判指标,旨在找出最能拟合高密度CO2处理下微生物失活曲线的数学模型,为高密度CO2杀菌的实际应用提供理论依据.结果表明:随着处理压力、温度、时间的增加,高密度CO2杀菌效果逐渐增强;预测值和实测值的相关决定系数R2表明三种模型都能较好的拟合生鲜调理鸡肉中细菌的失活曲线,其中Logistic模型较拟合度最好,Modified Gompertz其次,Weibull最差.本结果可为高密度CO2新型非热力杀菌技术在肉品上的实际应用提供理论依据.