V.P. Valdramidis

Application of Natural Antimicrobials for Food Preservation

In this review, antimicrobials from a range of plant, animal, and microbial sources are reviewed along with their potential applications in food systems. Chemical and biochemical antimicrobial compounds derived from these natural sources and their activity against a range of pathogenic and spoilage microorganisms pertinent to food, together with their effects on food organoleptic properties, are outlined. Factors influencing the antimicrobial activity of such agents are discussed including extraction methods, molecular weight, and agent origin. These issues are considered in conjunction with the latest developments in the quantification of the minimum inhibitory (and noninhibitory) concentration of antimicrobials and/or their components. Natural antimicrobials can be used alone or in combination with other novel preservation technologies to facilitate the replacement of traditional approaches. Research priorities and future trends focusing on the impact of product formulation, intrinsic product parameters, and extrinsic storage parameters on the design of efficient food preservation systems are also presented.

Development of a novel approach for secondary modelling in predictive microbiology: incorporation of microbiological knowledge in black box polynomial modelling

This research deals with the development of a novel secondary modelling procedure within the framework of predictive microbiology. The procedure consists of three steps: (i) careful formulation of the available microbiological information, both from literature and from the experimental case study at hand, (ii) translation of these requirements in mathematical terms under the form of partial derivatives throughout the complete interpolation region of the experimental design, and (iii) determination of parameter values with suitable optimisation techniques for a flexible black box modelling approach, e.g., a polynomial model or an artificial neural network model. As a vehicle for this procedure, the description of the maximum specific growth rate of Lactobacillus sakei in modified BHI-broth as influenced by suboptimal temperature, water activity, sodium lactate and dissolved carbon dioxide concentration is under study. The procedure results in a constrained polynomial model with excellent descriptive and interpolating features in comparison with an extended Ratkowsky-type model and classical polynomial model, by combining specific properties of both model types. The developed procedure is illustrated on the description of the lag phase as well. It is stressed how the confrontation with experimental data is very important to appreciate the descriptive and interpolating capacities of new or existing models, which is nowadays not always carefully performed. Alternatively, the first two steps of the novel procedure can be used as a tool to demonstrate clearly (possible) interpolative shortcomings of an existing model with straightforward spreadsheet calculations.

Recent applications of hyperspectral imaging in microbiology

Hyperspectral chemical imaging (HSI) is a broad term encompassing spatially resolved spectral data obtained through a variety of modalities (e.g. Raman scattering, Fourier transform infrared microscopy, fluorescence and near-infrared chemical imaging). It goes beyond the capabilities of conventional imaging and spectroscopy by obtaining spatially resolved spectra from objects at spatial resolutions varying from the level of single cells up to macroscopic objects (e.g. foods). In tandem with recent developments in instrumentation and sampling protocols, applications of HSI in microbiology have increased rapidly. This article gives a brief overview of the fundamentals of HSI and a comprehensive review of applications of HSI in microbiology over the past 10 years. Technical challenges and future perspectives for these techniques are also discussed.

Ozone Processing for Food Preservation: An Overview on Fruit Juice Treatments

This paper reviews the efficacy of ozone an emerging non-thermal food preservation technique for fruit juices and highlights changes in key microbial, quality and nutritional parameters. Ozonation of fruit juices has been identified as a potential technology to meet the United States Food and Drug Administrations requirement of a 5 log reduction in pertinent microorganisms found in juices. This review suggests that it is important to identify the critical extrinsic and intrinsic control parameters governing both the efficacy and quality effects during ozonation of fruit juices.

Inactivation of Escherichia coli by ozone treatment of apple juice at different pH levels.

This research investigated the efficacy of gaseous ozone on the inactivation of Escherichia coli ATCC 25922 and NCTC 12900 strains in apple juice of a range of pH levels, using an ozone bubble column. The pH levels investigated were 3.0, 3.5, 4.0, 4.5 and 5.0. Apple juice inoculated with E. coli strains (10(6)CFU/mL) was treated with ozone gas at a flow rate of 0.12L/min and ozone concentration of 0.048 mg/min/mL for up to 18 min. Results show that inactivation kinetics of E. coli by ozone were affected by pH of the juice. The ozone treatment duration required for achieving a 5-log reduction was faster (4 min) at the lowest pH than at the highest pH (18 min) studied. The relationship between time required to achieve 5log reduction (t(5d)) and pH for both strains was described mathematically by two exponential equations. Ozone treatment appears to be an effective process for reducing bacteria in apple juice and the required applied treatment for producing a safe apple juice is dependant on its acidity level.

Assisted ultrasound applications for the production of safe foods

Ultrasound requires high power and longer treatment times to inactivate micro‐organisms when compared to ultrasound combined with other technologies. Previous reports have shown that the effectiveness of ultrasound as a decontamination technology can be increased by combining it with another treatment such as pressure, heat and antimicrobial solutions. Assisted ultrasound, the combination of ultrasound with another technology, is more energy efficient, and it has less impact on the food properties. In this review paper, the power ultrasound antimicrobial mechanisms of action, the antimicrobial effects of ultrasound in combination with other physical processes and antimicrobial solutions are comprehensively discussed. Furthermore, the present interest on using these technologies as alternative processing and decontamination methods is presented. Research outputs on the application of ultrasound combined with physical processes are showcased including applications of thermosonication, manosonication, manothermosonication and osmosonication. Antimicrobial efficacy, energy requirements and optimal operation conditions of the different assisted ultrasound technologies are critically discussed, and their impact on the food industry for future applications is presented. Overall, this review paper highlights the importance and recent developments of assisted ultrasound for enhancing food safety.

Resistance of Cronobacter sakazakii in reconstituted powdered infant formula during ultrasound at controlled temperatures: A quantitative approach on microbial responses

Many of the documented outbreaks of Cronobacter sakazakii have been linked to infant formula. The aims of this work are to monitor the inactivation kinetics of C.sakazakii NCTC 08155 and ATCC 11467 and to determine quantitatively the effectiveness of ultrasonic treatments as an alternative to heat processing of reconstituted infant milk formula before feeding of infants at highest risk. Inactivation studies of C. sakazakii inoculated in reconstituted infant formula were performed at the combined conditions of temperature, i.e., 25 degrees C, 35 degrees C, 50 degrees C and amplitude, i.e., 24.4, 30.5, 42.7, 54.9, 61 microm and the kinetics were described by a range of inactivation models. The dependency of the specific inactivation rate with respect to the product of temperature and amplitude was described by a modified Bigelow type model. Ultrasound combined with temperature was efficient to reduce significantly the microbial levels of C. sakazakii. C. sakazakii strain NCTC 08155 was at the same range of temperature and amplitude resistance as strain ATCC 11467. Application of ultrasound is an alternative process for the production of safe reconstituted infant formula. This study contributes on the quantitative assessment of the resistance of C. sakazakii.

Stress-adaptive responses by heat under the microscope of predictive microbiology

Aims: In previous studies the microbial kinetics of Escherichia coli K12 have been evaluated under static and dynamic conditions ( Valdramidis et al. 2005, 2006 ). An acquired microbial thermotolerance following heating rates lower than 0·82°C min−1 for the studied micro‐organism was observed. Quantification of this induced physiological phenomenon and incorporation, as a model building block, in a general microbial inactivation model is the main outcome of this work.

Characterization and antimicrobial efficacy against E. coli of a helium/air plasma at atmospheric pressure created in a plastic package

A plasma source, sustained by the application of a floating high voltage (?15?kV) to parallel-plate electrodes at 50?Hz, has been achieved in a helium/air mixture at atmospheric pressure (P?=?105?Pa) contained in a zip-locked plastic package placed in the electrode gap. Some of the physical and antimicrobial properties of this apparatus were established with a view to ascertain its performance as a prototype for the disinfection of fresh produce. The current?voltage (I?V) and charge?voltage (Q?V) characteristics of the system were measured as a function of gap distance d, in the range (3???103???Pd???1.0???104?Pa?m). The electrical measurements showed this plasma source to exhibit the characteristic behaviour of a dielectric barrier discharge in the filamentary mode and its properties could be accurately interpreted by the two-capacitance in series model. The power consumed by the discharge and the reduced field strength were found to decrease quadratically from 12.0?W to 4.5?W and linearly from 140?Td to 50?Td, respectively, in the range studied. Emission spectra of the discharge were recorded on a relative intensity scale and the dominant spectral features could be assigned to strong vibrational bands in the 2+ and 1? systems of N2 and , respectively, with other weak signatures from the NO and OH radicals and the N+, He and O atomic species. Absolute spectral intensities were also recorded and interpreted by comparison with the non-equilibrium synthetic spectra generated by the computer code SPECAIR. At an inter-electrode gap of 0.04?m, this comparison yielded typical values for the electron, vibrational and translational (gas) temperatures of (4980???100)?K, (2700???200)?K and (300???100)?K, respectively and an electron density of 1.0???1017?m?3. A Boltzmann plot also provided a value of (3200???200?K) for the vibrational temperature. The antimicrobial efficacy was assessed by studying the resistance of both Escherichia coli K12 its isogenic mutants in soxR, soxS, oxyR, rpoS and dnaK selected to identify possible cellular responses and targets related with 5?min exposure to the active gas in proximity of, but not directly in, the path of the discharge filaments. Both the parent strain and mutants populations were significantly reduced by more than 1.5 log cycles in these conditions, showing the potential of the system. Post-treatment storage studies showed that some transcription regulators and specific genes related to oxidative stress play an important role in the E. coli repair mechanism and that plasma exposure affects specific cell regulator systems.

Assessing the microbial oxidative stress mechanism of ozone treatment through the responses of Escherichia coli mutants

Aims: To investigate the effect of the oxidative stress of ozone on the microbial inactivation, cell membrane integrity and permeability and morphology changes of Escherichia coli.