Volker Heinz

Review: Potential of High Hydrostatic Pressure and Pulsed Electric Fields for Energy Efficient and Environmentally Friendly Food Processing

The application of emerging, novel processing techniques such as high hydrostatic pressure or pulsed electric fields can be utilized to replace, enhance or modify conventional techniques of food production. In addition to quality improvements and consumer benefits by gentle microbial inactivation and improvement of mass transfer processes, their potential to improve energy efficiency and sustainability of food production will be discussed within this review.

Preservation of liquid foods by high intensity pulsed electric fields—basic concepts for process design

Abstract In excess of a critical transmembrane potential ΔϕM of −1 V produced by high intensity pulsed electric fields a rapid electrical breakdown and local conformational changes of cell membranes occur which result in a drastic increase in permeability and an equilibration of the electrochemical and electrical potential differences of the cell plasma and the extracellular medium. As irreverible membrane permeabilization impairs most vital physiological control systems, high intensity pulsed electric fields may be applied as a highly effective process for the microbial decontamination of liquid foods. The efficiency of the treatment is largely influenced by the inherent properties of the foods and of the spoiling microorganisms. In addition a number of technical limitations have to be considered. In this review an approach is presented which reduces the diversity of parameters that affect microbial inactivation during pulsed power treatment. In particular, the required total specific energy input is discussed.

Impact of temperature on lethality and energy efficiency of apple juice pasteurization by pulsed electric fields treatment

The applicability of pulsed electric fields as a non-thermal preservation process for liquid food decontamination has been shown in several studies. However, high costs of operation due to the occurrence of a high amount of dissipated electrical energy inhibited an industrial exploitation so far. In this study the focus was put on improving energy efficiency of this process for pasteurization of apple juice inoculated with Escherichia coli by investigating the relation between achieved reduction in survivor count and electric field strength and treatment temperature. An empirical mathematical model was derived to predict the required input of electrical energy for a given inactivation. Using synergistic effects of elevated treatment temperature of 35–65 °C on microbial inactivation the energy consumption could be reduced from above 100 to less than 40 kJ kg−1 for a reduction of 6 log cycles and the need to preheat the juice before treatment provided a possibility to recover the dissipated electrical energy after treatment, leading to a drastic reduction in operation costs. To evaluate the thermal load of the product the pasteurization unit (PU) and the cook value, key benchmarks for the thermal load, were used to compare PEF and conventional heat treatment.

High-Pressure-Mediated Survival of Clostridium botulinum and Bacillus amyloliquefaciens Endospores at High Temperature

ABSTRACT Endospores of proteolytic type B Clostridium botulinum TMW 2.357 and Bacillus amyloliquefaciens TMW 2.479 are currently described as the most high-pressure-resistant bacterial spores relevant to food intoxication and spoilage in combined pressure-temperature applications. The effects of combined pressure (0.1 to 1,400 MPa) and temperature (70 to 120°C) treatments were determined for these spores. A process employing isothermal holding times was established to distinguish pressure from temperature effects. An increase in pressure (600 to 1,400 MPa) and an increase in temperature (90 to 110°C) accelerated the inactivation of C. botulinum spores. However, incubation at 100°C, 110°C, or 120°C with ambient pressure resulted in faster spore reduction than treatment with 600 or 800 MPa at the same temperature. This pressure-mediated spore protection was also observed at 120°C and 800, 1,000, or 1,200 MPa with the more heat-tolerant B. amyloliquefaciens TMW 2.479 spores. Inactivation curves for both strains showed a pronounced pressure-dependent tailing, which indicates that a small fraction of the spore populations survives conditions of up to 120°C and 1.4 GPa in isothermal treatments. Because of this tailing and the fact that pressure-temperature combinations stabilizing bacterial endospores vary from strain to strain, food safety must be ensured in case-by-case studies demonstrating inactivation or nongrowth of C. botulinum with realistic contamination rates in the respective pressurized food and equipment.

Ultra high pressure treatments of foods

Contributors. Preface. Acknowledgments. Part I: Fundamental Aspects Of Treating Foods With High Pressure. 1. The Evolution of High Pressure Processing of Foods G.W. Gould. Introduction. Preservation Technologies. Evolution of High Pressure Processing. Conclusion. 2. The Effects of High Pressure on Biomaterials K. Heremans. Introduction. Pressure versus Temperature Effects. Stability Phase Diagrams of Food Macromolecules. Structure Property Relationship in Food Biopolymers. Conclusion. Part II: Effects Of High Pressure On Food Attributes. 3. Effects of High Pressure on Vegetative Microorganisms J.P. Smelt, J.C. Hellemons, M. Patterson. Introduction. Mode of Action of Temperature and Pressure on Microorganisms. Classes of Heat Resistance and Pressure Inactivation. The Effects of Food Constituents on Pressure Resistance. Design of Safe Pasteurization Conditions. Conclusion. 4. Effects of High Pressure on Spores V. Heinz, D. Knorr. Introduction. Pressure and Temperature. Microbiological Aspects. Modeling Approach. Spores under Pressure. Conclusion. 5. Effects of High Pressure on Enzymes Related to Food Quality L. Ludikhuyze, A. Van Loey, Indrawati, S. Denys, M.E.G. Hendrickx. Introduction. Mechanisms and Kinetics of Pressure Inactivation of Enzymes. The Effect of High Pressure on Enzymes Related to Food Quality. Kinetic Models To Describe Pressure-Temperature Inactivation of Enzymes Related to Food Quality. From Kinetic Information to Process Engineering. Conclusion. Glossary. 6. Effects of High Pressure on Chemical Reactions Related to Food Quality L. Ludikhuyze, M.E.G. Hendrickx. Introduction. The Effect of High Pressure on the Color of Food Products. The Effects of High Pressure on the Flavor of Food Products. The Effects of High Pressureon Texture of Food Products. The Effects of High Pressure on Nutritive Value and Health Components of Food Products. The Effect of High Pressure on Lipid Oxidation in Food Products. Conclusion. 7. Effects of High Pressure on Protein- and Polysaccharide-Based Structures M. Michel, K. Autio. Introduction. Pressure-Related Alterations in Food Raw Materials. Behavior of Starch Dispersions under Pressure. Influence of Pressure on Pectin. Pressure Effects on Protein Functionality. Structure Engineering by Pressure in Protein-Pectin Mixtures. Conclusion. 8. Effects of High Pressure on Water-Ice Transitions in Foods S. Denys, O. Schluter, M.E.G. Hendrickx, D. Knorr. Introduction. The Uses of Pressure in Freezing and Thawing. Modeling Heat Transfer during Processes with Phase Transitions at High Pressure. Conclusion. Part III: Food Products And Processes. 9. Industrial-Scale High Pressure Processing of Foods P. Rovere. Introduction. High Pressure Processing: State of the Art. Effects of Pressure on Real Foods. The Development of Combined Processing. Conclusion. 10. High Pressure Processing of Dairy Products E. Needs. Introduction. Milk Proteins. Dairy Foams, Emulsions, and Gels. Application of High Pressure in Cheese Production. Milk Enzymes. Conclusion. 11. High Pressure Equipment Designs for Food Processing Applications R.W. van den Berg, H. Hoogland, H.L.M. Lelieveld, L. van Schepdael. Introduction. Equipment for High Pressure Processing. Major Manufacturers of High Pressure Processing Equipment. Economics of High Pressure Processing. Conclusion. Index. About the Editors. List of Sources.

Application of ultrasound-assisted thermal processing for preservation and quality retention of liquid foods

A continuously working pilot plant-scale prototype was used to evaluate the effects of continuous-flow ultrasound-temperature treatment for bacterial decontamination of model suspensions and various liquid food systems such as milk, fruit, and vegetable juices. Escherichia coli K12 DH 5 alpha and Lactobacillus acidophilus were used as test microorganisms. In addition, treated juices were investigated for damage caused by heat or ultrasound-induced degradation of sensory and nutritional properties after treatment and storage. Changes in color and destruction of heat-labile and slightly oxidizable L-ascorbic acid content were monitored as an index to measure processing effects. Results were assessed with respect to the total energy requirement and compared with those using a conventional, indirect heating method having similar processing conditions. For the bacteriological process evaluation, the temperature- and time-dependent process lethality was used as the basis; for the quality- and energy-related investigations, the degree of bacterial inactivation was used. At identical degrees of bacterial inactivation, the ultrasound-assisted thermal treatments required a lower processing temperature than treatment with conventional thermal processing. However, according to energy balances, the total energy consumption was not reduced compared to conventional heating. Indications for a positive influence on shelf life, with improvements in surface color stability (lightness) and L-ascorbic acid retention, were found among quality parameters of treated orange juice.

Electrophysiological Model of Intact and Processed Plant Tissues: Cell Disintegration Criteria

Frequency versus conductivity relationships of food cell system, based on impedance measurements as characterized by polarization effects of the Maxwell−Wagner type at intact membrane interfaces, are presented. The electrical properties of a biological membrane (represented as a resistor and capacitor) are responsible for the dependence of the total conductivity of the cell system on the alternating current frequency. Based on an equivalent circuit model of a single plant cell, the electrical conductivity spectrum of the cell system in intact plant tissue (potato, carrot, banana, and apple) was determined in a frequency range between 3 kHz and 50 MHz. The electrical properties of a cell system with different ratios of intact/ruptured cells could also be predicted on the basis of a description of a cell system consisting of elementary layers with regularly distributed intact and ruptured cells as well as of extracellular compartments. This simple determination of the degree of cell permeabilization (cell disintegration index, po) is based upon electric conductivity changes in the cell sample. For accurate calculations of po, the sample conductivities before and after treatment, obtained at low‐ (fl) and high‐frequency (fh) ranges of the so‐called β‐dispersion, were used. In this study with plant cell systems, characteristic conductivities used were measured at frequencies fl = 3 kHz and fh = 12.5 MHz. The disintegration index was used to analyze the degree of cell disruption after different treatments (such as mechanical disruption, heating, freeze−thaw cycles, application of electric field pulses, and enzymatic treatment) of the plant tissues.

Kinetic studies on high-pressure inactivation of Bacillus stearothermophilus spores suspended in food matrices

Abstract Bacillus stearothermophilus spores ATCC 7953 can effectively be inactivated by high-pressure treatment, but only if it is applied at elevated temperatures; however, these temperatures are much lower compared to the temperature level used in heat inactivation under atmospheric pressure. Temperature and pressure in a range between 60 and 120°C and 50–600 MPa were applied to inactivate spores suspended in mashed broccoli and in cocoa mass. Utilizing an empirical mathematical model, derived from nth order kinetics, the survival curves of the spore strain investigated could be described accurately. The model can predict the impact of combined action of pressure and temperature on spore reduction. It was demonstrated that the inactivation of B. stearothermophilus spores ATCC 7953 improved with increasing treatment intensity. Beside intrinsic microbial inactivation mechanisms, the role of the pressure-induced shift in crystallization temperature of fat on spore inactivation in cocoa mass is discussed.

Quality considerations with high pressure processing of fresh and value added meat products

Pressure can be applied by high hydrostatic pressure, better known as high pressure processing (HPP), or by hydrodynamic pressure (HDP) in the form of shockwaves to alter quality parameters, such as shelf-life and texture of meat and meat products. The aim of this review is to give an overview of the use of pressure in the meat industry and to highlight its usage as a method to inactivate microorganisms but also a novel strategy to alter the structure and the quality parameters of meat and meat products. Benefits and possibilities of the technologies are presented, as well as how to overcome undesired product changes caused by HPP. The use of hydrodynamic shockwaves is briefly described and a promising newly developed industrial prototype for the generation of shockwaves by underwater explosion is presented.

High pressure inactivation kinetics of bacillus subtilis cells by a three‐state‐model considering distributed resistance mechanisms

Abstract Inactivation of vegetative Bacillus subtilis ATCC 9372 by high hydrostatic pressure treatment (200 ‐ 450 MPa) was tested at 20, 30 and 40°C. Time ‐ inactivation curves of the bacteria suspended in Ringers solution showed sigmoid asymmetric shapes when plotted in logarithmic scale. Kinetic analysis of the survivor data was performed by fitting a two‐step‐model. It was assumed that during pressure treatment, the bacterial cells pass through a metastable intermediate state which is reached after endogenous homeostatic mechanisms balancing the pressure induced displacements of equilibria can no longer be maintained. Combined pressure‐temperature‐pH effects may target this state and cause lethal cell damage. Modelling this concept, a distributive function describing the initial transition was used in combination with a first‐order reaction which was assumed to govern the irreversible second step. Regressively derived characteristic parameters showed logarithmic‐linear behaviour. Applicability of the ...