Ann Van Loey

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.

Pectin methylesterase and its proteinaceous inhibitor: a review.

Pectin methylesterase (PME) catalyses the demethoxylation of pectin, a major plant cell wall polysaccharide. Through modification of the number and distribution of methyl-esters on the pectin backbone, PME affects the susceptibility of pectin towards subsequent (non-) enzymatic conversion reactions (e.g., pectin depolymerisation) and gel formation, and, hence, its functionality in both plant cell wall and pectin-containing food products. The enzyme plays a key role in vegetative and reproductive plant development in addition to plant-pathogen interactions. In addition, PME action can impact favourably or deleteriously on the structural quality of plant-derived food products. Consequently, PME and also the proteinaceous PME inhibitor (PMEI) found in several plant species and specifically inhibiting plant PMEs are highly relevant for plant biologists as well as for food technologists and are intensively studied in both fields. This review paper provides a structured, comprehensive overview of the knowledge accumulated over the years with regard to PME and PMEI. Attention is paid to both well-established and novel data concerning (i) their occurrence, polymorphism and physicochemical properties, (ii) primary and three-dimensional protein structures, (iii) catalytic and inhibitory activities, (iv) physiological roles in vivo and (v) relevance of (endogenous and exogenous) enzyme and inhibitor in the (food) industry. Remaining research challenges are indicated.

A modeling approach for evaluating process uniformity during batch high hydrostatic pressure processing: combination of a numerical heat transfer model and enzyme inactivation kinetics

Abstract A numerical conductive heat transfer model for calculating the temperature evolution during batch high hydrostatic pressure (HHP) processing of foods was tested for two food systems: apple sauce and tomato paste. Hereto, relevant thermal and physical properties of the products were determined. For a comprehensive evaluation, both ‘conventional’ HHP processes with gradual, step by step pressure build-up and pressure release were simulated. In all cases, satisfactory agreement between experimental and predicted temperature profiles was obtained. The model provides a very useful tool to evaluate batch HHP processes in terms of uniformity of any heat- and/or pressure-related effect. Uniformity of inactivation of Bacillus subtilis α-amylase and soybean lipoxygenase during batch HHP processing was evaluated. Hereto, a theoretical as well as an experimental approach was used. The residual enzyme activity distribution appeared to be dependent on the inactivation kinetics of the enzyme under consideration and the pressure–temperature combinations considered. Good agreement between the theoretical considerations and experimentally obtained activity retentions was found for Bacillus subtilis α-amylase. In case of soybean lipoxygenase, less agreement was found. This work presents a first step in the development of indicators to assess process uniformity in HHP processing of foods.

Comparative study of the cell wall composition of broccoli, carrot, and tomato: Structural characterization of the extractable pectins and hemicelluloses

This study delivers a comparison of the pectic and hemicellulosic cell wall polysaccharides between the commonly used vegetables broccoli (stem and florets separately), carrot, and tomato. Alcohol-insoluble residues were prepared from the plant sources and sequentially extracted with water, cyclohexane-trans-1,2-diamine tetra-acetic acid, sodium carbonate, and potassium hydroxide solutions, to obtain individual fractions, each containing polysaccharides bound to the cell wall in a specific manner. Structural characterization of the polysaccharide fractions was conducted using colorimetric and chromatographic approaches. Sugar ratios were defined to ameliorate data interpretation. These ratios allowed gaining information concerning polysaccharide structure from sugar composition data. Structural analysis of broccoli revealed organ-specific characteristics: the pectin degree of methoxylation (DM) of stem and florets differed, the sugar composition data inferred differences in polymeric composition. On the other hand, the molar mass (MM) distribution profiles of the polysaccharide fractions were virtually identical for both organs. Carrot root displayed a different MM distribution for the polysaccharides solubilized by potassium hydroxide compared to broccoli and tomato, possibly due to the high contribution of branched pectins to this otherwise hemicellulose-enriched fraction. Tomato fruit showed the pectins with the broadest range in DM, the highest MM, the greatest overall linearity and the lowest extent of branching of rhamnogalacturonan I, pointing to particularly long, linear pectins in tomato compared with the other vegetable organs studied, suggesting possible implications toward functional behavior.

Effect of thermal processing on the degradation, isomerization, and bioaccessibility of lycopene in tomato pulp.

Thermal processing affects the nutritional value of food products. The nutritional value is not only determined by the content but also by the bioaccessibility of nutrients. The present study was performed to gain detailed insight into the influence of thermal processing on the degradation, isomerization, and bioaccessibility of lycopene isomers in tomato pulp, without adding any other ingredient. The bioaccessibility, which is defined as the fraction of the nutrient that can be released from the food matrix, was measured using an in vitro method. The results demonstrated the rather high thermal stability of lycopene. Although a treatment at 140 °C induced isomerization, the contribution of cis-lycopene to the total lycopene content remained small. Results also confirmed that thermal processing as such can improve the in vitro bioaccessibility of lycopene in tomato pulp, but the improvement was only significant upon treatments at temperatures of 130 and 140 °C. At such intense process conditions, one should be aware of the negative effect on other quality and nutrient parameters. Possibilities of thermal processing as such to improve the nutritional value of tomato pulp (without the addition of other ingredients) thus looks rather limited.

Comparative study of the inactivation kinetics of pectinmethylesterase in tomato juice and purified form.

Pectinmethylesterase (PME) extracted from tomato fruit was purified by affinity chromatography. A single peak of PME activity was observed, presenting a molar mass of 33.6 kDa, an isoelectric point higher than 9.3, and an optimal temperature and pH for activity of 55 °C and 8.0, respectively. The processing stability of purified tomato PME in buffer solution was compared to PME stability in tomato juice. In both media, thermal inactivation of PME presented first‐order inactivation kinetics, PME in tomato juice being more heat‐labile than purified PME. Regarding high‐pressure treatment, tomato PME showed to be very pressure‐resistant, revealing an outspoken antagonistic effect of temperature and pressure. To avoid cloud loss in tomato juice, a time‐temperature treatment of 1 min at 76.5 °C was calculated in order to have a residual PME activity of 1 × 10−4U/mL.

Inactivation kinetics of polygalacturonase in tomato juice

a ¸ ´´ ˜ ´ Abstract The inactivation kinetics of polygalacturonase (PG) in tomato juice was studied during thermal and high-pressureythermal processing. In the temperature range of 55-70 8C the thermal inactivation of polygalacturonase in tomato juice followed a fractional conversion model, with a thermostable fraction of approximately 14%. Under conditions of combined high-pressurey thermal processing, 200-550 MPay5-50 8C, PG inactivation presented first order kinetics. A mathematical model to describe the inactivation rate constant as a function of pressure and temperature was formulated. Industrial relevance: Polygalacturonase is responsible for the decrease of viscosity in tomato-based products. However, little research on thermal and high pressure ythermal inactivation kinetics of tomato Polygalacturonase has been reported. This research clearly shows that it is possible to selectively inactivate PG by high pressureythermal processing without applying high temperatures. This leads to tomato-based products with improved functional properties while other quality attributes (color, flavor, nutritional value ) are maintained. 2002 Elsevier Science Ltd. All rights reserved.

Particle size reduction leading to cell wall rupture is more important for the β-carotene bioaccessibility of raw compared to thermally processed carrots.

The amount of nutrients that can be released from food products (i.e., nutrient in vitro bioaccessibility) is often studied as it is a starting point for investigating nutrient bioavailability, an indicator for the nutritional value of food products. However, the importance of mastication as a particle size reduction technique is poorly understood and is often neglected during in vitro procedures determining bioaccessibility. Therefore, the aim of the present work was to study the effect of mechanical breakdown on the β-carotene bioaccessibility of carrot samples, having different textural/structural characteristics (as a result of thermal processing). In the first part of this study, the all-E-β-carotene bioaccessibility of carrot particles of different sizes (ranging from cell fragments up to large cell clusters), generated from raw as well as from gently and intensely cooked carrot samples, was determined. In the second part of the study, the effect of human mastication on the particle size reduction of raw as well as of gently and intensely cooked carrot samples was investigated in order to allow identification and validation of a technique that could mimic mastication during in vitro procedures. Results showed a strong dependency of the all-E-β-carotene bioaccessibility on the particle size for raw and gently cooked carrots. After intense cooking, on the other hand, a considerable amount of all-E-β-carotene could be released from cell fragments (smaller than a cell) as well as from small and large cell clusters. Hence, the importance of mechanical breakdown, and thus also of (in vitro) mastication, is dependent on the carrot sample that is considered (i.e., the extent to which the carrot sample has been thermally processed prior to the particle size reduction). Structural changes occurring during mechanical and thermal processing are hereby key factors determining the all-E-β-carotene bioaccessibility. The average particle size distribution curves of raw and cooked carrots, which were chewed by 15 persons, could be mimicked by mixing 50 g of carrots using a Grindomix (Retsch) at 2500 rpm during 5 s. Based on this scientific knowledge, the identified in vitro mastication technique was successfully integrated in the in vitro digestion procedure determining the all-E-β-carotene bioaccessibility of carrot samples.

Intrinsic time temperature integrators for heat treatment of milk

Abstract This paper reviews the available research information on intrinsic time temperature integrators (TTIs) for thermally processed milk. These are specific indicators present or formed in milk that allow direct and quantitative measurement of the impact of the process without knowledge of the actual thermal history. General principles concerning the characterization of intrinsic TTIs as well as the applicability and limitations of some milk compounds considered as potential intrinsic TTIs are discussed.

Strawberry Pectin Methylesterase (PME): Purification, Characterization, Thermal and High-Pressure Inactivation

Pectin methylesterase (PME) was extracted from strawberries ( Fragaria ananassa, cv Elsanta) and purified by affinity chromatography on a CNBr‐Sepharose 4B‐PME‐inhibitor column. A single protein and PME activity peak was obtained. A biochemical characterization in terms of molecular mass, pI, and kinetic parameters of strawberry PME was performed. In a second step, the thermal and high‐pressure stability of the enzyme was studied. Isothermal and combined isothermal‐isobaric inactivation of purified strawberry PME could be described by a fractional‐conversion model. Purified strawberry PME is much more stable toward high‐pressure treatments in comparison to those from oranges and bananas.