Henry Jaeger

Emerging Technologies in Food Processing

High hydrostatic pressure (HHP), pulsed electric fields (PEFs), ultrasound (US), and cold plasma (CP) are emerging technologies that have already found application in the food industry or related sectors. This review aims to describe the basic principles of these nonthermal technologies as well as the state of the art concerning their impact on biological cells, enzymes, and food constituents. Current and potential applications will be discussed, focusing on process-structure-function relationships, as well as recent advances in the process development.

The Maillard reaction and its control during food processing. The potential of emerging technologies.

The Maillard reaction between reducing sugars and amino acids is a common reaction in foods which undergo thermal processing. Desired consequences like the formation of flavor and brown color of some cooked foods but also the destruction of essential amino acids and the production of anti-nutritive compounds require the consideration of the Maillard reaction and relevant mechanisms for its control. This paper aims to exemplify the recent advances in food processing with regard to the controllability of heat-induced changes in the food quality. Firstly, improved thermal technologies, such as ohmic heating, which allows direct heating of the product and overcoming the heat transfer limitations of conventional thermal processing are presented in terms of their applicability to reduce the thermal exposure during food preservation. Secondly, non-thermal technologies such as high hydrostatic pressure and pulsed electric fields and their ability to extend the shelf life of food products without the application of heat, thus also preserving the quality attributes of the food, will be discussed. Finally, an innovative method for the removal of Maillard reaction substrates in food raw materials by the application of pulsed electric field cell disintegration and extraction as well as enzymatic conversion is presented in order to demonstrate the potential of the combination of processes to control the occurrence of the Maillard reaction in food processing.

Protective effect of milk constituents and sublethal injuries limiting process effectiveness during PEF inactivation of Lb. rhamnosus.

The inactivation of Lb. rhamnosus by pulsed electric field treatment (PEF) was studied in different fractions of raw milk and Ringer solution in order to evaluate the protective effect of nutrient rich media in comparison to aqueous buffer solutions. Apart from monitoring of culturability, analysis of the physiological fitness of Lb. rhamnosus was conducted aiming to identify sublethally damaged cells. Therefore, flow cytometry and a selective medium plating technique were used and compared to each other. The goal of the study was to apply three different parameters describing the physiological fitness of the model organism Lb. rhamnosus after PEF treatment such as culturability, membrane permeability and metabolic activity depending on treatment media and parameters. A concentration dependent protective effect of the milk protein fraction could be shown and allocated to micellar casein as the major milk protein. Increasing the concentration of whey proteins up to 2% showed a similar impact on limiting the PEF inactivation of Lb. rhamnosus. The evaluation of physiological fitness of cells was based on a determination of structural and functional characteristics by rapid cellular staining using carboxyfluorescein diacetate and propidium iodide. This approach showed good accordance to the conventional selective medium plating technique for the enumeration of sublethally-injured bacteria but flow cytometry provided additional information for the characterisation of this fraction. The extent of occurrence of dead, sublethal and vital fractions of cells was found dependent on the PEF treatment parameters such as electrical field strength and energy input as well as the different milk fractions used as treatment media.

Food Industry Applications for Pulsed Electric Fields

In this chapter the potential of pulsed electric fields (PEF) to enhance or create alternatives to conventional methods in food processing will be summarized. After a brief introduction of the historical background, some applications for gentle food preservation will be presented. The enhancement of mass transfer processes like extraction or drying by PEF-pretreatment will be pointed out by showing examples ranging from fruit juice and plant oil recovery to the disintegration of animal tissue. The use of PEF for the softening of plant tissue, for the induction of stress reactions, as well as for wastewater treatment will be illustrated. The discussion of energy requirements and cost-effectiveness will complete the chapter.

Minimization of Thermal Impact by Application of Electrode Cooling in a Co-linear PEF Treatment Chamber

A co-linear pulsed electric field (PEF) treatment chamber was analyzed and optimized considering electrical process conditions, temperature, and retention of heat-sensitive compounds during a continuous PEF treatment of peach juice. The applicability of a jacket heat-exchanger device surrounding the ground electrode was studied in order to provide active cooling and to avoid temperature peaks within the treatment chamber thus reducing the total thermal load to which the product is exposed. Simulation of the PEF process was performed using a finite element method prior to experimental verification. Inactivation of polyphenoloxydase (PPO) and peroxidase (POD) as well as the degradation of ascorbic acid (AA) in peach juice was quantified and used as indirect indicators for the temperature distribution. Peaks of product temperature within the treatment chamber were reduced, that is, from 98 to 75 °C and retention of the indicators PPO, POD, and AA increased by more than 10% after application of the active electrode cooling device. Practical Application:  The co-linear PEF treatment chamber is widely used for continuous PEF treatment of liquid products and also suitable for industrial scale application; however, Joule heating in combination with nonuniform electric field distribution may lead to unwanted thermal effects. The proposed design showed potential to reduce the thermal load, to which the food is exposed, allowing the retention of heat-sensitive components. The design is applicable at laboratory or industrial scale to perform PEF trials avoiding temperature peaks, which is also the basis for obtaining inactivation kinetic models with minimized thermal impact on the kinetic variables.

Emerging Technologies for Targeted Food Processing

High hydrostatic pressure, pulsed electric fields, ultrasound, and cold plasma are emerging technologies that have already found application in the food industry. This summary aims to describe the basic principles of these nonthermal technologies as well as the state of the art concerning their impact on biological cells, enzymes, and food constituents. Current and potential applications will be discussed focusing on process-structure-function relationships as well as recent advances in process development.

Food Safety: Shelf Life Extension Technologies

The aim of this article is to give an overview on advanced food preservation technologies resulting in a shelf life extension of food products. Basic principles as well as applications, process–product interactions, and technical aspects are outlined. Microbial inactivation kinetics and food quality considerations are discussed. Conventional thermal as well as emerging nonthermal food preservation technologies, such as high pressure and pulsed electric field processing, are presented. Methods to control microbial growth and to limit quality degradation of food during shelf life, such as the use of antimicrobials, fermentation, or modified atmosphere packaging, are highlighted. A Section on Surface Decontamination using plasma and steam covers an additional important area of shelf life extension technologies.