High pressure processing is a food processing method which has shown great potential in the food industry. Similar to heat treatment, high pressure processing inactivates microorganisms, denatures proteins and extends the shelf life of food products. But in the meantime, unlike heat treatments, high pressure treatment can also maintain the quality of fresh foods, with little effects on flavour and nutritional value. Furthermore, the technique is independent of the size, shape or composition of products. In this paper, many aspects associated with applying high pressure as a processing method in the food industry are reviewed, including operating principles, effects on food quality and safety and most recent commercial and research applications. It is hoped that this review will promote more widespread applications of the technology to the food industry.

Recent Advances in the Use of High Pressure as an Effective Processing Technique in the Food Industry

The International Association for the Properties of Water and Steam (IAPWS) encouraged an extensive research effort to update the IAPS Formulation 1985 for the Viscosity of Ordinary Water Substance, leading to the adoption of a Release on the IAPWS Formulation 2008 for the Viscosity of Ordinary Water Substance. This manuscript describes the development and evaluation of the 2008 formulation, which provides a correlating equation for the viscosity of water for fluid states up to 1173K and 1000MPa with uncertainties from less than 1% to 7% depending on the state point.

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New International Formulation for the Viscosity of H2O

The rate of water flow through hydrophobic nanocapillaries is greatly enhanced as compared to that expected from macroscopic hydrodynamics. This phenomenon is usually described in terms of a relatively large slip length, which is in turn defined by such microscopic properties as the friction between water and capillary surfaces and the viscosity of water. We show that the viscosity of water and, therefore, its flow rate are profoundly affected by the layered structure of confined water if the capillary size becomes less than 2 nm. To this end, we study the structure and dynamics of water confined between two parallel graphene layers using equilibrium molecular dynamics simulations. We find that the shear viscosity is not only greatly enhanced for subnanometer capillaries, but also exhibits large oscillations that originate from commensurability between the capillary size and the size of water molecules. Such oscillating behavior of viscosity and, consequently, the slip length should be taken into account in designing and studying graphene-based and similar membranes for desalination and filtration.

Commensurability Effects in Viscosity of Nanoconfined Water

New measurements have been made for the viscosity (η) of light and heavy water between the temperatures of 25565 K and 29815 K at pressures up to approximately 375 MPa with a falling-body viscometer A revised correlation function is used to represent the results as a function of temperature and molar volume (V) with a standard deviation of ±02% for both H2O and D2O The overall uncertainty is estimated at ±1% Comparison of the two sets of data shows that they are consistent with the correlation η(D2O,T,V) = 10544η(H2O,T − 6498 K,V) where 10544 is the square root of ratio the molar masses and 6498 K is the thermal offset proposed by Robinson and co-workers

https://pubs.acs.org/doi/pdf/10.1021/je049668%2B

Temperature and Volume Dependence of the Viscosity of Water and Heavy Water at Low Temperatures

Digital particle image thermometry/velocimetry (DPIT/V) is a relatively new methodology that allows for measurements of simultaneous temperature and velocity within a two-dimensional domain, using thermochromic liquid crystal tracer particles as the temperature and velocity sensors. Extensive research has been carried out over recent years that have allowed the methodology and its implementation to grow and evolve. While there have been several reviews on the topic of liquid crystal thermometry (Moffat in Exp Therm Fluid Sci 3:14–32, 1990; Baughn in Int J Heat Fluid Flow 16:365–375, 1995; Roberts and East in J Spacecr Rockets 33:761–768, 1996; Wozniak et al. in Appl Sci Res 56:145–156, 1996; Behle et al. in Appl Sci Res 56:113–143, 1996; Stasiek in Heat Mass Transf 33:27–39, 1997; Stasiek and Kowalewski in Opto Electron Rev 10:1–10, 2002; Stasiek et al. in Opt Laser Technol 38:243–256, 2006; Smith et al. in Exp Fluids 30:190–201, 2001; Kowalewski et al. in Springer handbook of experimental fluid mechanics, 1st edn. Springer, Berlin, pp 487–561, 2007), the focus of the present review is to provide a relevant discussion of liquid crystals pertinent to DPIT/V. This includes a background on liquid crystals and color theory, a discussion of experimental setup parameters, a description of the methodology’s most recent advances and processing methods affecting temperature measurements, and finally an explanation of its various implementations and applications.

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Digital particle image thermometry/velocimetry: a review

New experimental data for the viscosity of water at high pressures up to 700 MPa in the temperature range of −13 °C to 20 °C are presented. The measurements were carried out with two different types of viscometer, both gravity driven. The set-up of the viscometers and the pressure-dependent corrections are briefly described. The viscosity data are compared with available literature data. Reasons for the deviations are discussed. Models to describe pressure-viscosity behavior of water are applied to the data. The applicability to the moderate temperature viscosity data is discussed and it is checked whether the range of validity of the models can be extended to subzero temperatures.

The viscosity of water at high pressures – especially at subzero degrees centigrade

A first application of encapsulated thermochromic liquid crystals (TLCs) for visualizing temperature fields in pressurized liquids was studied experimentally. By means of a tempered high-pressure optical cell, investigations were performed in a wide temperature range and at pressures up to 7000 bar. The measured calibration curves of isochromes in the pressure/temperature domain as well as photographically documented temperature fields at high pressure are presented and discussed. The results found illustrate that TLCs provide an efficient instrument for investigating thermofluiddynamical processes even at high pressure.

First visualization of temperature fields in liquids at high pressure using thermochromic liquid crystals

The effect of the pressurization ramp on the inactivation kinetics of Listeria innocua suspended in Tris buffer has been studied experimentally in an optical pressure cell. Additionally, the thermofluiddynamical processes occurring at the different pressure ramps have been considered. The results obtained at room temperature show that the inactivation effect of high pressure remains the same in case of a fast pressurization ramp (500 MPa/min) and a slow depressurization ramp (100 MPa/min) in comparison to a slow pressurization ramp (100 MPa/min) and a fast depressurization ramp (500 MPa/min). At the chosen test conditions, the fluiddynamical and thermal processes of the two variations differ only slightly from each other. This has been ascertained by measuring the velocity and temperature distributions occurring at the pressure processes. The conclusion is that the pressurization and depressurization rate, respectively, do not effect per se the inactivation kinetics of Listeria innocua .

Effect of the pressurizing ramp on the inactivation of Listeria innocua considering thermofluiddynamical processes

New experimental data for the pressure dependence of the viscosity of aqueous solutions of different sugars are presented. Measurements were carried out with a gravity driven high pressure viscometer with a maximum pressure of 700 MPa. The influence of both concentration and temperature on the pressure dependence of the viscosity is considered. Next to the data, a viscosity model based on a suspension model is introduced and it is shown that it is able to predict the viscosity for sugar solutions in a broad parameter range, including pressure. It is demonstrated that the relative viscosity for varying sugar mass fraction at constant pressure coincides with the pressure-dependent relative viscosity for a fixed sugar mass fraction, suggesting that there are no structural changes occurring under pressure. A brief interpretation of the viscosity model is given.

On the pressure dependence of the viscosity of aqueous sugar solutions

In previous investigations it has been shown that thermofluiddynamical processes occur in food related substances at high hydrostatic pressure (HHP) treatment In order to gain insight into these processes an in-situ measuring technique for visualizing temperature and velocity fields has been developed [1] Based on extensive test series the thermal and fluiddynamical processes in water have been analyzed After pressurizing water onto 230 MPa within 12 seconds temperature gradients of 01 K/mm are generated in the visible field optical cell The present study comprises investigations on liquids of higher viscosity Sucrose solution of 50% (weight percent) has been chosen as model fluid because the viscosity data are available up to 600 MPa [2] The results show that the temperature gradients are six times higher than those in water under the same test conditions This in turn may cause heterogeneties of biochemical processes in foods This correlation has been confirmed by numerical simulations of an enzyme inactivation process [3] In the present contribution visualized inhomogeneous temperature fields arising in sucrose solution are presented and compared to the thermofluiddynamical processes in water

Franz Werner

Papers

The viscosity of water at high pressures – especially at subzero degrees centigrade

First visualization of temperature fields in liquids at high pressure using thermochromic liquid crystals

Effect of the pressurizing ramp on the inactivation of Listeria innocua considering thermofluiddynamical processes

On the pressure dependence of the viscosity of aqueous sugar solutions

Experimental investigation on thermofluiddynamical processes in pressurized substances