R.G.M. van der Sman

The science of food structuring

Food structuring is discussed from the viewpoints of soft matter physics and molecular gastronomy. Food is one of the most complex types of soft matter, with multiple dispersed phases and even hierarchical structure. Food structuring seems to be a kind of art, comprising a careful balance between forces driving the system towards equilibrium and arresting forces. A more scientific approach to this complex matter is desirable, using (1) concepts from soft matter physics, e.g. free energy and jamming, and (2) complex disperse system (CDS) notation as developed for molecular gastronomy. Combining CDS with state diagrams renders a new tool for the qualitative description of the complex process of making structured foods.

Prediction of the state diagram of starch water mixtures using the Flory–Huggins free volume theory

In this paper we analyse the phase and state transitions of starch and other glucose homopolymers and oligomers using the free volume extension of the Flory–Huggins theory by Vrentas and Vrentas, combined with the Couchman–Karasz theory for the glass transition. Using scaling relations of model parameters with molar weight we have obtained accurate predictions of moisture sorption and the freezing, boiling, and melting data obtained from literature for starch, dextrans, pullulan and maltodextrins. With the estimated model parameters we can construct the complete state diagram for starch, which can now be used as a quantitative tool for design and analysis of food structuring processes.

Moisture transport during cooking of meat: An analysis based on Flory-Rehner theory.

It is proposed that the moisture transport during cooking of meat can be described by the Flory-Rehner theory of rubber-elasticity. This theory contains the essential physics to describe the transport of liquid moisture due to denaturation and shrinkage of the heated protein matrix. The validity of the proposition is shown by a numerical model, which comprises a linearisation of the Flory-Rehner theory augmented with Darcys law for porous media flow. The model is used to simulate cooking experiments performed with a rectangular piece of beef. Reasonable comparison between simulations and experiments is obtained. Further analysis of simulations renders insight of yet unexplained phenomena observed during cooking of meat.

Emulsion droplet deformation and breakup with Lattice Boltzmann model

In this paper we have performed an extensive study of the effects of various dimensionless numerical parameters used in the Lattice Boltzmann implementation of the diffuse interface model describing deformation and breakup of an emulsion droplet in 2D. Such an extensive study on these parameter is absent in scientific literature of diffuse interface models. We have found that parameters like the dimensionless interface thickness and the Peclet number have to be within certain ranges for correct physical behavior. Outside these ranges droplets either dissolve, show incorrect Laplace pressures, or do not deform to stable shapes at subcritical capillary numbers. Furthermore, we have found that droplet breakup is sensitive to these parameters.

Prediction of airflow through a vented box by the Darcy–Forchheimer equation

A model is presented describing the airflow through a vented box packed with horticultural produce. The model is based on the Darcy–Forchheimer–Brinkman theory of flow through confined porous media. Though questions are raised on the applicability of this theory for the description of high airflow in vented boxes, we show that the model can reproduce experimental data on pressure drop over vented boxes quite accurately. Moreover, we confirm the hypothesis of a power law relationship between the pressure drop and the vent hole ratio of the box. Given the good comparison with experimental data, one can conclude that the model describes the airflow inside the box reasonably well, and when coupled to convection–diffusion models describing heat and water vapour transport, it can be used to improve designs of vented packages of horticultural produce.

Soft matter approaches to food structuring

We give an overview of the many opportunities that arise from approaching food structuring from the perspective of soft matter physics. This branch of physics employs concepts that build upon the seminal work of van der Waals, such as free volume, the mean field, and effective temperatures. All these concepts aid scientists in understanding and controlling the thermodynamics and (slow) dynamics of structured foods. We discuss the use of these concepts in four topics, which will also be addressed in a forthcoming Faraday Discussion on food structuring.

Classification and evaluation of microfluidic devices for continuous suspension fractionation

Membrane processes are well-known for separating and fractionating suspensions in many industries, but suffer from particle accumulation on the membrane surface. Currently, there are new developments using microfluidic devices for cell/DNA sorting and fractionation. We anticipate these devices are also applicable to fractionation of polydisperse and concentrated suspensions (e.g. foods), and may potentially have fewer problems with particle accumulation compared to membranes. This review article presents an overview of relevant microfluidic devices. We focus on their performance with respect to concentrated suspensions, as one finds in food industry. We give quantitative estimates on their yield, selectivity, and the potential for large-scale application. From this evaluation follows that deterministic ratchets seem most promising.

Simple model for estimating heat and mass transfer in regular-shaped foods

In this paper a simplified model is presented, which describes the cooling of high-moisture cylindrical food with evaporation at the surface. This simplified model is derived from the observation of simulation results of a detailed finite volume method, that the average temperature has a fixed location. The simplified model can be represented by an electrical network analogue, comprising of one or two heat capacities, heat resistances and a heat flow source (for the evaporation). By dividing the food body in a shell and a core, one can predict the average temperature and surface temperature with comparable accuracy as the finite volume model for any Biot number and moderate to large time scales.

Suspension flow modelling in particle migration and microfiltration

We review existing mixture models for shear-induced migration (SIM) in flowing viscous, concentrated particle suspensions via an analysis of the models from the perspective of a two-fluid formulation. Our analysis shows that particle suspensions in strong non-linear shear fields are a prime example of a driven soft matter system. The driving forces for particle migration can be expressed in terms of non-equilibrium osmotic pressure and chemical potential. Using the linear scaling of the effective temperature with the shear stress, we show that the osmotic pressure and shear-induced diffusion coefficients can be written in identical equations. This is similar to the equations for Brownian motion - with the temperature replaced by the effective temperature. As a guiding application we have taken crossflow microfiltration, where the driving is very strong and there is formation of a jammed state, cake layer, coexisting with the fluid state. The question whether the SIM mixture models holds for this aplication is investigated. Another questions is how SIM models can be extended for bidisperse suspensions, which is relevant for microfiltration applications involving particle fractionation. Analysis of existing closures of SIM mixture models from the two-fluid perspective learns us that the theory seems to be extendable towards bidisperse suspensions by means of the effective medium theory.

Modeling cooking of chicken meat in industrial tunnel ovens with the Flory-Rehner theory.

In this paper we present a numerical model describing the heat and mass transport during the cooking of chicken meat in industrial tunnels. The mass transport is driven by gradients in the swelling pressure, which is described by the Flory-Rehner theory, which relates to the water holding capacity (WHC). For cooking temperatures up to boiling point and practical relevant cooking times, the model renders good prediction of heat and mass transport and the total loss of moisture. We have shown that for cooking temperatures above boiling point, the model has to be extended with the dynamic growth of capillary water (drip) channels. Furthermore, we discuss that the Flory-Rehner theory provides the proper physical basis for describing the change of the WHC by a wide variety of factors like salt and pH.