Equilibrium and non-equilibrium structures in complex food systems

Abstract

The physics ruling the macroscopic behaviour of foods is discussed in a few selected examples in which the equilibrium/nonequilibrium nature can be directly related to the typical length scale of the food structure and the specific interaction strength, the latter describing the decrease in specific free energy (e.g., per mole of species or per single event) when going from a non-equilibrium to the equilibrium configuration. Liquid-crystalline phases in foods, such as those based on self-assembled lipids and water, are discussed as an example of equilibrium system, in which low correlation length scales ($nm) enable very-short times to re-organize molecules into equilibrium configurations. High internal phase emulsions and dry foams where length scales are very large ($10 1 -10 4 mm), are discussed as a typical example of non-equilibrium system, which however, can be stable for long times owing to the high free energy barrier and the large correlation lengths. Finally double emulsion systems are considered as an example where both interaction strength and correlation lengths have intermediate values. This allows tuning morphologies and making equilibrium behaviour to prevail over non-equilibrium by suitably tailoring the energetic interactions. In particular the case of osmotic pressure in the water phase of water/oil/water double emulsions is discussed as a viable route to control interaction strength in complex food systems.

Understanding Food Structures

“…The search data indicate that the authors of these papers have separately chosen to identify the topic of "food structure" to a roughly equal extent with the disciplines of biology, engineering, and chemistry. The association with physics is less well developed, but there is recent evidence that this trend is changing (Mezzenga, 2007;Ubbink, 2012). The data in Figure 1.1 also confirm the expected association of food structure with texture, taste, and rheology.…”

“…Depending on the osmotic pressure difference, there is a thermodynamic driving force for water to diffuse through the oily membrane from the inner aqueous phase to the outer one (or vice versa). In principle, this instability can be controlled by using an oil phase of low water solubility and by carefully balancing the osmotic pressure difference with simple solutes (sugars) and electrolytes (Mezzenga, 2007). In practice, however, the osmotic balance is difficult to achieve in the context of a manufactured food product.…”

Double Emulsions Stabilized by Food Biopolymers

“…The incorporation of the required concentration of simple electrolytes, sugars or polysaccharides to control the osmotic balance is an essential strategy for maintaining the thermodynamic stability of W/O/W emulsions. [33][34][35] In principle, the kinetics of mass transport can be reduced by using an oil phase of low water solubility.…”

A soft condensed matter approach towards mathematical modelling of mass transport and swelling in food grains

“…Mezzenga et al (2005) reviewed the nature of foods from a perspective of soft condensed matter physics. The details of structural changes at various scales in food systems often needs experimental and/or theoretical tools of soft matter physics, which are not fully adapted to food systems (Mezzenga, 2007;Mezzenga et al, 2005). An exposition of the potential of soft matter physics for explaining the complex food processes and structuring at various scales is also provided in van der Sman and van der Goot (2009) and van der Sman (2012).…”