In the last decade we have been developing theories for water holding capacity (WHC) of meat and vegetables, building on the seminal work of Flory and Rehner (Sman, Meat Sci.,2007). The Flory-Rehner theory is commonly applied to explain swelling of polymer gels as function their crosslink density and their osmotic pressure. In our more recent work on mushrooms, we have learned that water in the vacuoles and capillary water in extracellular space contribute to WHC, next to the water held in the cell wall material (Paudel, Boom, Sman, 2015-2016). The Flory-Rehner theory only applies to gel-like material like cell wall material in mushrooms and vegetables, or muscle fibers. Water in the vacuoles inside the cells of mushrooms and vegetables leads to the development of osmotic pressure, if the cell membrane is intact. Via het monophasic theory of large deformations of hydrogels of the group of Suo, we have investigated the change of WHC if the integrity of the cell membrane is lost (Sman, Soft Matter, 2016).<br/>The group of Suo is currently developing the theory of osmocapillarity, the interplay between gels and capillary water. We are investigating this theory to incorporate the effect of capillary water into the theory of WHC in biological tissue. Extracellular capillary water is also present in meat where the post-mortem process leads to the development of drip channels. Furthermore, in our current research on meat replacers we intentionally incorporate a capillary phase to modulate WHC of meat replacers. Hence, the ability to describe effects of capillary water is highly relevant for many biological tissues intended as food, but also for coarse gels.<br/>The above WHC theory is building upon work of Suo, where all contributions to WHC are incorporated in a single thermodynamic framework based on a free energy formulation. From this thermodynamic framework one can derive driving forces for mechanical deformation and moisture transport, which are concurrently happening during drying of biological food material like broccoli. We show how our theory can be used to describe this drying process, and show the interplay between large mechanical deformation and moisture transport. It can explain counter-intuitive phenomena like increase in moisture content in the centre of broccoli stems in the initial stages of drying.<br/>

Role of large deformation mechanics and osmocapillarity in water holding and drying of biological tissue

255th National Meeting (2018)

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