Expressible moisture retention

Figure B5.3.1 A comparison of water retention properties expressible moisture versus water uptake ability. Reprinted from Regenstein (1984) with permission from the American Meat Science Association.

Expressible moisture and water uptake ability measure different properties. Figure B5.3.2 shows the very different cation and anion dependencies of these methods using fish samples. Figure B5.3.3 shows that the pH profiles are also different. It is also apparent that WUA is often >100%, while expressible moisture must, of necessity, be <100%. Figure B5.3.4 shows an example where expressible moisture was actually correlated with a separate and independent functional measurement. In this case, the binding of cooked fish muscle as determined by a subjective sensory panel pulling samples of fish apparently paralleled the moisture retention of the raw fish (moisture retention = 1 - expressible moisture). Ideally, functional properties should show such correlations with other properties of interest in food systems. 

Fig. 12.14 Kerosene retention capacity (KRC) as affected by soil type and soil moisture conditions, expressed as volume of kerosene per bulk volume of air-dry soil. Reprinted from Jarsjo J, Destouni G, Yaron B (1994) Retention and volatilization of kerosene laboratory experiments on glacial and postglacial soils. J Contam Hydrol 17 167-185. Copyright 1994 with permission of Elsevier...

The separation of the solids is usually expressed as mass recovery or total efficiency (in filtration this is also known as retention ) as dealt with in depth in chapter 3, whilst the separation of the liquid is usually characterized by the moisture content of the cake or concentration of solids in the underflow. Separation efficiencies of the solids and the liquid are best considered separately because different applications place different emphasis on the two in thickening, for example, the emphasis is on the high efficiency for the hquid (i.e. high sohds content in cakes or underflows), whilst in recovery or clarification, high efficiency for the solids is required. If the emphasis placed on the two efficiencies is equal then they can be combined in one criterion, the entropy index, discussed in Part II, chapter 18. 

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