Moisture water uptake

Another major drawback of polysaccharides is their hydrophilic nature leading to low degrees of adhesion between fiber and matrix [11]. Moisture absorption takes place by three types of mechanisms namely diffusion, capillarity, and transport via micro cracks [2]. Among the three, diffusion is considered to be the major mechanism. Water absorption largely depends on the water-soluble or hygroscopic components embedded in the matrix, which acts as a semipermeable membrane. While, fiber/matrix adhesion and fiber architecture also affect the moisture absorption. The results of the water sorption experiment showed an interesting trend. The extent of water uptake was not very significant and also did not increase linearly with amount of filler (Table-2). 

This type of water uptake measurement is very general in application. It is applicable to most porous media, where moisture transport properties need to be measured. 

Water uptake causes a host of problems in drug products and the inactive and active ingredients contained in them. Moisture uptake has been shown to be an important factor in the decomposition of drug substances [1-8]. Moisture has also been shown to change surface properties of solids [9,10], alter flow characteristics of powders [11,12], and affect the compaction properties of solids [13]. This chapter discusses various mathematical models that can be used to describe moisture uptake by deliquescent materials. 

The resistance to moisture, hot water and pressurized steam is good without hydrolysis, but long exposures to water or moisture can lead to a significant water uptake, which plasticizes the material. 

A Relationship between net photosynthesis, foliage age, and foliage retention B Effect ofplant moisture stress on net photosynthesis C Relationship between mineral uptake and net photosynthesis D Relationship between net photosynthesis and carbohydrate storage E Relationship between water uptake and mineral nutrition F Relationship between carbohydrate storage and bark characteristics G Relationship between carbohydrate storage and wood H Relationship between carbohydrate storage and cone production... 

Effect of pathogens on tree carbohydrate concentration and relationship of carbohydrate concentrations to pathogen attack 24b Effect of path< ns on water uptake and transpiration 24c Relation ip between stem and root characteristics and pathogen attack 2Sa Effect of soil moisture and temperature on water uptake and transpiration 2Sb Effect of soil mineral concentration and temperature on mineral nutrition of... 

Water Uptake and Retention. The water binding capacity of soy protein isolate can be increased by treatment with neutral fungal protease (20). Since the number of free amino and carboxyl groups increases as a result of digestion and because moisture uptake by proteins is proportional to the number of ionic groups present ( ), it is not surprising that moisture uptake is increased by enzyme treatment. 

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.

Although the conditions used for the measurement of both expressible moisture and water uptake ability are arbitrary, the two can be performed under similar conditions. One of the real benefits of the two tests, with arbitrarily defined working parameters, is that they can, in theory, be done in parallel, e.g., by placing four samples for expressible moisture and four samples for water uptake ability in the same eight-cell centrifuge. In this case, the differences observed reflect the differences between... 

Drip loss, cooking or processing loss, and thaw loss are similar to expressible moisture. In most cases, however, the moisture is lost without the need to apply a force. Thus, the liquid that is expelled can simply be collected by carefully pouring off the excess liquid. The drip loss test is a very quick and easy test that can be used with many samples. Drip loss measurements are slower than expressible moisture or water uptake ability measurements because they must include time for significant losses to occur. 

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. 

Measurement of expressible moisture and water uptake ability both require <1 hr. Drip... 

Western blot, see Immunoblot Wet grinding, starch isolation, 674-676 Wheat and wheat starch enzymatic quantification, 682 isolation, 676 moisture content, 22 Whole-grain wheat, enzymatic quantification, 682 Wijs reagent, 467-468, 475 Wine, see also Grapes WUA. see Water uptake ability... 

During water immersion, 1 kg of mixed spruce and aspen wood chips at an average 50% water content would pick up an additional 0.51 kg of water and reach a terminal moisture level of about 67%. Water uptake is quick even after immersion for 3 h moisture levels exceed 63%. This is similar to the findings of Brebner (4) and Wasp et al. (6), who reported saturated wood values of 65%. We conducted two experiments with straw and found that moisture level rose from 14% as received to >80% after exposure of 3 h. This is similar to the findings of Jenkins et al. (9) for rice straw from California. 

In order to minimize water related damage, the primary purpose of protective agents is the reduction of the spontaneous uptake of moisture. With respect to the WTA recommendations for hydrophobations [2] a compound is considered to be effective if residual water uptakes < 30 % (relative to the untreated material) are obtained. As illustrated in Fig. 3 this criterion cannot be realized for all the combinations mentioned emphasizing that the application of a universal protective agent is not feasible. 

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