Expressible moisture

Data expressing moisture content in terms of elapsed time should be obtained and the results plotted as shown in Fig. 12-42. For purposes of analysis, the moisture-time curve must be differentiated... 

Jaurequi, C.A., Regenstein, J.M., and Baker, R.C. 1981. A simple centrifugal method for measuring expressible moisture A water-binding property of muscle foods. J. Food Sci. 46 1271 -1273. 

Expressible moisture Ability of a protein to retain water upon application of an external force, e.g., centrifugation or pressure, under specified conditions Expressible moisture content (%) = (wt. water released/inilial sample wl.) x 100 Advantages Tests are simple to perform. Disadvantages Sample structure may be destroyed or deformed by the applied force leading to results that do not correlate with a real food system. Kocher and Foegeding (1993) Jaurequi et al. (1981) Lee and Patel (1984)... 

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.

Drip losses, cooking/processing loss, and thaw loss are related to, but different from, expressible moisture. In these measurements, the moisture loss that is measured is the amount lost without the application of any force. Thus, the liquid that is expelled can be collected by carefully pouring off the excess liquid. Placing the food sample in a funnel and collecting the drip in a graduated cylinder is often the easiest way to practically accomplish this task. 

Expressible moisture measures the water expressed from a material under a force. Its measurement requires centrifugation of samples on filter paper to remove the released moisture. The filter paper needs to be weighed before and after centrifugation. Weight loss of the sample can also be measured by weighing before and after centrifugation. 

Determine the total moisture content of the initial sample (unit au) in order to calculate the moisture retained, which is the total initial moisture minus the expressible moisture. 

Expressible moisture. Water that can be squeezed out of a material by application of an external force. 

Expressible moisture (EM) measures the water that can be squeezed out of a material, generally under a force. Traditionally, the Carver press was used with meats (Forbes et al., 1974 Lee and Patel, 1984). A piece of meat was placed between large pieces of filter paper. The press squeezed out the moisture, and the investigator measured the diameter of the wet circle on the filter paper. One of the problems with the Carver press method is ensuring the use of consistent pressure each time. Also, one can only measure a single sample at a time. Because of the arbitrariness of the conditions, the exact relationship to a real sample is not known. The actual amount of moisture loss is also not determined. 

As an alternative, centrifugation can be used. The major issue in this approach is how to collect the expressed moisture. One way, as presented in this unit, is to collect the moisture on filter paper and measure either the weight gain of the filter paper or the weight loss of the sample. The material can be put into a few pieces of filter paper and centrifuged. As a practical matter, the author has found that a piece of nylon mesh placed between the meat sample and the filter paper make it easier to remove the meat sample after centrifugation... 

Another way to measure the expressible moisture in a centrifuge is to use some type of filter system so that the free solution is collected below the sample. This involves specialized equipment in each centrifuge tube that subsequently needs to be cleaned. 

In some cases, it is desirable to study the influence of various additives on the expressible moisture. To standardize this testing, solutions of test compounds were added to the food sample at an arbitrary 10% by weight and samples were mixed well but gently. The controls included both untreated samples and samples treated with 10% water. All solutions were added at 10% by weight. It is necessary to be... 

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... 

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... 

EI/MS electron impact/mass spectrometry ELSD evaporative light-scattering detector EM expressible moisture EPA (U.S.) Environmental Protection... 

Paredi, M.E., De Vido de Mattio, N.A., and Crupkin, M. 1996. Biochemical properties of actomyosin and expressible moisture of frozen stored striated adductor muscles of Aulacomya ater ater (Molina) Effects of polyphosphates. Journal of Agricultural and Food Chemistry 44 3108-3122. 

As a wet solid is usually swollen compared with its condition when free of moisture and its volume changes during the drying process, it is not convenient to express moisture content in terms of volume. The moisture content of a solid is usually expressed as the moisture content by weight of bone-dry material in the solid, X. Sometimes a wet basis moisture content W, which is the moisture-solid ratio based on the total mass of wet material, is used. The two moisture contents are related by the expression... 

A proprietary type of hard Surfacing material A cake which can be squeezed to express moisture... 

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