Water in foods

with a density of 1000 kg nr3, is denser than the oil components of foods oils and fats typically have densities in the range 850-950 kg nr3. Glycerols and sugar solutions are denser than water. 

Unlike the solid phase of most other liquids, ice is less dense than liquid water ice has lower thermal conductivity than water. These properties have an effect on the freezing of foods that are predominantly water based the formation of an ice layer on the surface of liquids and the outside of solids has the effect of slowing down the freezing rate. 

Because a molecule of water vapor is lighter (molecular weight =18) than that of dry air (molecular weight = about 29), moist air is lighter than dry air at the same temperature. This is somewhat unexpected, because the popular conception is that humid air (which contains more water) is heavier than dry air. 

If the sponge is left to dry in the sun, this adsorbed water will evaporate, leaving only a small proportion of water bound chemically to the salts and to the cellulose of the sponge fibers. Like water in sponge, water is held in food by various physical and chemical mechanisms (Table 3.1). It is a convenient oversimplification to distinguish between free and bound water. The definition of bound water in such a classification poses problems. Fennema (1985) reports seven different definitions of bound water. Some of these definitions are based on the freezability of the bound component, and others rely on its availability as a solvent. He prefers a definition in which bound water is that which exists in the vicinity of solutes and other non-aqueous constituents, exhibits reduced molecular activity and other significantly altered properties as compared with bulk water in the same system, and does not freeze at -40 C.  

Porportion of Typical 90% (Wet Basis) Moisture Content Food 

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E.B. Tribaldo, Residue analysis of carbamate pesticides in water, in Food Science Technology, Marcel Dekker, New York, pp. 537-570 (2000). 

R. R. Ruan, P. L. Chen 1998, Water in Foods and Biological Materials A Nuclear Magnetic Resonance Approach, Techno-mic, Lancaster, PA, USA. 

NMR. Proton NMR is obviously likely to give an enormous range of signals from a typical confectionery product. An NMR instrument to analyse water in foods has to be a low-resolution instrument, whether of the original continuous form or of the later pulsed type. The aim is to discriminate between the protons in water and those in other molecules. Fortunately, this is not too difficult. 

The importance of water in foods begins with the hydrological cycle and concludes with the consumption of safe, wholesome, and plentiful foods. In between, water is a vital component in the various stages of food production and preservation. Water in the final food product, whether fresh or processed, profoundly influences the chemistry, microbiological safety, nutritional value, texture, appearance, and taste of the food. Because of this intimate relationship between water and food quality and safety, a more complete understanding of water and its properties, behavior, and influence, alone and in foods, is of prime importance. 

NMR relaxation time measurements (7) and T2) can provide valuable information for investigating the molecular dynamics of water in food systems. However, a number of factors can seriously complicate the analysis... 

Labuza, T.P. et al. 2001. The Water in Foods Panel ISOPOW VIII September 16-21. Zichron Yaakov, Israel. What do we know and what do we agree on http //courses.che.umn.edu/ 02fscn4342-ls/Readings Folder/ISOPOW8 WaterInFood Panel.pdf January 12, 2004. 

Water in food products can be described as being free or bound. The definition of what consitiutes bound water is far from clear (see Fennema, 1985) but it can be considered as that part of the water in a food which does not freeze at — 40°C and exists in the vicinity of solutes and other non-aqueous constituents, has reduced molecular mobility and other significantly altered properties compared with the bulk water of the same system (Fennema, 1985). The actual amount of bound water varies in different products and the amount measured is often a function of the assay technique. Bound water is not permanently immobilized since interchange of bound water molecules occurs frequently. 

Karel, M., 1985. In Properties of Water in Foods. D. Simatos and J. Multon, eds, Nijhoff Publ. Dordrecht, Holland, p. 153. 

Humectants. In certain foods, it is necessary to control the amount of water that enters or exits the product. It is for this purpose that humectants are employed. Polyhydric alcohols (polyols), which include propylene glycol. CiHsO , glycerol, C,H 0,. sorbitol, CsHhOs. and mannilol C HuOb. contain numerous hyroxyl groups, Their stmemre makes them hydrophilic and enables them to bind water in Foods. See also Humecants and Moisture-Retaining Agents. 

Pulse NMR techniques, both low-field and high-field, were applied to study the properties of water in food systems. All three possible nuclei, H, 2H and 170, were probed, and various models for data interpretation were developed. An extensive review of the subject may be found in Schmidt and Lai 0. 

The explosive advancements in NMR technology in recent years have dramatically expanded the avenues and techniques available. NMR techniques for the study of food range from in-line/on-line oil and water analysis, to characterization and authentification of foods and beverages, water relations in foods and biological tissues, mobility of water in food and to probing microstructure of food. The applications of NMR techniques in food research were recently reviewed [2,3]. 

It is well known that N1R is an excellent tool for analyzing total amount of water in foods [5]. NIR also has the potential to determine the state of water in foods as well [6]. 

To get the water out of food without using heat, freeze-drying skips the liquid phase of water entirely. First, all the water in food is frozen solid in place. Then sublimation is used to convert the solid water into water vapor so it can be extracted without changing the shape or texture of the food. 

There is a much room for economy in the use of water in food production. For instance, to produce 10 g of protein in the form of beef requires five times as much water than for 10 g of rice, and for 500 Calories this difference is 20-fold. With a lavish meat diet, the average American requires 5.4L/day, whereas for a vegetarian this amount is halved. 

Maurice TJ, Slade L, Page C, Sirett R. In Simatos D, Multon JL, eds. Properties of Water in Foods. Dordrecht, The Netherlands Martinus Nijhoff 1985 211. 

T. P. Labuza and M. Saltmarch, The nonenzymatic browning reaction as affected by water in foods, in Water Activity Influences on Food Quality, L. B. Rockland and G. F. Stewart (eds), Academic Press, New York, 1981, 605-650. 

Epoxy is used as a lining for water reservoirs, water mains, and home plumbing systems (Heim and Dietrich, 2007a). These applications can impact sensory quality of tap water in food manufacturing, food service operations, and residential homes. This effect may be most noticeable in water but residual aroma and flavor compounds may cause a taint in foods prepared with these water sources. An odor assessment, using a water industry standard flavor profile analysis method, identified a strong relationship between water (simulated tap water, pH 7.7-7.9) stored in epoxy-lined copper pipes for 3-4 days and an odor described... 

In the area of water as a food component, the issue of the glass transition has received much attention. This demonstrates the important role of water in food properties. Lipids have received much attention lately mainly because of publicity related to nutritional problems. Sutructured... 

Hanafusa, N. In "Water in Foods" (Japanese Society of Scientific Fisheries, Ed.), Koseisha-Koseikaku K.K. Tokyo, 1973, 9. 

Q2 Water is produced as a result of metabolism, approximately 200 ml per day, water in food accounts for approximately 700 ml per day and the average daily intake of liquids is approximately 1.51. 

Tolstoguzov, V.B., Grinberg, V.Ya., and Gurov, A.N. (1985). Some physicalchemical approaches to the problem of protein texturization. J. Agric. Food Chem., 33, 151-159. Tombs, M.P. (1985). Phase separation in protein water systems and the formation of structure. In D. Simatos, and J.L. Multon (Eds.), Properties of Water in Foods, pp. 25-36. Martinus Nijhoff Publ., Dordrecht. 

Dumoulin, E., and Bimbenet, J.J. (1998). Spray drying and quality changes. In D.S. Reid (ed.). The Properties of Water in Food, Blackie Academic, London, pp. 210-232. 

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