Sensory properties of water

The sensory properties of waters involve those which affect the human senses, particularly taste, odour, appearance and touch. Among these temperature, taste, odour, colour and turbidity, are important characteristics. 

The terms solubility and insolubility are only relative from the viewpoint of water treatment. It is indicated in Section 3.2.8 that the sensory properties of waters are influenced by relatively low concentrations. From the biological viewpoint also very low concentrations can be of great importance. 

The content of iron in surface and normal groundwaters is not significant from the viewpoint of hygiene. However, it influences the sensory properties of water. Taste is affected at concentrations from about 0.1-1.5 mg 1 . At concentrations higher than 0.5 mg 1 separation of the hydrated oxide... 

Manganese has no adverse effects on health when present in the concentrations occurring in natural waters. However, it markedly influences the sensory properties of water, more so than iron does. The taste of water can be adversely influenced at concentrations greater than 0.1 mg 1 . As distinct from iron, materials in contact with water change its colour at low concentrations. This also concerns the possibility of a more intense growth... 

Chlorides are relatively stable, both chemically and biochemically. They do not change in natural waters. During infiltration they are only slightly adsorbed on different soil minerals. They have no adverse effects from the viewpoint of hygiene, however, they affect the taste of water. But the threshold concentration of taste also depends on the relative amounts of some cations. A concentration of 150 mg 1 does not influence the sensory properties of water. The maximum concentration of chlorides in drinking waters recommended by the World Health Organization is 250 mg 1 . ... 

Hydrogen sulphide seriously affects the sensory properties of water. The threshold odour concentration depends on pH because this odour is caused by non-dissociated HjS. Drinking water should have concentrations not greater than 0.01 mg 1 HjS. Hydrogen sulphide is very poisonous for... 

Humic matters cause a deterioration of the sensory properties of water, giving rise to a yellow to brown colour of the water and an unpleasant odour. The intensity of colour increases with increasing pH. 

In summary, there have been several physical/mechanical means developed to improve the functionality, safety, and sensory properties of psyllium. These previous investigations have indicated the possibility to improve the physicochemical, sensory, biological properties of psyllium for its optimal applications in foods. However, none of them could sufficiently solve the strong gelling and extreme water-uptake problems of psyllium. 

Kwiatkowski, M. J., Skouroumounis, G. K., Lattey, K. A., and Waters, E. J. (2007). The impact of closures, including screw cap with three different headspace volumes, on the composition, colour and sensory properties of a Cabernet Sauvignon wine during two years storage. Aust. ]. Grape Wine Res. 13, 81-94. 

One of the approaches found most suitable to explain the sensorial properties of sweet, bitter, and sweet-bitter substances proves to be the physico-chemical approach especially as concerns hydration and surface properties (DeSimone and Fleck, 1980 Funasaki et al., 1996 Fimasaki et al., 1999 Mathlouthi and Hutteau, 1999). Thus, solution properties of sweet and bitter molecules were found informative on their type of hydration (hydrophobic or hydrophilic) and on the extent of the hydration layer (Fiutteau et al., 2003). Physico-chemical properties (intrinsic viscosity, apparent specific volume, and surface tension) and NMR relaxation rates of the aqueous solutions of sucrose, caffeine, and sucrose-caffeine mixtures were used in the interpretation of the taste modalities of these molecules and to explain the inhibition of caffeine bitterness by sucrose (Aroulmoji et al., 2001). Caffeine molecules were found to form an adsorption layer whereas sucrose induces a desorption layer at the air/water interface. The adsorption of caffeine gradually increases with concentration and is delayed when sucrose is added in the caffeine solution (Aroulmoji et al., 2004). 

In a review, Dufosse et al. (1994) mentioned the flavor thresholds of some lactones, particularly the olfactory perception after dispersion in water and the perception in mouth after dispersion in aqueous or deodorized oily solution. They also insist on the different sensory properties of y-lactone enantiomers isolated by Mosandl and Gunther (1989). Guichard et al. (1990) studied the lactones in apricot cultivars and found that the (7 )-enantiomer is always predominant for the y-Q, to y-C)2 lactones (Q, C9 and Go lactones have been identified in green coffee). Certainly because of the small amount present, no study has been conducted in coffee, to our knowledge, on the enantiomeric distribution of the lactones. 

Both the total amount of each component and the microstructure i.e. the sizes, shapes and connectivity of the particles) are important. Together they determine the properties of the composite, i.e. the physical and sensory properties of ice cream. The amounts of the structural components are different for different types of ice cream. Table 7.1 shows typical volume fractions of each component at — 18 °C in standard, premium, low fat and soft scoop ice cream, and water ice. Premium ice cream contains more fat than a standard ice cream, whereas a low fat ice cream (obviously) contains less. Soft scoop ice cream contains less ice than the standard. Water ice is a composite of two materials, ice crystals and matrix, and contains no air or fat. 

The accumulation of thiazoles during the heating of a cysteine Dimethylhydroxy-furanone (DMHF) model system decreased with increasing water content while the accumulation of thiophenones and 3,5-dimethyl-l,2,4-trithiolane had an optimum moisture content (ca. 80%) and 2,4-hexanedione and 3-hydroxy-2-pentanone increased with moisture content [23.24], There is little question that the Aw (or moisture content) influences both the rate of the Maillard reaction and influences the sensory properties of a system on heating. 

More than 100 different pyrazines have been identified in various food products. The sensory properties of the pyrazines are quite diverse. The alkyl pyrazines (Figure 5.5a) generally possess roasted, nut-like notes while methoxypyrazines (Figure 5.5b) often possess earthy, vegetable notes [47]. The 2-isobutyl-3-methoxy pyrazine has a freshly cut green pepper flavor with a sensory threshold of 0.002 ppb in water. The acetyl pyrazines typically have a popcorn character, and 2-acetonyl pyrazine has a... 

In many cases, HSI may replace NIR spectrometers to compute concentrations of various compounds or to estimate quality parameters of agricultural and food products. HSI can be used to assess properties as diverse as oil content, moisture, flour yield, softness, sucrose solvent retention capacity, and alpha-amylase activity in grains [26-28] sugar content and maturity of fruits like apple or banana [29-31] drip loss, water-holding capacity, color, pH, and sensory properties of meat [32-39] analysis of mixtures to detect the presence of substances such as, in forages [40], or the concentration of n-3 polyunsaturated fatty acids in designer eggs [41]. 

Field Pea Flour in Other Baked Products. When McWatters (44) substituted 8% field pea flour and 4.6% field pea concentrate for milk protein (6%) in baking powder biscuits, sensory attributes, crumb color, and density of the resulting biscuits were adversely affected. No modifications were made in recipe formulation when pea products were incorporated. The doughs were slightly less sticky than control biscuits that contained whole milk. This might be due to lack of lactose or to the different water absorption properties of pea protein or starch. Panelists described the aroma and flavor of these biscuits as harsh, beany and strong. Steam heating the field pea flour improved the sensory evaluation scores, but they were never equivalent to those for the controls. 

Raidl and Klein (43) substituted 5, 10, and 15% field pea flour in chemically leavened quick bread. The viscosity of the pea flour batters was significantly lower than either the wheat control or soy containing batters. The starch composition of the pea flour and lower water absorption properties of the protein could have affected the viscosity. Volumes of pea flour loaves were lower than the control and soy loaves. Most of the sensory characteristics of the field pea loaves were similar to those of the control quick breads. However, all flavor scores were significantly lower for pea flour products, since they had a recognizably beany or off-flavor. 

It has been a continuous effort to improve the physicochemical, fimc-tional, sensory, and biological properties of psyllium for promoting its food utilization and enhancing its safety. It is a great challenge to disperse psyllium in water or aqueous solutions even with vigorous agitation... 

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