Phenolic compound taste

At present, chlorine dioxide is primarily used as a bleaching chemical in the pulp and paper industry. It is also used in large amounts by the textile industry, as well as for the aching of flour, fats, oils, and waxes. In treating drinking water, chlorine dioxide is used in this country for taste and odor control, decolorization, disinfection, provision of residual disinfectant in water distribution systems, and oxidation of iron, manganese, and organics. The principal use of chlorine dioxide in the United States is for the removal of taste and odor caused by phenolic compounds in raw water supplies. 

Various extraction methods for phenolic compounds in plant material have been published (Ayres and Loike, 1990 Arts and Hollman, 1998 Andreasen et ah, 2000 Fernandez et al., 2000). In this case phenolic compounds were an important part of the plant material and all the published methods were optimised to remove those analytes from the matrix. Our interest was to find the solvents to modily the taste, but not to extract the phenolic compounds of interest. In each test the technical treatment of the sample was similar. Extraction was carried out at room temperature (approximately 23 °C) for 30 minutes in a horizontal shaker with 200 rpm. Samples were weighed into extraction vials and solvent was added. The vials were closed with caps to minimise the evaporation of the extraction solvent. After 30 minutes the samples were filtered to separate the solvent from the solid. Filter papers were placed on aluminium foil and, after the solvent evaporahon, were removed. Extracted samples were dried at 100°C for 30 minutes to evaporate all the solvent traces. The solvents tested were chloroform, ethanol, diethylether, butanol, ethylacetate, heptane, n-hexane and cyclohexane and they were tested with different solvent/solid ratios. Methanol (MeOH) and acetonitrile (ACN) were not considered because of the high solubility of catechins and lignans to MeOH and ACN. The extracted phloem samples were tasted in the same way as the heated ones. Detailed results from each extraction experiment are presented in Table 14.2. 

Chlorofonn is too non-polar to dissolve the phenolic compounds under study, but it dissolves many of the monoterpenes, at least to some extent. Because the solubility of some monoterpenes into chloroform was low, different solvent/ solid ratios were tested. These were 50,20,10 and 5 1/kg of dry phloem. The extracts were bright yellow and the strongest colour was with the smallest solvent/solid ratio (51/kg). The colour of the solvent indicated that the solubility of the extractable compounds was not restricting the reaction even with the smallest solvent volume. The taste of the dry samples was evaluated by comparing them to the original phloem sample. The results showed that the mildest taste was in the phloem extracted with a solvent/solid ratio of 50 1/kg and 20 1/kg also had some effect on the taste. The taste of the chloroform-extracted phloem was stabile and it was the same after a week. 

EtOH extraction was the most efficient way to improve the flavour of the phloem. A solvent/solid ratio of at least 10 1/kg was needed to achieve a significant change in the taste. The loss of catechins was approximately 27% and that of lignans was 35%. All the catechins and lignans were found from the EtOH extract. Losses of lignans and catechins were smaller with other sovents, but either the taste was not modified or the cost of solvent treatment would be too high. Phenolic compounds like lignans and catechins also have a bitter taste and some improvement in flavour may have occurred because of the lower concentration of these. The disappearance of the characteristic... 

Phenolic compounds are of interest due to their potential contribution to the taste (astrin-gency, bitterness, and sourness) and formation of off-flavor in foods, including tea, coffee, and various fruit juices, during storage. Their influence on the appearance of food products, such as haze formation and discoloration associated with browning in apple and grape products, is also significant. Furthermore, analysis of these phenolic compounds can permit taxonomic classification of the source of foods. The importance of each phenolic compound and its association with the quality of various foods is described further in Sec. IV, on food applications. 

Since phenolic compounds occur in many fruits and most of them contribute to color and taste, phenolic analysis of fruits has been an active research area, especially in apple, grape, and citrus fruits and their products, such as juice, cider, and wine. 

Phenolic compounds also contribute directly to the flavor due to their astrin-gency and bitter taste characteristics [11]. In fact, astringency is believed to be due to the interaction between tannins and salivary proteins, resulting in the formation of protein-tannin aggregates in the mouth, as discussed in more detail below [12-15],... 

Much further work remains to be done to determine the reaction mechanisms involving phenolic compounds, their importance relative to each other in wine, and the nature and properties of the resulting products. Likewise, studies are needed to predict the actual taste of the various proanthoanthocyanins and of their numerous derivatives but also eventual synergistic or antagonist effects. In particular, the role of anthocyanins has to be investigated. 

PROP status. Individuals classified as tasters of the bitter compound propylthiouracil (PROP) (not found in wine) have been reported to perceive bitterness more intensely and have a higher number of taste pores per taste bud and higher density of fungiform taste papillae on the tongue than non-tasters of PROP (32- 36). Despite this, PROP status has not been demonstrated to affect perception of bitterness or astringency of phenolic compounds in wine (73, 29) or water (75, 77, 79, 30). 

Organic materials are generally removed by addition of powdered activated carbon. The carbon may be added at any point in the plant, although it is advantageous to have as much contact as possible. The adsorption reaction is slow at room temperature, since it is diffusion-controlled. Oxidation with chlorine, potassium permanganate, or ozone may destroy tastes and odors or it may intensify them, depending upon the particular compounds involved. For example, chlorination of phenolic compounds leads to gready increased tastes and odors. For this reason, the system must be studied in the laboratory prior to water treatment. 

Chlorinated phenolic compounds are examples of aromatics which may cause taste and odor problems in finished drinking-water [11 ]. These compounds may result from natural and domestic sources [12 ], from wood preservatives [13 ], or as by-products of chlorination in the treatment process [11 ]. A common treatment process for the occurrence of chlorinated taste and odor problems is super chlorination, which converts the odor causing mono- and di-chlorophenols to trichlorophenols [ 11 ] which do not cause odor, but are suspected carcinogens [ 5 ]. 

The Baxter Water Treatment Plant, Philadelphia, Pennsylvania, is a 12.35-m /s (282-MGD) conventional water treatment plant built in 1960. The plant supphes drinking water from the Delaware River to a population of over 800,000. Chemicals used in treatment include chlorine, ferric chloride or ferrous sulfate, hme, fluoride, and ammonia. Powdered activated carbon is used on demand for control of taste and odor, and chloride dioxide is used for control of THMs, tastes, and odors. The chlorine dioxide system was left over from the previous water treatment plant on that site. In the 1950s, it was used to oxidize phenolic compounds found in the watershed, which have since been eliminated. 

The tea bush and in particular its young leaves contain a high concentration of polyphenols and oxidative enzymes, thus the young leaves are better for tea manufacture. Tea polyphenols, previously called tea tannins, are also known as tea flavonoids. Among the polyphenols in fresh tea leaves, catechins are the predominant form of polyphenols, which account for 12-24% of the dry weight. Besides catechins, flavonol, and their glycosides, anthocyanidin and leucoanthocyanidin, phenolic acids and depsides are also present. Their typical concentrations are shown in table 8.1. These phenolic compounds are directly or indirectly associated with the characteristics of tea, including its color, taste, and aroma. 

Phenolic compounds play a vital role in the flavor of red wines. They are responsible for some positive tasting characteristics, but also for some rather unpleasant, negative aspects. Body, backbone, structure, fullness and roundness are all organoleptic qualities characteristic of great red wines. On the other hand, bitterness, roughness, harshness, astringency and thinness are faults that must be avoided as they are incompatible with quality. 

Table 6.9. Influence of the structure of different groups of phenolic compounds on the reactivity of the molecules (gelatin index) and the tasting qualities, in wines of different ages (Glories, 1992, unpublished)...

Voltammetric sensors based on chemically modified electrodes (conducting polymers, phthalocyanine complexes) with improved cross-selectivity were developed for the discrimination of bitter solutions [50], The performance and capability were tested by using model solutions of bitterness such as magnesium chloride, quinine, and four phenolic compounds responsible for bitterness in olive oils. The sensors gave electrochemical responses when exposed to the solutions. A multichannel taste sensor was constructed using the sensors with the best stabilities and cross-selectivities and PCA of the signals allowed distinct discrimination of the solutions. 

The family of hazardous pollutants also includes phenol and its nitro and chloro derivatives. They enter the aquatic environment through waste-waters from many industries, such as petroleum processing and production of plastics, dyes, cellulose, pharmaceuticals, etc., or as the products of pesticides decomposition. Phenols may also arise in drinking water from the reaction of natural humic and fulvic acids with chlorinating disinfectants. Even at non-toxic levels, they deteriorate the taste and odor of drinking water. To address the steady increase in water contamination with phenolic compounds and pesticides, the US Environmental Protection Agency (EPA) has included 26 phenoHc compounds and 32 pesticides and their metaboHtes in the list of priority contaminants. In accordance with regulatory requirements, the allowed tolerance hmit of these pollutants must not exceed O.lpg/L for individual species and 0.5 Xg/L... 

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