Of catechins

FIa.VOnoIOxida.tlon, The fermentation process is initiated by the oxidation of catechins (1) to reactive catechin quinones (13), a process catalyzed by the enzyme polyphenol oxidase (PPO) (56). Whereas the gaHocatechins, epigaHocatechin, and epigaHocatechin gaHate, are preferred, polyphenol oxidase can use any catechin (Table 2) as a substrate. This reaction is energy-dependent and is the basis of the series of reactions between flavanoids that form the complex polyphenoHc constituents found in black and oolong teas. 

Tea flavonoids, or tea extracts, have been linked to benefits in reducing the risk of certain cancers and cardiovascular diseases in experimental animals. However, epidemiological studies have produced inconsistent evidence in the relationship between tea drinking and cancer (Blot et a/., 1997 Goldbohm etal, 1996 Hertog eta/., 1997 Yang eta/., 1996). Therefore, further research is needed before definitive conclusions on the impact of tea consumption upon the cancer risk in humans can be reached. The metabolites of catechins and flavonols after consumption of tea infusions have scarcely been investigated, and thus more research is needed as to the role of those compounds in the reported health benefits of tea consumption. 

BRONNER w E and BEECHER G R (1998) Method for determining the content of catechins in tea infusions by high-performance liquid chromatography , J Chromatogr A, 805, 137-42. 

DALLUGE J J, NELSON B c, THOMAS J B, WELCH M J and SANDER L c (1997) Capillary liquid chromatography/electrospray mass spectrometry for the separation and detection of catechins in green tea and human plasma , Rapid Commun Mass Spectrom, 11, 1753-6. 

TSUCHIYA H, SATO M, KATO H, OKUBO T, JUNEJA L R and KIM M (1997) Simultaneous determination of catechins in human saliva by high-performance liquid chromatography , /CAwwatogr B, 703, 253-8. 

WANG H and HELLiWELL K (2000) Epimerisation of catechins in green tea infusions . Food Chem, 70, 337 4. 

WANG H, HELLiwELL K and YOU X (2000a) Isocratic elution system for the determination of catechins, caffeine and gallic acid in green tea using HPLC ,Pood Chem, 68 (1), 115-21. 

WORTH c c, wiESSLER M and SCHMITZ o J (2000) Analysis of catechins and caffeine in tea extracts by micellar electrokinetic chromatography . Electrophoresis, 21 (17), 3634-... 

TSUCHIYA H (2001) Stereospecificity in membrane effects of catechins. Chem Biol Interact. 134 41-54. 

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. 

The amount of catechins (i.e. (+)-catechin, (—)-epicatechin, (-)-epigallocatechin) is marked with number 1 in the original phloem sample. 

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... 

Despite the fact that phloem is rich in catechins the amount of these ingested daily in our phloem study was rather small when compared to previously conducted studies. In similar studies the amount of catechins ingested in the form of tea or red wine per day has varied from 81 mg to as high as 2490 mg (de Rijke et al., 1996 Carbormeau et al., 1997 Nigdikar et al., 1998 Princen et al., 1998). It would be interesting to test in the future whether increasing the ingested amount of phloem would further reduce the inhibition of lipid peroxidation. 

ARTS I c w, HOLLMAN p c H (1998) Optimization of a quantitative method for the determination of catechins in fruits and legumes, Journal of Agricultural and Food Chemistry, 46, 5156-62. 

FERNANDEZ P L, MARTIN M J, GONZALEZ A G, PABLOS F (2000) HPLC determination of catechins and caffeine in tea. Differentiation of green, black and instant teas, Analyst, 125,421-5. 

NICOLI M c, CALLIGARIS s and MANZOCCO L (2000) Effect of enzymatic and chemical oxidation on the antioxidant capacity of catechin model systems and apple derivatives , JAgric Food Chem, 48 (10) 4576-80. 

PEDRIELLI p, HOLKERi L M and SKIBSTED L H (2001b) Antioxidant activity of (+)-catechin. Rate constant for hydrogen atom transfer to peroxyl radicals, Eur Food Res Technol, 213, 405-8. 

Tabak, C. et al.. Chronic obstructive pulmonary disease and intake of catechins, flavonols, and flavones the MORGEN Study, Am. J. Respir. Crit. Care Med., 164, 61, 2001. 

The effects of catechin, epicatechin, procyanidin B2, caffeic acid, / -coumaric acid, myricetrin, and quercetrin on the color intensity and stability of malvidin 3-glucoside at a molar ratio of 1 1 under conditions similar to red wine were evaluated. " Flavan 3-ols appeared to have the lowest protective effects and flavonols the highest strong color changes were visually perceptible. " In the complexation of malvin chloride and natural polyphenols, flavonol glycosides by far exerted the best protector effect. ... 

Xanthine oxidase (XO) is not only an important biological source of ROS but also the enzyme responsible for the formation of uric acid associated with gout leading to painful inflammation in the joints. The XO inhibition effect by the enzymatically synthesized poly(catechin) increased as an increasing concentration of catechin units, while the monomeric catechin showed almost negligible inhibition effect in the same concentration range. ° This markedly amplified XO inhibition activity of poly(catechin) was considered to be due to effective multivalent interaction between XO and the condensed catechin units in the poly (catechin). 

Mutans streptococci are the major pathogenic organisms of dental caries in humans. The pathogenicity is closely related to production of extracellular, water-insoluble glucans from sucrose by glucosyltransferase and acid release from various fermentable sugars. Poly(catechin) obtained by HRP catalyst in a phosphate buffer (pH 6) markedly inhibited glucosyltransferase from Streptococcus sorbrinus 6715, whereas the inhibitory effect of catechin for this enzyme was very low. 

The conjugation of catechin on poly(allylamine) using ML as catalyst was examined under air. During the conjugation, the reaction mixture turned brown and a new peak at 430 nm was observed in the UV-vis spectrum. At pH 7, the reaction rate was the highest. The conjugation hardly occurred in the absence of laccase, indicating that the reaction proceeded via enzyme catalysis. 

Polyhedral oligomeric silsesquioxane (POSS) has been extensively studied as starting substrate to construct nanocomposites with precise control of nanoarchitecture and properties. Octahedral derivatives are the most representative ones of this family. It was reported that the HRP-catalyzed conjugation of catechin on amine-substituted octahedral silsesquioxane amplified the beneficial physiological property of flavonoids. The POSS-catechin conjugate exhibited great... 

Catechin-immobilizing polymer particles were prepared by laccase-catalyzed oxidation of catechin in the presence of amine-containing porous polymer particles. The resulting particles showed good scavenging activity toward stable free l,l-diphenyl-2-picryl-hydrazyl radical and 2,2 -azinobis(3-ethylbenzothiazoline-6-sulfonate) radical cation. These particles may be applied for packed column systems to remove radical species such as reactive oxygen closely related to various diseases. 

---