Kinetics Of Epimerization And Degradation Of Green Tea Biology Essay
Around 2327 B.C. tea leaves use and ingestion may hold started for medicative intents. At the present clip, tea has become the most widely consumed drink in the universe after H2O. Tea attracts the society non merely from its gustatory sensation and olfactory property but they besides believe that devouring tea may lend to many positive wellness benefits such as bar of malignant neoplastic disease, handling cardiovascular disease, and dental wellness. A batch of surveies have besides found that tea catechins have good effects on overall good wellness such as anti-inflammatory, anti-diabetic, anti-bacterial, anti-hypertensive, anti-arteriosclerotic and anti-ageing functionality ( Wang et al. , 2008, Chen et al. , 2000 ) .
Besides, in these past decennaries a broad assortments of tea foliages are processed and utilized non merely functioning as a imbibing drink but besides in nutrient as a colourant and preservative, kitchen deodorizer and a batch of decorative merchandises. In add-on, a batch of assortments of bottled or transcribed tea drinks are now available in the market ( Hara, 2001 ) .Tea is made from the foliages of Camellia sinensis that grows of course in many tropical to temperate states around the universe.
Following harvest home, the foliages are processed to undergo agitation to some extents to bring forth different tea merchandises: black tea, green tea or oolong tea. In peculiar, green tea which accounts for 22 % of the universe ‘s tea ingestion ( Blumberg, 2002 ) , made by steaming or drying fresh tea leaves at elevated temperatures to forestall polyphenol oxidization. Green tea is besides believed to be the most good among any other teas merely because its production merely involves small processing and agitation and hence, green tea brews are richer in catechins ( Boon, 2008 ) . The sum of entire catechins in a cup of tea is extremely variable depending on the type of tea, the ratio of tea leaves/water, every bit good as the extract clip.
By and large, an mean helping of 250 milliliter of a cup of brewed green tea contains 620-880 milligram of water-extractable stuffs of which tierces are catechins and 3-6 % are caffeine ( Yang et al. , 2009 )All sorts of tea including green tea all contain polyphenols, flavandiols, flavonoids and phenolic acids. Green tea polyphenols or normally known as green tea catechins are found to be the most abundant components. Green tea catechins are present chiefly as catechin ( C ) , catechin gallate ( CG ) , gallocatechin ( GC ) , gallocatechin gallate ( GCG ) , epicatechin ( EC ) , epicatechin gallate ( ECG ) , epigallocatechin ( EGC ) , and epigallocatechin galate ( EGCG ) . In add-on, the most important catechin that presents in green tea is EGCG ( Hara, 2001, Yamamoto, 1997 )The many benefits of green tea catechins make them to be the most of import components in green tea. Although catechins entirely already do up 20 % of the dry weight of green tea, which are chiefly EGCG ( Hara, 2001 ) , they are really prone to epimerization and debasement reactions during production or storage of tea drinks. These reactions are unwanted in many nutrient merchandises, particularly in bottled or transcribed tea drinks where merely small sum of catechins was found ( David Labb & A ; eacute ; , 2008 ) .
As a consequence, several surveies have been done to look into the dynamicss of the stableness of tea catechins in aqueous solutions ( Wang and Helliwell, 2000, Wang et al. , 2008b, Wang et al. , 2006 ) . In order to better the quality of tea drinks in the nutrient industry, it is of import to to the full understand the belongingss of green tea catechins non merely at a higher temperature scope, where most thermic procedures occur, but besides at a lower temperature scope which is besides normally used in some nutrient procedures and storage. Some surveies on the dynamicss of the stableness of green tea catechins in green tea solutions have been done both at a higher temperature ( 100-165 & A ; deg ; C ) and a lower temperature scope ( 25-100 & A ; deg ; C ) . Both surveies have succeeded in developing a mathematical theoretical account sing the stableness of the catechins EGCG and GCG ( Wang et al.
, 2006, Wang et al. , 2008b ) . However, farther surveies still need to be done on the dynamicss of the stableness of tea catechins in a green tea extract, in peculiar to analyze the effects of different values of pH at lower temperature scope.Green Tea Polyphenols2.1 Chemistry of Green TeaThe largest constituents of green tea are saccharides and proteins but seemingly these constituents are about indissoluble in a green tea extract. Merely comparatively little molecular weight constituents can be soluble in hot H2O and they are chiefly polyphenols ( Yamamoto, 1997 ) . Apart from polyphenols, a few other minor constituents are besides present such as caffeine ( 0.15-0.
2 % ) , theophylline ( 0.02-0.04 % ) and other methylxanthines, lignin ( 6.5 % ) , organic acids ( 1.5 % ) , chlorophyll ( 0.5 % ) , free amino acids ( 1-5.5 % ) , and other minor spirit compounds ( Hamilton-Miller et al. , 2005 )The little styptic and acrimonious gustatory sensation of a green tea extract is attributed to the catechins ( Yamamoto, 1997 ) .
Almost all of the features of manufactured tea, including its gustatory sensation, coloring material, olfactory property are associated straight or indirectly with the alterations of catechins ( Wang et al. , 2000 ) . Catechins or polyphenols belong to the group known as flavonoids which have a C6-C3-C6 C construction with two aromatic rings. The four major types of catechins in green tea are EGCG, EGC, ECG and EC. These catechins are present non merely in tea foliages but besides in many parts of a works ( Hara, 2001 ) . In the instance of green tea polyphenols, it is a category of flavanols which are C15 compounds, and their derived functions are composed of two phenolic karyons ( A ring and B ring ) connected by three C units ( C-2, C-3, and C-4 ) ( Yamamoto, 1997 ) .
As can be seen from Figure 2.1, the construction of tea catechins is characterized by dihydroxyl or trihydroxyl permutations on the B ring and the m-5,7-dihydroxyl permutations on the A ring. Catechins and its derived functions besides have nucleophilic centres at C-6 and C-8 which are reactive with electrophilic specimens. They are chemically reactive and able to hold the belongingss of metal chelator, oxidative groups scavenger, nitrosation inhibitor and etc ( Susanne Valcic, 2000, Yang et al. , 2009, Yamamoto, 1997 )Figure 2.1 Structure of basic polyphenols, EGCG, Epicatechin, EGC and ECG.Adapted from ( Yang et al. , 2009 )Catechins synthesized inside the buds and tea foliages undergo malonic acid- and shikimic acid-metabolic tracts.
Gallic acid is derived from an intermediary merchandise produced in the shikimic acid-metabolic tracts ( Yamamoto, 1997 ) .2.2 Biological Activities of Green Tea Polyphenols2.
2.1 Antioxidative Activity of Tea PolyphenolsIt is believed that the presence of free groups in our organic structure can do oxidization reactions that may harm homo ‘s Deoxyribonucleic acid or cell membranes which will later ensue in many diseases such as malignant neoplastic disease, bosom disease, and autoimmune diseases ( Wang et al. , 2000 ) . Antioxidants are substances that significantly decrease the inauspicious effects of both reactive O and N species. A batch of research have been done and proved that the flavonoids compounds in tea are even more effectual as an antioxidant than Vitamin C and E ( Wang et al. , 2000, Hara, 2001 ) .
Furthermore, both in vitro and in vivo experiments have given positive consequences, broadening the possibilities for practical applications of green tea catechins as an antioxidant ( Hara, 2001, Yamamoto, 1997 ) .Furthermore, the antioxidative activities of green tea can besides be applied in nutrient industries, for illustration in forestalling oxidization of fats and oils and stain of ruddy nutrient. In an probe of antioxidative activity of tea infusions, green tea proved to be more effectual antioxidants to canola oil compared to butylated hydroxytolune ( BHT ) .
In add-on, in the instance of oolong tea ( semi fermented merchandise ) merely a moderate activity of antioxidant was found and in black tea ( to the full fermented merchandise ) really small antioxidative activity was found ( Yamamoto, 1997 ) . These consequences are sensible because that same sum of tea catechins have been destroyed during agitation of oolong and black tea or in other words, oxidization reactions already proceed before heat intervention and drying, whereas green tea is produced by heat-treatment after crop, hence oxidation reaction can be prevented ( Yamamoto, 1997, Boon, 2008 ) .In another survey where antioxidative activity of single catechins are examined, it was found that EGCG, which is the major constituent of tea polyphenols, is the strongest antioxidant ( Yamamoto, 1997 ) . The polyphenolic construction of EGCG allows electron delocalization and extinction of free groups ( Sang et al. , 2006 ) .
This is supported in another survey, which showed that catechins that have a galloyl mediety in the 3-position have the highest antioxidant activity and besides the most effectual inhibitors of lipid peroxidation ( Valcic et al. , 2000, Yang et al. , 2008 ) . As can be seen from Figure 2.
1, EGCG and ECG have this sort of construction.2.2.2 Antimicrobial Activity of Tea PolyphenolsA batch of surveies have shown that polyphenols in tea can kill a broad scope of infective bacteriums or at least cut down their concentration ; such bacteriums viz. are Clostridium perfringens, Staphylococcus aureus, Bacillus Cereus, Vibrio fluvialis and a few others ( Hara, 2001 ) . Harmonizing to Hara ( 2001 ) , green tea catechins EGC, EGCG, ECG inhibit the growing of methicilin-resistant Staphylococcus aureus in vitro by an equivalent of 1:10 dilution of tea foliages to H2O. This peculiar pathogenic bacteriums, being immune to the most common antibiotic used, is indispensable to be eliminated because it can do some serious jobs in infirmaries where the patients have a lower immune system ( Hara, 2001 ) .Another common illustration of the antimicrobic activity of tea polyphenols can be observed in the suppression of the growing of Streptococcus mutans and Streptococcus sobrinus that are the major causes of dentitions disintegrating ( Yamamoto, 1997, Wang et al.
, 2000 ) . It was proposed that the three major causes of dental carries are host ( tooth ) , bacteriums and substrate ( sucrose ) for the bacterial metamorphosis ( Yamamoto, 1997 ) .It was believed that under normal conditions tea would cut down acid on the tooth enamel where amylum is trapped in the dentition, and this is how it exerts its anti-carries consequence ( Wang et al. , 2000 ) .2.
2.3. Cancer Prevention of Tea PolyphenolsIt takes a long procedure for a malignant neoplastic disease cell to develop ( carcinogenesis ) , and it must goes through the phases of induction, publicity and patterned advance. The construct of malignant neoplastic disease bar is by utilizing a man-made or natural compound to decelerate, block, or reverses the development of malignant neoplastic disease cell. It has been widely accepted that tea polyphenols, in peculiar EGCG catechins, has a malignant neoplastic disease preventative consequence.
The grounds showed that the repressive effects of EGCG on carcinogensis is by the ordinance of cell signalling tracts. EGCG activates cell decease signals and bring on programmed cell death in the malignant neoplastic disease cells, ensuing the suppression of malignant neoplastic disease development ( Khan et al. , 2006 ) . Besides, there is a possibility that tea polyphenols will demobilize some viruses that cause malignant neoplastic disease ( Hara, 2001 ) .Numerous surveies have been done on the anticarcinogenic effects of tea polyphenols but the existent relationship between tea ingestion and happening of malignant neoplastic diseases is non conclusive because of the contradictory of the consequences of different surveies ( Yamamoto, 1997, Boon, 2008 ) . This could be because of the diverseness of malignant neoplastic disease in different site of variety meats ( Yamamoto, 1997 ) , the difference of quality and measure of tea ingestion, and lifestyle factors such as coffin nail smoke and intoxicant ingestion ( Yang et al.
, 2009 ) . Apart from that, the writers admited that green tea was the most possible natural malignant neoplastic disease chemo preventative agent with low toxicity ( Yamamoto, 1997, Wang et al. , 2000 ) .
2.2.4. Lipid Lowering Effectss of Tea PolyphenolsBunch of some diseases such as fleshiness, high blood pressure, hypercholesteremia, diabetes and normally taking to cardiovascular diseases, can be termed as metabolic syndrome. The major determiner for this metabolic syndrome is the accretion of fat or lipoid ( Alexander et al. , 2003, Isomaa et al. , 2001 ) . A lessening of organic structure weight, organic structure mass index, organic structure fat, waist perimeter, systolic blood force per unit area, low denseness lipoprotein cholesterin and hypodermic fat country, were found to be greater in a group of panel that consumed green tea infusions that were high in catechins compared to the control ( Nagao et al.
, 2007, Boon, 2008, Blumberg, 2002 ) . It is besides of import to observe that waist perimeter and systolic blood force per unit area are two of import indexs of metabolic syndrome ( Nagao et al. , 2007 ) . Therefore it is sensible to propose that the ingestion of green tea may forestall fleshiness and diminish the hazard of cardiovascular disease.A batch of in vitro surveies in animate beings every bit good as worlds found that green tea catechins, particularly EGCG, can suppress the addition of mass in adipose tissue and besides cut down saccharide and fat soaking up by suppression of assorted digestive enzymes ( Kao et al. , 2006, Moon et al.
, 2007, Juhel et al. , 2000 ) .2.3 Bioavailability and Metabolism of Tea PolyphenolsThe major wellness benefits of tea polyphenols have been studied in vitro extensively and some of them have been discussed in this study. However, it is indispensable to discourse about how effectual is the soaking up of the catechins, particularly EGCG, inside homo ‘s organic structure. A proper metabolic tract of green tea polyphenols in the human organic structure is still under probe ( Yamamoto, 1997 ) .
However, to give an thought, the metabolic tract of EGCG in rats is shown in Figure 2.2. Kohri et Al ( 2001 ) proposed that for tea catechins in rats after unwritten consumption, foremost it would come in the little bowel and a portion of them would undergo junction and be absorbed to the portal vena.
At this phase the EGCG in the liver undergo both junction and methylations, and a portion of them will be excreted into the gall and the remainder of them ( including integral EGCG ) will come in the blood circulation. After 2 hours, the sum of EGCG in the blood will make its upper limit. However, it has besides been reported that the bioavailability of EGCG in the blood circulation was really low, estimated to be 0.26 % ( Kohri et al.
, 2001 ) . The writer believed this was because a great proportion of EGCG that was absorbed undergone hepatic riddance reactions. On the other manus, the unabsorbed EGCG moves into the bowel and undergoes farther debasement by enteric bacteriums to EGC so to 5- ( 3′,5′-dihydroxyphenyl ) -?-valerolactone ( M-1 ) . Further, a big proportion of M-1 undergoes glucoronidation in the enteric mucous membrane and/or liver, to organize 5- ( 5′-hydroxyphenyl ) -?-valerolactone 3′-O-?-glucuronide ( M-2 ) , which enters the blood circulation, distributed to assorted tissues, and is eventually excreted in the piss.Figure 2.2. Possible metabolic path of EGCG orally administered to rats.
GA, Gallic acid ; M-1, 5- ( 3′,5′-dihydroxyphenyl ) -?-valerolactone ; M-2, 5- ( 5′-hydroxyphenyl ) -?-valerolactone 3′-O-?-glucuronide.Adapted from ( Kohri et al. , 2001 )Harmonizing to Lipinski ( 2001 ) , there are some compounds that will be ill absorbed after disposal, they are compounds that have ; five or more hydrogen bond givers ( OH and NH groups ) , ten or more hydrogen bond acceptors ( notably N and O ) , molecular weight greater than 500 g/mol. In respects to the old statement, tea catechins EGCG, which has a molecular weight of 458g/mol and have 8 hydroxyl groups ( Yang et al. , 2008 ) , will be ill absorbed.
However, other catechins that have a smaller molecular weight and fewer H bonds such as ( – ) epicatechin and ( + ) -catechin ( Yang et al. , 2008 ) , will be absorbed better than EGCG. This is proven in another probe by Wang et Al ( 1994 ) , where 200 milligram of catechins/kg organic structure weight of rats was orally administered, radiation consequences showed about 30-40 % of ( + ) -catechin was observed in the rat ‘s little bowel after one hr.
Therefore, it can be suggested that more research is need to be done to understand the soaking up of tea polyphenols particularly EGCG in vivo. Nevertheless, the molecular weight of green tea catechins are still lower than theaflavins, which is the polyphenols in black tea ( Yang et al. , 2009 ) , therefore it can be proposed that green tea catechins will hold greater bioavailability compared to black tea ‘s theaflavins.3. ToxicologyHeavy tea drinkers by and large consume more than 10 cups ( 150 milliliter ) a twenty-four hours, which is besides estimated to hold consumed about 1 g of tea catechins a twenty-four hours. As a consequence, the heavy tea drinkers have a decreased serum concentration of entire cholesterin, LDL cholesterin, triglycerides, and an increased proportion of HDL cholesterin as compared with the moderate tea drinkers group ( Hara, 2001 ) . Besides, there are harmful effects due to over ingestion harmonizing to Cabrera et Al ( 2006 ) . Notably there are three possible causes: tea ‘s caffeine content, presence of aluminum, and the effects of tea polyphenols on the Fe handiness.
Different types of tea have different composings, including its caffeine content. The order of caffeine content in different types of tea is black tea & A ; gt ; oolong tea & A ; gt ; green tea & A ; gt ; fresh tea foliage ( Lin et al. , 2003 ) . The caffeine content in green tea extract is about to be 5 % at the upper limit ( Yamamoto, 1997 ) .
There are harmful effects due to over ingestion of caffeine, such as jitteriness, difficult to kip, kiping upsets, purging, concern, epigastric hurting, and tachycardia ( Cabrera et al. , 2006 ) .It was found that some minerals particularly aluminium is present in black and green tea.
It will do jobs particularly for patients with nephritic failure because Al can be accumulated in the organic structure and do many diseases, for illustration neurodegenerative upsets or Alzheimer ‘s disease ( Costa et al. , 2002 ) . In add-on, it was suggested that Al dietetic consumption should be no more than 6mg/day ( MINOIA, 1990 ) . In many surveies, it was found that the concentrations of Al in green tea is lower than black tea, and the writers proposed that the difference of Al content in tea is due to different dirt conditions, reaping periods and influence of H2O quality ( Costa et al. , 2002 )Apparently some surveies have found that tea catechins may suppress the bioavailability of non-heme Fe by 79-94 % whenever consumed wholly ; nevertheless this depends on the Fe position and consumption of the person ( Tuntawiroon et al. , 1991 ) . It can be suggested to anaemia patients to avoid tea ingestion ( Costa et al. , 2002 ) .
It can be proposed that the chief causes of harmful effects are from the other constituents of tea apart from tea polyphenols, such as caffeine and aluminum. Furthermore, the content of those two compounds are lower in green tea than any other tea. Green tea catechins are besides a natural merchandise that is proven to hold no acute toxicity when consumed orally and even if a immense sum of catechins are consumed over a life-time will non harm human existences ( Hara, 2001 ) .4. Separation of Individual Green Tea Catechins from Green TeaFigure 4 presents a flow chart of readying of green tea catehins from green tea.
Hot H2O and organic dissolvers are normally used in the extraction method. However, it is suspected by Masuzawa ( 2007 ) that hot H2O may destruct some of the catechins every bit good as the overall green tea quality. Extraction at low temperatures is more desirable even though the efficiency of the extraction will besides be low.Green teaExtracted with hot H2O by spray dryingWater-soluble green tea pulverizationDissolved in hot H2OWashed with trichloromethaneAqueous bed Chloroform bedExtracted with ethyl ethanoateEthyl ethanoate bed Aqueous bedEvaporatedConcentrated solutionFreeze driedGreen tea catechinsFigure 4.1 The readying of green tea catechinsAdapted from ( Hara, 2001 )In a batch of surveies, reversed stage HPLC is often used for the analysis and quantification of tea catechins ( Wang et al. , 2008b, Wang et al. , 2006, Chen et al.
, 2000, Wang and Helliwell, 2000 ) . In the HPLC analysis, acidic nomadic stages such as methyl alcohol or acetonitrile qualifiers are normally used because catechins are more stable at lower pH ( Nanjo et al. , 1996, Lun Su et al. , 2003, Wang and Helliwell, 2000 ) .
Therefore, it can be suggested to command the pH to be acidic in order to acquire a stable reaction and accurate consequences. Besides, it was proved that the add-on of little measures of ascorbic acid in the nomadic stage could be bettering the extremum forms ( Donovan et al. , 1999 ) .Mentioning to Figure 4.2, it can be observed that a successful separation of green tea catechins was obtained by the HPLC processs.
Catechins criterions were besides used in the analysis, which enables standardization secret plans for the finding of catechin concentrations in tea extract. Besides, the consequence of galloyl group on keeping clip can be found harmonizing to Table 4.1. It was found that the ratio of keeping clip of ECG/EC is about equal to the EGCG/EGC for both criterions and tea infusions, proposing that the presence of gallate residue in catechin molecule might hold a consistent consequence on keeping clip ( He et al. , 2010 ) .Figure 4.2 HPLC chromatograms of criterions ( A ) and tea infusions ( B ) .
( nomadic stage: M1=aqueous solution of 0.2 % CH3CN, M2=CH3OH ; Column: Hypersil ODS C18, 150×4.0 millimeter, 5 millimeter ; Flow rate: 1.2mL=min ; Detector: UV-DAD, 280 nanometer ; Injection volume: 20 ?l ; Gradient: 0-12 min with 0-50 % M2, 13-20 min with 50-100 % M2 )Adapted from ( He et al. , 2010 ) .Table 4.1 Retention times ( min ) for Catechins and Caffeine ( n=3 )ComponentEGC ( C )EGCGECGCGElectrocardiogramCaffeineStandards9.
186 ( 0.38a )11.346 ( 0.19 )11.932 ( 0.19 )12.812 ( 0.66 )14.
032 ( 0.45 )10.679 ( 0.71 )Infusions9.
219 ( 1.41 )11.352 ( 1.27 )11.949 ( 1.53 )12.851 ( 0.
48 )14.109 ( 1.13 )10.
709 ( 1.10 )aRSD values ( % ) are given in paranthesesAdapted from ( He et al. , 2010 ) .Many HPLC sensing methods have been applied to sensing of different types of catechins, such as UV or photodiode array ( Wang et al. , 2008a, Wang et al. , 2006 ) fluorescence ( Ho et al. , 1995 ) , electrochemical ( Donovan et al.
, 1999 ) , chemiluminescence, and mass spectroscopy sensing ( Robb et al. , 2002 ) . Furthermore, HPLC separation with UV sensor is the most common method used for the analysis of polyphenols in fruits and drinks ( Donovan et al. , 1999 ) . UV-Vis optical density spectra ( 210-400 nanometer ) can be collected continuously for each chromatogram ( Bronner and Beecher, 1998 ) .
In many surveies, HPLC analysis with UV sensing method is equal for tea catechins quantification ( Wang et al. , 2008b, Wang et al. , 2006 ) . HPLC-UV sensing ensures a right designation of a individual catechin and is besides able to separate between the similarity of the UV spectra of the catechins ( Pelillo et al. , 2002 ) . However, it was besides proposed that UV sensing was non suited for the analysis of flavanols and their metabolites in complex samples such as human plasma due to its deficiency of selectivity, sensitiveness and qualitative information available ( Donovan et al.
, 1999 ) . Therefore, different sensings methods may be used depending on the suitableness and complexness of the sample.The content of catechins found in green tea may be varied between different species of green tea, clime, and cultural patterns ( Pelillo et al. , 2002 ) . More significantly, the content of green tea catechins besides varied in different tea extracts ( Wang et al. , 2000 ) . Based on Table 4.2 below, the content of catechins was found highest in the first extract and decreased well in the ulterior extracts.
The sum of EGCG was besides found to be the highest amongst the other catechins, this consequence is besides consistent with other probes ( Wang et al. , 2008a, Bronner and Beecher, 1998, Wang et al. , 2008b, He et al. , 2010 )Table 4.2 Comparison of catechins and flavonols in different tea infusionsa ( mg L-1 )Infusions1st2nd3rdEntire
( + ) -GC30.018.73.8052.
5( – ) -EGC22813137.2396.2( + ) -C10.45.
900.9017.2( – ) -EGCG3062232.
30531.3( – ) -EC52.828.16.
3087.2( – ) -GCG10.09.60Ndb19.
6( – ) -ECG76.852.00.50129.3( – ) -CG1.401.40Neodymium2.8
8Kaempferol9.006.503.5019.0a Harmonizing to the conventional brewing method, 1 g of gunpowder tea leaves was infused with 100 milliliters of boiling distilled H2O for 5 min, 70 milliliter liquid were filtered away and cooled to room temperature under running H2O ; a 2nd extract was added by adding a farther 70 milliliter boiling distilled H2O to the tea leaves for 5 min, filtrating off 70 milliliter which was cooled to room temperature under running H2O ; a 3rd extract was utilizing the same process. B Nd= non noticeableAdapted from ( Wang et al. , 2000 )Stability of Green Tea Polyphenols.5.
1 Epimerization and Degradation ReactionsIt has been reported the four major green tea catechins, viz. EC, ECG, EGC, and EGCG, are really unstable when they are exposed to high temperatures, alkalic solutions, O degrees, metal ions and concentrations of other ingredients in the extract ( Wang et al. , 2006, Sang et al. , 2005, Wang and Helliwell, 2000 ) . The four chief green tea catechins mentioned antecedently are cis compounds and besides be termed as epicatechins. In green tea extracts, the prevailing alteration appears from epicatechins that convert to their epimers that are non-epicatechins, i.
e. C, CG, GC and GCG severally ( Wang et al. , 2008b ) . This reversible transition of tea catechins to their corresponding isomers is called epimerization and is pictured on Figure 5.1 ( Wang and Helliwell, 2000 ) .Figure 5.1 Epimerization between EGCG and GCG ; k1: reate invariable of the epimerizationfrom EGCG to GCG ; K2s: rate invariable of the epimerization from GCG to EGCGAdapted from ( Wang et al.
, 2008a ) .Green tea catechins are besides prone to debasement and decomposition which lead to oxidization, dimerization and polymerisation ( Lun Su et al. , 2003, Wang et al.
, 2008b ) . It was speculated by Chen et Al. ( 2000 ) that the low concentrations of catechins found in many bottled or transcribed tea drinks was due to thermic debasement of catechins during the production, storage and conveyance of tea drinks and drinks. In add-on, debasement and epimerization of catechins can happen at the same time in a tea extract both in higher ( 100-165 & A ; deg ; C ) or lower temperature scope ( 25-100 & A ; deg ; C ) ( Wang et al.
, 2008b, Lun Su et al. , 2003 ) . The transition of green tea epicatechins to their corresponding epimers would besides cut down the concentration of green tea catechins ( Xu et al.
, 2003 ) .Therefore, it is of import to see both reactions in analyzing the kinetic stableness of green tea catechins.In comparing the stableness of epimer braces in the solution, it was found that ECG-CG are more stable than EGCG-GCG in thermic processing since the value of A in EGCG-GCG was greater than the other brace. This statement is supported based on the fact that EGCG-GCG holding three hydroxyl group ( OH ) at 3 ‘ , 4 ‘ , and 5 ‘ in the B-ring are more vulnerable to devastations than the others with merely two next – Ohio groups at 3 ‘ and 4 ‘ such as ECG and CG ( Lun Su et al. , 2003 ) .
In add-on, the value of A remained unchanged in the same solution of a selected catechins brace in the temperature scope of 25-165 & A ; deg ; C ( Wang et al. , 2008b ) .5.2. Consequence of HeatingTea drinks must hold undergone heat intervention either during the procedure of fabrication, in canned or bottled tea drinks, or brewing tea foliages or bags before ingestion. Therefore it is indispensable to cognize the effects of heating on the catechins content of tea. Despite the fact that epimerization and debasement reactions are temperature dependant, green tea catechins in general are more stable than theaflavins ( Lun Su et al. , 2003 ) .
Harmonizing to Chen et Al ( 2000 ) , as the temperature increased the rate of epimerization besides increased. In an probe of the kinetic stableness of green tea in higher temperature ( 100-165 & A ; deg ; C ) , it was found that the lessening in concentrations of epi-structured catechins was counteracted by the exponential addition of nonepi-structured catechins. Furthermore, the rate of addition in nonepi-structured catechins and the rate of lessening of epicatechins besides gave a similar tendency ( Wang et al. , 2006 ) . This besides proves that catechins and their epimers have similar kinetic features.It is besides indispensable to analyze the stableness of catechins under a lower temperature scope where most tea foliages and drinks are stored and transported.
Epimerization and debasement of catechins besides occur in low temperature scope, but takes a long period of clip ( Chen et al. , 2000 ) . The epimerization of catechins at 25-100 & A ; deg ; C showed a lessening of epi-structured catechins and an addition of the nonepi-structured catechins to a maximal so decreased with an increasing clip ( Wang et al. , 2006 ) . Further, it was reported that there was a decrease in catechins concentrations when tea extracts were kept at 40 & A ; deg ; C for 6 months ( Wang and Helliwell, 2000 ) .5.3. Consequence of pHThe debasement of catechins is pH dependant.
Assorted surveies have shown that in an acidic environment ( pH ? 4 ) tea catechins are the most stable. As the pH increases the rate of debasement additions every bit good ( Lun Su et al. , 2003, Wang et al. , 2006, Chen et al. , 2000 ) . In a kinetic survey of green tea catechins done by Wang et Al. ( 2006 ) , it was found that as the rate invariable increased with an addition of pH, the frequence factor was postulated to increase but Ea remained the same.
It was found in another survey that pH 7 tea catechins were really unstable and would degrade about wholly in a few proceedingss ( Chen et al. , 2000 ) . At impersonal or alkalic pH tea catechins are more susceptible to debasement, they are able to organize their corresponding free groups easier due to their addition of proton donating possible ( Wang et al. , 2006 ) .A survey on the pH stableness of single catechin confirmed that among the four major green tea catechins, EGCG and EGC were most unstable.
EGC was about wholly degraded when incubated for 3 hours, while EGCG was wholly destroyed after 6 hours of incubation, both at pH 7.4 ( Lun Su et al. , 2003 ) . Similarly, another survey concluded that EGCG and EGC were highly unstable in alkalic solutions while EC and ECG were comparatively stable ( Zhu et al. , 1997 ) . Again, this besides confirmed that EGCG and EGC are more vulnerable to devastations ( Lun Su et al. , 2003 ) .The consequence of pH on the epimerization of EGCG at 120 & A ; deg ; C for 30 min was studied by Seto et Al ( 1997 ) which showed that at pH ? 5 transition of EGCG proceeded readily.
However, at pH 7 there was no important concentration of EGCG and its epimer detected. The writers postulated that this result was because the catechins might hold been degraded, polymerized or undergone oxidization reaction ( Komatsu et al. , 1992, Seto et al. , 1997 ) . It was besides found that at lower pH values, the epimerization reaction would diminish until no epimerization reaction of EGCG will be detected any longer at pH 2. Additionally, another survey suggested that the difference of pH was the chief factor for the difference of the rate of epimerisation ( Wang and Helliwell, 2000 ) .
To sum up, the lower the pH the greater the stableness of the green tea catechins.5.4. Consequence of Ascorbic Acid, Metal Ions, and Oxygen ConcentrationsHarmonizing to Chen et Al ( 1998 ) , the add-on of organic acids such as ascorbic acid, may increase the stableness of green tea catechins although non straight take downing the pH value of the solution. In their experiment, ascorbic acid merely dropped the pH value of the mixture from 7.
42 to 7.38 but drastically improved the stableness of the four major green tea catechins in the mixture, peculiarly EGC and EGCG. It is believed that ascorbic acerb reacts as a reducing agent that can protect the catechins by recycling their free extremist signifier.It is by and large agreed that ascorbic acid may better the stableness of catechins ( Chen et al.
, 1998, Chen et al. , 2000 ) but non needfully better the stableness at longer period of clip. Ascorbic acid may protect the solution of green tea catechins for the first month, but after that it may advance the debasement procedure because ascorbic acid is shown to hold both antioxidant and prooxidant features ( Chen et al. , 2000 ) .
In a survey where factors that influence the stableness of catechins were looked at, it was shown that the stableness of catechins was more affected by the consequence of metal ions in the H2O than the pH of the H2O itself. However, in the same ionic environment, the catechins were still more stable in the lower pH ( Wang and Helliwell, 2000 ) . Besides, the antioxidative activities of catechins were affected by the metal ions. Metallic ions such as Cu and Mns are able to trip O in H2O to organize composites that may catalyze the oxidization of catechins, whereas iron inhibited the oxidization reaction ( Kumamoto et al. , 2001 ) . Metallic ions are able to interrupt the stableness of tea catechins during reactions, therefore it can be suggested to replace normal H2O with deionized H2O for future experiments sing the stableness of catechins.Zimeri and Tong ( 1999 ) have found that the rate invariable of debasement dynamicss of EGCG increased log-linearly with regard to pH and besides dissolved oxygen concentration.
This is in understanding with another survey suggesting the cut down in concentration of dissolved O in the mixture may suppress the oxidization of green tea catechins ( Chen et al. , 2000 ) . This is sensible because, O is the most of import acceptor of negatron. Molecular O O2 has two odd negatrons busying separate outer orbitals and each of these outer orbitals can suit an extra negatron ( Zhao et al. , 1989 ) .
This transportation of negatrons species may advance other reactions including oxidization.6. Kinetic StudyIn many surveies, the debasement of tea catechins was found to follow first-order dynamicss ( Wang et al. , 2008b, Wang et al. , 2006, Komatsu et al. , 1992 ) , i.e. it was assumed that the concentrations decrease exponentially with clip.
Orwhere ten is the concentration of catechins at the clip T, is the initial concentration of the catechins, and is the rate invariable of the debasement or epimerisation of the catechins ( Wang et al. , 2006 ) .However, this debasement can be disturbed by other viing reactions, chiefly epimerization. This can be observed at 82 & A ; deg ; C where different manners of reaction dynamicss can be observed ( Wang and Helliwell, 2000 ) . Among other reactions besides epimerization that besides occurred is superoxide mediated autoxidation in the presence of O ( Wang et al. , 2008b, Wang and Helliwell, 2000 ) .
As a consequence, there are limited surveies on the dynamicss particularly mathematical modeling that consider all of the interfering reactions when mensurating the stableness of green tea catechins.Another premise was made in patterning the debasement of entire epi- and nonepicatechins. The premise was that the rate invariables of debasement between epi- and nonepicatechins were similar. This was because of their similar construction, 2R, 3R ( 2,3-cis, epi signifier ) and 2S,3R ( 2,3-trans, nonepi-form ) . Therefore, the debasement rate invariable of entire epi- and non-epicatechins would follow the Arrhenius equation:where A is the frequence factor, Ea is the activation energy, R is the ideal gas invariable and T is the temperature in Kelvin. In the instance of EGCG and GCG, the rate changeless Bluegrass State could be obtained from the gradient of the line of best tantrum of ln ( [ EGCG ] + [ GCG ] ) / ( [ EGCG ] 0 + [ GCG ] 0 ) against clip, t. It was subsequently confirmed that Bluegrass State was similar between braces of catechins but shown to increase with an addition of temperature, irrespective if the experiment was carried in higher or lower temperature conditions ( Wang et al. , 2006, Wang et al.
, 2008a ) .Activation energy ( Ea ) refers to the alteration of possible energy of a chemical system that is required to change over reactants into merchandises by a reaction. The activation energy was besides found to be unchanged in a selected catechin solution regardless of the changing concentrations in the temperature scope of 25-165 & A ; deg ; C.
Table 7.1 shows the activation energy and frequence factor obtained from Purified EGCG Powder ( PEP ) solution at this temperature scope ( Wang et al. , 2008b ) .Table 6.1. Activation Energy ( Ea ) and Frequency Factor ( A ) of Tea Catechins in the PEP solutionsAdapted from ( Wang et al.
, 2008b ) .In another probe of kinetic stableness of catechins but at higher temperature, it was found that the A or frequence factor of the epimerization from epi-structured to nonepi-structured catechins was 104 greater than the epimerization from nonepi-structured to epi-structured catechins. Frequency factor refers to the figure of hits between the reactants to hold the right orientation taking to the concluding merchandises. This indicates lower rate of hit in the epimerization of nonepi-structured to epi-structured catechins ( Wang et al. , 2006 ) .
This consequence is besides in understanding with another survey which proposed that GCG/CG in the 2,3-trans signifier had a smaller steric hinderance and a possibility to hold a lower rate of hit than that of EGCG/ECG in the 2,3-cis signifier in a thermic reaction ( Wang and Helliwell, 2000 ) .7. DecisionIt is believed that the wellness benefits found in green tea are associated with the high content of catechins present in green tea. With the increasing market of tea drinks and merchandises that use tea infusions, it is necessary to understand the stableness of those catechins to be able to better the quality of merchandises and forestall its unwanted epimerization and debasement reactions. Therefore, the chief aim of this survey is to analyze the dynamicss of debasement and the epimerisation of green tea catechins in aqueous solutions under different conditions peculiarly at different pH and low temperature scope.