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Green tea is being used more and more in cosmetic preparations, and although a lot of anecdotal references exist regarding the efficacy of green tea in topical applications on the skin, more research was done to prove what people have known for some time. On this page we take a brief look at green tea and the benefits of it in cosmetic skin care products.
On this page
References used in general REF 301 - REF 320 unless otherwise stipulated.
Tea is a small tree original from Asia but at present it is cultivated in different regions and therefore classified according to the country where it comes from.
This tree has evergreen, petiolate, simple, elliptical leaves, 5 to 10 cm long and 2 to 4 cm wide, blunt at apex, the first two thirds of margin shortly serrate.
The young, still undeveloped leaves are harvested manually and only the terminal undeveloped buds (pekoe, pekko) and the first young small leaves (tips) are elected.
In manufacturing Green Tea, the harvested leaves are steamed to prevent fermentation, which would yield black tea. According to the original method, leaves are firstly placed on matting, which are in turn placed on boiling-water so that the exposition to steam inactivates the enzymes (polyphenol oxidases) thus preventing polyphenol oxidation and preserving the chlorophyll.
Subsequently, the Tea is spread under the sun, pressed and dried.
According to a different procedure, the harvested product immediately undergoes pressure steaming into rotating cylindrical containers and is subsequently pressed and dried in several steps.
The presence of polyphenols and methylxanthines are the basic characteristic of the Green Tea chemical composition.
Polyphenols are the most abundant compounds in Green Tea leaves, its abundance depending on the area where the tea plant has been cultivated and the age of the leaves.
They amount up to 17 to 30 % of the dry leaf weight. The most important ones are flavonols (catechins), which include the following compounds (Ho et al., 1992):
- (+)-Catechin
- (-)-Epicatechin (3.0 – 9.0%)
- (+)-Gallocatechin
- (-)-Epigallocatechin (1.0 –12.0%)
- (-)-Epicatechin gallate (8.0 – 18.0%)
- Epigallocatechin gallate (30 - 53%)
The Methylxanthine contents, which vary between 2 and 6 % depending on the tea variety, consist of caffeine (1.5 – 5.5%) and smaller amounts of theophylline (0.002 – 0.02%) and theobromine (0.1 – 0.4%). Additionally, traces of adenine and xanthine can be found. These methylxanthines are partially combined with tannins.
The compounds responsible for the flavor and aroma of Tea are about 0.01-0.02% of the dry leaf weight. They conform a heterogeneous group of substances consisting of alcohols (1-hydroxy-3-hexene, geraniol), monoterpenic aldehydes and also free amino acids.
Other compounds present in these leaves are vitamins (C and the group B) although the most relevant one is folic acid since vitamin C gets completely degraded as a consequence of the processes applied to the plants. There are also enzymes involved in the fermentation process.
- METHYLXANTHINES
- Caffeine
- Theophylline
- Theobromine
- POLYPHENOLS (Catechins)
- (+)-Catechin
- (-)-Epicatechin
- (+)-Gallocatechin
- (-)-Epigallocatechin
- (-)-Epicatechin gallate
- Epigallocatechin gallate
Its cosmetic properties are based on the specific action of its active compounds:
- Polyphenols
- anti-oxidant
- anti-metalloproteinase
- anti-inflammatory
- photo protective
- Methylxanthines
- lipolytic and anti-lipogenic action
- blood flow stimulation
Polyphenols, mainly epigallocatechin gallate, are the compounds responsible for the antioxidant and anti-inflammatory effects of Green Tea. In this context, Lunder et al. 1992, demonstrated that external applications of a polyphenolic Tea extract before exposition to the sun resulted in a decreased lipid peroxidation and a reduction of the leukocyte infiltration, the later being responsible for inflammation. Santosh et al., 1999 confirmed these results and mentioned that the compound responsible for this action was (-)epigallocatechin gallate.
Ho et al., 1992 assessed the anti-oxidant action of Green Tea extracts by using the Rancimat method. This method measures conductivity changes caused by the generation of small free fatty acids when certain oil undergoes oxidation at high temperatures and ventilation rates. Ho et al., 1992 and Guo et al., 1996 found that the polyphenols present in Green Tea inhibit the enzyme lipooxygenase, which is responsible for the metabolism of arachidonic acid and the peroxidation of inflammation- and tumour-promoting lipids, thus demonstrating their anti-radical action against the hydroxyl radical. Fourneau et al., 1996 also demonstrated the anti free radical action of Green Tea.
The inhibitory effect of Green Tea on collagenase activity is another important action from the cosmetic point of view. Several studies demonstrate that polyphenols have the ability to inhibit the enzymatic activity of metalloproteinases, specifically collagenase, the enzyme responsible for the degradation of structural components in the extra-vascular matrix (collagen) and the vascular endothelium (Morazzoni et al., 1995; Makimura et al., 1993). Such an inhibitory action is mainly due to the presence of polyphenols with the gallic radical (epicatechin gallate and epigallocatechin gallate).
Because of this latter activity, Green Tea extracts may be added to anti-aging products to reduce the detrimental effects of skin metalloproteinases.
Several studies reported the positive photo protective effects resulting of external applications, as well as of oral intake, of the Green Tea polyphenols (Wang et al., 1992).
UV radiations produce several harmful effects such as inflammation and immune suppression, which cause carcinogenesis (Ahmad et al., 2001). Additionally, it induces IL1 proliferation, which plays an important role in skin hypersensitivity and skin tumour proliferation. It has been found (Craig et al., 2001) that Green Tea exerts photo protective actions preventing these kind of problems and reduces erythema formation.
Its action mechanism is based on the anti-oxidant and anti free radical properties of this plant and on its immunoregulatory effects, which result from its ability to inhibit UVB-induced infiltration of macrophages into the epidermis.
Because of the later action, Green Tea extracts may be added to sun protection products and facial products, in which protection against the harmful effects of UVB is required.
Several studies demonstrated that Green Tea has an effect on the lipidic metabolism, the methylxanthines being responsible for this effect. Methylxanthines act by inhibiting the enzyme phosphodiesterase thus inducing cAMP accumulation. However, there are other additional mechanisms involved, such as the calcium mobilization induced by this group of active compounds and increased membrane permeability.
Their action results in a potent inhibition of lipogenesis and a slight lipolytic effect, all of which reduces lipid accumulation into the adipocytes.
Additionally, methylxanthines stimulate cutaneous microcirculation since they act as adenosine antagonists and influence the beta-adrenergic system (Tofovic et al., 1991) thus promoting the vasodilator response.
Recent studies demonstrated a possible synergistic action between caffeine and catechin polyphenols in Green Tea, which seems to modulate and prolong adrenergic stimulation.
Because of the later action it can be added to anti-cellulite products and products aimed at the control of adipose tissues.
Enzymatic inhibition
Collagen is the main structural protein in skin representing almost 90% of the proteins present in dermis. Skin aging is related to deep functional alterations in these protein fibers. The abundance of the enzyme collagenase in skin is rather important. Its main function is to catalyze the collagen degradation. Thus, collagenase inhibition would allow maintaining the protein levels and the flexibility of skin.
One method used to evaluate the efficacy of an anti-aging product is to determine its ability to inhibit collagenase. An assay to evaluate the inhibition of collagenase by our Green Tea extract has been carried out.
Experimental Method
The degradation reaction of the substrate (collagen) starts when it is incubated with the enzyme (collagenase from Clostridium histolycum , type I-A) and the tested substances into a bath at 37ºC. The final concentration of Green Tea in the assay medium was 0.5%. After 5 hours, L-leucine was measured by staining with Ninhydrin and reading at 600 nm.
TES buffer 0.05 M pH=7.5 was used as the negative control.
1,10-Phenanthroline and Dithiothreitol at a final concentration of 0.5 mM in the assay medium were used as positive controls.
The maximal absorbance values were recorded for the tubes containing the negative control. Collagenase inhibition would result in smaller amounts of L-leucine residues and consequently, smaller absorbance values.
Results
The following graphic shows the values recorded for the present assay.
It can be observed that Green Tea exerts an inhibitory action on collagenase. After incubating this product with the enzyme, a 100 % inhibition was recorded.
According to the present results, it can be concluded that Green Tea has an ability to completely inhibit the collagen degradation, which produces beneficial effects on skin such as maintenance of skin elasticity.
Cosmetic application
- SKIN CARE treatments
- for all types of skins with free radical scavenger action and for sensitive or irritated skins with anti-inflammatory effect.
- BODY CARE
- slimming and anti-cellulite treatments. - Skin and Body Sun Protectors with anti-ageing and anti-wrinkles effects.
- HAIR CARE
- repairing and protector products, to improve gloss and strength.
QUANTITATIVE DETERMINATION OF TANNINS
Colorimetric determination of Tannins using pyrogallic acid as a standard.
Weight 0.50g of powdered sample or dry extract, or else 5.0 g if it is liquid extract, into a flat bottom 250 ml flask. Add 150 ml distilled water and the tip of a spatula of pumice. Keep refluxing for 30 minutes in a sand bath. Make sure that the whole sample boils. After that time, cool the preparation under running water or into an ice bath, transfer to a 250 ml flask and level off with distilled water. Shake and let it rest for about 5 minutes. Filter using a filter paper and discard 30 or 50 ml. The remaining filtered liquid is solution 1.
Determination of total polyphenols (A-1) 
Take 5 ml of solution 1 using a volumetric pipette and dilute with distilled water until reaching 25 ml, shake and level off (duplicate the analysis). From this point on, work under a diffuse light. Take 5 ml of this later diluted solution (5/25) using a volumetric pipette and pour into a volumetric 50 ml amber coloured flask or a flask previously wrapped in aluminium foil. Add exactly 1 ml phospho-tungstic acid, shake and level off with sodium carbonate 15%. Take a spectrophotometer reading (A-1) at 715 nm wavelength just 2 minutes after the addition of phospho-tungstic acid. Use distilled water as a blank control.
Determination of the not absorbed polyphenols (A-2)
Weight 0.5g of skin powder into a 50 ml beaker. Add 10 ml solution 1 using a volumetric pipette. Cover with aluminium foil and stir strongly (at about 1600 RPM) using a magnetic stirrer, without heating, for one hour. Fixate the beaker with holders to prevent falling and pouring out the sample. After stirring, filter twice with the same folded filter paper, into assay tubes by means of a 5 cm diameter funnel (the filter paper has to be as small as possible). Take 2 ml of this filtered solution with a volumetric pipette, dilute with distilled water until reaching 10 ml and stir. From this point on, work under a diffuse light. Take 5 ml of the later diluted solution (2/10) with a volumetric pipette and pour into a volumetric 50 ml amber coloured flask or a flask previously wrapped in aluminium foil (duplicate the analysis). Add 1 ml phospho-tungstic acid, shake and level off with sodium carbonate 15%.
Take the spectrophotometer reading (A-2) at 715 nm wavelength just 2 minutes after the addition of phospho-tungstic acid. Use distilled water as a blank control.
Standard assay with pyrogallic acid (A-3)
Weigh 0.050 g pyrogallic acid in a scale (1g capacity) with 0.0001 g precision. Transfer into a volumetric 100 ml flask, add distilled water, shake and level off. The stability of this solution lasts for only 15 minutes. That is the longest time available since its preparation until the end of the assay. From this point on, work under a diffuse light. Take 5 ml of this solution with a volumetric pipette (duplicate this assay). Dilute it with distilled water into a 100 ml volumetric flask. Take 5 ml of this later diluted solution (5/100) and transfer to a 50 ml amber coloured volumetric flask or a flask previously wrapped in aluminium foil. Add 1 ml phospho-tungstic acid, shake and level off with sodium carbonate 15%. Take the spectrophotometer reading (A-3) at 715 nm wavelength just 2 minutes after the addition of phospho-tungstic acid. Use distilled water as a blank control.
Calculations
QUANTITATIVE DETERMINATION OF CATECHINS
Quantitative determination of catechins (Catechin, Epicatechin and Epigallocatechin gallate) by means of high performance liquid chromatography.
The employed chromatographic conditions were as follows:
- Apparatus: Hewlet-Packard 1050 with automatic injector and DAD (Diode Array detector)
- Column: Kromasyl C-18 5µm 250x4.6 mm.
- Cartridge: C18 de extracción en fase sólida.
- Flow: 1.6 ml/min.
- Detection: 280 nm.
- Column temperature: 40ºC
- Mobile phase: phase A: Phosphoric buffer pH 2.45 and phase B:
- Acetonitrile/phase A (80:20) according to the gradient shown in the following table.
Quantification of the Catechins in the sample is obtained by interpolation with a calibration curve, or else by comparing areas with an already known concentration of a standard. © Provital 2006
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