Effect of fermentation on teas

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Centella asiatica leaves were exposed to fermentation/oxidation for varying amounts of time: no fermentation (0 min), partial fermentation (90 min) and full fermentation (24 h). The chemical composition of the teas was determined and compared with commercial Camellia sinensis teas. The results of proximate analysis showed Centella asiatica herbal teas contained significantly higher amounts of protein, fat and ash than Camellia sinensis teas. Compared to Camellia sinensis teas, all Centella asiatica tea infusion extracts contained significantly more total free amino acids (24.87-54.44 mg l-glutamic acid equivalent/g) but significantly less total free polysaccharides (24.33-31.52 mg glucose equivalent/g) and were caffeine free. High thiamine, riboflavin, niacin and ascorbic acid contents were found in all Centella asiatica teas, but biotin was found only in fully fermented Centella asiatica tea (CAFF). Colour measurements demonstrated that Centella asiatica infusions generally had lower a (greenness) and b (yellowness) values than Camellia sinensis teas. All infusions exhibited low turbidity levels (less than 10%), except for CAFF. However, the Centella asiatica teas exhibited significantly lower total phenolic (3.53-6.22mg gallic acid equivalent/g), total flavonoid (1.81-2.54 mg quercetin equivalent/g) and total anthocyanin (0.99-1.49mg catechin equivalent/g) contents than Camellia sinensis teas and thus had lower antioxidant capacities (DPPH: 21.86-32.64 ?m trolox equivalent/g and FRAP: 25.86-43.09 ?m trolox equivalent/g) than Camellia sinensis teas. Partially-fermented Centella asiatica (90 min) showed no significant change in antioxidant properties, but its total free polysaccharide content increased, and it produced the darkest infusion.

Keywords: Centella asiatica; herbal tea; chemical properties; water soluble vitamins; antioxidant properties


In recent years, there has been an increased effort to find foods and beverages with high antioxidant contents and health-promoting properties. Herbs traditionally used in folk medicine have attracted consumer interest because of their long historical consumption and ready acceptability. Herbal teas or tisanes have gained popularity all over the world due to their antioxidant activity and fragrance (thought to exert a calming effect on the mind) (1). According to the World Health Organization (2), over 80% of the world's population relies on largely plant-based traditional medicine for primary healthcare needs. In addition, the international herbal market, which includes herbal teas, is vast and is estimated to grow up to US$ 5 trillion by the year 2050 (3). The Malaysian herbal market was valued at US $3.8 billion in 2002 and is predicted to grow at an annual rate of 10 to 20% (4).

Most Malaysians are habitual herbal tea consumers and believe that herbal teas are safe to consume, assist in health promotion, boost energy level, prevent diseases and have cosmetic properties (5). Herbal teas can be easily prepared from any part of a plant, including the roots, flowers, seeds, berries and bark. The preparation of an herbal infusion, which may consist exclusively of one or more herbs, is simple and can be performed by means of decoction, infusion or maceration (6).

Centella asiatica (L.) Urban, synonym Hydrocotyle asiatica, is locally known as "pegaga" and belongs to the plant family Apiaceae (Umbelliferare). The herb is well known and is called various names all over the world, including "gotu kola", "Mandukaparni", "Brahmi" and Indian pennyworth. The herb is native to both tropical and subtropical countries such as China, India, South America, Madagascar and Malaysia. Centella asiatica is famous in Ayurvedic medicine for the treatment of leprosy, insanity, asthma, ulcers, eczema, skin tuberculosis, wounds, stomach aches, arthritis, varicose veins, and high blood pressure; it is also known as a memory enhancer (7). The major components of the herb are triterpenes and polyphenols, which have been reported to inhibit colon cancer cell growth (8), elicit neuroprotective effects in a mouse model of permanent cerebral ischaemia (9) and increase the antioxidant enzymes in lymphoma-bearing mice (10). The nutritional value of Centella asiatica is promising, as it is rich in carotenoids and vitamins B and C (11); the herb is commonly used as porridge for feeding pre-school children in Sri Lanka in order to combat nutritional deficiencies (12). The benefits of the herb are becoming popular among Malaysians, and commercial Centella asiatica cultivars are available in Malaysia. Centella asiatica has also become an important medicinal herb in international medicinal herb trading (11).

Studies have shown that herbal teas may be a promising source of antioxidants (13). Polyphenols such as flavonoids are commonly present in herbs. Catechin is the major flavonoid in Camellia sinensis tea (14) and is well known for its antioxidant properties. In Centella asiatica, quercetin and kampferol are present as major antioxidants (15). The phenolic hydroxyl group in flavonoids is found to be a strong antioxidant capable of effectively scavenging reactive oxygen species (16).

Centella asiatica is available on the market in the form of tea, soft drinks and syrup. The tea is prepared by simple drying and usually mixed with black tea to achieve a more yellow infusion. The natural presence of vallerin in Centella asiatica contributes to its bitter taste (7) and is not always acceptable to consumers. However, previous studies have shown that the fermentation process enhances the quality of herbal tea in terms of colour, flavour and taste (17). As there is a dearth of information on the use of fermented Centella asiatica teas in beverage production, the main objective of this research was to explore the feasibility of Centella asiatica as an herbal tea produced by three types of fermentation: no fermentation (CANF), partial fermentation (CAPF) and full fermentation (CAFF). The chemical properties, water soluble vitamin content, sensory properties (colour and turbidity) and antioxidant capacity of the products were studied and compared with commercial Camellia sinensis teas: green tea (GT), oolong tea (OT) and black tea (BT).


Plants, materials and chemicals. Fresh Centella asiatica was obtained from a local wet market in Penang, Malaysia. Commercial Camellia sinensis teas were bought from a local market. Folin-Ciocalteu's phenol reagent, sodium carbonate, aluminium chloride, sodium hydroxide, caffeine, iron (III) chloride and phenol were purchased from Merck (Darmstadt, Germany). Gallic acid, sodium nitrite, quercetin, vanillin, DPPH (1,1-diphenyl-2-picrylhydrazyl) radical, TPTZ (2,4,6-tripyridyl-s-triazine), ninhydrin, DL-panthenol, nicotinamide, pyridoxine, biotin and ascorbic acid were purchased from Sigma-Aldrich (St. Louis, MO., USA). All other chemicals used were of analytical grade.

Preparation of Centella asiatica leaves. Centella asiatica leaves were washed under running tap water. The cleaned leaves were withered in a locally obtained forced air oven at 30 oC for 2 h. The withered leaves were used to prepare three kinds of tea beverages.

Non-fermented (unprocessed) Centella asiatica (CANF) tea. The withered leaves were dried in a hot air oven at 100 oC until the moisture content was less than 6.5%. The dried leaves were kept in an air tight container.

Partially-fermented (CAPF) and fully-fermented (processed) (CAFF) Centella asiatica tea. The withered leaves were manually twisted and torn for 20 min. The crumpled leaves were allowed to undergo partial fermentation for 90 min. For CAFF, a similar procedure was repeated, but the fermentation time was prolonged to 24 h. The fermented leaves were dried in a hot air oven at 100 oC until the moisture content was less than 6.5%. The dried matter was kept in an air tight container.

Tea infusion preparation. For all experiments, 1 g of tea leaves was weighed into a beaker. Hot distilled water (100 mL) was then added and allowed to infuse the leaves for 10 min. The infusions were filtered through Whatman filter paper No. 1 prior to analysis.

Proximate analysis. Determination of the moisture, crude protein, crude fat and crude ash contents were performed according to the AOAC method (18). The protein conversion factor used was 6.25.

Determination of total free amino acids. The total free amino acids were determined using the method described by Yao et al. (19). Tea infusions (1 mL), 0.5 mL of phosphate buffer solution and 0.5 mL of 2% ninhydrin solution containing 0.8 mg/mL of tin chloride were placed into a 25-mL volumetric flask. The mixture in the volumetric flask was then heated in a boiling water bath for 15 min. The flask was quickly cooled down, and the volume was adjusted to 25 mL with distilled water. After the solution was left standing for 10 min, the resulting blue-purple products were read at 570 nm using a spectrophotometer (Shimadzu UV 1240). Results were expressed as mg L-glutamic acid equivalent/100 mL infusion. The measurement was performed in triplicate.

Determination of total free polysaccharides. The polysaccharide content was determined by the phenol-sulphuric colourimetric method (20). Tea infusions (0.5 mL) and 0.6 mL of 5% phenol solution were added into each test tube, followed by 0.3 mL of concentrated sulphuric acid. Each tube was mixed well and kept at room temperature for 30 min. The resulting dark brown solution was measured at 490 nm using a spectrophotometer (Shimadzu UV 1240). Results were expressed as mg glucose equivalent/100 mL infusion. Measurements were performed in triplicate.

Water soluble vitamin determination

Vitamin B determination using LC/MS. An Agilent LC-MS system 1100 (USA) was equipped with a binary pump, degasser, wellplate sampler and thermostatted column compartment directly connected with a positive ESI mass spectrometer system. The optimisation step was carried out in flow injection mode using a scan range of m/z 100-900. The separation was performed on a ZORBAX RRHT SB-Aq (100 - 3.0 mm, 1.8 ?m) with a mobile phase of (A) 20 mM ammonium formate and 0.1% formic acid in water and (B) 20 mM ammonium formate and 0.1% formic acid in methanol. The gradient elution was programmed as follows: 0-8min, 10% B; 8-8.1min, 55% B; 8.1-10min, 10% B at a flow rate of 0.5mL/min with an injection volume of 10?L. Nitrogen gas was used as the nebulising gas (30 psig) and as the drying gas (10 L/ min). The drying temperature was kept at 350 oC. The capillary exit was 1850 V.

Vitamin C determination using HPLC. Tea infusions (10 mL each) were extracted using an equal volume of 4.5% (w/v) metaphosphoric acid solution. Samples were filtered through a 0.45-µm membrane filter in aliquots of 20 µL for each tea infusion. A Jacob HPLC system (Jasco, Tokyo, Japan) equipped with a Jasco PU-2080 Plus Intelligent HPLC Pump, a Jasco AS-2055 Plus Intelligent Sampler, a Jasco UV-2077 PLUS 4-? Intelligent UV/Vis detector and a Jasco ChromNAV version 1.11.02 (Build 4) was used. The separation was performed with a Hypersil ODS C18 column (250-4.6 mm, 5 ?m) (Thermo Scientific, Waltham, MA, USA) fitted with a Hypersil ODS guard column. The deionised water mobile phase was adjusted with metaphosphoric acid to pH 2.2 at a flow rate of 1.0 mL/min and detected at 276 nm (21). Results were expressed as mg ascorbic acid/100 mL infusion.

Caffeine determination using HPLC. The tea infusions were diluted with deionised water and filtered through a 0.45-µm membrane filter and injected into a Jasco HPLC system (Jasco, Tokyo, Japan). The separation was performed on a Hypersil ODS C18 column (250-4.6 mm, 5 ?m) (Thermo Scientific, Waltham, MA, USA) fitted with a Hypersil ODS guard column containing a mobile phase of 25 methanol:75 deionised water at a flow rate of 1.0 mL/min and detected at 276 nm. Results were expressed as mg caffeine/100 mL infusion.

Colour measurements. A Konica Minolta spectrophotometer CM-3500d (Minolta, Kyoto, Japan) with illuminant D65 was used to measure the CIE L*, a* and b* colour space of tea infusions (L* [lightness (0 = black, 100 = white)], a* (-a = greenness, +a = redness) and b* (-b = blueness, +b = yellowness)). Results were obtained using SpectraMagic™ computer software version 3.61 G (Cyber Chrome, Inc., Minolta Co. Ltd).

Turbidity. The turbidity of tea infusions was measured according to the method described by Harboune et al. (22) using a spectrophotometer (Shimadzu UV 1240 ) at 400 nm. The percent transmittance (T%) was recorded, and (100 -T%) was used as a measure of turbidity.

Antioxidant activity

Total phenolic content (TPC). The total phenolic content of each tea infusion was measured using the method described by Kahkonen et al. (23). The tea infusion (3 mL) was added to 1.5 mL of Folin-Ciocalteu's phenol reagent (10% v/v) and allowed to react for 5 min. Next, 1.2 mL of 7.5% w/v sodium carbonate was added to the reaction mixture and incubated for 30 min. The resulting blue complex was measured at 765 nm, and TPC was expressed as mg gallic acid equivalents (GAE)/100 mL infusion. Measurements were performed in triplicate.

Total flavonoid content (TFC). Total flavonoid content (TFC) was assayed as described by Zhishen et al. (24). In brief, 0.5 mL of tea infusion was mixed with 2 mL of distilled water and 0.15 mL of 20% w/v sodium nitrite and left to stand for 5 min. Then, 0.3 mL of 10% w/v aluminium chloride was added to this mixture. After 6 min, 2 mL of 1M sodium hydroxide and 0.2 mL of distilled water were added. The absorbance was read at 510 nm. Quercetin was used as the standard for the calibration curve due to its high concentration in Centella asiatica (15). The results were expressed as mg quercetin equivalents (QE)/100 mL infusion; measurements were performed in triplicate.

Total anthocyanidin content (TAC). The total anthocyanidin content of the tea infusions was measured using the method described by Sun et al. (25). First, 2.5 mL of 1% (w/v) vanillin in methanol and 2.5 mL of 9.0 N hydrochloric acid in methanol were added to 1 mL of tea infusion. After incubation at 30 oC for 20 min, the absorbance was measured at 500 nm using a spectrophotometer (Shimadzu UV 1240) and expressed as mg catechine equivalents (CE)/100 mL infusion. Measurements were performed in quintuplicate.

DPPH (1,1-diphenyl-2-picrylhydrazyl) free radical scavenging activity. The DPPH free radical scavenging activity of each tea infusion was determined according to the method described by Leong and Shui (26). A 0.1 mM solution of DPPH in methanol was prepared. An aliquot of 0.1 mL of tea infusion was added to 2.9 mL of methanolic DPPH solution and kept in the dark for 30 min. Absorbance was assayed at 517 nm using a spectrophotometer (Shimadzu UV 1240). Trolox solution was used to perform the calibration curves. Results were expressed as ?mol Trolox equivalents/100 mL infusion. The measurement was performed in triplicate.

Ferric reducing antioxidant potential (FRAP) assay. The ability to reduce ferric ions was measured according to the method described by Benzie and Strain (27). The FRAP reagent was prepared using 300 mM sodium acetate buffer at pH 3.6, 20 mM iron chloride and 10 mM 2,4,6-tripyridyl-s-triazine dissolved in 40 mM hydrochloric acid at a ratio of 10:1:1 (v:v:v). The reagent was incubated in a water bath at 37 °C for 5 min before use. The initial reading of the reagent was measured at 593 nm using a Shimadzu UV 1240 spectrophotometer. An aliquot of 0.1 mL of tea infusion was then added to 2.9 mL of FRAP reagent and kept in the dark for 30 min. Trolox solution was used to create the calibration curves. Results were expressed as ?mol Trolox equivalents/100 mL infusion. Measurements were performed in triplicate.

Statistics. Experimental data were analysed using Excel 2007 (Microsoft Inc.) and Statistical Package for the Social Sciences (SPSS) 17.0 for Windows® (SPSS Inc.). A one-way ANOVA procedure followed by a Duncan test was used to determine the significant difference (p<0.05) between treatment means. A Pearson correlation analysis was performed to determine the correlationship between the polyphenols and the antioxidant capacity of tea infusions.


Three types of Centella asiatica teas (CANF, CAPF and CAFF) were successfully prepared in this study. The tea infusions were yellow, as shown in Figure 1.

Chemical properties of Centella asiatica and Camellia sinensis teas. Controlling moisture content is an important factor in tea preservation, particularly for the inhibition of microbial growth. Owuor (28) suggests that the moisture content of tea products should be below 6.5%. However, tea leaves with a moisture content of 2.5% or less may evidence a 'smoky' taste (28). Based on the results obtained (Table 1), the moisture contents of CANF, CAPF and CAFF were 6.42, 6.41 and 6.42%, respectively; for the three types of Camellia sinensis teas, GT, OT and BT, the moisture contents were 6.13, 6.49 and 7.47%, respectively. All the teas analysed fell within the suggested limit, with the exception of BT.

There was no significant difference observed in all types of Centella asiatica teas during protein analysis. The protein contents of Centella asiatica teas were significantly higher than those of Camellia sinensis teas. The protein content remained constant in all Centella asiatica teas. This was in accordance with the results of Tsai et al. (29), who reported that the nitrogen content of tea leaf was not affected by harvesting and fermentation process. Yu et al. (30) found that crude tea proteins contribute to antioxidant activity. A similar trend was found for ash contents, which remained unchanged in the three samples (CANF, CAPF, and CAFF). This may be due to the stability of minerals present in ash, as the temperature used for drying was 100 oC. The fat content of CANF tea was significantly higher than CAPF and CAFF teas. The fat content of all Centella asiatica teas was also significantly higher than that of Camellia sinensis teas. The fat content reduced with fermentation time, which could have been due to the release of volatile fat content from the samples during fermentation.

Free amino acid content is regarded as an important criterion for tea quality assurance and contributes to overall quality in terms of taste, flavour and colour (19). In CANF and CAPF tea infusions, the total free amino acid released showed no significant change but was significantly higher than that released by CAFF tea and Camellia sinensis teas. There were no significant differences for all Camellia sinensis teas. The dramatic decrease in total free amino acid content in CAFF may have been due to the breakdown of protein during the 24-h fermentation time (19). GT had the highest total free polysaccharide content, followed by OT and BT. These contents were significantly higher than those of CANF and CAFF. However, the polysaccharide content of CAPF was not found to be significantly different from that of OT. However, it was significantly higher than that of BT. Polysaccharides in GT were found to cause antioxidant activity in a DPPH assay, but their contribution was less than that of polyphenol and protein (30).

No caffeine was found in any Centella asiatica tea. In contrast, the caffeine contents in GT, OT and BT were 21.29, 12.72 and 24.35 mg/100mL, respectively. This indicates that Centella asiatica teas possess great potential for the growing caffeine-free tea market. Recently, decaffeination has become popular for minimising caffeine content in various sources, including tea and coffee. The caffeine content in beverages should be minimised due to caffeine-related side effects, including anxiety, nausea, jitteriness, nervousness, a decrease in heart rate and an increase blood pressure and the risk of cardiovascular disease (31).

Water-soluble vitamins. Vitamins are organic compounds present in trace amounts in our diet. Individual vitamins have specific functions to promote health and life. The amount of water-soluble B and C vitamins present in tea infusions was determined. Vitamin B is made up of a complex group and consists of eight vitamins: vitamin B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), vitamin B6 (pyridoxine), B7 (biotin), B9 (folic acid) and vitamin B12 (cyanocobalamine).

The amounts of water soluble vitamins in Centella asiatica and Camellia sinensis teas are shown in Table 2. The amount of thiamine in Centella asiatica teas was significantly higher than in GT. However, thiamine was not detected in OT or BT. CAPF had a significantly higher amount of thiamine than CAFF and CANF. Centella asiatica teas also contained significantly more riboflavin than Camellia sinensis teas. There was no significant difference between GT and OT, and both teas had a significantly higher riboflavin content than BT. Niacin was the predominant B-vitamin type present in both tea types (Centella asiatica and Centella sinensis). Niacin content was found to decrease along with fermentation time. CANF exhibited the highest niacin content (1179.85 µg/100 mL); niacin contents were 786.78 and 269.16 µg/100 mL in CAPF and CAFF, respectively. At the same time, CANF and CAPF had higher niacin content than GT, OT and BT. The pyridoxine content in both tea types increased with fermentation time. Camellia sinensis teas were shown to have a higher pyridoxine content than CANF and CAPF. The pyridoxine content of CAFF was not significantly different from that of BT, and it was higher than those of GT and OT. Biotin was found only in CAFF. Pantothenic acid, folic acid and vitamin B12 were not detected in any of the tea infusions. The absence of folic acid may be due to its sensitivity to sunlight, air, light and the heat from the boiling water (32). Vitamin B12 (cyanocobalamine) was reported as not present in black teas (33). The high concentration of thiamine, riboflavin and pyridoxine present in Centella asiatica teas, especially CAPF, suggested that it is a potential isotonic or energy drink.

The amount of vitamin C or ascorbic acid in Centella asiatica teas was generally higher than in Camellia sinensis teas; CANF had the highest amount. Ascorbic acid was found to decrease with fermentation degree, indicating that ascorbic acid oxidised during fermentation. Similar results were also shown by Camellia sinensis teas.

Colour and turbidity. Tea colour and turbidity are important sensory qualities. The CIE Lab and turbidity values for Centella asiatica and Camellia sinensis tea infusions are given in Table 3. The L value decreased (from 99.42 to 98.38) with the degree of fermentation in Centella asiatica teas. A similar trend was found in Camellia sinensis teas. The L values showed that the infusions of both major tea types were bright and clear. The greenish value (-a) of GT and BT was significantly higher than all the Centella asiatica teas, although the -a of CANF was higher than that of OT. However, the b values of all the Camellia sinensis teas were greater than those of the Centella asiatica teas. This implies that Camellia sinensis teas were darker than Centella asiatica teas. In Centella asiatica teas, fermentation significantly improved the redness and yellowness of the infusions.

Turbidity is the optical property that describes the scattering and absorption of light as it travels through a tea infusion, making the infusion look cloudy or smoky (34). The turbidity values of the three types of Camellia sinensis teas were generally lower than Centella asiatica teas, except for that of CANF, which was significantly lower than that of OT and not significantly different from that of GT and BT. In Centella asiatica teas, turbidity increased with fermentation time with the following trend: CANF < CAPF < CAFF. Results showed that the turbidity values of both tea types were generally lower than 10%, indicating a low level of turbidity. However, CAFF exhibited a high level of turbidity. The breakdown of compounds in leaves during fermentation probably allowed these compounds to diffuse easily, therefore increasing the turbidity value of the infusion. A high level of turbidity in beverages is known to decrease their aesthetic value, as mentioned by Harbourne et al (22).

Antioxidant activity. The TPC, TFC and TAC of Centella asiatica and Camellia sinensis infusions were determined and are given in Figure 2. Polyphenols are aromatic secondary metabolites widely found in herbs and associated with colour, sensory qualities, nutritional and antioxidant properties of food (35). All Camellia sinensis teas had higher total polyphenol contents than Centella asiatica teas. BT had the highest TPC, followed by GT and OT, then CANF, CAPF and CAFF. There was no significant difference between the TPCs of CANF and CAPF, but both were significantly higher than that of CAFF. This suggests that prolonged fermentation time broke down the polyphenols in Centella asiatica teas. Teas with a high TPC also exhibited high TFC and TAC values. However, BT had a higher TPC than GT but had a lower TAC than GT. Herbal teas contain no caffeine and therefore have lower TPC contents than Camellia sinensis teas (1). Moreover, the Camellia sinensis teas also exhibited high polyphenol contents (17-25% dry weight) contributed mainly by catechin, theaflavins, thearubigins and theabrownins. About 45% of these tea constituents can be infused into hot water (14)

The results of antioxidant activities of tea infusions are shown in Figure 3. In order to obtain a reliable result, two antioxidant assays, a DPPH free radical scavenging assay and a FRAP assay, were used to determine the antioxidant activities of tea infusions. DPPH assays are easy, rapid, reproducible and widely used for the determination of primary antioxidant activity in herb extracts (36). The DPPH is stable at room temperature and produces a violet solution in methanol. The assay is based on the discolouration of DPPH, which is reduced by the antioxidant present. FRAP assays measure the ability of an antioxidant to reduce the ferric-TPTZ (Fe (III) -TPTZ) complex to blue ferrous-TPTZ (Fe (II) -TPTZ) complex at low pH (27). The assay is also simple, speedy, inexpensive and highly reproducible (37). The Trolox equivalent antioxidant capacity (TEAC) was used as the antioxidant parameter and expressed as Trolox equivalent/100 mL of tea infusion. The TEAC is a more meaningful and descriptive expression than assays that report antioxidant activity as the percentage decrease in absorbance. The results also provide a direct comparison of the antioxidant activity with Trolox and allow comparisons to be made with other herbal teas examined by other researchers (36).

Extracts that contain a high amount of TPC also generally exhibit high antioxidant activity. In our study, all Camellia sinensis teas with high TPC values showed high antioxidant activities. GT had the highest TEACDPPH value, followed by BT and OT, then CANF, CAPF and CAFF. A similar trend was also demonstrated in TEACFRAP. The higher antioxidant activity of GT in comparison with other teas, including OT and BT, was probably due to its high antocyanin content (65.62 mg/100 mL infusion). These results are in accordance with the findings of Aoshima et al. and Atoui et al. (1, 13), who reported that green and black teas have higher antioxidant activity rates than herbal teas like sage, mint, chamomile, ginkgo and peppermint. Furthermore, the high caffeine content of Camellia sinensis contributed to a higher TEAC. The antioxidant ability of caffeine was reported to be higher than ascorbic acid and displayed a strong ability to scavenge the hydroxyl radical and singlet oxygen at a constant rate of 7.3•109 M-1s-1 and 2.9•107 M-1s-1, respectively (38). The high amount of catechin derivative present in Camellia sinensis also contributed to the high rate of antioxidant activity (14).

Correlation study of polyphenols and antioxidant capacity. A correlation analysis was performed to determine the correlation between polyphenol content and the antioxidant capacity of tea infusions. A strong relationship between total phenolic content and total flavanoid content (r=0.971) showed that flavonoids were the major polyphenols present in both types of teas compared to antocyanin (r=0.868). Polyphenols are a complex group that consists mainly of flavonoids, phenolic acids and hydroxycinnamic acids. The major polyphenols in Camellia sinensis are catechine and its derivatives (14), and quercetin and kaempferol in Centella asiatica (15) are compounds from flavonoids. As such, polyphenol type showed a clear relationship with TEACDPPH; a high correlation was found between TEACDPPH and TPC (r=0.914), followed by TFC (r=0.830) and TAC (r=0.769). A similar trend was evident regarding polyphenols and TEACFRAP. The phenolic hydroxyl group in flavonoids was found to be a strong antioxidant capable of effectively scavenging reactive oxygen species (16). Moreover, a strong correlation was observed in TEACDPPH and TEACFRAP. The strong correlation between TEACDPPH and TEACFRAP in edible tropical plants has also been reported by Wong et al. (36). This indicated that compounds able to reduce DPPH radicals are also capable of reducing ferric ions.

The present study showed that Camellia sinensis teas have TPC, TFC, TAC and antioxidant properties superior to those of Centella asiatica teas. Nevertheless, the CANF and CAPF possess great potential as herbal teas as a result of their higher physiochemical property values, soluble vitamin contents and lack of caffeine when compared to Camellia sinensis teas. CAPF exhibited no significant difference in antioxidant properties but had a higher free polysaccharide total and infusion yellowness compared to CANF. However, prolonged fermentation (full fermentation) inverted these effects.


This work was supported by a Research University (RU) Grant from Universiti Sains Malaysia (1001/PTEK IND/815040) and a USM Fellowship.


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