Phenolic compound content and Antioxidant activity of Infusion dregs  

C. A. Uthurry1,2 , C. Gmez-Cordovs1
1. Departamento de Caracterizacin, Calidad y Seguridad (DCCS), Instituto de Ciencia y Tecnologa de Alimentos (ICTAN), Consejo Superior de Investigaciones Cientficas (CSIC), C/Juan de la Cierva, 3, 28006 Madrid, Spain 2. Escuela de Produccin, Tecnologa y Medio Ambiente, Universidad Nacional de R­o Negro (UNRN), Mitre 331, 8336 Villa Regina, Rio Negro, Argentina
Author    Correspondence author
Journal of Tea Science Research, 2015, Vol. 5, No. 2   doi: 10.5376/jtsr.2015.05.0002
Received: 10 Dec., 2014    Accepted: 13 Jan., 2015    Published: 02 Feb., 2015
© 2015 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:

Uthurry and Gómez-Cordovés, 2015, Phenolic compound content and Antioxidant activity of Infusion dregs, Journal of Tea Science Research, Vol.5, No.2, 1-10 (doi: 10.5376/jtsr.2015.05.0002)

Abstract

The dregs of infusions (prepared as in the home) were examined to determine their antioxidant activity (AOA) and their potential as sources of phenolic compounds. Infusions of red tea, green tea and classic tea, chamomile, mint pennyroyal, linden, chamomile with anise and blends of different plants were made using commercially available ‘tea bags’. The AOAs of the original infusion material extracts and dreg extracts were measured using the ORAC-FL (Oxygen Radical Absorbance Capacity – Fluoresceine) method; their total phenolic compound contents (TPC)were determined using the Folin-Ciocalteu assay. Classic tea dreg extract retained some 52.8% of the AOA of the original infusion extract; TPC retention was also high (up to 99.5%). A positive linear correlation was found between AOA and the TPC in all the dreg extracts. Significant differences were observed between the dreg extracts in terms of their TPC and AOA retentions. The potential of infusion dregs as a new source of antioxidants is discussed.

Keywords
Tea; Dregs; Antioxidants; Polyphenols; ORAC-FL

Agroindustrial wastes have been identified as potentially valuable sources of antioxidants. Moure et al. (2001) reviewed the natural antioxidants found in such wastes and reported grape seeds and peels and tea leaves to be particularly rich in antioxidant compounds. They also discussed the importance of the extraction process on the yield of antioxidants that might be obtained from such residues. Similarly, Balasundram et al. (2006) indicated agroindustrial wastes to be good sources of phenolic compounds. They too discussed extraction efficiency, along with the problems of availability of supply of raw material.
The antioxidant activity and phenolic compound contents of many agricultural wastes have now been investigated. For example, Lafka et al. (2007) reported ethanol extracts of winery waste (seeds and grape skins) produced during red winemaking to have strong antioxidant activity; indeed it was higher than that of the synthetic food antioxidant BHT, ascorbyl palmitate, and vitamin E. However, no positive correlation was reported between the total phenolic compound content and the antioxidant activity of the extracts. In other work on Chardonnay grape pomace, Lu and Foo (1999) reported the presence of 17 polyphenols (including gallic acid, catechin, epicatechin and quercetin). Lu and Foo (2000) also reported apple pomace polyphenols to show high antioxidant activity; indeed, their DPPH-scavenging activity was some 2-3 times better than that of vitamins C and E. Further, their scavenging of superoxide anion radicals was 10-30 times more effective than those of vitamins C and E.
Solid olive wastes have been identified as an interesting source of polyphenols. Hydroalcoholic and purified extracts examined for their ability to quench free radicals were reported to show strong antioxidant activity (Aldini et al., 2006). Indeed, in in vitro experiments involving human umbilical endothelial cells, purified olive residue extract was found to prevent lipid peroxidation damage and cell death in a dose-dependent manner (Aldini et al., 2006).
Acetone extracts of mango peel have also shown good antioxidant activity in different systems, and its use in nutraceutical and functional foods has been proposed (Ajila et al., 2007). Moreover, these extracts were reported to protect erythrocytes against oxidative stress, indicating them to have potential health benefits (Ajila and Prasada Rao, 2008). Berardini et al. (2007) reported methanol–based extracts of lyophilised mango peel to contain large amounts of polyphenols and to have strong antioxidant activity, and concluded this waste to be a good source of compounds beneficial to human health.
Okonogi et al. (2007), who studied the peels of eight fruits commonly consumed in Thailand, indicated that of rambutan to be a natural source of non-cytotoxic antioxidants that could be used in food and drug products. Similarly, Shui and Leong (2006) suggested star fruit residues might be used as food additives given their high phenolic compound content and strong antioxidant activity.
Extracts of apple, goldenrod and artichoke by-products showed antioxidant activities similar to that of established antioxidants such as 0.01 % butylated hydroxytoluene (BHT) (Peschel et al., 2006). The latter authors reported the possibility of recovering large amounts of phenolic substances with antioxidant properties from vegetable residues, which could be of use in food and cosmetic formulations.
Onion waste is reported to show good antioxidant properties after its processing to make a pasteurised, stabilized paste (Roldán et al, 2008), and has been proposed as an ingredient of functional foods and anti-browning agents. Prakash et al. (2007) studied the composition and antioxidant properties of the seeds and agri-wastes of certain varieties of soybean (Glycine max). The agri-wastes of some varieties had high polyphenol (27.4-167 mg GAE.g-1) and flavonoid (10.4-63.8 mg QE.g-1) contents, and showed remarkable antioxidant activities, with the highest values recorded for the leaves, followed by the pods, pericarp, and twigs. Pumpkin seeds, seed skins, peel and oil have also been investigated as possible sources of antioxidant molecules. Peri?in et al. (2009) reported p-hydroxybenzoic acid to be the major compound in all such samples.
Broinizi et al. (2007) studied raw concentrated, aqueous and ethanol extracts of cashew apple pulp, as well as the free and esterified phenolic acid fractions. They reported the latter fractions to owe their antioxidant activity to the presence of gallic, ferulic, caffeic, protocatechuic, quinic, cinnamic, gentisic, p-coumaric and salicylic acids. In a work on pressed blackcurrant seeds, Helbig et al. (2008) concluded phenols and tocopherols to be major components.
De Oliveira et al. (2009) screened the antioxidant capacity of methanol extracts of powders of acerola, passion fruit and pineapple industrial residues, and reported all to show antioxidant activity, particularly acerola extract (which had a high phenolic compound content). They suggested the use of this extract as an antioxidant supplement or food additive.
The antioxidant activities of agroindustrial wastes can, however, change over time, and be altered by processing. For example, ?ata (2008) reported that antioxidant compound content of apple peel varied with storage time, in fact increasing over the first 45 days. A controlled atmosphere, rather than common cold storage, better preserved the antioxidant content at 90 days of storage. Interestingly, Kuljarachanan et al. (2009) reported that the high temperatures involved in the water blanching and hot air drying of lime residues reduced their polyphenol content. The phenolic compound content of this material correlated well with its antioxidant power; indeed, it was responsible for most of this activity.
Teas and other infusions have recently received much scientific and media attention as sources of antioxidants (?uczaj and Skrzydlewska, 2005; Almajano et al., 2008; Fu et al., 2011; Yang and Liu, 2013). Hot water, ethyl acetate and methanol extracts of industrial black tea wastes have been reported to show antioxidant activities similar to, or even better than, those of old tea leaves (Farhoosh et al., 2007). These authors suggested that both black tea wastes and old tea leaves, which are often disposed of, could be used as sources of powerful, natural antioxidants. The literature, however, contains no information of the phenolic content or antioxidant activity of the dregs of home-produced tea or other infusions. The present work shows that such dregs, which are always discarded, could in fact be an interesting source of antioxidant compounds.
1 Results and Discussion
Table 1 shows the TPC and AOA results for the original and dreg extracts.


Table 1 Antioxidant activity and total phenolic compound content of the original and dreg extracts

The AOA of the original extracts ranged from 0.190 to 1.822 mmol Trolox.mg-1, while the TPC ranged from 0.933 to 1.761 mg GAE.g-1. For the dreg extracts, AOA ranged from 0.033 to 0.628 mmol Trolox.mg-1, and TPC ranged from 0.667 to 1.914 mg GAE.g-1. Unexpectedly, the TPC of the linden infusion (T18) and green tea (TV24) dreg extracts were higher than those of the respective original extracts. Boiling water might favour hydrolysis reactions during infusion-making, producing molecules with more free hydroxyl groups, or other reducing compounds, able to reduce the Folin-Ciocalteu reagent.
A better correlation (R2 = 0.6692) between the AOA and TPC was found for the dreg extracts. In the original extracts, no correlation was observed (R2 = 0.1916), probably due to the presence of antioxidant substances other than polyphenols. These might have been solubilised during the infusion-making procedure. Figures 1 (A) and 1(B) show the plots of AOA against TPC. The much stronger correlation for the dreg extracts (Figure 1 (B)) suggests that most of their antioxidant activity is owed to the phenolic substances they contain.


Figure 1 Correlations between antioxidant activity and phenolic compound content in the original (A) and dreg extracts (B)

The TPC values of the dreg extracts are reminiscent of those reported by Roldán et al. (2008) for industrial onion by-products [0.569 - 2.118 mg GAE.g-1 (118.56 -441.31 mg CAE.(100 g)-1 dw) for frozen onion residues, and 0.616 -2.176 mg GAE.g-1 (128.23 – 453.29 mg CAE.(100 g)-1 dw) and 0.735 - 2.838 mg GAE.g-1 (153.15 – 591.25 mg CAE. (100 g)-1 dw) in pasteurised and sterilized residues respectively]. However, the dreg extracts generally showed higher AOAs than previously studied residues. Helbig et al. (2008), who examined the post-oil extraction seed press residues of berries (e.g., blackcurrant), reported hydrophilic AOA values of 0.020-0.084 mmol Trolox.mg-1 - much lower than for most of the examined dreg extracts (0.033-0.628 mmol Trolox.mg-1). The TPC of these berry seed residues (1.0-2.3 mg GAE.g-1) was, however, similar to those obtained for the dreg extracts (0.667-1.914 mg GAE.g-1). The peel and seed residues of passion fruit contain around 1 mg GAE.g-1 of phenolic compounds (De Oliveira et al., 2009), below the TPC value obtained for some 64% of the present dreg extracts. The same is true for pineapple and passion fruit pulp, which contain 0.217 and 0.200 mg GAE.g-1 respectively (De Oliveira et al., 2009). Infusion dregs therefore appear to be a low cost source of antioxidants.
The dreg extracts retained a variable percentage of the overall antioxidant power of the original extracts, ranging from 10.45% (for chamomile with anise MA7) to nearly 52.78% (for classic tea EB30) (Table 2).


Table 2 Retention of antioxidant capacity and total phenolic compound content by the dregs

Nearly half of the dreg extracts (those of 28-10, TV24, 23-10, 24-10, EB30, 4-9, 37-10, MA-15, 2-9, 15-10, T18, 18-10 and 33-9) showed more than 25% of the corresponding original extract’s AOA. The retention of the phenolic compound ranged from 51.26% (for chamomile with anise 19-10) to 126.88% (for green tea TV24); as suggested above, the latter figure might be explained by hydrolysis phenomena during the infusion-making process. After discarding this and the other outlying value returned by sample T18, 10 (TR28, TR6, 28-10, 23-10, 24-10, EB30, 4-9, 37-10, MEZ32-MMEAV and 33-9) out of 25 dreg extracts retained more than 90% of the phenolic compound content of the original extracts. Thus, although AOA decreased to a variable extent, the TPC values remained high for almost all the dreg extracts.
Strategies for further enhancing the phenolic concentration and antioxidant power of dreg extracts might include their treatment by tannase. This would transform the catechins present into lower molecular weight phenols with greater antioxidant activity. Lu and Chen (2008) studied the effect of tannase on long-maceration green tea aqueous extracts and observed an increase in their antioxidant properties and in their chelation effect on Cu2+ and Fe2+ ions. Processes already used to recover phenolic compounds from agroindustrial wastes might be applicable to tea dregs (Correia et al., 2004; Jeong et al., 2004). Research is needed to determine which is best.
Analyses of variance showed significant differences (p<0.05) in the retention of AOA by the different types of dreg extract (Figure 2). This analysis excluded the blends because of their uncertain qualitative and quantitative compositions, as well as the mint pennyroyal, since only one type was available.


Figure 2 Antioxidant activity retention by dregs. Note: CH: chamomile, CHA: chamomile with anise, CT: classic tea, GT: green tea, L: linden, RT: red tea

Dregs from the classic teas retained the highest AOA (mean 43.95 %); indeed, they retained significantly greater AOA than green tea (mean 31.95 %) and chamomile infusion (mean 30.95%) dregs which retained the second and third highest AOAs respectively. The chamomile with anise infusion dregs showed the lowest AOA retention (mean 14.84 %).
Significant differences were also recorded between the dreg extracts in terms of TPC retention (Figure 3).


Figure 3 Total phenolic content retention by dregs. Note: CH: chamomile, CHA: chamomile with anise, CT: classic tea, GT: green tea, L: linden, RT: red tea

The dregs from the red teas, green teas and classic teas retained the highest TPCs, with means of 93.29%, 95.97% and 93.53% respectively. Chamomile with anise dregs showed the lowest TPC retention (mean 60.97%).
The present results suggest that infusion dregs, which are discarded after making infusions at home, are in fact a promising source of antioxidants that might be used, for example, as food additives for preventing oxidation. Supplies of dregs might be acquired from cafeterias, homes, etc. In addition, they suggest that the short steeping times used in domestic infusion preparation do not allow for the phenolic pool of the starting material to be completely extracted. Longer infusion times would extract more, and likely provide greater health benefits.
The phenolic composition of the present original and dreg extracts is now being studied. This might provide more information on how to make better use of tea dregs.
2 Conclusions
These preliminary results show a much stronger correlation between AOA and TPC in the dreg extracts than in the corresponding original extracts, suggesting that phenolic substances are responsible for a good deal of their antioxidant activity.
The TPC of the studied dregs are similar to those reported in the literature for other types of residue, such as onion by-products and berry seed press wastes. Pineapple and passion fruit residues have lower TPCs than the present dregs. In addition, the present dregs showed higher AOA values than berry seed press residues.
Generally, the dregs retained a high percentage of the TPC of the original infusion material; red, green and classic teas showed retentions of 93-96%.
Compared to the original extracts, the dreg extracts of the classic teas retained the highest AOA values (around 44%), followed by those of green tea (around 32%) and chamomile infusion (around 31%). The chamomile with anise dregs retained the lowest AOA (14.84%) and TPC (around 61%).
Infusion dregs are potentially an interesting source of antioxidants. Different strategies, e.g., tannase treatment, might even improve their AOA. Nevertheless, the chemical composition of dregs must be known in order for the best strategy to be chosen.
In order to get the best health benefits out of infusions, longer-term macerations might be recommendable.
3 Materials and Methods
3.1 Samples
The infusions examined in this work were three red teas (Camellia sinensis), three green teas (Camellia sinensis), three classic teas (Camellia sinensis), three chamomile infusions (Matricaria chamomilla L.), three chamomile with anise infusions (Matricaria chamomilla L. with Pimpinella anisum), three linden infusions (Tilia spp.), six different blend infusions [chamomile, mint and green anise (Matricaria chamomilla L., Folium menthae piperiteae and Pimpinella anisum); green tea, mallow, green anise and elder (Camellia sinensis, Malva sylvestris L., Pimpinella anisum and Sambucus nigra L.); thyme, eucalyptus, rosemary and mint (Thymus vulgaris L., Eucalyptus globulus Labill., Rosmarinus officinalis and Folium menthae piperiteae); chamomile, mint and green anise (Matricaria chamomilla L., Folium menthae piperiteae and Pimpinella anisum); linden, orange blossom, lemon balm and vervain (Tilia spp., flowers from Citrus limonum Risso and Citrus sinensis {L.} Osbeck, Melisa officinalis L. and Lippia citriodora); and red tea, anise and plum (Camellia sinensis, Pimpinella anisum and Prunus subg. Prunus)], and finally, one mint pennyroyal infusion (Mentha pulegium L.) (Table 3). All were commercially available and purchased in ‘tea bag’ form.


Table 3 Infusion samples examined

3.2 Extraction solvents
Methanol (Chromasolv for HPLC, ³99.9%), used in the preparation of methanol-water (50:50) mixtures, and acetone (ACS reagent, ³99.5%), used for preparing extraction solvent (acetone-water 80:20), were purchased from Sigma-Aldrich (Sigma-Aldrich Chemie Gmbh, Steinheim, Germany). Distilled water was used to prepare all mixtures.
3.3 Preparation of extracts
Each bag of each type of infusion was weighed for comparison with the weight information on the boxes. No significant weight differences between bags were detected within boxes. Since the weight of the bags coincided with the labelled net weight, the weight of the empty bag was deemed negligible.
3.3.1 Solid-liquid extraction of the original infusion material
Solid-liquid extractions were performed using a Dionex ASE 200 Accelerated Solvent Extractor (Thermo Fisher Scientific Inc., Waltham, MA, USA). The stainless steel extraction cartridge was assembled so that the filter disc completely covered the bore of the tube; a spatula of sand was then added. The full content of a ‘tea’ bag was then transferred to a beaker, two spatulas of sand were added, and these components mixed before being placed in the extraction cartridge with the aid of a funnel. The cartridge was then positioned in the Dionex extractor carrousel. The extraction procedure was performed at 80ºC according to the manufacturer’s instructions, using 25 mL of acetone-water (80:20). Each extraction was completed in 35 min and the extract collected in a screw-cap vial. The extract was then placed in a water bath at 40ºC and evaporated to dryness (at 96 min) under a nitrogen flow (pressure 20 KPa for the first 10 min, then 140 KPa for the remaining time). Two millilitres of methanol-water (50:50) were then added to this solid extract and shaken. The resulting solution was then filtered and kept under nitrogen at 4ºC until further analysis. This liquid sample is hereafter referred to as ‘original extract’.

3.3.2 Solid-liquid extraction of infusion dregs
Infusions were prepared by macerating each bag in 100 mL of boiling water for 5 min. The water was then discarded. The bags were dried in an oven at 60ºC for 24 h before opening. The dregs were then subjected to solid-liquid extraction as above. The final liquid sample obtained is hereafter referred to as ‘dreg extract’.
3.4 Phenolic content
The total phenolic compound content (TPC) of the different original and dreg extracts was determined in duplicate using the Folin-Ciocalteu assay. The results were expressed as milligrams of gallic acid equivalents per gram of solid material (mg GAE.g-1) (Singleton et al., 1999).
3.5 Antioxidant activity
The antioxidant activity (AOA) of the original and dreg extracts was measured using the ORAC-FL (Oxygen Radical Absorbance Capacity – Fluoresceine) method (Dávalos et al., 2004). The results were reported as mmol Trolox.mg-1 of solid material. The reaction time was set to 100 min to ensure the completion of the reaction. All reaction mixtures were prepared in triplicate. Three independent assays were performed for each sample.
3.6 Statistical analyses
One-way ANOVA with the multiple range test option was used to compare the retention of AOA and TPC by the different dreg extracts. These calculations were performed using Statgraphics Plus 5.0 software (Manugistics Group, Inc., Rockville, MD, USA). The Pearson correlation test was used to determine correlations between the AOA and TPC results. These calculations were performed using Microsoft Office Excel 2007 (Microsoft Corporation, One Microsoft Way, Redmond, WA, USA).
Authors´ Contributions
CGC collected and provided TPC data and interpreted the results. CAU performed AOA assays, made data treatment and drafted the manuscript.
Acknowledgements
The authors thank María Isabel Izquierdo for helpful guidance and for sharing her technical expertise on the extraction procedure followed.
None of the authors of this work have a conflict of interest to declare.
References
Ajila C.M., Naidu K.A., Bhat S.G., and Prasada Rao U.J.S., 2007, Bioactive compounds and antioxidant potential of mango peel extract, Food Chem, 105: 982-988
http://dx.doi.org/10.1016/j.foodchem.2007.04.052
Ajila C.M., and Prasada Rao U.J.S., 2008, Protection against hydrogen peroxide induced oxidative damage in rat erythrocytes by Mangifera indica L. peel extract, Food Chem Toxicol, 46: 303-309
http://dx.doi.org/10.1016/j.fct.2007.08.024
Aldini G., Piccoli A., Beretta G., Morazzoni P., Riva A., Marinello C., and Maffei Facino R., 2006, Antioxidant activity of polyphenols from solid olive residues of c.v. Corantina, Fitoterapia, 77: 121-128
http://dx.doi.org/10.1016/j.fitote.2005.11.010
Almajano M.P., Carbó R., Limenéz A.L., and Gordon M.H., 2008, Antioxidant and antimicrobial activities of tea infusions, Food Chem, 108: 55-63
http://dx.doi.org/10.1016/j.foodchem.2007.10.040
Balasundram N., Sundram K., and Samman S., 2006, Phenolic compounds in plants and agri-industrial by-products: Antioxidant activity, occurrence, and potential uses, Food Chem, 99: 191-203
http://dx.doi.org/10.1016/j.foodchem.2005.07.042
Berardini N., Knödler M., Schieber A., and Carle R., 2007, Utilization of mango peels as a source of pectin and polyphenolics, Food Chem, 105: 982-992
Broinizi P.R.G., de Andrade-Wartha E.R.S., Silva A.M.O., Novoa A.J.V., Torres R.P., Azeredo H.M.C., Alves R.E., and Mancini- Filho J., 2007, Evaluation of the antioxidant activity of phenolic compounds naturally contained in by-products of the cashew apple (Anacardium occidentale L.), Ciencia Tecnol Alime, 27(4): 902-908
http://dx.doi.org/10.1590/S0101-20612007000400035
Correia R.T.P., McCue P., Magalh?es M.M.A., Macedo G.R., and Shetty K., 2004, Production of phenolic antioxidants by the solid-state bioconversion of pineapple waste mixed with soy flour using Rhizopus oligosporus, Process Biochem, 39: 2167-2172
http://dx.doi.org/10.1016/j.procbio.2003.11.034
Dávalos A., Gómez-Cordovés C., and Bartolomé B., 2004, Extending applicability of the oxygen radical absorbance (ORAC) assay, J Agr Food Chem, 52: 48-54
http://dx.doi.org/10.1021/jf0305231
De Oliveira A.C., Valentim I. B., Silva C.A., Henriques Bechara E.J., Paes de Barros M., Mano C. M., and Fonseca Goulart M.O., 2009, Total phenolic content and free radical scavenging activities of methanolic extract powders of tropical fruit residues, Food Chem, 115: 469-475
http://dx.doi.org/10.1016/j.foodchem.2008.12.045
Farhoosh R., Golmovahhed G.A., and Khodaparast M.H.H., 2007, Antioxidant activity of various extracts of old tea leaves and black tea wastes (Camellia sinensis L.), Food Chem, 100: 231-236
http://dx.doi.org/10.1016/j.foodchem.2005.09.046
Fu L., Xu B-T., Gan R-Y., Zhang Y., Xu X-R., Xia E-Q., and Li H-B., 2011, Total Phenolic Contents and Antioxidant Capacities of Herbal and Tea Infusions, Int J Mol Sci, 12 (4): 2112-2124
http://dx.doi.org/10.3390/ijms12042112
Helbig D., Böhm V., Wagner A., Schubert R., and Jahreis G., 2008, Berry seed press residues and their valuable ingredients with special regard to blackcurrant seed press residues, Food Chem, 111: 1043-1049
http://dx.doi.org/10.1016/j.foodchem.2008.05.017
Jeong S-M., Kim S-Y., Kim D-R., Jo S-C., Nam K.C., Ahn D.U., and Lee S-Ch., 2004, Effect of heat treatment on the antioxidant activity of extracts from citrus peels, J Agr Food Chem, 52: 3389-3393
http://dx.doi.org/10.1021/jf049899k
Kuljarachanan T., Devahastin S., and Chiewchan N., 2009, Evolution of antioxidant compounds in lime residues during drying, Food Chem, 113: 944-949
http://dx.doi.org/10.1016/j.foodchem.2008.08.026
Lafka T.I., Sinanoglou V., and Lazos E.S., 2007, On the extraction and antioxidant activity of phenolic compounds from winery wastes, Food Chem, 104: 1206-1214
http://dx.doi.org/10.1016/j.foodchem.2007.01.068
?ata B., 2008, Apple peel antioxidant status in relation to genotype, storage type and time, Sci Hortic-Amsterdam, 117: 45-52
http://dx.doi.org/10.1016/j.scienta.2008.03.011
Lu M.J., and Chen Ch., 2008, Enzymatic modification by tannase increases the antioxidant activity of green tea, Food Res Int, 41: 130-137
http://dx.doi.org/10.1016/j.foodres.2007.10.012
Lu Y., and Foo L.Y., 1999, The polyphenol constituents of grape pomace, Food Chem, 65: 1-8
http://dx.doi.org/10.1016/S0308-8146(98)00245-3
Lu Y., and Foo L.Y., 2000, Antioxidant and radical scavenging activities of polyphenols from apple pomace, Food Chem, 68: 81-85
http://dx.doi.org/10.1016/S0308-8146(99)00167-3
?uczaj W., and Skrzydlewska E., 2005, Antioxidative properties of black tea, Prev Med, 40: 910-918
http://dx.doi.org/10.1016/j.ypmed.2004.10.014
Moure A., Cruz J.M., Franco D., Dominguez J.M., Sineiro J., Dominguez H., Núñez M.J., and Parajó J.C., 2001, Natural antioxidants from residual sources -a review, Food Chem, 72: 145-171
http://dx.doi.org/10.1016/S0308-8146(00)00223-5
Okonogi S., Duangrat Ch., Anuchpreeda S., Tachakittirungrod S., and Chowwanapoonpohn S., 2007, Comparison of antioxidant capacities and cytotoxicities of certain fruit peels, Food Chem, 103: 839-846
http://dx.doi.org/10.1016/j.foodchem.2006.09.034
Peri?in D., Krimer V., Trivi? S., and Radulovi? L., 2009, The distribution of phenolic acids in pumpkin´s hull-less seed, skin, oil cake meal, dehulled kernel and hull, Food Chem, 113: 450-456
http://dx.doi.org/10.1016/j.foodchem.2008.07.079
Peschel W., Sánchez-Rabaneda F., Dieckmann W., Plescher A., Gartzía I., Jiménez D., Lamuela -Raventós R., Buxaderas S., and Codina C., 2006, An industrial approach in the search of natural antioxidants from vegetable and fruit wastes, Food Chem, 97: 137-150
http://dx.doi.org/10.1016/j.foodchem.2005.03.033
Prakash D., Upadhyay G., Singh B.N., and Singh H.B., 2007, Antioxidant and free radical – scavenging activities of seeds and agri-wastes of some varieties of soybean (Glycine max), Food Chem, 104: 783-790
http://dx.doi.org/10.1016/j.foodchem.2006.12.029
Roldán E., Sánchez-Moreno C., de Ancos B., and Cano M.P., 2008, Characterisation of onion (Allium cepa L.) by-products as food ingredients and antibrowning agents, Food Chem, 108: 907-916
http://dx.doi.org/10.1016/j.foodchem.2007.11.058
Shui G., and Leong L.P., 2006, Residue from star fruit as valuable source for functional food ingredients and antioxidant nutraceuticals, Food Chem, 97: 277-284
http://dx.doi.org/10.1016/j.foodchem.2005.03.048
Singleton V.L., Orthofer R., and Lamuela-Raventos R.M., 1999, Analysis of total phenols and other oxidation substrates and antioxidants by means of Folin-Ciocalteu reagent, Method Enzymol, 299: 152-178
http://dx.doi.org/10.1016/S0076-6879(99)99017-1
 

Yang J., and Liu R.H., 2013, The phenolic profiles and antioxidant activity in different types of tea, Int J Food Sci Tech, 48: 163-171
http://dx.doi.org/10.1111/j.1365-2621.2012.03173.x

Journal of Tea Science Research
• Volume 5
View Options
. PDF(918KB)
. FPDF
. HTML
. Online fPDF
Associated material
. Readers' comments
Other articles by authors
pornliz suckporn porndick pornstereo . C. A. Uthurry
. C. Gmez-Cordovs
Related articles
. Tea
. Dregs
. Antioxidants
. Polyphenols
. ORAC-FL
Tools
. Email to a friend
. Post a comment