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Effect of Brewing Water on the Antioxidant Capacity of Green Tea Infusion with DPPH Assay

Effect of Brewing Water on the Antioxidant Capacity of Green Tea Infusion with DPPH Assay Hindawi Journal of Chemistry Volume 2022, Article ID 7736117, 8 pages https://doi.org/10.1155/2022/7736117 Research Article Effect of Brewing Water on the Antioxidant Capacity of Green Tea Infusion with DPPH Assay 1,2 1 1,3 1 1 Qing-Qing Cao , Yan-Qing Fu, Cheng-Bin Zhang, Yan Zhu, Jun-Feng Yin , 4 5 1 Daniel Granato, Predrag Putnik, and Yong-Quan Xu Tea Research Institute Chinese Academy of Agricultural Sciences, Key Laboratory of Tea Biology and Resources Utilization, Ministry of Agriculture, Hangzhou 310008, China Graduate School of Chinese Academy of Agricultural Sciences, Beijing 100081, China College of Life and Environmental Science, Hangzhou Normal University, Hangzhou 310036, China Department of Biological Sciences, Faculty of Science and Engineering, University of Limerick, Limerick V94T9PX, Ireland Department of Food Technology, University North, Koprivnica 48000, Croatia Correspondence should be addressed to Jun-Feng Yin; yinjf@tricaas.com and Yong-Quan Xu; yqx33@126.com Received 26 July 2021; Accepted 27 November 2021; Published 4 January 2022 Academic Editor: Damião Pergentino de Sousa Copyright © 2022 Qing-Qing Cao et al. 2is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Brewing water plays a crucial role in flavor and potential healthy functions of tea infusion. In this study, seven water samples with different physicochemical properties were selected to brew green tea. Results showed that the brewing water with higher minerals level and pH value would reduce the yield of catechins in tea infusion, which in turn caused the decrease of antioxidant activity to a large extent. Besides, it was found that EGCG, as a major contributor to the antioxidant activity of green tea infusion, was 2+ 2+ influenced differently by different metal ions, among which Ca /Mg could enhance the antioxidant activity of EGCG solutions 2+ with different concentration through synergistic effect, particularly Ca , and the effect was more markable at a higher EGCG concentration. 2ese results offered theoretical direction to the selection of tea brewing water for consumers and gave a new sight to the effects of metal ions on the antioxidant capacity of EGCG. ions in brewing water [8–14]. 2is susceptibility is mainly 1. Introduction due to the instability of catechins, including degradation, Now, apart from water, tea has become the most widely oxidation, and epimerization [9, 15]. consumed beverage all over the world [1]. Green tea is a kind On the one hand, pH is an important factor affecting the of unfermented tea and one of the most popular kinds of tea stability of catechins during tea brewing. 2rough the study due to its distinct flavor and powerful healthcare functions of the reaction kinetics on the catechins of green tea infu- [2–4]. 2e health benefits of green tea owe a great deal to its sion, Komatsu et al. [16] found that the catechins would degrade when pH was above 6.0, and they were more stable bioactive substances, such as theanine and catechins, which attract more and more researchers to study their various when pH was below 5.0. It indicated that the stability of potential in healthy benefits [5, 6]. As a kind of efficient catechins in aqueous solutions was pH-dependent to a great antioxidant, catechins have been applied to food preserva- extent [9]. Usually, catechins were stable at weak acid tion and medical treatment [7]. Antioxidant capacity of condition (pH 3.0–5.0); when pH was lower or higher, the green tea is mostly originated from the total catechins, stability of catechins would be affected [17]. among which EGCG plays a dominant role. On the other hand, metal ions also act on catechins However, the antioxidant activity of green tea is sus- stability and antioxidant capacity of tea infusion. It was ceptible to various environmental conditions during pro- found that both pH and conductivity of brewing water could cessing, storage, and brewing, such as pH, temperature, and influence the antioxidant capacity of tea infusions negatively 2 Journal of Chemistry [10]. Significant negative correlations between mineral L) were used to study the effect of the types and concen- concentration and the extraction yield of polyphenols in tea trations of metal ions on the antioxidant activity of EGCG infusion were reported by Mossion et al. [18]. But the study solutions. pointed that the effect of metal ions on the antioxidant 2e mixed solutions of EGCG (10, 20, 40, 50, 80, and 2+ 2+ activity of EGCG solution was very limited. 100 mg/L) and Ca /Mg ions (10, 20, 40, and 80 mg/L) 2+ 2+ 2is study aimed to investigate the effect of different were used to study the effect of Ca /Mg ions on the types of water on the catechins concentration and the an- antioxidant activity of EGCG solution with different tioxidant capacity of green tea infusion and further explore concentrations. the effect of metal ions on the antioxidant capacity of EGCG All the concentrations mentioned above were the final solution. Seven types of water with different pH value and concentrations in (mixed) solutions, and all the sample metal ions were chosen for tea brewing. 2e differences of solutions were prepared with pure water. 2e sample so- total catechins extraction yield and antioxidant capacity of lutions obtained were used for conducting the analysis of green tea infusion brewed with different waters were antioxidant activity using DPPH assay in triplicate. compared. Afterwards, the addition of different metal ions was performed to investigate their influences on the anti- 2.4. Determination of Metal Ions and pH. 2e metal ions in oxidant capacity of EGCG monomer solution. 2e results these seven types of water were determined by using In- would reveal the influence of metal ions on the antioxidant ductively Coupled Plasma Mass Spectrometry with a charge- capacity of catechins and tea infusion, which could provide injection device detector (ICP-MS, 2ermo Jarrell Ash knowledge and guidance on the selection of water when Corp., USA), as described in our previous work [20]. 2e brewing green tea. detailed conditions were as follows: the maximum inte- gration times of the low wavelength and high wavelength 2. Materials and Methods were set as 15 s and 5 s, respectively. 2e nebuliser pressure was set at 28 psi. 2e pump speed was 100 r/min. 2e 2.1. Reagents. 1,1-Diphenyl-2-picrylhydrazyl (DPPH), auxiliary gas flow was set as medium (1 L/min), and the RF (−)-epigallocatechin gallate (EGCG), and Trolox (6-hy- power was 1150 W. droxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) were 2e pH values of different waters and tea infusions were purchased from Sigma (Shanghai, China). Methanol, dried determined using a pH meter (SG2, Mettler-Toledo In- CaCl , MgCl , KCl, and NaCl were purchased from 2 2 struments (Shanghai) Co., Ltd., Shanghai, China). 2e buffer Shanghai Suke Chemical Co., Ltd. (Shanghai, China). Green solutions at pH 4.01 and 7.01 (Mettler-Toledo) were used to tea was obtained from the Tea Research Institute of the calibrate the pH meter. Chinese Academy of Agricultural Sciences. Seven types of water used for the present study were obtained from dif- ferent water sources: distilled water (DW) from Guangzhou 2.5. Determination of Catechins Concentration. Catechins Watson’s Food & Beverage Co., Ltd. (Guangzhou, China); concentration in different tea infusions was determined by pure water (PW) from Hangzhou Wahaha Group Co., Ltd. using high performance liquid chromatography (HPLC, (Hangzhou, China); tap water (TW) from Hangzhou; nat- Shimadzu LC-20A) with an ultraviolet detector (SPD-10A, ural water (NW), Nongfu Spring, from Nongfu Spring Co., Shimadzu Suzhou Corporation, Suzhou, China) [21]. 2e Ltd. (Hangzhou, China); mountain spring water (MSW), TM HPLC conditions were as follows: column: Diamonsil C18 Hupao Cool Spring, from Hangzhou Tongsheng Water Co., column (4.6 × 250 mm, 5μm, Waters); injection volume: Ltd. (Hangzhou, China); mineral water 1 (MW1) from 10μL; temperature: 35 C; mobile phase A: 2% acetic acid; Kunlun Mountains Mineral Water Co., Ltd. (Geermu, mobile phase B: acetonitrile 100%. 2e following elution China); and mineral water 2 (MW2) from Tibet 5100 Water gradient plan was adopted: 0–16 min, 6.5% B; 16–25 min, 15% Resources Holdings Ltd. (Dangxiong, China). B; and 25–30 min, 6.5% B. Post-run-time was 5 min. 2e flow rate was 1 mL/min. 2e detection wavelength was set as 280 nm. Before injection, the cooled tea infusion should be 2.2. Preparation of Green Tea Infusion. According to the filtered through the 0.22μm Millipore filter. Chinese national standards of tea sensory evaluation [19], the tea leaves were brewed with a leaf/water ratio of 1 : 50 (w/ w) by using different boiling water (DW, PW, TW, NW, 2.6. Determination of Antioxidant Activity. 2e antioxidant MSW, MW1, and MW2) for 5 min at room temperature capacity of the tea infusion or EGCG solution was deter- (RT, 25± 2 C). 2e leaves were removed by filtration, and mined using DPPH assay, following the method reported by the infusion was quickly cooled in a cooling tank. Subse- Xu et al. [10]. 2e sample or Trolox standard of 100 μL was quently, the pH value, catechins concentrations, and anti- −5 added to 3.9 mL of a DPPH stock solution (6 ×10 mol/L, in oxidant capacity of the tea infusion were determined. All methanol), and the reaction was left for 2 h in the dark at RT. treatments were performed in triplicate. 2e absorbance of the reaction mixture was determined at 515 nm using a spectrophotometer (UV 2550, Shimadzu 2.3. Preparation of Metal Ions or EGCG Solutions with Dif- Suzhou Corporation, Suzhou, China). Methanol was used as ferent Concentrations. 2e mixed solutions of EGCG the blank. 2e total antioxidant capacity was expressed as mg (50 mg/L) and different metal ions (5, 10, 20, 40, and 80 mg/ Trolox equivalents/L. Journal of Chemistry 3 2.7. Statistical Analysis. All analyses were carried out in lessening of CO dissolved in it [18]. For another, the ex- triplicate, and the results were recorded as mean± standard traction of some components from green tea, such as amino deviation (SD). 2e analysis of significant differences acids, phenols, and alkaloids, can also affect final pH of tea (p< 0.05) between the means was performed by one-way infusion differently. 2is may be attributed to the pH analysis of variance (ANOVA) using SPSS statistics (version buffering capacity of green tea according to Vuong et al. [17], 16, SPSS Inc., Chicago, IL, USA), and all the figures were and similar results for black tea were also reported by Liang plotted by GraphPad Prism (version 9.00, GraphPad Soft- and Xu [23]. ware Inc., San Diego, CA). 2e concentrations of total catechins and EGCG in green tea infusion brewed with above types of water were much different (see Figures 2(a) and 2(b)). On the whole, the 3. Results and Discussion higher pH value of the water and the lower concentrations of the total catechins and EGCG in green tea infusions were 3.1. <e Physicochemical Properties of Water Samples. found. In particular, the concentrations of total catechins Seven types of water were chosen to brew green tea to and EGCG in the tea infusions brewed by MW1 and MW2 understand the relationship of water and tea infusion in the were greatly lower than those brewed by the other types of present study. 2ese types of water varied greatly in the water. Similar results were also found in green tea infusion, mineral composition and pH, as shown in Table 1. 2+ 2+ + oolong tea infusion, and black tea infusion brewed by 2e types of water contained metal ions Ca , Cu , K , 2+ + mineral water [10], as well as even all the six types of tra- Mg , and Na with different concentrations, among which 2+ 2+ ditional tea in China [24]. On one hand, it was due to the fact Cu was very little and could be ignored, whereas Ca was that the stability of catechins is pH-dependent [9, 10]. Be- the dominant ion except only for MW2 (mineral water 2). It cause of the epimerization and degradation reaction at could be found that MW1 (mineral water 1) and MW2 had higher pH value [25], usually the catechins were unstable the most minerals with total ions concentrations of above when pH> 6.0, and lowering the pH of tea infusion could 90 mg/L, followed by TW (tap water). MW1 had the highest 2+ 2+ help increase the stability of catechins in tea infusion concentrations of Ca and Mg , while MW2 had the + + [26–28]. On the other hand, metal ions in water also affected highest concentrations of K and Na . 2e concentrations of the existence of catechins. 2ere were significant negative these cations were almost all above 40 mg/L. TW also 2+ correlations between metal ions concentration and extrac- contained quite a lot of Ca with a concentration of 2+ 2+ tion yield of total catechins (Ca :r � −0.757, p< 0.05; Mg : 25.43± 1.17 mg/L. However, for DW (distilled water), the 2+ r � −0.939, p< 0.01) and EGCG (Ca : r � −0.755, p< 0.05; concentrations of above ions were very low and even zero, 2+ Mg : r � −0.949, p< 0.01). Mossion et al. [18] reported that similar to PW (purified water). the higher the mineral content in the water, the lower the 2e pH values of MW1 and MW2 were higher than 7.5, extraction yield of total polyphenols in tea infusion. Yasuda while those of DW and MSW (mountain spring water) were et al. [29] studied the HPLC peaks of catechins in the absence below 6.0, and other types of water were between 6.0 and 7.0. 2+ 2+ 3+ and presence of metal cations (Cu , Fe , and Fe ) and It was not difficult to find that the trend of pH was strikingly found that HPLC intensities of esterified catechins reduced similar to the minerals content mentioned above. 2ere were markedly with the increasing of metal ions. significant positive correlations between the pH values and 2+ 2e results of total antioxidant activity, analyzed in the concentration of total ions (r � 0.909, p< 0.01), Ca DPPH assay, of tea infusions, are shown in Figure 2(c). (r � 0.830, p< 0.05), and Na (r � 0.852, p< 0.05). We Similarly, the significant differences (p< 0.05) between the supposed that the obvious differences of pH could partly be + + tea infusions brewed with different types of water could also attributed to such alkali (K and Na ) and alkaline earth 2+ 2+ be found, and there was significant positive correlation (Ca and Mg ) metal ions in the types of water, and their (r � 0.836, p< 0.05) between the antioxidant capacity and existence could promote the alkalinity in aqueous solution. the concentrations of the total catechins in green tea infu- Plusquellec et al. [22] also found that higher pH would be + + sions, which indicated that the catechins were the main obtained if alkali ions such as Na and K were present in the antioxidant components of the green tea infusion. Cate- pore solution of concrete. chins, accounting for 70–80% of tea polyphenols, had been demonstrated to be the main antioxidant components of 3.2. Effect of Different Water Samples on Catechins Concen- green tea infusion in previous studies [9, 10, 30]. tration and Antioxidant Capacity of Green Tea Infusion. However, it was worth noting that there were a few Just as mentioned above, the types of water selected in the contradictions between the results of total catechins (see Figure 2(a)) and antioxidant activity (see Figure 2(c)), present study varied greatly from each other in pH value, ranging from 5.17 to 7.97 (see Table 1). After tea brewing, the particularly for MW1 and MW2. 2e tea infusion of MW2 pH value of their corresponding tea infusion changed sig- contained much more total catechins than MW1, while its nificantly and ranged from 6.06 to 6.96 (see Figure 1). It antioxidant activity was significantly lower than that of indicated that the gap between the pH values of different MW1. It implied that the antioxidant activity of green tea types of water was narrowed greatly after tea brewing. 2is was originated from catechins though, affected greatly by phenomenon of neutralization may be caused by the tea other factors as well, such as pH or ions of solution system. brewing process. For one thing, the pH of water itself can get 2e influence of pH and metal ions of sample solution on the rise after heating, especially boiling, due to the substantial antioxidant capacity determined by DPPH assay had been 4 Journal of Chemistry Table 1: 2e mineral concentrations (mg/L) and pH value of different types of water. 2+ 2+ + 2+ + Water Ca Cu K Mg Na pH f b f f f f DW 0.04± 0.00 0.00± 0.00 0.00± 0.00 0.08± 0.04 0.00± 0.00 5.17± 0.07 f b f g f d PW 0.08± 0.04 0.01± 0.01 0.01± 0.01 0.01± 0.00 0.00± 0.00 5.94± 0.03 b a b c c c TW 25.43± 1.17 0.05± 0.00 6.46± 2.42 3.49± 0.20 8.50± 0.18 6.83± 0.08 d b d d d c NW 13.22± 0.61 0.00± 0.00 1.04± 0.01 2.23± 0.06 1.92± 0.03 6.95± 0.07 e b e e e e MSW 3.72± 0.17 0.00± 0.00 0.22± 0.13 1.49± 0.03 0.83± 0.01 5.57± 0.03 a b c a b b MW1 34.00± 0.46 0.00± 0.00 1.59± 0.54 38.06± 0.73 18.91± 0.16 7.63± 0.08 c b a b a a MW2 18.87± 1.02 0.00± 0.00 28.48± 0.42 12.64± 0.43 32.60± 0.42 7.97± 0.05 DW: distilled water; PW: purified water; TW: tap water; NW: natural water; MSW: mountain spring water; MW1: mineral water 1; MW2: mineral water 2. a, b, c, d, e, f Data are means (±SD) of three replicates. Different letters in the same column indicate significant differences between mean values (p< 0.05). ** ** ns ** ** DW PW TW NW MSW MW1 MW2 Water Samples Water Tea infusion Figure 1: 2e pH values of types of water and tea infusions with corresponding water. DW: distilled water; PW: purified water; TW: tap water; NW: natural water; MSW: mountain spring water; MW1: mineral water 1; MW2: mineral water 2. 2e marks above the column show ∗ ∗∗ the significance of differences between water and tea infusion, ns indicates p> 0.05, indicates p< 0.05, and indicates p< 0.01. ab ab 0 0 DW PW TW NW MSW MW1 MW2 DW PW TW NW MSW MW1 MW2 Water Samples Water Samples (a) (b) Figure 2: Continued. Content (mg/L) PH value Content (mg/L) Journal of Chemistry 5 bc DW PW TW NW MSW MW1 MW2 Water Samples (c) Figure 2: 2e contents of total catechins (a), EGCG (b), and antioxidant activity (c) of tea infusions brewed with different types of water. DW: distilled water; PW: purified water; TW: tap water; NW: natural water; MSW: mountain spring water; MW1: mineral water 1; MW2: a,b,c,d mineral water 2. Different letters above the column indicate significant differences between tea infusions brewed with different types of water (p< 0.05). 2+ 2+ reported widely [12, 31, 32]. Our study found that there were metal ions (such as Ca and Mg ) would influence the significant negative correlations between the DPPH anti- correct evaluation for the antioxidant capacity of EGCG oxidant activity of tea infusions and the pH values of types of solutions or tea infusions. 2e higher concentrations of water (r � −0.957, p< 0.001), which confirmed the effect of metal ions may result in higher antioxidant capacity. pH. When it came to ions, the total ions concentrations of MW1 and MW2 did not show difference (p> 0.05) yet. But 2+ 2+ 2+ 2+ 3.4. Effect of Ca and Mg on the Antioxidant Capacity of the dominant ions were Ca and Mg in MW1, whereas + + EGCG Solutions with Different Concentrations. It seemed the dominant ions were Na and K in MW2 as mentioned 2+ 2+ that Ca and Mg had potential for improving the anti- above. Maybe different ions would exert different effects on oxidant activity of EGCG solution. To confirm it, the effect of the antioxidant activity. To illustrate it, here taking EGCG the two cations on the antioxidant activity of EGCG solu- monomer as an example, the specific effect of different metal tions with different concentrations (ranging 0–100 mg/L) ions on the antioxidant activity of EGCG solution was was further investigated. further studied. 2+ 2+ 2e cations of Ca and Mg themselves possessed certain antioxidant capacity, which increased with their 3.3. Effect of Different Types of Metal Ions and <eir Con- concentrations (see Figures 4(a) and 4(b)). 2ere were centrations on the Antioxidant Capacity of EGCG Solutions. significant positive correlations between the DPPH values 2+ 2+ + + 2+ Metal ions Ca , Mg , Na , and K were selected to in- and the concentrations of Ca (r � 0.982, p< 0.01) and 2+ vestigate their effects on the antioxidant capacity of EGCG Mg (r � 0.987, p< 0.01). 2e significant positive correla- 2+ 2+ solution of 50 mg/L, which was the dominant composition of tions (Ca :r � 0.963, p< 0.01; Mg : r � 0.904, p< 0.05) still catechins and one of the major antioxidant components in existed when EGCG was added to them, respectively. It 2+ 2+ 2+ green tea [9, 10]. As shown in Figure 3, addition of Ca and indicated that the potential of Ca and Mg to improve the 2+ Mg could enhance the antioxidant capacity of EGCG antioxidant capacity of EGCG may be just due to their 2+ solutions of 50 mg/L with a dose effect, especially Ca . 2e additive effect with EGCG. 2+ 2+ antioxidant capacity of EGCG solutions increased by 16% 2e effects of Ca and Mg at 40 mg/L on the anti- 2+ 2+ and 10% with addition of 80 mg/L Ca or Mg . Similar oxidant capacity of EGCG with different concentrations results were also concluded by Kumamoto et al. [12]. 2ey were also analyzed, as shown in Figure 5. It could be found 3+ 2+ 2+ 2+ −6 2+ 2+ found that Al , Mg , Mn , and Cu with 8.06 ×10 M that addition of Ca /Mg (40 mg/L) greatly enhanced the could increase the antioxidant capacity of EGCG solutions. antioxidant capacity of EGCG solution with different con- 2+ However, the influence of different concentrations of metal centrations, particularly Ca . 2e antioxidant capacity of + + ions was not reported in their study. Addition of Na and K EGCG solution rose by 51.58± 6.02% and 39.83± 9.42% on 2+ 2+ was found to have little influence on the antioxidant capacity average due to the addition of Ca or Mg , respectively. of EGCG solutions. 2e results could explain well the 2e higher the EGCG concentration was, the higher the rise 2+ 2+ contradictions in Figure 2. rate was found. 2e results implied that Ca or Mg 2e differences in the effect of metal ions on the anti- improved the antioxidant capacity of EGCG solution oxidant capacity of EGCG solutions may be due to the through synergistic effect rather than additive effect formation of different metal complexes with catechins and (Figure S1). Besides, the concentration of EGCG played a the change in oxidation potentials [12]. 2e existence of dominant role during the binary interactions. 2e mg Trolox equivalents (L) 6 Journal of Chemistry 150 150 2+ 2+ Ca Mg ** ns ns ns ** ns ** ns 100 100 50 50 0 0 0 5 10 20 40 80 0 5 10 20 40 80 Ions concentration (mg/L) Ions concentration (mg/L) 150 150 + + K Na ns ns ns ns ns ns ns ns ns ns 100 100 50 50 0 0 0 5 10 20 40 80 0 5 10 20 40 80 Ions concentration (mg/L) Ions concentration (mg/L) Figure 3: Effect of different metal ions on the antioxidant activity of EGCG solutions of 50 mg/L. R1/R0: the antioxidant activity of EGCG solution added with/without metal ion, respectively. 2e marks above the column show the significance of differences, ns indicates p> 0.05, ∗ ∗∗ indicates p< 0.05, and indicates p< 0.01. 250 250 200 200 150 150 c a b ab a 100 100 50 50 10 a 10 8 8 ab ab 6 6 bc bc 4 4 2 2 0 0 010 20 40 80 0 10204080 2+ 2+ Ca concentration (mg/L) Mg concentration (mg/L) CK CK +EGCG +EGCG (a) (b) 2+ 2+ Figure 4: Effect of Ca (a) and Mg (b) with different concentrations on the antioxidant activity of EGCG solutions of 50 mg/L. CK: a,b,c,d control check, ion solution without EGCG; +EGCG: ion solution with EGCG. Different letters above the column indicate significant differences among different concentrations of ions (p< 0.05). mg Trolox equivalents (L) R1/R0 (%) R1/R0 (%) R1/R0 (%) R1/R0 (%) mg Trolox equivalents (L) Journal of Chemistry 7 ** ** ** ** ** ** ** ** ** ns ns 0 10204080 100 EGCG concentration (mg/L) CK 2+ +Ca 2+ +Mg 2+ 2+ Figure 5: Effect of Ca and Mg of 40 mg/L on the antioxidant activity of EGCG solutions with different concentrations. CK: control 2+ 2+ 2+ 2+ check, EGCG solution without ion; +Ca : EGCG solution with Ca ; +Mg : EGCG solution with Mg . 2e marks above the column show 2+ 2+ ∗ ∗∗ the significance of differences between CK with +Ca or +Mg , ns indicates p> 0.05, indicates p< 0.05, and indicates p< 0.01. synergistic effects were more remarkable at a higher con- Acknowledgments centration of EGCG. 2is research was funded by the Natural Science Foundation of Zhejiang (LR17C160001), the Key Research and Devel- 4. Conclusions opment Program of Zhejiang (2019C02072), the Agricul- tural Major Technologies Cooperative Extension of Zhejiang 2e green tea infusions, prepared with different types of (2018XTTGCY02), and the Innovation Project for Chinese water, showed different antioxidant capacities. On one hand, Academy of Agricultural Sciences. brewing water affected the yield of total catechins, particularly EGCG, to impact on the antioxidant capacity of tea infusion indirectly. 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De Weerdt, “Determination of the pH and the free alkali metal content in the pore solution of concrete: review and experimental comparison,” Cement and Concrete Research, vol. 96, pp. 13–26, 2017. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Chemistry Hindawi Publishing Corporation

Effect of Brewing Water on the Antioxidant Capacity of Green Tea Infusion with DPPH Assay

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Copyright © 2022 Qing-Qing Cao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Hindawi Journal of Chemistry Volume 2022, Article ID 7736117, 8 pages https://doi.org/10.1155/2022/7736117 Research Article Effect of Brewing Water on the Antioxidant Capacity of Green Tea Infusion with DPPH Assay 1,2 1 1,3 1 1 Qing-Qing Cao , Yan-Qing Fu, Cheng-Bin Zhang, Yan Zhu, Jun-Feng Yin , 4 5 1 Daniel Granato, Predrag Putnik, and Yong-Quan Xu Tea Research Institute Chinese Academy of Agricultural Sciences, Key Laboratory of Tea Biology and Resources Utilization, Ministry of Agriculture, Hangzhou 310008, China Graduate School of Chinese Academy of Agricultural Sciences, Beijing 100081, China College of Life and Environmental Science, Hangzhou Normal University, Hangzhou 310036, China Department of Biological Sciences, Faculty of Science and Engineering, University of Limerick, Limerick V94T9PX, Ireland Department of Food Technology, University North, Koprivnica 48000, Croatia Correspondence should be addressed to Jun-Feng Yin; yinjf@tricaas.com and Yong-Quan Xu; yqx33@126.com Received 26 July 2021; Accepted 27 November 2021; Published 4 January 2022 Academic Editor: Damião Pergentino de Sousa Copyright © 2022 Qing-Qing Cao et al. 2is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Brewing water plays a crucial role in flavor and potential healthy functions of tea infusion. In this study, seven water samples with different physicochemical properties were selected to brew green tea. Results showed that the brewing water with higher minerals level and pH value would reduce the yield of catechins in tea infusion, which in turn caused the decrease of antioxidant activity to a large extent. Besides, it was found that EGCG, as a major contributor to the antioxidant activity of green tea infusion, was 2+ 2+ influenced differently by different metal ions, among which Ca /Mg could enhance the antioxidant activity of EGCG solutions 2+ with different concentration through synergistic effect, particularly Ca , and the effect was more markable at a higher EGCG concentration. 2ese results offered theoretical direction to the selection of tea brewing water for consumers and gave a new sight to the effects of metal ions on the antioxidant capacity of EGCG. ions in brewing water [8–14]. 2is susceptibility is mainly 1. Introduction due to the instability of catechins, including degradation, Now, apart from water, tea has become the most widely oxidation, and epimerization [9, 15]. consumed beverage all over the world [1]. Green tea is a kind On the one hand, pH is an important factor affecting the of unfermented tea and one of the most popular kinds of tea stability of catechins during tea brewing. 2rough the study due to its distinct flavor and powerful healthcare functions of the reaction kinetics on the catechins of green tea infu- [2–4]. 2e health benefits of green tea owe a great deal to its sion, Komatsu et al. [16] found that the catechins would degrade when pH was above 6.0, and they were more stable bioactive substances, such as theanine and catechins, which attract more and more researchers to study their various when pH was below 5.0. It indicated that the stability of potential in healthy benefits [5, 6]. As a kind of efficient catechins in aqueous solutions was pH-dependent to a great antioxidant, catechins have been applied to food preserva- extent [9]. Usually, catechins were stable at weak acid tion and medical treatment [7]. Antioxidant capacity of condition (pH 3.0–5.0); when pH was lower or higher, the green tea is mostly originated from the total catechins, stability of catechins would be affected [17]. among which EGCG plays a dominant role. On the other hand, metal ions also act on catechins However, the antioxidant activity of green tea is sus- stability and antioxidant capacity of tea infusion. It was ceptible to various environmental conditions during pro- found that both pH and conductivity of brewing water could cessing, storage, and brewing, such as pH, temperature, and influence the antioxidant capacity of tea infusions negatively 2 Journal of Chemistry [10]. Significant negative correlations between mineral L) were used to study the effect of the types and concen- concentration and the extraction yield of polyphenols in tea trations of metal ions on the antioxidant activity of EGCG infusion were reported by Mossion et al. [18]. But the study solutions. pointed that the effect of metal ions on the antioxidant 2e mixed solutions of EGCG (10, 20, 40, 50, 80, and 2+ 2+ activity of EGCG solution was very limited. 100 mg/L) and Ca /Mg ions (10, 20, 40, and 80 mg/L) 2+ 2+ 2is study aimed to investigate the effect of different were used to study the effect of Ca /Mg ions on the types of water on the catechins concentration and the an- antioxidant activity of EGCG solution with different tioxidant capacity of green tea infusion and further explore concentrations. the effect of metal ions on the antioxidant capacity of EGCG All the concentrations mentioned above were the final solution. Seven types of water with different pH value and concentrations in (mixed) solutions, and all the sample metal ions were chosen for tea brewing. 2e differences of solutions were prepared with pure water. 2e sample so- total catechins extraction yield and antioxidant capacity of lutions obtained were used for conducting the analysis of green tea infusion brewed with different waters were antioxidant activity using DPPH assay in triplicate. compared. Afterwards, the addition of different metal ions was performed to investigate their influences on the anti- 2.4. Determination of Metal Ions and pH. 2e metal ions in oxidant capacity of EGCG monomer solution. 2e results these seven types of water were determined by using In- would reveal the influence of metal ions on the antioxidant ductively Coupled Plasma Mass Spectrometry with a charge- capacity of catechins and tea infusion, which could provide injection device detector (ICP-MS, 2ermo Jarrell Ash knowledge and guidance on the selection of water when Corp., USA), as described in our previous work [20]. 2e brewing green tea. detailed conditions were as follows: the maximum inte- gration times of the low wavelength and high wavelength 2. Materials and Methods were set as 15 s and 5 s, respectively. 2e nebuliser pressure was set at 28 psi. 2e pump speed was 100 r/min. 2e 2.1. Reagents. 1,1-Diphenyl-2-picrylhydrazyl (DPPH), auxiliary gas flow was set as medium (1 L/min), and the RF (−)-epigallocatechin gallate (EGCG), and Trolox (6-hy- power was 1150 W. droxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) were 2e pH values of different waters and tea infusions were purchased from Sigma (Shanghai, China). Methanol, dried determined using a pH meter (SG2, Mettler-Toledo In- CaCl , MgCl , KCl, and NaCl were purchased from 2 2 struments (Shanghai) Co., Ltd., Shanghai, China). 2e buffer Shanghai Suke Chemical Co., Ltd. (Shanghai, China). Green solutions at pH 4.01 and 7.01 (Mettler-Toledo) were used to tea was obtained from the Tea Research Institute of the calibrate the pH meter. Chinese Academy of Agricultural Sciences. Seven types of water used for the present study were obtained from dif- ferent water sources: distilled water (DW) from Guangzhou 2.5. Determination of Catechins Concentration. Catechins Watson’s Food & Beverage Co., Ltd. (Guangzhou, China); concentration in different tea infusions was determined by pure water (PW) from Hangzhou Wahaha Group Co., Ltd. using high performance liquid chromatography (HPLC, (Hangzhou, China); tap water (TW) from Hangzhou; nat- Shimadzu LC-20A) with an ultraviolet detector (SPD-10A, ural water (NW), Nongfu Spring, from Nongfu Spring Co., Shimadzu Suzhou Corporation, Suzhou, China) [21]. 2e Ltd. (Hangzhou, China); mountain spring water (MSW), TM HPLC conditions were as follows: column: Diamonsil C18 Hupao Cool Spring, from Hangzhou Tongsheng Water Co., column (4.6 × 250 mm, 5μm, Waters); injection volume: Ltd. (Hangzhou, China); mineral water 1 (MW1) from 10μL; temperature: 35 C; mobile phase A: 2% acetic acid; Kunlun Mountains Mineral Water Co., Ltd. (Geermu, mobile phase B: acetonitrile 100%. 2e following elution China); and mineral water 2 (MW2) from Tibet 5100 Water gradient plan was adopted: 0–16 min, 6.5% B; 16–25 min, 15% Resources Holdings Ltd. (Dangxiong, China). B; and 25–30 min, 6.5% B. Post-run-time was 5 min. 2e flow rate was 1 mL/min. 2e detection wavelength was set as 280 nm. Before injection, the cooled tea infusion should be 2.2. Preparation of Green Tea Infusion. According to the filtered through the 0.22μm Millipore filter. Chinese national standards of tea sensory evaluation [19], the tea leaves were brewed with a leaf/water ratio of 1 : 50 (w/ w) by using different boiling water (DW, PW, TW, NW, 2.6. Determination of Antioxidant Activity. 2e antioxidant MSW, MW1, and MW2) for 5 min at room temperature capacity of the tea infusion or EGCG solution was deter- (RT, 25± 2 C). 2e leaves were removed by filtration, and mined using DPPH assay, following the method reported by the infusion was quickly cooled in a cooling tank. Subse- Xu et al. [10]. 2e sample or Trolox standard of 100 μL was quently, the pH value, catechins concentrations, and anti- −5 added to 3.9 mL of a DPPH stock solution (6 ×10 mol/L, in oxidant capacity of the tea infusion were determined. All methanol), and the reaction was left for 2 h in the dark at RT. treatments were performed in triplicate. 2e absorbance of the reaction mixture was determined at 515 nm using a spectrophotometer (UV 2550, Shimadzu 2.3. Preparation of Metal Ions or EGCG Solutions with Dif- Suzhou Corporation, Suzhou, China). Methanol was used as ferent Concentrations. 2e mixed solutions of EGCG the blank. 2e total antioxidant capacity was expressed as mg (50 mg/L) and different metal ions (5, 10, 20, 40, and 80 mg/ Trolox equivalents/L. Journal of Chemistry 3 2.7. Statistical Analysis. All analyses were carried out in lessening of CO dissolved in it [18]. For another, the ex- triplicate, and the results were recorded as mean± standard traction of some components from green tea, such as amino deviation (SD). 2e analysis of significant differences acids, phenols, and alkaloids, can also affect final pH of tea (p< 0.05) between the means was performed by one-way infusion differently. 2is may be attributed to the pH analysis of variance (ANOVA) using SPSS statistics (version buffering capacity of green tea according to Vuong et al. [17], 16, SPSS Inc., Chicago, IL, USA), and all the figures were and similar results for black tea were also reported by Liang plotted by GraphPad Prism (version 9.00, GraphPad Soft- and Xu [23]. ware Inc., San Diego, CA). 2e concentrations of total catechins and EGCG in green tea infusion brewed with above types of water were much different (see Figures 2(a) and 2(b)). On the whole, the 3. Results and Discussion higher pH value of the water and the lower concentrations of the total catechins and EGCG in green tea infusions were 3.1. <e Physicochemical Properties of Water Samples. found. In particular, the concentrations of total catechins Seven types of water were chosen to brew green tea to and EGCG in the tea infusions brewed by MW1 and MW2 understand the relationship of water and tea infusion in the were greatly lower than those brewed by the other types of present study. 2ese types of water varied greatly in the water. Similar results were also found in green tea infusion, mineral composition and pH, as shown in Table 1. 2+ 2+ + oolong tea infusion, and black tea infusion brewed by 2e types of water contained metal ions Ca , Cu , K , 2+ + mineral water [10], as well as even all the six types of tra- Mg , and Na with different concentrations, among which 2+ 2+ ditional tea in China [24]. On one hand, it was due to the fact Cu was very little and could be ignored, whereas Ca was that the stability of catechins is pH-dependent [9, 10]. Be- the dominant ion except only for MW2 (mineral water 2). It cause of the epimerization and degradation reaction at could be found that MW1 (mineral water 1) and MW2 had higher pH value [25], usually the catechins were unstable the most minerals with total ions concentrations of above when pH> 6.0, and lowering the pH of tea infusion could 90 mg/L, followed by TW (tap water). MW1 had the highest 2+ 2+ help increase the stability of catechins in tea infusion concentrations of Ca and Mg , while MW2 had the + + [26–28]. On the other hand, metal ions in water also affected highest concentrations of K and Na . 2e concentrations of the existence of catechins. 2ere were significant negative these cations were almost all above 40 mg/L. TW also 2+ correlations between metal ions concentration and extrac- contained quite a lot of Ca with a concentration of 2+ 2+ tion yield of total catechins (Ca :r � −0.757, p< 0.05; Mg : 25.43± 1.17 mg/L. However, for DW (distilled water), the 2+ r � −0.939, p< 0.01) and EGCG (Ca : r � −0.755, p< 0.05; concentrations of above ions were very low and even zero, 2+ Mg : r � −0.949, p< 0.01). Mossion et al. [18] reported that similar to PW (purified water). the higher the mineral content in the water, the lower the 2e pH values of MW1 and MW2 were higher than 7.5, extraction yield of total polyphenols in tea infusion. Yasuda while those of DW and MSW (mountain spring water) were et al. [29] studied the HPLC peaks of catechins in the absence below 6.0, and other types of water were between 6.0 and 7.0. 2+ 2+ 3+ and presence of metal cations (Cu , Fe , and Fe ) and It was not difficult to find that the trend of pH was strikingly found that HPLC intensities of esterified catechins reduced similar to the minerals content mentioned above. 2ere were markedly with the increasing of metal ions. significant positive correlations between the pH values and 2+ 2e results of total antioxidant activity, analyzed in the concentration of total ions (r � 0.909, p< 0.01), Ca DPPH assay, of tea infusions, are shown in Figure 2(c). (r � 0.830, p< 0.05), and Na (r � 0.852, p< 0.05). We Similarly, the significant differences (p< 0.05) between the supposed that the obvious differences of pH could partly be + + tea infusions brewed with different types of water could also attributed to such alkali (K and Na ) and alkaline earth 2+ 2+ be found, and there was significant positive correlation (Ca and Mg ) metal ions in the types of water, and their (r � 0.836, p< 0.05) between the antioxidant capacity and existence could promote the alkalinity in aqueous solution. the concentrations of the total catechins in green tea infu- Plusquellec et al. [22] also found that higher pH would be + + sions, which indicated that the catechins were the main obtained if alkali ions such as Na and K were present in the antioxidant components of the green tea infusion. Cate- pore solution of concrete. chins, accounting for 70–80% of tea polyphenols, had been demonstrated to be the main antioxidant components of 3.2. Effect of Different Water Samples on Catechins Concen- green tea infusion in previous studies [9, 10, 30]. tration and Antioxidant Capacity of Green Tea Infusion. However, it was worth noting that there were a few Just as mentioned above, the types of water selected in the contradictions between the results of total catechins (see Figure 2(a)) and antioxidant activity (see Figure 2(c)), present study varied greatly from each other in pH value, ranging from 5.17 to 7.97 (see Table 1). After tea brewing, the particularly for MW1 and MW2. 2e tea infusion of MW2 pH value of their corresponding tea infusion changed sig- contained much more total catechins than MW1, while its nificantly and ranged from 6.06 to 6.96 (see Figure 1). It antioxidant activity was significantly lower than that of indicated that the gap between the pH values of different MW1. It implied that the antioxidant activity of green tea types of water was narrowed greatly after tea brewing. 2is was originated from catechins though, affected greatly by phenomenon of neutralization may be caused by the tea other factors as well, such as pH or ions of solution system. brewing process. For one thing, the pH of water itself can get 2e influence of pH and metal ions of sample solution on the rise after heating, especially boiling, due to the substantial antioxidant capacity determined by DPPH assay had been 4 Journal of Chemistry Table 1: 2e mineral concentrations (mg/L) and pH value of different types of water. 2+ 2+ + 2+ + Water Ca Cu K Mg Na pH f b f f f f DW 0.04± 0.00 0.00± 0.00 0.00± 0.00 0.08± 0.04 0.00± 0.00 5.17± 0.07 f b f g f d PW 0.08± 0.04 0.01± 0.01 0.01± 0.01 0.01± 0.00 0.00± 0.00 5.94± 0.03 b a b c c c TW 25.43± 1.17 0.05± 0.00 6.46± 2.42 3.49± 0.20 8.50± 0.18 6.83± 0.08 d b d d d c NW 13.22± 0.61 0.00± 0.00 1.04± 0.01 2.23± 0.06 1.92± 0.03 6.95± 0.07 e b e e e e MSW 3.72± 0.17 0.00± 0.00 0.22± 0.13 1.49± 0.03 0.83± 0.01 5.57± 0.03 a b c a b b MW1 34.00± 0.46 0.00± 0.00 1.59± 0.54 38.06± 0.73 18.91± 0.16 7.63± 0.08 c b a b a a MW2 18.87± 1.02 0.00± 0.00 28.48± 0.42 12.64± 0.43 32.60± 0.42 7.97± 0.05 DW: distilled water; PW: purified water; TW: tap water; NW: natural water; MSW: mountain spring water; MW1: mineral water 1; MW2: mineral water 2. a, b, c, d, e, f Data are means (±SD) of three replicates. Different letters in the same column indicate significant differences between mean values (p< 0.05). ** ** ns ** ** DW PW TW NW MSW MW1 MW2 Water Samples Water Tea infusion Figure 1: 2e pH values of types of water and tea infusions with corresponding water. DW: distilled water; PW: purified water; TW: tap water; NW: natural water; MSW: mountain spring water; MW1: mineral water 1; MW2: mineral water 2. 2e marks above the column show ∗ ∗∗ the significance of differences between water and tea infusion, ns indicates p> 0.05, indicates p< 0.05, and indicates p< 0.01. ab ab 0 0 DW PW TW NW MSW MW1 MW2 DW PW TW NW MSW MW1 MW2 Water Samples Water Samples (a) (b) Figure 2: Continued. Content (mg/L) PH value Content (mg/L) Journal of Chemistry 5 bc DW PW TW NW MSW MW1 MW2 Water Samples (c) Figure 2: 2e contents of total catechins (a), EGCG (b), and antioxidant activity (c) of tea infusions brewed with different types of water. DW: distilled water; PW: purified water; TW: tap water; NW: natural water; MSW: mountain spring water; MW1: mineral water 1; MW2: a,b,c,d mineral water 2. Different letters above the column indicate significant differences between tea infusions brewed with different types of water (p< 0.05). 2+ 2+ reported widely [12, 31, 32]. Our study found that there were metal ions (such as Ca and Mg ) would influence the significant negative correlations between the DPPH anti- correct evaluation for the antioxidant capacity of EGCG oxidant activity of tea infusions and the pH values of types of solutions or tea infusions. 2e higher concentrations of water (r � −0.957, p< 0.001), which confirmed the effect of metal ions may result in higher antioxidant capacity. pH. When it came to ions, the total ions concentrations of MW1 and MW2 did not show difference (p> 0.05) yet. But 2+ 2+ 2+ 2+ 3.4. Effect of Ca and Mg on the Antioxidant Capacity of the dominant ions were Ca and Mg in MW1, whereas + + EGCG Solutions with Different Concentrations. It seemed the dominant ions were Na and K in MW2 as mentioned 2+ 2+ that Ca and Mg had potential for improving the anti- above. Maybe different ions would exert different effects on oxidant activity of EGCG solution. To confirm it, the effect of the antioxidant activity. To illustrate it, here taking EGCG the two cations on the antioxidant activity of EGCG solu- monomer as an example, the specific effect of different metal tions with different concentrations (ranging 0–100 mg/L) ions on the antioxidant activity of EGCG solution was was further investigated. further studied. 2+ 2+ 2e cations of Ca and Mg themselves possessed certain antioxidant capacity, which increased with their 3.3. Effect of Different Types of Metal Ions and <eir Con- concentrations (see Figures 4(a) and 4(b)). 2ere were centrations on the Antioxidant Capacity of EGCG Solutions. significant positive correlations between the DPPH values 2+ 2+ + + 2+ Metal ions Ca , Mg , Na , and K were selected to in- and the concentrations of Ca (r � 0.982, p< 0.01) and 2+ vestigate their effects on the antioxidant capacity of EGCG Mg (r � 0.987, p< 0.01). 2e significant positive correla- 2+ 2+ solution of 50 mg/L, which was the dominant composition of tions (Ca :r � 0.963, p< 0.01; Mg : r � 0.904, p< 0.05) still catechins and one of the major antioxidant components in existed when EGCG was added to them, respectively. It 2+ 2+ 2+ green tea [9, 10]. As shown in Figure 3, addition of Ca and indicated that the potential of Ca and Mg to improve the 2+ Mg could enhance the antioxidant capacity of EGCG antioxidant capacity of EGCG may be just due to their 2+ solutions of 50 mg/L with a dose effect, especially Ca . 2e additive effect with EGCG. 2+ 2+ antioxidant capacity of EGCG solutions increased by 16% 2e effects of Ca and Mg at 40 mg/L on the anti- 2+ 2+ and 10% with addition of 80 mg/L Ca or Mg . Similar oxidant capacity of EGCG with different concentrations results were also concluded by Kumamoto et al. [12]. 2ey were also analyzed, as shown in Figure 5. It could be found 3+ 2+ 2+ 2+ −6 2+ 2+ found that Al , Mg , Mn , and Cu with 8.06 ×10 M that addition of Ca /Mg (40 mg/L) greatly enhanced the could increase the antioxidant capacity of EGCG solutions. antioxidant capacity of EGCG solution with different con- 2+ However, the influence of different concentrations of metal centrations, particularly Ca . 2e antioxidant capacity of + + ions was not reported in their study. Addition of Na and K EGCG solution rose by 51.58± 6.02% and 39.83± 9.42% on 2+ 2+ was found to have little influence on the antioxidant capacity average due to the addition of Ca or Mg , respectively. of EGCG solutions. 2e results could explain well the 2e higher the EGCG concentration was, the higher the rise 2+ 2+ contradictions in Figure 2. rate was found. 2e results implied that Ca or Mg 2e differences in the effect of metal ions on the anti- improved the antioxidant capacity of EGCG solution oxidant capacity of EGCG solutions may be due to the through synergistic effect rather than additive effect formation of different metal complexes with catechins and (Figure S1). Besides, the concentration of EGCG played a the change in oxidation potentials [12]. 2e existence of dominant role during the binary interactions. 2e mg Trolox equivalents (L) 6 Journal of Chemistry 150 150 2+ 2+ Ca Mg ** ns ns ns ** ns ** ns 100 100 50 50 0 0 0 5 10 20 40 80 0 5 10 20 40 80 Ions concentration (mg/L) Ions concentration (mg/L) 150 150 + + K Na ns ns ns ns ns ns ns ns ns ns 100 100 50 50 0 0 0 5 10 20 40 80 0 5 10 20 40 80 Ions concentration (mg/L) Ions concentration (mg/L) Figure 3: Effect of different metal ions on the antioxidant activity of EGCG solutions of 50 mg/L. R1/R0: the antioxidant activity of EGCG solution added with/without metal ion, respectively. 2e marks above the column show the significance of differences, ns indicates p> 0.05, ∗ ∗∗ indicates p< 0.05, and indicates p< 0.01. 250 250 200 200 150 150 c a b ab a 100 100 50 50 10 a 10 8 8 ab ab 6 6 bc bc 4 4 2 2 0 0 010 20 40 80 0 10204080 2+ 2+ Ca concentration (mg/L) Mg concentration (mg/L) CK CK +EGCG +EGCG (a) (b) 2+ 2+ Figure 4: Effect of Ca (a) and Mg (b) with different concentrations on the antioxidant activity of EGCG solutions of 50 mg/L. CK: a,b,c,d control check, ion solution without EGCG; +EGCG: ion solution with EGCG. Different letters above the column indicate significant differences among different concentrations of ions (p< 0.05). mg Trolox equivalents (L) R1/R0 (%) R1/R0 (%) R1/R0 (%) R1/R0 (%) mg Trolox equivalents (L) Journal of Chemistry 7 ** ** ** ** ** ** ** ** ** ns ns 0 10204080 100 EGCG concentration (mg/L) CK 2+ +Ca 2+ +Mg 2+ 2+ Figure 5: Effect of Ca and Mg of 40 mg/L on the antioxidant activity of EGCG solutions with different concentrations. CK: control 2+ 2+ 2+ 2+ check, EGCG solution without ion; +Ca : EGCG solution with Ca ; +Mg : EGCG solution with Mg . 2e marks above the column show 2+ 2+ ∗ ∗∗ the significance of differences between CK with +Ca or +Mg , ns indicates p> 0.05, indicates p< 0.05, and indicates p< 0.01. synergistic effects were more remarkable at a higher con- Acknowledgments centration of EGCG. 2is research was funded by the Natural Science Foundation of Zhejiang (LR17C160001), the Key Research and Devel- 4. Conclusions opment Program of Zhejiang (2019C02072), the Agricul- tural Major Technologies Cooperative Extension of Zhejiang 2e green tea infusions, prepared with different types of (2018XTTGCY02), and the Innovation Project for Chinese water, showed different antioxidant capacities. On one hand, Academy of Agricultural Sciences. brewing water affected the yield of total catechins, particularly EGCG, to impact on the antioxidant capacity of tea infusion indirectly. 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Journal of ChemistryHindawi Publishing Corporation

Published: Jan 4, 2022

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