Synergistic Antioxidant Performance of Lignin and Quercetin Mixtures

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Synergistic Antioxidant Performance of Lignin and Quercetin Mixtures Di Liu, Ying Li, Yong Qian, Yang Xiao, Shengjun Du, and Xueqing Qiu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02282 • Publication Date (Web): 02 Aug 2017 Downloaded from http://pubs.acs.org on August 8, 2017

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ACS Sustainable Chemistry & Engineering

Synergistic

Antioxidant

Performance

of

Lignin

and

Quercetin Mixtures Di Liu,† Ying Li,† Yong Qian,*,†, ‡ Yang Xiao,† Shengjun Du,† and Xueqing Qiu,*,†, ‡ †School

of Chemistry and Chemical Engineering, South China University of

Technology, 381 Wushan Road, Tianhe District, Guangzhou 510640, P. R. China ‡ State

Key Laboratory of Pulp and Paper Engineering, South China University of

Technology, 381 Wushan Road, Tianhe District, Guangzhou 510640, P. R. China E-mail: [email protected] (Y. Qian), [email protected] (X. Q. Qiu)

ACS Paragon Plus Environment


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ABSTRACT: A natural, effective and inexpensive hindered phenolic antioxidant mixture was prepared by blending lignin into quercetin. The antioxidant performance of lignin and quercetin mixture was analyzed by determining the DPPH radical scavenging capacity and a low-cost and high-efficient ratio was found to be 4:1 (w/w). After UV radiation for 4 hours, the DPPH scavenging ratio of the quercetin/lignin mixture decreased only 13.8%, while that of quercetin and lignin decreased 42.9% and 28.6%, respectively. The UV and fluorescence analysis indicated that quercetin molecules inserted into the lignin to weaken its aggregation and form new conjugated structures. Adding lignin may provide a green alternative to the expensive quercetin or synthetic antioxidants used in food, cosmetics and pharmaceuticals. KEYWORDS: Lignin, Quercetin, Antioxidant, Synergistic effect, UV radiation.


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 INTRODUCTION Natural antioxidants are widely used in food, cosmetics, pharmaceuticals due to the high activity, low toxicity and green properties, 1-4 and thus are more popular than synthetic antioxidants. As one of the most excellent natural antioxidants, quercetin is a typical flavonoid with benefits on human health including antioxidative, anticancerous, anti-inflammatory and antidiabetic activities.5-8 However, Quercetin tend to degrade under UV radiation and other severe environments.9 Therefore, several efforts have been invested to maintain its activity. The photodegradation behavior of quercetin in creams would be effectively released when it was protected by cellulose.10 Zheng and Chow prepared a chemically stable and readily water-soluble solid complex of quercetin with hydroxypropyl-b-cyclodextrin (HP-b-CD) by spray drying and it displayed excellent thermal stability.11 Zhang el al. encapsulated quercetin in the chitosan nanoparticles by ionic gelating of chitosan with tripolyphosphate anions.12 The nano complexes improved the bioavailabilty of quercetin in pharmaceutical formulation.12 Therefore, mixing quercetin with other substances will significantly improve its stability.13-15 Lignin, the unique aromatic polymer in plants, is a natural polyphenolic antioxidant as well as a natural broad-spectrum sun blocker.16-19 Studies on its antioxidative protections for materials, cosmetics, foods and pharmaceuticals attract considerable attention, especially under UV radiation.20-23 KoŠíková et al. investigated the protective effect of lignin antioxidants against H2O2-induced oxidative damage of DNA in human carcinoma cells and male rats, as well as the stabilization effects during the processing of polypropylene (PP) composites and thermo-oxidative aging of styrene-butadiene vulcanizates.20 Their work indicated that the lignin preparations show great potential as antioxidants in human diets and polymer blends. 20 Lately, Gadioli et al. compared lignin with industrial Irganox 1010 as the primary stabilizer in formulations for PP during accelerated aging and confirmed the better antioxidant performance of lignin due to its cross-linking macromolecule nature.21 Aguiébéghin et



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al. found that ethanol extracts obtained from biorefinery grass lignins could compete with commercial rosemary antioxidant extracts for food and packaging matrices.22 Moreover, self-assembling polysaccharide films were applied as active hydrogels for controlled release of antioxidant molecules.22 In previous study, it is found that lignin from different technical resources could significantly boost the performance of the sunscreen lotions and dramatically improved their photostability. 24 The synergistic effect between lignin and chemical sunscreen actives was also due to the antioxidant protection of lignin.24,25 Shahidi et al. also found the synergistic antioxidant effect between

lignin

unit

like

3-tertiary-butyl-4-hydroxyanisole

(BHA)

and

2,6-di-tertiary-butyl-4-methylphenol (BHT).26 Synergistic antioxidant effects between quercetin and small molecular such as vitamins E, C and rutin have been demonstrated.27, 28 Lignin not only has excellent antioxidant ability, but also has good photo stability. As lignin and quercetin coexist in many plants such as pine in the whole lifecycle, there might be some cooperation between them, especially under UV radiation. In this work, the antioxidant performance of quercetin, lignin and their mixtures were investigated by determining their free radical scavenging abilities. Their synergistic antioxidant behavior was conformed and their combination antioxidant effect after UV radiation was further studied. The results demonstrate low-coat lignin has potential to partially replace the expensive quercetin in natural antioxidant applications.

 EXPERIMENTAL SECTION Materials. The lignin used in this work was extracted from pine wood and purified according the procedure described in the reference.18 Simply, the pine chips were cooked by ethanol/water mixture (65:35, vol/vol) under 180 ºC for 60 min. The catalyst was 1.5wt% sulfuric acid (98 wt%). After filtering with a nylon colth, the filtrate was poured into water to precipitate lignin. The physicochemical properties of lignin and its 2D HQSC NMR spectrum are shown in Table S1 and Figure S1 respectively

in

the

Supporting

Information.


Quercetin

and

1,

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1-Diphenyl-2-picrylhydrazyl (DPPH) were purchased from Aldrich-Sigma (Shanghai, China). Deionized water with resistivity > 18 MΩ/cm was obtained from a Millipore water purification system. Other reagents and solvents were of analytical grade and purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China) without further purification. Evaluation of the Antioxidant Activities of Lignin, Quercetin and Their Mixtures. DPPH was used as the radical generator. The antioxidant activity of the lignin and quercetin was determined based on the radical-scavenging capability. 3.8mL of lignin, quercetin and their mixtures aqueous dioxane solutions with different concentrations (5-500mg/L) were mixed with 11.80 mL of a 6.1 × 10-5 mol/L DPPH methanol solution at 25 °C for 16 min and 60min respectively.18 The mixtures of lignin and quercetin were prepared by blending quercetin dioxane/water (90:10, vol/vol) solution with lignin dioxane/water (90:10, vol/vol) solution under different ratios. The concentrations of DPPH radicals at 0, 16 and 60 min were monitored at 517 nm (λ max) using a UV-vis spectrometer (Shimadzu Co., Japan). The inhibition percentage (IP) of the DPPH radical was calculated using the following equation: IP =

A2−A1+A0 A2

× 100%

(1)

A2= Absorbance at 0 min；A1= Absorbance at 16min or 60min; A0= Absorbance of the blank solution. Characterizations. The molecular weights of lignin was measured by Agilent 1100 series gel permeation chromatography (Agilent Technologies Corp., USA) with PLgel 5 μm 500 Å columns. The mobile phase was THF with a flow rate of 1 mL/min. Elemental analysis of lignin was measured using an Elementar Vario EL cube (Elementar, German). The fixed carbon content and moisture of lignin were measured by Thermogravimetric analysis (Q500, TA, USA) and the ash content was determined by muffle furnace (P330, German) with lignin ashing at 800℃. The 1H NMR spectra of lignin and quercetin and their mixtures were recorded on a NMR spectrometer (Bruker, AVANCE HD Ⅲ 600, Germany). The data was processed using the Bruker Topspin-NMR software. For 2D HQSC NMR of lignin, around 100 mg of lignin was



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dissolved in 0.6 mL of DMSO-d6. The widths of the spectra were 5000 and 20000 Hz respectively for the 1H and 13C dimensions. The UV-vis absorption spectra of quercetin, lignin and their mixtures before and after irradiating were recorded in range of 250–450 nm with the UV-vis spectrophotometer (UV-2450, Shimadzu Co., Japan). The aqueous dioxane was scanned at the same wavelength as baseline. Emission fluorescence spectra of quercetin, lignin and their mixtures were recorded on a fluorescence spectrophotometer (F-4500, Hitachi Co., Japan).The excitation wavelengths of lignin and quercetin were 291 nm and 370 nm when excited at 375 nm.

 RESULTS AND DISCUSSION The Antioxidant Activities of Lignin, Quercetin and Their Mixtures. DPPH radical assay was performed to estimate the radical scavenging ability of lignin, quercetin and their mixtures. After adding lignin and quercetin, the purple DPPH solution turned yellow and the absorbance peak at 517 nm decreased. Figure 1a shows the IP of different concentrations of lignin. Lignin at low concentration has a good free radical scavenging ability and the best concentration of lignin lies between 150mg/L-200mg/L. After 60min, its reaction with DPPH was still going on. With the increase of the concentration of lignin, the free radical scavenging rate was firstly increased and then decreased a little after 250mg/L. Usually, the antioxidant ability is not directly proportional to the concentration. One possible explanation for lignin is that the high concentration promotes the aggregation of lignin and reduces the exposure of reactive groups to DPPH.29 Since quercetin provides active hydrogen to DPPH rapidly, it has much better antioxidant performance than lignin and its free radical scavenging rate is as high as 90% even at a 15mg/L, as shown in Figure 1b. However, the poor stability and high cost of quercetin hinder its application. Lignin is thus applied to blend with quercetin to reduce the cost and keep the stability. As expected, the IP of lignin/quercetin mixture increased with the proportion of quercetin. However, the IP reached a maximum of 94.2% at 60 min when the proportion of quercetin was


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beyond 0.2, which is even better than that of pure quercetin, as shown in Figure 1c. Blending with lignin can not only lower the cost dramatically, but also maintain the antioxidant activity of quercetin. In addition, the DPPH scavenging kinetics of lignin/quercetin mixtures under different ratios were measured, as shown in Figure 2. The scavenging processes of lignin/quercetin mixtures can be fitted by the second order exponential decay functions except the mixture with ratio of 1:1, which is fitted normal exponential decay function. As shown in Table 1, the decay times of the mixtures with ratio 3:1, 4:1 are close to that of the mixture with ratio of 1:1. When the ratio of the mixture is more than 6:1, the decay time is several times longer, which indicates the free radical scavenging rate is much slower. The Antioxidant Activities of Lignin, Quercetin and Their Mixtures before and after UV Radiation. DPPH antioxidants, especially small molecules such as quercetin, are photo unstable and needed protection. After UV radiation for 4h, the antioxidant activity of quercetin and lignin both reduced significantly, while that of the mixture decreased a little, as shown in Figure 3a. Taking the scavenge time of 30 min as example, the free radical scavenging activity of quercetin and lignin was reduced by 42.9% and 28.6% respectively, while that of the mixture reduced only 13.8%, as shown in Figure 3b. The detailed calculation procedure is present in Table S2. The phenolic hydroxyl groups of antioxidants were easy to be oxidized into quinoid structures after UV radiation and their free radial scavenging activity weakened. 9 However, the three-dimensional macromolecular structure of lignin is beneficial for protecting its phenolic hydroxyl groups from photo deactivation. 24,30 Therefore, the activity reduction of lignin is less significant than quercetin. When quercetin was blended with lignin, macromolecular structure of lignin protected quercetin and quercetin inversely protected lignin to some degree too. Thus, decrease of the antioxidant activity of their mixture was less than half of that of both lignin and quercetin. The Photo-Stable Mechanism of Lignin/Quercetin Mixture. To explore the photo-stable mechanism of lignin/quercetin mixture, the UV spectra of lignin, quercetin and their mixture before and after UV radiation were obtained, as shown in



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Figure 4. After 4 hours irradiation, the characteristic peak of lignin around 280 nm had no change, only the absorbance decreased a little. However, the characteristic peak of quercetin at 375 nm underwent a gradual blue shift to 295nm, indicating the breakage of its cinnamoyl conjugated structures.9,31 Without the stablization of big cinnamoyl conjugated structure, quercetin couldn’t trap the free radicals effectively as before, thus its antioxidant ability decreased. When quercetin was blended with lignin, the characteristic peak of lignin shifted from 288 nm to 294 nm, indicating that new conjugated aromatic structures were formed. The conjugated structures between aromatic rings of quercetin and lignin were also demonstrated in their 1H NMR spectra, as shown in Figure S2. Comparatively, the aromatic rings in quercetin are electron-rich, while those in lignin are electron-poor. When lignin and quercetin form conjugated structures, the electron cloud density of aromatic rings in lignin increases and the electron cloud density of aromatic rings in quercetin decreases. Therefore, most of the aromatic hydrogen in lignin shifts to high field and that in quercetin shifts to lower field after mixing. After being irradiated by UV for 4 hours, the characteristic peak of quercetin disappeared and the conjugated aromatic peak red shifted to 300 nm. It means more conjugated structures were formed, although original cinnamoyl conjugated structures of quercetin were still broken. Therefore, the antioxidant activity could be reserved in maximum. The fluorescence quenching of lignin dioxane/water solution in the presence of quercetin was observed and conformed the aromatic combination, as shown in Figure 5. Lignin exhibited characteristic fluorescence peak at 480nm when excited at 375 nm, while the fluorescence of quercetin could be neglected. When quercetin was added into lignin dioxane/water solution, the fluorescence intensity of lignin decreased significantly. The gradual quenching process of lignin dioxane/water solution was also observed by adding different amount of quercetin, as shown in Figure S3. It indicates that quercetin molecules successfully inserted into lignin macromolecules and weakened the aggregation of lignin. The proposal mixing structure of quercetin and lignin was shown in Figure 6. Formation of lignin/quercetin complexes was beneficial for the antioxidant protection of both lignin and quercetin, especially after UV


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radiation.

 CONCLUSION Lignin and quercetin were mixed as a nature, effective and low-cost hindered phenolic antioxidant. The best ratio of lignin and quercetin was 4:1 and their free radical scavenging ability was even better than pure quercetin. Since quercetin effectively inserted into lignin and formed conjugated structures, their antioxidant property could be preserved to maximum extent under long time UV radiation. The work provides potentials for more efficient antioxidant application for lignin and reduction the antioxidant cost of quercetin.

 ASSOCIATED CONTENT Supporting Information The physicochemical properties of lignin, UV absorbance of initial and remaining DPPH radicals after being scavenged by lignin, quercetin and their mixture, 2D HQSC NMR spectra of lignin, 1H NMR spectra of lignin, quercetin and their mixtures, and fluorescence spectra of lignin in dioxane aqueous solution with increasing concentration of quercetin. This material is available free of charge via the Internet at http://pubs.acs.org/.

 AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]. * E-mail: [email protected]. Notes The authors declare no competing ﬁnancial interest.

 ACKNOWLEDGEMENTS ACS Paragon Plus Environment


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We gratefully acknowledge the financial support from the National Natural Science Foundation of China (21606089), the Guangdong Province Science and Technology Research Project of China (2014B050505006) and The Fundamental Research Funds for the Central Universities (2015ZM149)

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Captions of Table and Figures Table 1. Parameters for fitting the DPPH scavenging kinetic curves of quercetin/lignin mixtures with different ratios. Figure 1. (a) The DPPH inhibition percentage (IP) of lignin solution at different concentrations; (b) The DPPH IP of quercetin solution at different concentrations; (c)The DPPH IP of quercetin/lignin mixtures at different ratios (wL+wQ=100mg/L). Figure 2. The DPPH scavenging kinetics of quercetin/lignin mixtures at different ratios (wL + wQ =100mg/L). Figure 3. (a) The DPPH scavenging kinetics of quercetin and lignin mixtures before and after UV radiation for 4h; (b) The decrease rate of DPPH radicals after UV radiation on lignin, quercetin and their mixture at 30 min. Figure 4. The UV spectra of lignin, quercetin and their mixture before and after UV radiation for 4h. Figure 5. Fluorescence spectra of lignin, quercetin and their mixture in dioxane aqueous solution. Figure 6. Mechanism illustration of the interaction between lignin and quercetin in solution.


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Table 1.

Mass Ratio (L:Q) 1:1 3:1 4:1 6:1 8:1 11.5:1 15.6:1 1:0

A0

k1

г1(s)

k2

г2(s)

R2

0.03 0.04 0.04 0.04 0.05 0.10 0.10 0.19

0.05 0.10 0.22 0.10 0.14 0.16 0.18 0.19

24.63 45.82 55.42 434.41 464.81 378.58 520.89 760.38

0.10 0.02 0.09 0.08 0.05 0.05 0.04

45.82 246.73 46.20 50.89 37.70 48.16 100.74

0.9994 0.9998 0.9999 0.9999 0.9999 0.9995 0.9999 0.9999



Figure 1.

a

80

The DPPH IP

70

IP%-16min IP%-60min

60 50 40 30

0

100

200

300

400

500

wL- mg/L

95

b

The DPPH IP

90

IP%-16min IP%-60min

85 80 75 70 65

5

10

15

20

25

30

35

40

45

wQ - mg/L 100

c

90

The DPPH IP

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

IP%-16min IP%-60min

80 70 60 50 0.0

0.1

0.2

0.3

0.4

0.5

w Q/(w L+wQ)


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Figure 2. 0.5

Absorbance of DPPH

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


15.6:1-wL:wQ

11.5:1-wL:wQ

8:1-wL:wQ

6:1-wL:wQ

4:1-wL:wQ

3:1-wL:wQ

1:1-wL:wQ

1:0-wL:wQ

0.4 0.3 0.2 0.1 0.0

0

200

400

600

800

1000

Time (s)



Figure 3.

Absorbance of DPPH

0.5

a

0.4 0.3

after UV

L-250mg/L L+UV4h Q-10mg/L Q+UV4h L+Q L+Q+UV4h

0.2 L

0.1

L+Q

before UV Q

0.0 0

1000

2000

3000

4000

Time (s)

40

Decrease of DPPH (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

b

30 20 10 0

D-L

D-Q

D-LQ


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Figure 4. 2.5

L-0h L-4h Q-0h Q-4h L+Q-0h L+Q-4h

2.0

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1.5 1.0 0.5 0.0

250

300

350

400

450

Wavenumber (nm)



Figure 5. 250

Blank L-80mg/L Q-20mg/L L+Q

200

Intensity(a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

150 100 50 0

400

450

500

550

600

Wavenumber (nm)


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

For Table of Contents Use Only Synopsis: A natural, effective and inexpensive hindered phenolic antioxidant mixture was prepared by blending lignin into quercetin.


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Synergistic Antioxidant Performance of Lignin and Quercetin Mixtures

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