Mechanism of the interaction between insoluble wheat bran and polyphenols leading to increased antioxidant capacity

    Mechanism of the interaction between insoluble wheat bran and polyphenols leading to increased antioxidant capacity Ezgi Do˘gan, Vural G¨okmen PII: DOI: Reference:

S0963-9969(14)00826-6 doi: 10.1016/j.foodres.2014.12.037 FRIN 5640

To appear in:

Food Research International

Received date: Accepted date:

22 November 2014 23 December 2014

Please cite this article as: Do˘gan, E. & G¨okmen, V., Mechanism of the interaction between insoluble wheat bran and polyphenols leading to increased antioxidant capacity, Food Research International (2015), doi: 10.1016/j.foodres.2014.12.037

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ACCEPTED MANUSCRIPT Mechanism of the interaction between insoluble wheat bran and polyphenols leading to increased antioxidant capacity

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Ezgi Doğan, Vural Gökmen*

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Food Engineering Department, Hacettepe University, 06800 Beytepe, Ankara, Turkey

Running Title: Mechanism of the interaction between insoluble wheat bran and

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polyphenols

* Corresponding Author

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Prof. Dr. Vural Gökmen

Food Engineering Department, Hacettepe University, 06800 Beytepe, Ankara, Turkey,

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E-mail: [email protected], phone: +90 312 2977108, fax: +90 312 2977108

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ACCEPTED MANUSCRIPT Abstract This study aimed to investigate in-depth the interaction between insoluble wheat bran

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and polyphenols. Treatment with tannic acid, but not gallic acid, increased bound

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antioxidant capacity of insoluble wheat bran depending on its aqueous concentration (p<0.05). Among the beverages tested (white and red wines, black and green tea infusions), treatment with green tea infusion caused the highest increase in the total

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antioxidant capacity. Temperature, time, air and pH were found to affect significantly the reaction between insoluble wheat bran and polyphenols. The bound antioxidant

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capacity of insoluble bran increased to above 100 mmol TE.kg -1 after treatment with

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green tea infusion at optimum conditions (50 C, pH 9.0, no air flow). Concentration of free amino groups available in wheat bran significantly decreased (59.5%) after the

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treatment. The results suggested that polyphenols are oxidized to quinones under

wheat bran.

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alkaline conditions further bound to free amino groups available on the surface of

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Keywords: Insoluble wheat bran; bound antioxidant capacity; free polyphenols; green tea infusion; free amino groups

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ACCEPTED MANUSCRIPT 1. Introduction Epidemiological studies have shown that diets rich in whole grains reduce the risk of

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type 2 diabetes, obesity, cancer and cardiovascular diseases (Jacobs, Slavin, &

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Marquart, 1995; Koh-Banerjee & Rimm, 2003; Liu, et al., 1999; Meyer, et al., 2000). Whole grains, especially their bran fraction (Chandrasekara & Shahidi, 2010), contain dietary fibers in addition to antioxidant compounds. Antioxidant compounds in whole

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grains may exist in free, soluble conjugate, and insoluble bound forms. Among them,

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insoluble bound antioxidants, which are associated with cell wall materials are dominant (Bunzel, Ralph, Marita, Hatfield, & Steinhart, 2001; Sosulski, Krygier, &

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Hogge, 1982). Soluble antioxidants that are ingested with diet cause a rapid increase in plasma antioxidant capacity upon absorption in small intestine. However, this effect of

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soluble antioxidant compounds disappears within a few hours (Lotito & Frei, 2004). On

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the other hand, a significant part of antioxidant compounds bound to dietary fiber reach the colon without being digested through the small intestine (Liyana-Pathirana &

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Shahidi, 2005) and contribute to the formation of reduced environment in colon (Pérez-Jiménez & Saura-Calixto, 2005). Some part of the bound antioxidants is converted to free form by the colon microbiota, and is released slowly and continuously (Kroon, Faulds, Ryden, Robertson, & Williamson, 1997). It provides increase in the basal plasma antioxidant capacity via absorption by the system (Jacobs, Pereira, Stumpf, Pins, & Adlercreutz, 2002). Thus, antioxidants bound to dietary fiber exert effect much longer than soluble antioxidants in living organisms. Therefore, increase in the amount of antioxidants bound to dietary fiber ingested with diet has a potential significance in human health.

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ACCEPTED MANUSCRIPT The importance of ‘dietary fiber-antioxidant compounds’ complex has been recently emphasized by some researchers (Jiménez-Escrig, Rincón, Pulido, & Saura-Calixto,

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2001; Martinez-Tome, et al., 2004; Saura-Calixto, 1998; Yu, et al., 2002). Increasing the

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amount of dietary fiber or antioxidant compounds in food has also come into prominence (Acosta-Estrada, Lazo-Vélez, Nava-Valdez, Gutiérrez-Uribe, & SernaSaldívar, 2014; Anil, 2007). However, there is no in-depth study about the mechanism

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of increasing the bound antioxidant capacity of dietary fibers.

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In a recent study conducted by our group, positive interaction between soluble antioxidants and antioxidants bound to insoluble dietary fibers was observed (Çelik &

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Gökmen, 2014). This kind of interaction offer great advantages as it allows designing new dietary fiber materials with increased antioxidant capacity. However, the

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mechanism behind such interactions still remains unclear. Therefore, this study aimed

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to investigate in depth the mechanism of the interaction between insoluble wheat bran fraction and polyphenols. Insoluble wheat bran was reacted with polyphenols

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from different sources under different conditions to understand better the reaction mechanism leading to increased bound antioxidant capacity. 2. Materials and Methods 2.1. Chemicals All chemicals and solvents used were of analytical grade. Potassium peroxydisulfate, 2,2′ -azinobis

(3-ethylbenzothiazoline-6-sulfonic

acid)

(ABTS),

6-hydroxy-2,5,7,8

tetramethylchroman-2 carboxylic acid (Trolox), 2,4,6-trinitrobenzene sulfonic acid (TNBSA), leucine, Folin-Ciocalteu reagent, tannic acid, gallic acid, sodium carbonate were purchased from Sigma-Aldrich Chemie (Steinheim, Germany). Ethyl alcohol,

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ACCEPTED MANUSCRIPT methanol, n-hexane, sodium hydroxide and hydrochloric acid, sodium bicarbonate were purchased from Merck (Darmstadt, Germany). Wheat bran, red wine, white

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wine, black tea and green tea were purchased from local market. Powder of green tea

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extract was purchased from Danisco (Copenhagen, Denmark). 2.2. Preparation of insoluble wheat bran

Wheat bran was used in this study due to its rich dietary fiber content. Ground wheat

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bran was subjected to washing cycles as described in Çelik et al. (2013). After washing

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cycles, the wheat bran fraction, which is free of water and alcohol soluble substances as well as lipid phase and lipid soluble compounds, was prepared to obtain insoluble

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powder (Celik, Gokmen, & Fogliano, 2013).

2.3. Preparation of beverages rich in antioxidants and pure solutions of antioxidants

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Red wine, white wine, black tea and green tea were selected as the beverages rich in

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soluble antioxidant compounds. Red wine and white wine were used in the treatments with insoluble wheat bran fraction as it is or after ten-fold dilution (v/v) with distilled

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water. Green tea and black tea were used after brewing. A total of 3 g tea was brewed in 100 ml of boiling water for 15 min. Tea infusions were filtered through a coarse filter paper and used in the treatments with insoluble wheat bran fraction as is or after tenfold dilution (v/v) with distilled water. Aqueous solutions of green tea extract were prepared at concentrations of 0.5% and 1.0% (w/v) by dissolving appropriate amounts in distilled water. Aqueous solutions of tannic acid and gallic acid, representing polymeric and monomeric phenolic standard compounds, respectively, were prepared at concentrations of 10, 20, 50, 100, 200 μmol.L-1.

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ACCEPTED MANUSCRIPT 2.4. Treatment of insoluble wheat bran with soluble antioxidants Insoluble wheat bran was treated with beverages rich in soluble antioxidants (white

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wine, red wine, black tea, green tea) and aqueous solutions of pure antioxidants

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(tannic acid, gallic acid) prepared as explained above. A total of 50 mg insoluble wheat bran was weighed into a tube. The reaction was initiated by adding 5 ml of beverages or aqueous solutions of pure antioxidants. The reaction tube was mixed using a

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magnetic stirrer at a speed of 350 rpm at 25 C for 30 min. After reaction, the tube was

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centrifuged at 6080 xg for 2 min, and the supernatant was removed. The remaining soluble antioxidant compounds that were not bound to insoluble wheat bran were

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removed by washing four times with ethanol and water, respectively. The antioxidant capacity of the water used in the last step was measured in order to be sure that final

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precipitate was free of soluble antioxidant compounds. Then, the final precipitate of

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insoluble wheat bran fraction was lyophilized prior to measurement of antioxidant capacity. The total antioxidant capacity was measured using the direct QUENCHER

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procedure described elsewhere, and expressed as mmol Trolox equivalent kg-1 (mmol TE.kg-1) (Serpen, Gökmen, & Fogliano, 2012; Celik & Gökmen 2013). In order to understand the effect of phenoxy radical formation on the reaction, insoluble wheat bran treated with ABTS•+ radical solution was reacted with aqueous solutions of tannic acid under the conditions described above. In order to investigate the effects of different parameters, the reaction between soluble antioxidant compounds in beverage (green tea) and insoluble wheat bran fraction was carried out at different temperatures (25 C or 50 C), time (0.5 or 1 h) and pH values (2, 4, 6, 7, 8, 9, 10, 12) as well as with or without O 2 flow. In this manner,

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ACCEPTED MANUSCRIPT the optimum conditions for increasing the antioxidant capacity of insoluble wheat bran were determined. In addition, the reaction kinetics was investigated by treating

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insoluble wheat bran with two concentrations of green tea extract (0.5% and 1.0%) at

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optimum conditions. The reaction was carried out up to 3 hours and the antioxidant capacity of wheat bran was measured after 0.5, 1, 2 and 3 hours of treatment. 2.5. Determination of the binding of phenolic compounds to insoluble wheat bran

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Insoluble wheat bran fractions, untreated and treated with green tea infusion at

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optimum conditions, were analyzed for bound phenolic compounds. Analyses were performed using the QUENCHER method with Folin-Ciocalteu reagent. 10 mg of

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samples were transferred to a test tube and 0.8 ml of 0.2 M Folin-Ciocalteu reagent was added for oxidation. After 5 min, the mixture was neutralized with 1.25 ml of 20%

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aqueous Na2CO3 solution and kept at dark for 1 h. After the mixture was centrifuged at

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6080g for 2 min, the optically clear supernatant was transferred into a cuvette and the absorbance was measured at 765 nm against the solvent blank using a Shimadzu

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model 2100 variable-wavelength UV-visible spectrophotometer (Shimadzu Corp., Kyoto, Japan). The bound phenolic content was determined by means of a calibration curve prepared with gallic acid, and expressed as mg of gallic acid equivalent per kg on a dry basis. 2.6. Determination of free amino groups in insoluble wheat bran Insoluble wheat bran fractions, untreated and treated with green tea infusion at optimum conditions, were analyzed for free amino groups. Analyses were performed using TNBS assay as reported in Hermanson, 1996 (Hermanson, 1996). 10 mg of samples and 1 ml of 0.1 M sodium bicarbonate buffer solution (pH 8.5) were

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ACCEPTED MANUSCRIPT transferred to a test tube and the reaction was initiated by adding 0.5 ml of 0.01% (w/v) TNBSA. Following to incubation at 37 C for 2 h, the mixture was centrifuged at

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6080 xg for 2 min. After optically clear supernatant and 0.25 ml of the 1 N HCl was

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transferred into a cuvette, the absorbance was measured at 335 nm by using a Shimadzu model 2100 variable-wavelength UV-visible spectrophotometer (Shimadzu Corp., Kyoto, Japan). The free amino content of treated or untreated wheat bran was

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determined by means of a calibration curve prepared with leucine, and expressed as

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mmol leucine equivalent (LE) per kg on a dry basis. 2.7. Statistical Analysis

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The analytical data were reported as the mean ± standard deviation of duplicate independent measurements and were subjected to one-way ANOVA. The significance

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of mean differences was determined by Tukey HSDa post hoc test using SPSS version

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17.0. p values of <0.05 were considered statistically significant. 3. Results and Discussion

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3.1. Interaction of insoluble wheat bran with polyphenols The wheat bran used in this study was found to have an initial total antioxidant capacity of 63.0±1.8 TE.kg-1. After washing with water and alcohol, its antioxidant activity decreased to 6.8±0.2 mmol TE.kg-1.This insoluble fraction of wheat bran was treated with polyphenols in order to understand the mechanisms of reaction between insoluble wheat bran and soluble antioxidant compounds. As shown in Fig. 1a, increasing the concentration of tannic acid during the treatment (30 min at room temperature) led to a significant increase (p<0.05) in the antioxidant capacity of insoluble wheat bran. However, there were no statistically significant differences

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ACCEPTED MANUSCRIPT (p>0.05) in increasing antioxidant capacity of wheat bran when itself or its radical pretreated form was used as the insoluble material. This indicated that the reason of

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increased antioxidant capacity was not the radicals that formed on the surface of

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insoluble wheat bran. Under similar conditions, treatment with gallic acid, a monomeric form of tannic acid didn’t cause any significant increase in the antioxidant capacity (data not shown). This was probably due to the fact that tannic acid as a

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bran matrix but gallic acid could not.

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polymeric compounds, produced more quinones that enhanced its binding ability to

As shown in Fig. 1b, treatment with green tea infusion (3g/100 ml) increased significantly (p<0.05) the antioxidant capacity of insoluble wheat bran from 6.8±0.2

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mmol TE.kg-1 (control) to 18.8±0.4 mmol TE.kg-1. However, treatment with white wine

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had no statistically significant effect (p<0.05) on the antioxidant capacity of insoluble

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wheat bran. It is known that green tea infusions is rich in flavan-3-ols (epicatechin, epigallocatechin, epigallocatechin gallate) that can be oxidized to quinones and

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polymerize easily during the treatment (Wang & Ho, 2009). Comparing to control, treatment with black tea infusion and red wine also caused statistically significant increases (p<0.05) in the antioxidant capacity of insoluble wheat bran, most probably due to presence of polymeric phenolic compounds in high quantities. The effects of red wine, black tea and green tea infusions were found depending on concentration. In fact, diluted forms of these beverages were significantly less effective (p<0.05) than their undiluted forms (Fig. 1b).

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ACCEPTED MANUSCRIPT Since green tea infusion was the most efficient beverage among others tested, it was used as the source of polyphenols to determine the effects of different conditions

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(temperature, time, pH, air flow) on the antioxidant capacity of insoluble wheat bran.

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Increasing the treatment time from 30 min to 60 min caused 1.49 times and 1.96 times increase at 25 oC and 50 oC, respectively, in the antioxidant capacity of insoluble wheat bran. The highest level of antioxidant capacity was attained after the treatment of

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insoluble wheat bran with green tea infusion at 50 oC for 60 min (Fig. 2). At these

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conditions (50 oC, 60 min), changing the pH value of the reaction medium from 2.0 to 12.0 had strong influence on the resulting antioxidant capacity (Fig. 3). Increasing pH of reaction medium from 2.0 to 9.0 linearly increased the antioxidant capacity reaching

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an apparent maximum level of 126.8±0.6 mmol TE.kg-1. However, further increase of

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pH to 10.0 and 12.0 caused a sharp decrease in the antioxidant capacity (Fig. 3). It is a

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fact that polyphenols turn into phenolate ions at alkaline conditions followed by quinones formation (Hurrell & Finot, 1984). This might be affecting their binding ability

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onto insoluble bran matrix. However, highly acidic and basic conditions (pH 2.0 or 12.0) were found as the least effective probably due to loss of bound phenolic acids as a result of hydrolysis. The reaction medium was aerated to determine its effect on the resulting antioxidant capacity of insoluble wheat bran treated with green tea infusion. It was found that applying air stream during the treatment adversely affected the binding ability of soluble phenolic compounds onto insoluble bran matrix. Comparing to the treatment with green tea infusion for 1 h at 50 C and pH 9.0, the antioxidant capacity of insoluble wheat bran reached to 81.3±0.3 mmol TE.kg-1 that was 35.9% lower when the

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ACCEPTED MANUSCRIPT reaction medium was aerated (p<0.05). It is thought that applying air stream caused soluble phenolic compounds to polymerize in the liquid phase, but limited their

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binding to bran surface. The same procedure was repeated using black tea infusion

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instead of green tea infusion as a source of soluble antioxidants in polymeric forms. After reaction, antioxidant capacity of insoluble wheat bran treated with or without aeration of reaction medium was 31.8±2.8 mmol TE.kg-1 or 35.6±1.9 mmol TE.kg-1,

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respectively. In this case, no statistically significant difference (p>0.05) was observed

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due to the fact that black tea had already polymeric compounds, and the aeration did not affect polymerization in liquid phase.

In addition, wheat bran that contains both soluble and insoluble fractions (unwashed

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wheat bran) also reacted with green tea infusion at optimal conditions (50 C, pH 9.0,

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no air flow). After reaction, the antioxidant capacity of final insoluble precipitate was

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found as 90.8±2.9 mmol TE.kg-1. Interestingly, the level of resulting antioxidant capacity was lower when the reaction was started with unwashed wheat bran instead

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of its insoluble fraction. It is thought that some parts of polyphenols present in green tea infusion was bound to soluble fraction of wheat bran that was lost during the washing cycles. Total bound phenolic compounds were analyzed before and after the treatment of insoluble wheat bran with green tea infusion to confirm the binding of soluble phenolic compounds. The initial concentration of bound phenolic compounds was found 1099.1±61.4 mg gallic acid kg-1 for untreated insoluble wheat bran. The treatment with green tea infusion for 1 h at 50 C and pH 9.0 caused to increase the bound phenolic compounds concentration of insoluble wheat bran to 12593±170.5 mg

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ACCEPTED MANUSCRIPT gallic acid kg-1. Similarly, antioxidant capacity of insoluble wheat bran also reached to 126.8±0.6 mmol TE.kg-1 from 6.8±0.2 mmol TE.kg-1 after treatment with green tea. The

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coherence between the increase of antioxidant capacity and bound phenolic

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compounds of insoluble wheat bran indicated the binding of phenolic compounds present in the green tea infusion (liquid phase) to the insoluble wheat bran (solid phase).

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3.2. Determination of the binding mechanism and kinetics

Initial concentration of free amino groups was found as 2.62±0.06 mmol LE.kg-1 for

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insoluble wheat bran fraction. It significantly decreased to 1.06±0.17 mmol LE.kg-1

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after the reaction of insoluble wheat bran with green tea infusion (p<0.05). The reason of 59.5% reduction in free amino groups of insoluble wheat bran should be due to

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binding of polyphenols present in green tea infusion via their oxidation to

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corresponding quinones. It has been previously reported that quinones, being a reactive electrophilic intermediate, could readily undergo attack by nucleophiles such

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as lysine, methionine, cysteine and tryptophan moieties in a protein chain reversibly or irreversibly (Bittner, 2006; Hurrell & Finot, 1984). As reported by others, insoluble wheat bran subjected to alkaline hydrolysis contains 1.4% of protein (Zhang, et al., 2011). So, the results suggest that green tea polyphenols is first oxidized to quinones under alkaline conditions, and then, they are further bound to free amino groups available on the surface of wheat bran matrix as shown in Fig. 4. The binding kinetics was investigated during the treatment of insoluble wheat bran with green tea extract (Fig. 5). Aqueous solutions of green tea extract were used at two concentrations (0.5% and 1.0%) to determine their effect on the binding rate. A

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ACCEPTED MANUSCRIPT biphasic kinetic behavior was observed for the increase of antioxidant capacity of insoluble wheat bran during the treatment with green tea extract. There was a very

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sharp increase in the antioxidant capacity within the first 15 min. In the first phase, the

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rate was independent of the concentration of soluble phenolic compounds in the liquid phase. Afterwards, the antioxidant capacity continued to increase with noticeably lower rate depending on the concentration of soluble phenolic compounds.

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In the first phase, sharp increase of the antioxidant capacity is thought to be due to the

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binding of phenolic compounds via the formation of quinones that further react with free amine groups available in the bran matrix (Bittner, 2006; Hurrell & Finot, 1984;

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Zhang, et al., 2011). In second phase, it is thought that soluble phenolic compounds continue to polymerize at solid surface that further increase the bound antioxidant

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capacity of insoluble wheat bran.

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4. Conclusion

Required daily intake of dietary antioxidants is estimated as 9-11 mmol TE.kg-1 to

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prevent postprandial oxidative stress relative to a daily energy intake of 2000-2500 kcal (Prior, et al., 2007). The researchers previously reported that green tea polyphenols inhibit cyclooxygenase and lipoxygenase activities in human colon mucosa cells and human colon cancer cells (Hong, Smith, Ho, August, & Yang, 2001). On the other hand, importance of green tea polyphenols as radical and oxidant scavengers in vivo might be minor, based on their limited concentrations achieved in plasma and tissues for a few hours (Frei & Higdon, 2003). However, fiber-bound antioxidants may reach the colon without being digested, and contribute to the formation of a reduced environment. Nevertheless, the levels of antioxidant capacity bound to naturally

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ACCEPTED MANUSCRIPT occurring dietary fibers are very limited. The present study revealed that the antioxidant capacity of insoluble wheat bran could be increased from a level less than

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10 mmol TE.kg-1 to a remarkable high level exceeding 100 mmol TE.kg-1 by means of its

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treatment with free polyphenols under alkaline conditions. The results suggest that the reaction between oxidized polyphenols and free amino groups available on bran surface might be responsible for the increased antioxidant capacity of insoluble wheat

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bran. The findings can be used to develop functional dietary fibers rich in bound

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antioxidant capacity.

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ACCEPTED MANUSCRIPT References Acosta-Estrada, B. A., Lazo-Vélez, M. A., Nava-Valdez, Y., Gutiérrez-Uribe, J. A., &

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Serna-Saldívar, S. O. (2014). Improvement of dietary fiber, ferulic acid and calcium

mays). Journal of Cereal Science, 60, 264-269.

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contents in pan bread enriched with nejayote food additive from white maize (Zea

Journal of Food Engineering, 80, 61-67.

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Anil, M. (2007). Using of hazelnut testa as a source of dietary fiber in breadmaking.

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Bittner, S. (2006). When quinones meet amino acids: chemical, physical and biological consequences. Amino Acids, 30, 205-224.

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Bunzel, M., Ralph, J., Marita, J. M., Hatfield, R. D., & Steinhart, H. (2001). Diferulates as structural components in soluble and insoluble cereal dietary fibre. Journal of the

PT

Science of Food and Agriculture, 81, 653-660.

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Çelik, E. E., & Gökmen, V. (2014). Investigation of the interaction between soluble antioxidants in green tea and insoluble dietary fiber bound antioxidants. Food

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Research International, 63, Part C, 266-270. Celik, E. E., Gokmen, V., & Fogliano, V. (2013). Soluble antioxidant compounds regenerate the antioxidants bound to insoluble parts of foods. Journal of Agricultural and Food Chemistry, 61, 10329-10334. Chandrasekara, A., & Shahidi, F. (2010). Content of insoluble bound phenolics in millets and their contribution to antioxidant capacity. Journal of Agricultural and Food Chemistry, 58, 6706-6714. Frei, B., & Higdon, J. V. (2003). Antioxidant Activity of Tea Polyphenols In Vivo: Evidence from Animal Studies. The Journal of Nutrition, 133, 3275S-3284S.

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ACCEPTED MANUSCRIPT Hermanson, GT. (1996). Bioconjugate Techniques,. Academic Press, San Diego, California ,p.112-113

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Hong, J., Smith, T. J., Ho, C. T., August, D. A., & Yang, C. S. (2001). Effects of purified

SC RI

green and black tea polyphenols on cyclooxygenase- and lipoxygenase-dependent metabolism of arachidonic acid in human colon mucosa and colon tumor tissues. Biochemical Pharmacology, 62, 1175-1183.

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Hurrell, R. F., & Finot, P. A. (1984). Nutritional consequences of the reactions between

MA

proteins and oxidized polyphenolic acids. Advances in Experimental Medicine and Biology, 177, 423-435.

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Jacobs, D. R., Jr., Pereira, M. A., Stumpf, K., Pins, J. J., & Adlercreutz, H. (2002). Whole grain food intake elevates serum enterolactone. British Journal of Nutrition, 88,

PT

111-116.

CE

Jacobs, D. R., Jr., Slavin, J., & Marquart, L. (1995). Whole grain intake and cancer: a review of the literature. Nutrition and Cancer, 24, 221-229.

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Jiménez-Escrig, A., Rincón, M., Pulido, R., & Saura-Calixto, F. (2001). Guava Fruit (Psidium guajava L.) as a New Source of Antioxidant Dietary Fiber. Journal of Agricultural and Food Chemistry, 49, 5489-5493. Koh-Banerjee, P., & Rimm, E. B. (2003). Whole grain consumption and weight gain: a review of the epidemiological evidence, potential mechanisms and opportunities for future research. Proceedings Of The Nutrition Society, 62, 25-29. Kroon, P. A., Faulds, C. B., Ryden, P., Robertson, J. A., & Williamson, G. (1997). Release of Covalently Bound Ferulic Acid from Fiber in the Human Colon. Journal of Agricultural and Food Chemistry, 45, 661-667.

16

ACCEPTED MANUSCRIPT Liu, S., Stampfer, M. J., Hu, F. B., Giovannucci, E., Rimm, E., Manson, J. E., Hennekens, C. H., & Willett, W. C. (1999). Whole-grain consumption and risk of coronary heart

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disease: results from the Nurses' Health Study. The American Journal of Clinical

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Nutrition, 70, 412-419.

Liyana-Pathirana, C. M., & Shahidi, F. (2005). Antioxidant Activity of Commercial Soft and Hard Wheat (Triticum aestivum L.) as Affected by Gastric pH Conditions. Journal

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of Agricultural and Food Chemistry, 53, 2433-2440.

MA

Lotito, S. B., & Frei, B. (2004). The increase in human plasma antioxidant capacity after apple consumption is due to the metabolic effect of fructose on urate, not apple-

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derived antioxidant flavonoids. Free Radical Biology and Medicine, 37, 251-258. Martinez-Tome, M., Murcia, M. A., Frega, N., Ruggieri, S., Jimenez, A. M., Roses, F., &

PT

Parras, P. (2004). Evaluation of antioxidant capacity of cereal brans. Journal of

CE

Agricultural and Food Chemistry, 52, 4690-4699. Meyer, K. A., Kushi, L. H., Jacobs, D. R., Jr., Slavin, J., Sellers, T. A., & Folsom, A. R.

AC

(2000). Carbohydrates, dietary fiber, and incident type 2 diabetes in older women. The American Journal of Clinical Nutrition, 71, 921-930. Pérez-Jiménez, J., & Saura-Calixto, F. (2005). Literature Data May Underestimate the Actual Antioxidant Capacity of Cereals. Journal of Agricultural and Food Chemistry, 53, 5036-5040. Prior, R. L., Gu, L., Wu, X., Jacob, R. A., Sotoudeh, G., Kader, A. A., & Cook, R. A. (2007). Plasma antioxidant capacity changes following a meal as a measure of the ability of a food to alter in vivo antioxidant status. The Journal of the American College of Nutrition, 26, 170-181.

17

ACCEPTED MANUSCRIPT Saura-Calixto, F. (1998). Antioxidant Dietary Fiber Product:  A New Concept and a Potential Food Ingredient. Journal of Agricultural and Food Chemistry, 46, 4303-

PT

4306.

cooked meats. Meat Science, 90, 60-65.

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Serpen, A., Gökmen, V., & Fogliano, V. (2012). Total antioxidant capacities of raw and

Sosulski, F., Krygier, K., & Hogge, L. (1982). Free, esterified, and insoluble-bound

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phenolic acids. 3. Composition of phenolic acids in cereal and potato flours. Journal

MA

of Agricultural and Food Chemistry, 30, 337-340.

Wang, Y., & Ho, C.-T. (2009). Polyphenolic Chemistry of Tea and Coffee: A Century of

ED

Progress. Journal of Agricultural and Food Chemistry, 57, 8109-8114. Yu, L., Haley, S., Perret, J., Harris, M., Wilson, J., & Qian, M. (2002). Free Radical

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Scavenging Properties of Wheat Extracts. Journal of Agricultural and Food

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Chemistry, 50, 1619-1624.

Zhang, Y., Pitkänen, L., Douglade, J., Tenkanen, M., Remond, C., & Joly, C. (2011).

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Wheat bran arabinoxylans: Chemical structure and film properties of three isolated fractions. Carbohydrate Polymers, 86, 852-859.

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ACCEPTED MANUSCRIPT Figure Captions Fig. 1. Increase of the antioxidant capacity of insoluble wheat bran during treatment

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with (a) different concentrations of tannic acid, and (b) antioxidant-rich beverages at

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room temperature for 30 min

Fig. 2. Effect of temperature (25 oC and 50 oC) and time (30 min and 60 min) on the

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increase of antioxidant capacity of insoluble wheat bran during treatment with green tea infusion (3g/100 ml)

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Fig. 3. Effect of pH on the increase of antioxidant capacity of insoluble wheat bran during treatment with green tea infusion (3g/100 ml) at 50 oC for 60 min

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Fig. 4. Proposed mechanism for reaction between soluble antioxidants and insoluble

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wheat bran

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Fig. 5. Change of the antioxidant capacity of insoluble wheat bran during treatment

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with two different concentration of green tea extract at 50 oC and pH 9.0

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ACCEPTED MANUSCRIPT Fig. 1

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Wheat Bran

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120 Radical Pretreated Wheat Bran 100

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d

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80 60

c

40 20

a,b a

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a,b

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c

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Antioxidant capacity (mmol TE.kg-1)

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0 0

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50

100

200

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Beverage

20

f

Diluted Beverage (1/10)

c

AC

Antioxidant capacity (mmol TE.kg-1)

25

(a)

PT

ED

Tannic acid concentration (μM)

c b

15

d

e

10

a

a

a

5

0 No treatment (Control)

White wine

Red wine

Black tea infusion

Green tea infusion

Beverage Treatment

(b)

20

ACCEPTED MANUSCRIPT

PT

Fig. 2

30

20

10

b

a

0

25°C - 30 min

25°C - 60 min 50°C - 30 min 50°C - 60 min

ED

Control

c

NU

c

SC RI

40

d

MA

Antioxidant capacity (mmol TE.kg-1)

50

AC

CE

PT

Treatment conditions

21

ACCEPTED MANUSCRIPT

140

SC RI

120 100

c 80

NU

b

60 b 40 a 20

a

ED

0

4

6

7

a

8

9

10

12

pH

AC

CE

PT

2

b

MA

Antioxidant capacity (mmol TE.kg-1)

d

PT

Fig. 3

22

ACCEPTED MANUSCRIPT

AC

CE

PT

ED

MA

NU

SC RI

PT

Fig. 4

23

ACCEPTED MANUSCRIPT

PT

Fig. 5

0.5%

70

1.0%

SC RI

80

60

NU

50 40 30 20

MA

Antioxidant capacity (mmol TE.kg-1)

90

10 0 30

60

90

120

150

180

Time (min)

AC

CE

PT

ED

0

24

ACCEPTED MANUSCRIPT Highlights Wheat bran is a rich source of dietary fiber.



Treatment with polyphenols increases bound antioxidant capacity of bran.



Polyphenols bind favorably to insoluble bran matrix under alkaline conditions.



They are first oxidized to quinones then bound to free amino groups of

SC RI

PT



AC

CE

PT

ED

MA

NU

insoluble bran.

25