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Keywords:

  • antioxidant capacity;
  • bread;
  • riboflavin;
  • rye;
  • thiamine

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

ABSTRACT:  The effect of rye flour extraction rates and baking on thiamine and riboflavin content, and antioxidant capacity of traditional rye bread were studied and compared with white wheat flour. The content of thiamine was higher (10.9%) in rye dough formulated with dark rye flour (F-100%; extraction rate of 100%) than in rye dough formulated with brown rye flour (F-92%; extraction rate of 92%) that was similar to dough made with wheat flour. The riboflavin content in rye dough made from flour F-100% was also higher (16%) than in dough formulated with flour F-92%, and both provided larger riboflavin content than wheat dough. Baking led to reductions in thiamine of 56% for wheat bread and of 20% for both rye breads; however, this process caused only a 10% decrease in riboflavin for wheat bread and a 30% decrease for rye breads. Trolox equivalent antioxidant capacity, peroxyl radical scavenging capacity, DPPH radical scavenging activity, and Folin–Ciocalteu reducing capacity were higher in rye than in wheat dough and bread. Baking process produced slight changes in antioxidant activity, except for Superoxide Dismutase-like activity where a sharp decrease was observed. Our findings showed that rye breads are an important source of B vitamins and rye breads formulated with dark and brown flours showed better antioxidant properties than wheat bread. Therefore, rye breads should be more widely recommended in human nutrition.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

Rye (Secale cereale L.) grain is an excellent raw material for healthy and tasty foods. Like other cereals, it provides carbohydrate and protein as well as a variety of micronutrients, in particular certain B vitamins, vitamin E, and minerals. Milling and baking are the most common techniques used in cereal grain processing for human food. The main nutritional benefit of processing is to increase the bioavailability of the nutrients present in the cereal grain (Salovaara and Autio 2001).

The majority of rye is consumed as a different kind of bread baked from rye flours with different extraction rates. Traditional rye bread is prepared from fermented dough (Lonner and Preve-Akesson 1989). During fermentation, lactic acid bacteria and sourdough yeast grow and flavor compounds are formed due to the microbial activity and the enzymatic reaction of the microflora (Zielinski and others 2008). The main components formed are lactic and acetic acids. After fermentation, more flour, water, and other ingredients are mixed to the sourdough to make the dough. The dough is then left to rise for a short period, after which the breads are shaped, left to rise again, and baked (Decock and Cappelle 2005).

Rye bread is a recommended part of the diet because it is a good source of biologically active substances, especially those with antioxidant properties (Michalska and others 2007a). This wide range of bioactive compounds includes phytochemicals, such as lignans, phenolic acids, phytosterols, tocopherols and tocotrienols, inositol hexaphosphate, and other vitamins, as well as water-soluble low molecular weight antioxidants (Andlauer and Furst 1998; Honke and others 2000; Meagher and Beecher 2000; Amarowicz and Weidner 2001; Zielinski and others 2001; Michalska and others 2007a). Moreover, dough fermentation during breadmaking provides some additional benefits for consumers because this process increases the solubility of pentosans in bread, which is optimal at lower pH, and also reduces enzymatic activity that improves the dough processability (Kariluoto and others 2004; Katina and others 2007). Moreover, the antioxidant properties of bread are probably enhanced by nonenzymatic browning reactions occurring during baking, due to complex chemical events based on a series of subsequent and parallel reactions of free amino groups of lysine, peptides, or proteins with carbonyl groups of reducing sugars or other components (Michalska and others 2008).

The milling process of rye grains and rye breadmaking can affect the contents of vitamins B in bakery foods. Earlier studies reported the effect of the milling process of whole rye grain on dietary fiber (Glitso and Bach Knudsen 1999) and associated bioactive compounds such as the B vitamins, tryptophan, and lignans content (Nilsson and others 1997) while no information was available about the effect of the rye breadmaking process on the contents of these nutrients in bread. More recently, Michalska and Zielinski (2006) and Michalska and others (2007b) demonstrated that milling and baking processes in rye affect the level of phenolic compounds, inositol hexaphosphate, reduced glutathione, tocopherols, and tocotrienols, most of which are known for their contribution to the antioxidant capacity of rye bread.

Currently, knowledge about the antioxidant activity of vitamins B in vitro has been established (Gliszczyńska-Świgło 2006) in terms of standardized methods (Prior and others 2005, Huang and others 2006). Therefore, the present study was undertaken to find out the impact of rye flour extraction rates and the baking process on thiamine (vitamin B1) and riboflavin (vitamin B2) contents and on the antioxidant capacity of doughs and their respective rye breads. The dark rye flour with an extraction rate of 100% (F-100%) and brown rye flour with an extraction rate of 92% (F-92%) were used to study rye bread baking, whilst the commercially available white wheat flour with an extraction rate of 70% (F-70%) was used to provide a typical bakery wheat product as a reference (Bakke and Vickers 2007). The antioxidant properties of phosphate buffered saline (PBS) and 80% methanol dough and bread extracts were evaluated as free radical scavenging activities against ABTS•+ radical cations (Trolox equivalent antioxidant capacity; TEAC) and peroxyl radicals (ROO) (peroxyl radical scavenging capacity; PRSC). PBS dough and bread extracts were used to determine the scavenging activities against superoxide anion radicals (O2−•) (SOD-like activity), whereas 80% methanol extracts were assessed for radical scavenging activities against 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH RSA). Moreover, the reducing capacity of both PBS and 80% methanol extracts were provided by the means of Folin–Ciocalteu reagent (FCR) application.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

Reagents

Thiamine and riboflavin standards were obtained from Merck (Darmstad, Germany). Ferulic acid, 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), 2,2′-azobis (2-amidopropane) dihydrochloride (ABAP), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) were purchased from Sigma (St. Louis, Mo., U.S.A.). The superoxide dismutase kit (RANSOD, Cat nr SD 125) originated from Randox Lab. Ltd., (Crumlin, U.K.). Folin–Ciocalteu's reagent and other reagents of reagent-grade quality were from POCh (Gliwice, Poland).

Materials

Polish rye cultivar Warko was selected from breeding materials grown in central Poland (DANKO, Plant Breeding Co., Laski, Poland) in 2005, based on the grain quality parameters. Samples were tempered to 14% moisture and milled on a Quadrumat Senior laboratory mill (Brabender GmbH & Co., Duisburg, Germany) to obtain straight grade flour with extraction rates of 100% (F-100%) and 92% (F-92%), respectively. White wheat flour with an extraction rate of 70% (F-70%) was purchased from a local commercial grocery.

Characterization of rye flours and breads

Flour and breads were characterized with the following analyses: moisture, ash, protein, and starch content. Protein content was measured following AACC method 46-11B (AACC 2000) using Foss Tecator apparatus (Tecator, Sweden), whereas starch content was determined by the polarimetric method (AACC 2000). Moisture and ash content of flours were analyzed according to AOAC 15.950.01 and 15.955.03, respectively (AOAC 1990). All analyses were carried out in triplicate.

Rye breadmaking process

Rye breads were made in a pilot-scale bread maker following the process shown in Figure 1. Salt and baker's yeast used in the formulation of bread dough were purchased from a local food manufacturer. For each type of bread, the sourdough starters were prepared from the respective type of flour. Dough samples were allowed to stand before baking. Four loafs of each type of bread were obtained. Two kinds of bread were baked, type I based on dark rye flour F-100% and type II based on rye brown flour F-92%. At least 4 breads of each type were baked in replicate. The reference wheat bread was prepared as previously described by Michalska and others (2007a). Rye dough and bread samples as well as reference dough and wheat bread samples were freeze-dried, ground, and sieved though a 60-mesh screen. Powdered samples were stored at −20 °C until analysis.

image

Figure 1—. Diagram of breadmaking process.

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Determination of thiamine and riboflavin content

Thiamine and riboflavin were extracted by a single extraction procedure according to Vidal-Valverde and others (1997). Briefly, 1 g of ground sample was extracted by acid hydrolysis with 30 mL of 0.3 M HCl in an autoclave for 15 min at 121 °C. The pH of the solution was then adjusted to the range of 5 to 5.4 with 2 M sodium acetate. After cooling, extracts were incubated with 5 mL of a 15% aqueous Taka-Diastase (Fluka) for 3 h at 45 °C. Afterward, samples were filtered through Whatman nr 40 filter paper, filled to 100 mL, and filtered through a 0.2 μm pore size nylon filter membrane. Thiamin content was analyzed by high-performance liquid chromatography (HPLC) provided by a postcolumn derivatization system according to Prodanov and others (1997). The chromatographic system was equipped with both M510 and M45 Model pumps (Waters Associates, Milford, Conn., U.S.A.), a Rheodyne M-7125 injector (Cocati, Calif., U.S.A.), a μBondapak C18 column (300 × 3.9 mm i.d.), a Porasil B Bondapak C18 guard column (20 × 3.9 mm i.d.), and a Waters 470 scanning fluorescence detector set up at λexc= 360 nm and λem= 435 nm. The detector signal was recorded on a Maxima 820 chromatography workstation (Waters Associates). The mobile phase methanol/water/acetic acid (31/68.5/0.5), containing 5 mM sodium hexasulfonate, was pumped at a flow rate 1.5 mL/min. The column temperature was 35 °C and the injection volume was 50 μL. Riboflavin content was analyzed by HPLC according to Prodanov and others (1997). For riboflavin analysis, a precolumn (3.2 mm i.d. × 4.0 cm) packed with C18 Porasil B (Waters Associates), a ODS Spherisorb column (3.9 mm i.d. × 30 cm), and a 470 scanning fluorescence detector were used at λexc= 445 nm and λem= 520 nm. The mobile phase was methanol/water/acetic acid (31/68.5/0.5), containing 5 mM sodium hexasulfonate with flow rate at 1.2 mL/min. The column temperature was 25 °C and the injection volume was 20 μL. The level of thiamine and riboflavin was quantified using the respective standards curves.

Preparation of dough and bread crude extracts for determination of antioxidant capacity

Lyophilized and ground samples of dough and bread were extracted in triplicate with PBS pH 7.4 (1 g/15 mL) or with 80% aqueous methanol (1 g/10 mL) for 2 h of shaking at 37 °C. Samples were then centrifuged at 12000 ×g for 15 min in a Beckman GS-15 R centrifuge (Beckman Instruments, Fullerton, Calif., U.S.A.).

TEAC assay

The Trolox equivalent antioxidant capacity assay was based on the reduction of the ABTS•+ radical cation by antioxidants present in PBS and 80% methanolic extracts. The ABTS•+ radical cation was prepared by mixing ABTS stock solution (7 mM in water) with 2.45 mM potassium persulphate. This mixture was allowed to stand overnight at room temperature until the reaction was completed and the absorbance was stable. TEAC was determined following the procedure described by Re and others (1999) with a minor modification. For measurements, the ABTS•+ solution was diluted with PBS or 80% methanol until absorbance readings reached 0.700 ± 0.020 at 734 nm. For the photometric assay, 1.48 mL of the ABTS•+ solution and 20 μL of the extracts or Trolox standards were mixed and measured immediately at 30 °C after 6 min at 734 nm using a spectrophotometer (UV-160 1PC, Shimadzu, Kyoto, Japan). Appropriate solvent blanks were run in each assay. The TEAC of PBS and 80% methanolic extracts was expressed as percentage of inhibition of absorbance at 734 nm using Trolox standard curve.

Peroxyl radical scavenging capacity (PRSC) assay

A simple method of determining the PRSC based on the use of 2,2′-azobis (2-amidopropane) hydrochloride (ABAP) decomposition as a free radical source and the use of ABTS oxidation as reaction indicator was employed to express antioxidant activity as described by Bartosz and others (1998). Briefly, 0.1 M sodium phosphate buffer, pH 7 was preheated to 37 °C, and added to a cuvette to obtain a 3 mL final volume. Further, 90 μL of 5 mM ABTS solution and 90 μL of PBS, or 80% methanol extracts, or Trolox solution were added followed by 300 μL of 200 mM ABAP solution. The cuvettes were placed in a thermostatted recording spectrophotometer UV-160 1PC with CPS-Controller (Shimadzu, Japan) adjusted to 37 °C and induction time of ABTS oxidation was measured at 414 nm. The standard curve based on induction time of ABTS oxidation compared with Trolox concentration was constructed within the range of 0.05 to 2.5 mM of Trolox.

DPPH radical scavenging activity (DPPH RSA) assay

The DPPH RSA assay was based on a modified method of Brand-Williams and others (1995). In this assay, antioxidants present in the sample reduce the DPPH radicals, which have an absorption maximum at 515 nm. The DPPH radical solution was prepared by dissolving 10 mg DPPH in 25 mL 80% methanol. First, the extinction of the disposable cuvette using 250 μL of the methanolic DPPH solution and 2.1 mL 80% methanol was measured as blank. Then, 80% methanol extracts (100 μL) were added to 250 μL of the methanolic DPPH solution and 2 mL 80% methanol. The mixture was shaken vigorously and allowed to stand at room temperature in the dark for 20 min. The decrease in absorbance of the resulting solution was monitored at 517 nm for 20 min using a spectrophotometer (UV-160 1PC, Shimadzu, Kyoto, Japan). The Trolox standard solution (concentration 0.1 to 2.0 mM) was prepared in 80% methanol and assayed at the same conditions. DPPH scavenging activity was expressed in terms of Trolox equivalents, on the basis of percentage inhibition of absorbance at 515 nm of standards and samples.

FCR reducing capacity assay

FCR reducing capacity was studied using the FCR application described recently by Zielinska and others (2007). Briefly, 0.25 mL of extracts were mixed with 0.25 mL FCR previously diluted with distilled water (1: 1 v/v), 0.5 mL saturated sodium carbonate (Na2CO3), and 4 mL of water. The mixture was incubated at room temperature for 25 min and centrifuged at 2000 ×g for 10 min. Supernatant absorbance was measured spectrophotometrically at 725 nm. The data were calculated as milligram ferulic acid equivalents on a dry matter (dm) basis and converted to micromol Trolox per gram dry matter when TEAC of ferulic acid was used (TEAC = 1.90) as described previously by Rice-Evans and others (1996).

Superoxide dismutase-like activity assay

The superoxide dismutase-like activity (SOD-like activity) of the PBS extracts was measured with the superoxide dismutase RANSOD kit. The assays were performed using a thermostatted recording spectrophotometer (UV-160 1PC with CPS-Controller, Shimadzu, Kyoto, Japan) adjusted to 37 °C. The test required 50 μL of sample with a reading time of 3 min. In general, 1 unit of SOD activity is defined as the amount of enzyme required to inhibit the rate of reduced adenine nucleotide (NADH, NADPH) oxidation of the control by 50%. The percent of reaction inhibition was plotted against log10 of different SOD activities (SOD/mL) giving a standard curve and then the SOD-like activity of the sample was calculated as SOD units/mL of extract. The results were finally calculated on milligrams of soluble protein assayed according to the bicinchonic acid (BCA) protein microassay (Smith and others 1985).

Statistical analysis

Data were subjected to one-way analysis of variance (ANOVA) using the Fischer LSD test with the Statgraphic 5.0 Program (Statistical Graphic, Rockville, Md., U.S.A.) for Windows using a PC-Pentium.

Results and Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

Characterization of rye flours and breads

The proximate chemical compositions of rye flours and respective types of bread are compiled in Table 1. The dark rye flour (F-100%) showed a higher content of proteins and ash whereas the brown flour (F-92%) contained a significantly (P≤ 0.05) higher amount of starch. The breads based on dark and brown flour contained similar (P≤ 0.05) protein and ash levels but starch content was significantly (P≤ 0.05) higher in brown rye bread (F-92%).

Table 1—.  Proximate chemical composition of rye flour with extraction rate of 100% and 92% and their respective rye breads.
Flour and bread typeDry matter (%)Protein content (%)Ash content (%)Starch content (%)
  1. Data expressed as mean ± standard deviation (n= 3). The same superscript for each column between flours or breads means not significantly different (P≤ 0.05).

Flour (F-100%)88.5 ± 0.04a11.02 ± 0.02b 1.8 ± 0.01b 53.3 ± 0.28a
Flour (F-92%)88.3 ± 0.02a10.44 ± 0.02a 1.6 ± 0.06a 54.2 ± 0.28b
Rye bread (F-100%)27.5 ± 0.04b10.32 ± 0.01a2.22 ± 0.04a45.54 ± 0.18a
Rye bread (F-92%)25.2 ± 0.02a10.20 ± 0.01a2.15 ± 0.14a50.86 ± 0.28b

Thiamine and riboflavin content in rye doughs and breads formulated with flours of different extraction rates

Table 2 shows the thiamine and riboflavin content in wheat and rye doughs and breads. Thiamine and riboflavin concentrations were significantly (P≤ 0.05) higher in rye dough with a 100% extraction rate than in wheat dough, which was made with wheat flour with a 70% extraction rate. Rye dough based on flour with extraction rate of 92% brought about significant (P≤ 0.05) reductions in thiamine and riboflavin (9.8% and 14% reduction, respectively) contents which indicated that milling of rye grains into flours led to higher reductions in thiamine and riboflavin. Most of the vitamins B are present in the bran and germ: therefore, milling or extensive flour extraction is liable to severely reduce B vitamins such as thiamine and riboflavin (Pederson and others 1989; Nilsson and others 1997).

Table 2—.  Thiamine and riboflavin content in wheat and rye doughs and breads formulated with flours of different extraction rates.
SampleThiamine (μg/100g dm)Riboflavin (μg/100g dm)
  1. Data expressed as mean ± standard deviation (n= 3). The same superscript for each column between doughs or breads means not significantly different (P≤ 0.05).

Wheat dough280.48 ± 0.37a 50.52 ± 0.21a
Rye dough (F-100%)310.73 ± 7.16b211.22 ± 5.74c
Rye dough (F-92%)280.18 ± 4.14a182.11 ± 2.78b
Wheat bread123.20 ± 0.77a 45.48 ± 0.22a
Rye bread (F-100%)248.56 ± 7.19c147.34 ± 0.82c
Rye bread (F-92%)217.60 ± 1.06b120.38 ± 1.91b

In rye breads, the thiamine and riboflavin contents were also significantly (P≤ 0.05) higher than in wheat bread (Table 2). The wheat bread baking process led to a 56% reduction in thiamine while significantly lower reductions (approximately 20%) were observed during the rye bread baking process, which were even less pronounced in breads with a 100% extraction rate. This agrees with findings reported by Batifoulier and others (2006) in which the decrease in thiamine concentration was lower in whole wheat breads. Several studies reported a wide range of thiamine losses (5% to 37%) during wheat bread baking (Ryley and Kajda 1994; Tanphaichitr 2001; Batifoulier and others 2006). Thiamine is a water-soluble vitamin and is stable in slightly acidic water up to the boiling point. The phosphorylated form of thiamine represents only 5% of thiamine in flour (Ndaw and others 2000) and is more thermolabile than other forms, which were also shown to be destroyed by baking. Batifoulier and others (2005) suggested a possible conversion of thiamine to thiamine phosphate (more unstable during cooking) during wheat dough fermentation. The differences in thiamine reductions found in this study may be due to a higher formation of thiamine phosphate during wheat dough fermentation compared to rye. Nevertheless, more research is required on this topic to establish firm conclusions. In relation to riboflavin contents, wheat bread baking led to a 10% reduction in this vitamin while significantly higher reductions (approximately 30%) were observed during the rye bread baking process independently of the extraction rate of the flour. Riboflavin is stable to heat and atmospheric oxygen, especially in an acid medium, so losses reported in the literature after a heating process correspond to only about 10% (Batifoulier and others 2005). The effect of the baking process on the riboflavin content of wheat bread depended on the breadmaking method used, as described recently (Batifoulier and others 2006). For instance, baking reduced riboflavin content when classical yeast was used for whole wheat and white wheat dough fermentation. However, increases or the same levels of riboflavin content were observed after baking of white bread or whole wheat bread, respectively, when sourdough was used in the fermentation process (Dwivedi and Arnold 1973; Batifoulier and others 2006). Most Western human populations exhibit a relatively low consumption of carbohydrates (45% compared with 55% recommended), at the expense of complex carbohydrates and high intake of lipid (40% compared with 25% to 35% recommended) (Borgies and others 2001). These lifestyle changes have resulted in the emergence of a marginal deficiency in vitamins B together with other micronutrients and have been associated with the increasing incidence of obesity, cancers, and cardiovascular diseases (Kaas and others 1998; Van der Berg and others 2002; Bruce and others 2003; Wolters and others 2003). Whole cereal products have been identified as a major source of thiamine especially if breadmaking is optimized (Tanphaichitr 2001). Riboflavin is essentially provided by dairy products, but wheat bread could provide up to 20% of the daily requirements of riboflavin (Rivlin and Pinto 2001). Our findings demonstrated that rye bread with 100% extraction rate appeared to be an even better source of B vitamins than wheat bread.

Total antioxidant capacity (TEAC) of rye doughs and breads formulated with flours of different extraction rates

The PBS and 80% methanol extracts of wheat and rye doughs and breads were examined for their free radical scavenging activity against ABTS•+ radical (Table 3). It was observed that PBS extracts of doughs and breads provided 2-fold higher TEAC values than 80% methanol extracts. These results were in accordance with our previous study (Zielinski and others 2007). Antioxidant activity found in PBS and 80% methanol extracts from rye doughs were approximately 2- and 6-fold higher, respectively, than those recorded in wheat dough. Furthermore, no statistically significant differences were found between the antioxidant capacity of rye doughs prepared with flour F-100% and F-92%. The baking process caused about a 30% reduction of TEAC in wheat bread and a 10% to 16% reduction in rye breads when PBS extracts were evaluated. In contrast, TEAC values of rye breads obtained by 80% methanol were not modified after the baking process while a 2-fold increase of TEAC values in wheat bread was observed compared to wheat dough. The impact of rye flour extraction rates used for breadmaking was observed since rye bread from F-100% showed higher TEAC values by 7% (PBS) and 20% (80% methanol) than respective values for rye bread from F-92%. These findings indicated the importance of antioxidant compounds present in the outer layer of the kernel, which is removed during milling (Michalska and others 2007b). Therefore, since the milling process caused a reduction in the amount of antioxidants and bioactive compounds in flours (Heinio and others 2003; Michalska and others 2007b), the TEAC values of rye breads partly depend on flour extraction rate. On the other hand, it was recently reported that rye bread baking favored the formation of antioxidant compounds due to the Maillard reaction, a complex chemical event associated with thermal treatment (Michalska and others 2008). It could, therefore, be suggested that both remaining natural antioxidants and those formed during baking could contribute to the TEAC of rye breads (Manzocco and others 2001).

Table 3—.  Trolox equivalent antioxidant capacity (TEAC) of wheat and rye doughs and breads formulated with flours of different extraction rates.
SampleTEAC (μmol Trolox/g dm)
PBS80% methanol
  1. Data expressed as mean ± standard deviation (n= 3). The same superscript for each column between doughs or breads means not significantly different (P≤ 0.05).

Wheat dough 7.41 ± 0.07a1.25 ± 0.18a
Rye dough (F-100%)15.36 ± 0.20b8.81 ± 0.37b
Rye dough (F-92%)15.19 ± 0.09b7.39 ± 0.85b
Wheat bread 5.17 ± 0.03a2.57 ± 0.45a
Rye bread (F-100%)13.78 ± 0.26c8.57 ± 0.35c
Rye bread (F-92%)12.78 ± 0.06b6.79 ± 0.02b

PRSC of rye doughs and breads formulated with flours of different extraction rates

The PRSC of rye doughs was about 7- (PBS extracts) and 3-fold higher (80% methanol extract) than that of wheat dough. The same trend was observed in rye breads for which the PRSC was 4- (PBS) and 3-fold higher (80% methanol) than that of wheat bread (Table 4). These findings were in accordance with our previous PRSC study related to legume-germinated seeds when the same extraction system was used (Zielinski 2002). Flour extraction rates of 100% and 92% had no apparent effect on PRSC of rye doughs. Baking caused an increase in ability to scavenge peroxyl radicals in wheat bread whilst no changes were noted in rye breads, except for the 80% methanol extract of bread formulated with whole-meal flour (F-100%). In this case, the PRSC of the bread was 87% higher than the respective dough. This finding suggested that rye breadmaking from whole meal flour (F-100%) possibly favored the formation of antioxidant compounds due to Maillard's reaction since no differences in PRSC values were found in dough formulated with rye flour type F-100% and F-92%. The importance of the ability of antioxidants to remove peroxyl radicals is that they are effective in the aqueous phase. This was reflected by the data describing PRSC values obtained from the respective PBS extracts of dough and bread. Other compounds, such as proteins, could be expected to be responsible for the PRTC of these extracts (Bartosz and others 1998). Moreover, peroxyl radical scavengers can also act in the hydrophobic phase: these are, of course, the chain-breaking antioxidant inhibitors of lipid peroxidation (Halliwell and others 1995). It can, therefore, be suggested that both remaining hydrophobic natural antioxidants and those formed during baking were responsible for the PRSC values of the methanolic extracts (Manzocco and others 2001).

Table 4—.  Peroxyl radical scavenging capacity (PRSC) of wheat and rye doughs and breads formulated with flours of different extraction rates.
SamplePRTC (μmol Trolox/g dm)
PBS80% methanol
  1. Data expressed as mean ± standard deviation (n= 3). The same superscript for each column between doughs or breads means not significantly different (P≤ 0.05).

Wheat dough0.32 ± 0.02a0.61 ± 0.05a
Rye dough (F-100%)2.46 ± 0.12b1.67 ± 0.22b
Rye dough (F-92%)2.12 ± 0.12b1.72 ± 0.15b
Wheat bread0.56 ± 0.03a0.80 ± 0.02a
Rye bread (F-100%)2.50 ± 0.06c3.13 ± 0.15c
Rye bread (F-92%)1.91 ± 0.06b1.67 ± 0.22b

DPPH scavenging activity of rye doughs and breads formulated with flours of different extraction rates

Figure 2 shows the DPPH scavenging activity (DPPH RSA) of wheat and rye doughs and breads when examination was performed on the 80% methanol extracts. The DPPH RSA of wheat bread was higher than dough. In contrast, the DPPH RSA of rye bread formulated with flour F-100% was slightly decreased compared with its dough, whilst bread from flour F-92% did not show significant changes against its dough. These results indicate that the antioxidants present in baked goods have different effective scavenging activity against peroxyl and DPPH radicals suggesting that their activity can be modified during thermal processing depending on the flour extraction rate.

image

Figure 2—. Changes in DPPH radical scavenging activity (DPPH RSA) of wheat and rye breads due to baking process.

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Reducing capacity of rye doughs and breads formulated with flours of different extraction rates

In this study, the FCR-reducing capacity by means of the FCR application, as described by Huang and others (2005), was used to evaluate antioxidant properties of wheat and rye doughs and breads formulated with flours of different extraction rates. PBS extracts of wheat and rye doughs and breads exhibited FCR reducing capacity values (Table 5) comparable to TEAC values in PBS (Table 3). This may indicate that low molecular weight antioxidants, including free or protein-binding phenolic compounds, are responsible for the antioxidant and reducing capacity of dough and bread. Moreover, it was noticed that the FCR-reducing capacity of 80% methanol extracts from dough and bread showed comparable results to the antioxidant capacities provided by PRSC (Table 4) and DPPH RSA (Figure 2).

Table 5—.  FCR-reducing capacity of wheat and rye doughs and breads formulated with flours of different extraction rates.
SampleFCR-reducing capacity (μmol Trolox/g dm)
PBS80% methanol
  1. Data expressed as mean ± standard deviation (n= 3). The same superscript for each column between doughs or breads means not significantly different (P≤ 0.05).

Wheat dough 8.99 ± 0.09a10.56 ± 0.19a
Rye dough (F-100%)20.94 ± 0.28c20.94 ± 0.98c
Rye dough (F-92%)19.78 ± 0.02b18.82 ± 0.16b
Wheat bread 5.97 ± 0.14a 8.28 ± 0.19a
Rye bread (F-100%)17.82 ± 1.33c22.23 ± 0.46c
Rye bread (F-92%)15.28 ± 0.43b19.15 ± 0.30b

Superoxide dismutase-like activity of rye doughs and breads formulated with flours of different extraction rates

The superoxide dismutase-like activities (SOD-like activity) of wheat and rye doughs and breads are shown in Figure 3. In contrast to the ability to scavenge ABTS•+, peroxyl, and DPPH radicals, the wheat dough exhibited higher SOD-like activity than rye dough, indicating the importance of cereal origin selected for processing and type of breadmaking technology. Moreover, rye dough formulated with flour F-100% showed significantly higher SOD-like activity than dough based on F-92%. These SOD-like activity values clearly showed the importance of flour type used for breadmaking since the process was exactly the same in this case. These data support the previous findings recommending whole rye meal flour for breadmaking. A dramatic decrease in SOD-like activity was noted after baking both in wheat and rye breads, probably due to the thermal instability of compounds responsible for scavenging superoxide anion radicals.

image

Figure 3—. Changes in SOD-like activity of wheat and rye breads due to baking process.

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Correlation between thiamine and riboflavin content and antioxidant properties

The changes in thiamine content during the baking process were found to be weakly correlated with the ability of PBS extracts to scavenge ABTS•+ radicals (r= 0.68), ROO radicals (r= 0.47), O2−• radicals (r= 0.69), and FCR reducing capacity (r= 0.71), whereas no correlations with 80% methanol extracts were found. In contrast, the changes in riboflavin content were strongly correlated with the TEAC of PBS extracts (r= 0.96), PRSC (r = 0.92), FCR reducing capacity (r= 0.98), but not with SOD-like activity (r= 0.01). Weaker correlations were noted regarding the 80% methanol extracts. Only riboflavin, but not thiamine content, was correlated with DPPH radical scavenging activity of 80% methanol extracts (r= 0.81).

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

Our findings showed that rye breads are an important source of B vitamins since only a 200 g daily intake of bread formulated with flour type F-100% might provide about 40% and 22% of thiamine and riboflavin daily requirements for adolescents and adults, respectively. Rye breads provided higher antioxidant capacity (TEAC, PRSC, DPPH RSA, and FCR) than wheat bread.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

This study was supported by the Polish State Committee for Scientific Research (project nr PBZ-KBN-094/P06/2003/13) and Spanish–Polish common project interchange 006PL0012. This article is part of the PhD thesis of A. Michalska.

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  6. Conclusions
  7. Acknowledgments
  8. References
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