Impact of Wheat Bran Hydration Properties As Affected by Toasting

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Impact of wheat bran hydration properties as affected by toasting and degree of milling on optimal dough development in bread making Pieter J. Jacobs, Silke Bogaerts, Sami Hemdane, Jan A. Delcour, and Christophe M. Courtin J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.5b05958 • Publication Date (Web): 19 Apr 2016 Downloaded from http://pubs.acs.org on April 23, 2016

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Journal of Agricultural and Food Chemistry

IMPACT OF WHEAT BRAN HYDRATION PROPERTIES AS AFFECTED BY TOASTING AND DEGREE OF MILLING ON OPTIMAL DOUGH DEVELOPMENT IN BREAD MAKING

Pieter J. Jacobs1, Silke Bogaerts 2, Sami Hemdane1, Jan A. Delcour1, and Christophe M. Courtin1

1

Laboratory of Food Chemistry and Biochemistry, Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven, Kasteelpark Arenberg 20 - box 2463, 3001 Leuven, Belgium.

2

Provincial Control Unit Antwerp - Sector Transformation, Federal Agency for the Safety of the Food Chain, Italiëlei 4 - bus 18, 2000 Antwerpen, Belgium.

Corresponding author: Prof. C.M. Courtin, Laboratory of Food Chemistry and Biochemistry, Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven, Kasteelpark Arenberg 20 - box 2463, 3001 Leuven, Belgium. Tel: +32 16 321917. Fax: +32 16 321997. E-mail: [email protected]. 1 ACS Paragon Plus Environment


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ABSTRACT

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The impact of the hydration capacity and hydration rate of wheat bran on optimal bread dough

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development and loaf volume was investigated using coarse bran, both native as well as after

4

toasting, milling, presoaking and combinations of the latter. It was found that toasting reduces

5

bran’s hydration rate which, during mixing, results in a temporary excess of water in which

6

dough development takes place inefficiently and hence requires additional time. This

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mechanism was further substantiated by the observation that delayed dough development can

8

be counteracted by presoaking of bran. Milling of bran increases its hydration rate and results in

9

faster optimal dough development. Presoaking of non-milled bran, however, did not result in

10

faster dough development. Smaller bran particles do lead to faster dough development,

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probably due to increased proper contacts between flour particles. Optimal loaf volumes did

12

not change upon milling and toasting.

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KEYWORDS

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Wheat bran, bread making, dough development, loaf volume, particle size reduction, heat

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stabilization, prehydration, hydration kinetics, hydration capacity.

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INTRODUCTION

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The growing evidence for health promoting effects of dietary fiber and consumer interest in

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healthy food has led to an increase in the demand for dietary fiber enriched foods. To boost the

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daily intake of dietary fiber, staple foods such as bread constitute a convenient target for

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incorporation of dietary fiber. As a wheat milling byproduct, wheat bran is a highly available,

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convenient and cheap source of dietary fiber.1 However, despite the availability of wheat bran

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and the demand for healthy food, the daily intake of wheat bran is rather low. This discrepancy

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is largely explained by the fact that incorporation of wheat bran negatively affects food

24

processing and the organoleptic properties of the resultant product,2,3 and leads to higher

25

ingredient costs.

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Although the adverse impact of wheat bran on bread making has been investigated extensively,

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there is no consensus yet on the mechanisms which govern the negative effects of wheat bran

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on bread making. This is the result of the complex nature of wheat bran which may affect bread

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making in multiple ways and hence complicates wheat bran related research.4 To start with,

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wheat bran is characterized by its distinctive ability to bind considerable amounts of water in

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either a strong or weak fashion.5,6 This peculiar water binding potential may result in

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competition for hydration amongst bran and key flour constituents which may affect the bread

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making process. Moreover, the hydration kinetics during water uptake may be involved in these

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phenomena as well. In this perspective, Sanz Penella et al.7 ascribe prolonged dough

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development times in case of large bran particles to the fact that coarse bran requires more

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time to absorb its water in comparison with small particles. The observed changes in dough

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development upon particle size modification may, however, also be related to a size-dependent



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physical interference effect of bran on the dough matrix.7,8 In this perspective, the presence of

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relatively more particles in case of finely milled bran is suggested to cause more severe

40

disruption of the gluten network.7,9 In addition, wheat bran’s detrimental impact may also result

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from the presence of reactive biochemical components. These include enzymes such as

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endoxylanases, α-amylases, and endopeptidases10-13 which many may have an adverse impact

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above a specific threshold.13-16 Reactive chemicals in bran such as glutathione17 can weaken the

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gluten network. Taken together, the joint action of hydration phenomena, physical

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mechanisms, and reactive (bio)chemicals may determine the overall detrimental impact of

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wheat bran on bread making.

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To gain insight in the mechanisms at work and the relevance of each of these individual bran

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characteristics, considerable research has been conducted over the past years. Often, targeted

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bran modification were performed as these would allow a clear-cut approach to uncover cause

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effect relationschips. Nevertheless, many contradicting observations have been reported ever

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since. This is witnessed for instance in case of studies in which the role of bran hydration

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kinetics is assessed. Lai and others,18 for example, observed that presoaking of bran results in

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higher loaf volumes whereas no increase or even a slight decrease in bread volume was

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observed by Chen and others.19 Similar contradicting reports can be found with regard to the

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effect of bran particle size which is, amongst others, believed to affect bread making through

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bran size-dependent hydration phenomena. Whereas Özboy and Köksel20, de Kock et al.21,

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Campbell et al.22, Noort et al.23, and Cai et al.24 found that ground bran has a more detrimental

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effect on loaf volume, Lai et al.18, Moder et al.8, and Pomeranz et al.25 observed the opposite. In

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addtion, Zhang and Moore2 and Coda et al.26 found that an intermediate particle size resulted in


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the highest loaf volume and Gaillard and Gallagher27, Özboy and Köksel20, Curti et al.28, and Cai

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et al.24 observed that bran particle size did not affect bread volume at all. Conflicting

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observations have also been reported for various heat treatments. For instance, de Kock et al.21

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and Nelles et al.29 observed an increase in loaf volume upon dry autoclave treatment and boiling

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of bran, respectively, while Wang et al.30 and Gómez et al.31 reported no effect or a loss of loaf

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volume following bran extrusion. This may be due to the fact that heat treatments which are

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applied mainly to inactivate reactive (bio)chemicals can affect additional wheat bran properties

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such as hydration properties as well.32,33

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Against this background, the main aim of this study was to gain insight in the impact of wheat

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bran hydration properties on bran enriched bread making. For this purpose, different wheat

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bran treatments including particle size reduction, heat treatment, prehydration, and

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combinations thereof were performed to modify wheat bran’s hydration properties. The use of

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these treatments simultaneously allows for an estimation of the relevance of other bran

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properties such as reactive (bio)chemicals and potential size-related effects on bread making.

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MATERIALS AND METHODS

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Materials

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Commercial coarse wheat (Triticum aestivum L.) bran and white wheat flour from Crousti were

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provided by Dossche Mills (Deinze, Belgium). Amygluten was obtained from Syral (Aalst,

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Belgium). Chemicals, solvents and reagents were purchased from Sigma-Aldrich (Bornem,

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Belgium).



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Reduction of bran particle size

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The commercial wheat bran originally had an average particle size (dav) of 1377 µm. To allow for

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a wide particle size range to be investigated, the commercial wheat was sieved on a sieve with a

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mesh size of 1 mm which yielded bran with a dav of 1687 µm and a more narrow particle size

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distribution compared to the original sample. Bran samples with a dav of 520 µm and 77 µm

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were obtained by milling the sieved material using a Cyclotec 1093 Sample mill (FOSS, Höganäs,

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Sweden) as described by Jacobs et al.5

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Toasting of bran

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Wheat bran samples were toasted in a Condilux oven (Hein, Strassen, Luxemburg) at 170 °C

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during 30 min to inactivate wheat bran associated enzymes.33

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Presoaking of bran prior to bread making

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Presoaking of bran was performed prior to its use in bread making by mixing bran with the

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amount of water required to meet the baking absorption. The remaining ingredients were

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added to the bran – water mixture after presoaking to avoid wash-out effects. Non-toasted

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samples were hydrated during 15 min to guarantee complete hydration of coarse and fine

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bran.5 Longer presoaking periods were avoided to prevent enzyme activity or spontaneous

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fermentation. Heat stabilized bran samples were presoaked during 60 min to compensate for

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the reduced hydration rate upon toasting.33

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Chemical analyses

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The dietary fiber content was determined according to AOAC Official Method 991-4334 using the

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Megazyme Total Dietary Fiber Kit (Bray, Ireland). Arabinoxylan (AX) and starch contents were

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estimated through analysis by gas chromatography as described by Courtin et al.35 Analysis of 6 ACS Paragon Plus Environment

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water extractable AX involved aqueous extraction of the bran prior to analysis. β-glucan content

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was determined according to the Megazyme β-glucan assay (Bray, Ireland). The water

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extractable β-glucan was determined following aqueous extraction of bran prior to analysis.

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Damaged starch content was determined using the Megazyme damaged starch assay. Protein

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content was determined following a modification of AOAC Official Method 990-0334 to an

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automated Dumas protein analysis system (EAS Variomax N/CN, Elt, Gouda, The Netherlands)36

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using 6.31 as protein conversion factor.37 The lipid content was analyzed as described by Gerits

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et al.38 Ash and moisture contents were determined following AACC International Methods 08-

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01-01 and 44-15-02, respectively.36 Analyses were performed in triplicate.

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Analysis of enzyme activity levels

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The peroxidase catalyzed formation of tetraguaiacol using guaiacol and hydrogen peroxide as

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substrates was used to determine peroxidase activity39 in bran extracts which were prepared by

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extracting 1.0 g of bran in 10.0 mL potassium phosphate buffer (100 mM, pH 5.0) during 30 min

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at 180 rpm and centrifuging for 10 min at 1250 g. Afterwards, 100 µL extract, 50 µL guaiacol, 50

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µL hydrogen peroxide, and 2.80 mL potassium phosphate buffer were transferred in a cuvette

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to monitor the formation of tetraguaiacol spectrophotometrically at 436 nm and 25°C every

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minute during 9 min. After correction for the blank (100 µL extract and 2.90 mL buffer), the rate

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of increase in extinction at 436 nm represented the peroxidase activity. α-Amylase and

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endoxylanase activity were determined with the Amylazyme and Xylazyme methods,

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respectively (Megazyme, Bray, Ireland) while endopeptidase activity was determined using

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azocasein as substrate.40 These enzyme activity measurements were performed as described by

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Hemdane et al.41 7 ACS Paragon Plus Environment


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Water holding capacity

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The Enslin-Neff device42 was used to determine the water absorption kinetics and water holding

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capacity of bran (50.0 mg) as described by Jacobs et al.5 Analyses were performed in triplicate.

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Swelling capacity

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The method of Kuniak et al.43 was used with slight modifications as described by Jacobs et al.5 to

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determine the swelling capacity of bran. Analyses were performed in triplicate.

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Water retention capacity

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The water retention capacity was determined using two experimental approaches: the drainage

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centrifugation water retention capacity method and the commonly used traditional

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centrifugation water retention capacity method. Both analyses were performed as described in

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detail by Jacobs et al.5 and were each time performed in triplicate.

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Meal composition

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Bran enriched meal was composed with 75% white wheat flour, 20% wheat bran, and 5% vital

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wheat gluten. Control meal consisted of 95% white wheat flour and 5% vital gluten.

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Mixograph analysis

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Assessment of dough development and water absorption with a Mixograph (National

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Manufacturing, Lincoln, NE, USA) was performed according to AACC International Method 54-

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40-01 on a 10 g meal basis.36


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Farinograph analysis

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Dough development and water absorption were analyzed on a 10 g scale using a Brabender

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Farinograph (Duisburg, Germany) according to AACC International Method 54-21-01.36

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Bread making

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Bread making trials were performed according to the straight dough procedure of Shogren and

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Finney.44 Breads were prepared on a 100 g meal basis (14.0 %moisture content) to which 5.3 g

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compressed fresh yeast, 6.0 g sucrose, and 1.5 g salt were supplemented. Water absorption and

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kneading time were varied to determine the optimal bread making potential of each sample in

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terms of loaf volume. Pin mixers (National Manufacturing, Lincoln, NE, USA) for 100 g meals

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were used to knead the ingredients. Dough fermentation was performed in a fermentation

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cabinet (National Manufacturing) at 30 °C and 90% relative humidity. Dough was punched after

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52 and 77 min fermentation. After 90 min of fermentation, dough was punched, molded and

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proofed an additional 36 min. Dough was baked for 24 min at 215 °C in a rotary oven (National

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Manufacturing, Lincoln, NE, USA). Loaf volumes were determined with a Volscan (Stable Micro

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Systems, UK) using a vertical step of 1 mm and a rotational speed of 1 rps.

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Statistical analysis

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Statistical analysis of the results was performed using the Statistical Analysis Software 9.3 (SAS

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Institute Inc., Cary, NC,USA). One-way analysis of variation (ANOVA) was performed to analyze

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significant differences between mean values of several variables. A Tukey multiple comparison

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procedure was used with a 5% family significance level.



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RESULTS

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Wheat bran characteristics

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Chemical composition

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The bran sample with a dav of 1687 µm was composed of 50.2% dietary fiber of which more

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than half (27.7%) was arabinoxylan and a small fraction β-glucan (1.0%), 20.6% protein, 17.4%

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starch, 7.1% ash, and 6.1% lipids. This overall composition was not modified by the different

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bran treatments. Whereas the overall composition was not modified by the bran treatments, an

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increase in accessibility or extractability of bran constituents was observed upon milling. The

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amount of extractable lipids increased from 3.60% to 6.14% when going from a bran dav of 1687

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µm to a dav of 77 µm. The water extractable AX content and water extractable β-glucan content

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increased from 0.57% to 1.01% and from 0.13% to 0.21%, respectively. Furthermore, the

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damaged starch content increased slightly from 0.86% to 1.19%.5

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Hydration properties

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Table 1 shows that particle size reduction and heat treatment had little to no effect on either

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the drainage water retention capacity of bran or the Farinograph absorption of meal containing

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20% of the different bran samples. In contrast, large particles were clearly characterized by

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larger values for the traditional water retention capacity, the swelling capacity and Enslin water

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absorption in comparison with smaller particles. Heat treatment of coarse and fine bran in both

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cases did not affect these parameters. Considering the hydration kinetics, it was observed that

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milling reduced the time that bran requires to completely hydrate while dry heat treatment

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resulted in the opposite effect.


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Enzyme activities

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Reduction of the particle size from a dav of 1687 µm to a dav of 77 µm did not result in

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substantial changes in peroxidase, α-amylase, endoxylanase, or endopeptidase activity.

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Alternatively, the toast treatment successfully inactivated these enzymes (Table 1).

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Analysis of dough development

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Dough development of meals enriched with the different wheat bran samples was evaluated by

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means of Farinograph and Mixograph analyses using bran enriched meals which consisted of

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75% white wheat flour, 20% wheat bran and 5% vital gluten and a control meal which was

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composed of 95% white wheat flour and 5% vital gluten. The Farinograph water absorption did

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not change to great extent upon milling, heat treatment and a combination of both. All bran

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enriched meals were characterized by comparable dough water absorptions which varied

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around an average of 67.4 ± 1.5% (Table 1). In comparison, control meal showed a Farinograph

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water absorption of 59.3% ± 0.1%. When studying the Farinograph profiles (Figure 1), it was

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clear that in the presence of coarse bran (Figure 1A) dough developed considerably slower in

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comparison with the control meal. Practically, the dough development time increased from 2.0

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min to 10.0 min upon substitution of 20% flour with 20% coarse bran with a dav of 1687 µm.

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Upon reduction of bran particle size to a dav of 520 µm and 77 µm, the dough development time

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decreased to 8.4 min and 4.2 min, respectively (Figure 1B & 1C). Concerning the shape of the

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Farinograph profiles, the dough development curves displayed a lot of fluctuations in case of

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large particles while smoother curves were observed in the presence of the finest bran sample.

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Regarding the impact of toasting on dough development, a significant increase in dough

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development time was observed. For the coarse sample with a dav of 1687 µm, the 11 ACS Paragon Plus Environment


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development time increased from 10.0 min to 12.2 min while for the milled sample with a dav of

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77 µm an increase from 4.2 min to 10.8 min was observed. The shape of the curves also

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changed. Whereas an uninterrupted curved profile was observed in the presence of untreated

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bran samples, a slope discontinuity was seen in the presence of toasted bran samples.

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The optimal water absorptions as determined with the Mixograph were situated around a 67.5

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± 1.0% in the presence of each of the bran samples while the optimal absorption was situated at

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60.0 ± 1.0% for the control meal. In contrast to the Farinograph analyses, the Mixograph profiles

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did not show clear differences amongst the bran enriched samples (results not shown). The

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dough development times varied around 4.0 ± 0.5 min for all bran enriched samples while a

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dough development time of 3.0 ± 0.5 min was observed for control meal.

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Bread making potential of untreated and heat treated coarse and fine wheat bran and impact

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of prehydration

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The impact of the various bran samples on bread making was assessed by means of bread

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making trials in which both water absorption and mixing times were varied (Figure 2). Based on

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these experiments, several general phenomena were observed. To start with, each of the

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mixing time – loaf volume response curves for a given water absorption displayed an optimal

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mixing time at which the loaf volume reached a maximum value. With increasing water

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absorption, the curves typically shifted to longer mixing times such that the optimal mixing

223

times were prolonged. At the same time, the loaf volume optimum at each water level was

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found to increase with increasing water absorption. This phenomenon was observed up to a

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water absorption of 80%. Further increase of the water absorption led to sticky doughs that


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were difficult to handle, did not yield higher loaf volume and displayed a heterogeneous crumb

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structure. Hence, a water absorption of 80% emerged as optimal for all bran samples.

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Figure 3 shows the mixing time – loaf volume response curves for bran samples with non-

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toasted and toasted bran with a dav of 1687 µm and 77 µm at the optimal water absorption of

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80%. Upon particle size reduction of non-toasted as well as toasted samples, the mixing time –

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loaf volume response curves shifted towards shorter mixing times such that optimal dough

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development was achieved at shorter mixing times. In case of the non-toasted samples, the

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optimal dough development time decreased from 9.0 min to 7.5 min and eventually to 4.5 min

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for bran samples with a dav of 1687 µm, 520 µm, and 77 µm, respectively (Figure 2A, B & C,

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Figure 3A & C). A similar size-effect was observed for the toasted samples. Practically, the

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optimal dough development time decreased from 10.5 min to 7.5 min for toasted bran samples

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with a dav of 1687 µm and 77 µm, respectively (Figure 3B & D). Considering the impact of

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toasting, it was found that the mixing time – loaf volume response curves shifted towards

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longer mixing times for both coarse and fine bran. Accordingly, the optimal mixing time shifted

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from 9.0 min to 10.5 min for bran with a dav of 1687 µm (Figure 3A & B) and from 4.5 min to 7.5

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min for bran with a dav of 77 µm (Figure 3C & D). Finally, presoaking of the various bran samples

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was performed to investigate the role of bran hydration dynamics on bread making. It was

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observed that presoaking of toasted bran samples caused the mixing time – loaf volume

244

response curve to shift to shorter mixing times for both large and small particle sizes (Figure 3B

245

& D). For non-toasted samples, the non-presoaked samples and presoaked samples displayed

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similar mixing time – loaf volume response curves (Figure 3A & C).



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The volumes of breads prepared with the different wheat bran samples at their optimal water

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absorption and optimal mixing times together with an illustration of their crumb structure are

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shown in Figure 4. In comparison with the white bread control with a loaf volume of 727 mL, all

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wheat bran enriched breads displayed significantly lower loaf volumes. The loaf volumes of

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wheat bran enriched breads, however, were very comparable as their average volume was 538

252

± 20 mL. Statistical analysis of the data moreover indicated that changes in bread making

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potential of bran upon milling or toasting were not significant. Regarding the bread crumb,

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variations in crumb color and crumb structure between the control bread and bran enriched

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breads were the most outspoken differences. Bran enriched bread in general displayed darker

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crumb compared to white bread and amongst bran enriched samples a darker color was

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obtained upon milling and toasting. Furthermore, white control bread was characterized by a

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homogeneous crumb structure consisting of small gas cells in contrast to bran enriched breads

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where the crumb displayed a more heterogeneous gas cell distribution. Based on comparison of

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multiple breads for each sample, no additional clear differences in crumb structure were

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distinguishable amongst the samples (Figure 4).

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DISCUSSION

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Impact of particle size reduction and toasting on wheat bran properties

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The composition of the considered bran sample is in agreement with data found in literature.4

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Concerning bran’s hydration properties, the impact of particle size on the capacity of bran to

266

bind water either strong or weakly has been described in previous work of the authors. From

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that work it was concluded that the water bound by bran during dough mixing is water which is

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relatively strongly bound and that this strong water binding capacity is independent of bran 14 ACS Paragon Plus Environment

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particle sizes in a range of 1687 to 77 µm.5 Additional research pointed out that toasting of bran

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during 30 min at 170°C did not have a considerable impact on bran’s hydration at equilibrium

271

(Table 1). In contrast, the hydration kinetics were modified by both particle size reduction and

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heat treatment (Table 1). The increased hydration rates upon particle size reduction may be

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ascribed to the increased specific surface,5 while the reduced hydration rates upon heat

274

treatment are ascribed to an increased surface hydrophobicity.33 In comparison, a reduction in

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the Enslin-Neff hydration rate after a toast process of coarse bran at 230 °C for 7.5 min was

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observed by Caprez et al.32 Moreover, Ralet et al.45 witnessed a similar effect on the Enslin-Neff

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water absorption upon a high energy-input extrusion cooking process at 100°C.

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Besides changes in hydration properties, the increase in extractable lipids, water extractable AX,

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and water extractable β-glucan content upon milling points out an increased accessibility of

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bran constituents which can be ascribed to the fact that cells are damaged during the impact

281

milling process.5 De Kock et al.21 suggested that this cell breakage may simultaneously lead to

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release of reactive components. Based on the measured enzyme activities, such phenomenon

283

was not observed though (Table 1). This may be related to the fact that a large share of bran

284

related enzymes originate from microorganisms which renders them readily accessible.10 Upon

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heat treatment, lipases, endoxylanases, α-amylases, and peroxidases were inactivated. Since

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peroxidase is associated with high heat stability, it is likely that all of the wheat bran related

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enzymes were inactivated.33

288

Assessment of the role of (modified) wheat bran hydration properties during bread making

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The role of specific bran characteristics during bread making may be evaluated based on

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analyses such as Farinograph analyses, Mixograph analyses, and bread making trials. However, 15 ACS Paragon Plus Environment


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comparison of these analyses reveals that the phenomena observed in Mixograph and

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Farinograph analyses only correspond to a greater or lesser extent to those observed in the

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baking trials. To start with, the baking absorptions of approximately 67.5% as determined by

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Farinograph and Mixograph analyses does not correspond to the baking absorption which

295

coincides with the maximal loaf volume. The bread making optimization trials (Figure 2)

296

indicated that increasing the baking absorptions and mixing time results in higher loaf volumes

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until the water absorption exceeds a level (80%) beyond which dough becomes too sticky and

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unmanageable. This observation is in agreement with the findings of Roels et al.46 and Oliver &

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Allen47 who saw a similar phenomenon for white flour. The increase in time required to obtain

300

optimal mixing with higher water absorption is furthermore ascribed to a less efficient energy

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transfer from the mixer into the developing dough at higher water content. For wheat bran

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enriched bread making, Lai et al.18 also found that water absorptions higher than those

303

indicated by Mixograph analyses gave rise to increased loaf volumes. Hence, given the fact that

304

the Farinograph and Mixograph are not suited to predict the optimal baking conditions, their

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use to assess the role of certain wheat bran properties on bread is reliable only up to a certain

306

extent. For instance, both analyses correctly indicate that the water absorption did not change

307

through particle size reduction or heat treatment. The Farinograph also picked up the decrease

308

and increase in dough development time upon milling and toasting, respectively, which were

309

observed in the baking trials (Figure 2). Similar to the observations of Cai et al.24, such trends

310

were not observed in Mixograph analyses. Ultimately, the mixing time – loaf volume response

311

curves (Figure 2) should primarily be considered to assess the role of wheat bran properties on

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bread making.


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Impact of particle size dependent hydration properties on bread making

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Whereas particle size did not have an outspoken effect on the relative strong water binding

315

capacity of wheat bran, which is relevant during dough development,5 the time required for

316

complete hydration of bran is dependent on particle size as shown by the Enslin-Neff water

317

uptake experiments (Table 1). The fact that the optimal water absorption remained constant for

318

samples with varying particle size is in agreement with the former finding. The small differences

319

in strong water binding capacity that were observed in some cases (Table 1) thus did not appear

320

to exert a significant effect during bread making. To evaluate whether or not the modified

321

hydration kinetics affect the bread making process, the mixing time – loaf volume response

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curves obtained for the non-toasted samples before and after prehydration are considered

323

(Figure 3A & C). Comparison of these profiles shows that, for both bran samples with a dav of

324

1687 µm and 77 µm, prehydration of bran did not significantly affect the mixing time – loaf

325

volume response curves. This indicates that particle size dependent differences in bran

326

hydration kinetics are not relevant towards bread making and cannot explain the alteration in

327

mixing time – loaf volume response curves upon milling. The irrelevance of particle size

328

dependent bran hydration kinetics may be ascribed to the fact that water uptake in the Enslin-

329

Neff test occurs in a passive fashion while mixing will most likely promote water uptake.

330

Considering the above, it is clear that size dependent wheat bran hydration properties cannot

331

explain the outspoken differences in mixing time – loaf volume profiles of coarse and fine bran.

332

The effect of milling on these profiles must therefore be related to a pure particle size effect or

333

a potential release of detrimental reactive (bio)chemicals.21 The latter possibility can be

334

excluded given the independency of enzyme activities from particle size and the fact that bran 17 ACS Paragon Plus Environment


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samples with different dav have the same bread making potential (Figure 4). Therefore, the

336

correlation between milling of bran and a decrease in mixing time which correlates with optimal

337

loaf volumes appears to be primarily the resultant of a particle size related effect. This effect is

338

ascribed to the hypothesis that bran particles physically hinder interaction amongst flour

339

particles due a shielding effect which is more outspoken in case of larger particles. It can be

340

reasoned that this effect is minimal in case of the finest bran sample with a dav of 77 µm, since

341

this particle size is of the same order of magnitude of flour particles48 which would therefore

342

hinder contact amongst flour particles to a lesser extent. This hypothesis is substantiated by the

343

trends observed in the Farinograph analyses where coarse particles with a dav of 1687 µm

344

display a dough development time of 10.0 min which decreases to 8.4 min and 4.2 min for bran

345

with a dav of 520 µm and 77 µm, respectively (Figure 1). With regard to the optimal loaf

346

volumes, the bran samples with variable dav did not show significant differences. Hence, it can

347

be concluded that the impact of wheat bran on bread making is independent of particle size

348

given the prerequisite that optimal dough development is achieved during mixing.

349

Validation of these results based on literature is rather complicated given the great controversy

350

which exists with regard to the effect of particle size reduction on loaf volume. While Özboy and

351

Köksel20, de Kock et al.21, Campbell et al.22, Noort et al.23, Cai et al.24 found fine bran to exert a

352

more detrimental effect on loaf volume, Lai et al.18, Moder et al.8, and Pomeranz et al.25,

353

observed the opposite. However, Zhang and Moore2 and Coda et al.26 found that an

354

intermediate particle size resulted in the highest loaf volume while Gaillard and Gallagher27 and

355

Curti et al.28, Özboy and Köksel20, and Cai et al.24 saw no effect of bran particle size on loaf

356

volume. Alternatively, these contradictions may be clarified based on the results from the 18 ACS Paragon Plus Environment

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357

baking trials (Figure 2). Depending on the selected water absorption and mixing time,

358

conclusions similar to those found in literature can be drawn. For instance, at 80% water

359

absorption (Figure 3A & 3C) and at a constant mixing time in the range of three to six minutes,

360

smaller bran particles will emerge as the most beneficial bran samples in terms of loaf volume.

361

In contrast, the coarse bran particles start to emerge as the most favorable sample at a mixing

362

time of 9 min. Though, at their optimal dough development times, bran particle size does not

363

significantly affect the loaf volume (Figure 4). Inappropriate estimation of mixing time as well as

364

water absorption will thus lead to a wrong evaluation of its impact on bread making and may

365

explain the contradictions that are found in literature. For instance, Pomeranz et al.25, Noort et

366

al.23, and Cai et al.24 used either the Farinograph or Mixograph to determine water absorption

367

and mixing times while it was found that these devices were not able to predict their optimal

368

values. In the studies of Campbel et al.22, de Kock et al.21, Gaillard & Gallagher27, Moder et al.8,

369

Zhang & Moore2 , Coda et al.26, Curti et al.28, Lai et al.18, and Özboy & Köksel20 the approach to

370

determine baking conditions was not specified which renders comparison of the results difficult.

371

Impact of toasting on wheat bran hydration and its functionality during bread making

372

As evidenced by the reduced Enslin water uptake rate, toasting of bran causes a significant

373

reduction in hydration speed (Table 1) which is ascribed to an increase in surface hydrophobicity

374

during dry heat treatment.33 To assess whether or not the reduced hydration kinetics affect

375

bread making, the baking trials in which toasted and presoaked toasted bran were used are

376

considered (Figure 3B & D). The profiles demonstrate that, at relative short mixing times,

377

incorporation of presoaked bran results in larger loaf volumes compared to breads prepared

378

with non-presoaked bran. This indicates that relatively more optimal dough must have been 19 ACS Paragon Plus Environment


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379

developed in the presence of presoaked bran. The underlying mechanism through which bran’s

380

modified hydration behavior governs dough development can be clarified when considering the

381

water distribution in developing dough after a specific mixing time for both cases. For

382

formulations including presoaked heat treated bran, it can be reasoned that the amount of

383

readily available water at the start of mixing amounts to approximately 75% of the total amount

384

added, under the assumption that 20 mL out of the 80 mL of added water is already absorbed

385

by the 20 g of bran. At the start of mixing, an additional share of water is absorbed by flour so

386

that a proper water distribution is achieved which concurs with normal dough development.

387

Alternatively, incorporation of non-presoaked bran implies that an excess of 20 mL of water or

388

33% more water than what is required for a proper hydration is initially present in an unbound

389

state during mixing. Due to the slow water uptake rate of toasted bran, the excess of water

390

gives rise to a batter-like system in which energy transfer from mixers to the developing gluten

391

network occurs less efficient. Only as the excess water gets absorbed slowly in the act of mixing,

392

the batter-like system will evolve to a normal developing dough system such that proper dough

393

development is eventually achieved after an extended period. This phenomenon can also be

394

deduced from the Farinograph profiles of the toasted samples (Figure 1). Initially, they display a

395

limited but fast dough development which can be ascribed to both the viscosity of the meal –

396

water mixture and limited dough development. After a subsequent slope discontinuity, the

397

consistency builds up slowly as the relative slow water absorption causes a long-lasting high free

398

water content and inefficient dough development. Gómez et al.31 observed a similar effect in

399

Doughlab analyses upon bran extrusion indicating that other (hydro)thermal treatments may

400

also result in less efficient dough development. In contrast to the modified hydration kinetics,


Page 21 of 37


401

toasting did not have a considerable effect on wheat bran’s equilibrium water uptake (Table 1).

402

Since the optimal loaf volumes were obtained at the same dough water absorption as the

403

untreated bran, the small differences in strong water binding capacity that were observed in some

404

cases (Table 1) were not relevant during bread making. For the optimal loaf volumes (Figure 4), no

405

significant differences were observed. Hence, whereas toasting delays bran hydration and

406

consequently dough development, its impact on bread making at optimal dough development is

407

not affected. Given that this impact does not change upon toasting, it can furthermore be

408

concluded that, at least in this case, heat sensitive bran components including various enzymes

409

such as α-amylase, endoxylanases, and peptidase (Table 1) did not determine this impact.

410

Despite the relative high concentration of enzymes, their impact in bread making may be less

411

pronounced due to dilution of these components in meal. It can moreover be argued that

412

enzyme activity in dough may not be optimal due to limited substrate accessibility, inhibition

413

phenomena, and non-optimal incubation temperature and pH.

414

Validation of these conclusions is hard since data on the impact of (hydro)thermal treatments

415

on the influence of bran on bread making is limited and inconclusive. For instance, de Kock et

416

al.21 and Nelles et al.29 observed an increase in loaf volume upon dry autoclave treatment and

417

boiling of bran, respectively. However, Wang et al.30, Gómez et al.31 reported no effect or a loss

418

of bread making potential of wheat bran following extrusion of bran. In any of these cases,

419

there is no guarantee though that breads were prepared under optimal conditions due to the

420

limited information on the water absorption and mixing time that was provided in these studies.

421

The baking trials in this paper (Figure 2) demonstrated that these optimal conditions are,

422

amongst others, dependent on the modified bran hydration kinetics and should be taken into 21 ACS Paragon Plus Environment


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423

account to correctly assess the impact of bran on bread making. In this perspective, it is

424

noteworthy to mention that Wang et al.30 used a software supported response surface method

425

to determine the optimal baking absorption and mixing time and at least in one case came to a

426

similar result.

427

On a final note, comparison of the mixing time – loaf volume response curves (Figure 3) and

428

Farinograph profiles (Figure 1) of all differently treated bran samples indicates that the effects

429

of milling and toasting of bran on dough development are cumulative in nature. For instance,

430

particle size reduction results in a similar decrease of the optimal dough development time in

431

case of the non-toasted as well as the toasted bran. Alternatively, toasting delays optimal dough

432

development for both coarse and fine bran particles. The cumulative nature of the effect of

433

both treatments on optimal dough development is schematically represented in Figure 5.

434

Whereas high hydration rates are associated with short optimal dough development times,

435

large particles prolong the optimal dough development time. Furthermore, the dough

436

development time may be modified by means of wheat bran modifications such as toasting,

437

which reduces the hydration rate and increases the dough development time or milling, which

438

decreases particle size and hence the optimal dough development time.

439

ABBREVIATIONS

440

dav, average particle size

441

AX, arabinoxylan


Page 23 of 37


442

ACKNOWLEDGEMENTS

443

Pieter J. Jacobs acknowledges the Institute for the Promotion of Innovation through Science and

444

Technology in Flanders (IWT-Vlaanderen, Brussels, Belgium) for financial support (IWT-121702).

445

Sami Hemdane acknowledges Flanders’ FOOD (Brussels, Belgium) for financial support within

446

the framework of the BranTech project. This research is also part of the Methusalem program

447

Food for the Future (2007-2014) at the KU Leuven.

448

NOTES

449

The authors declare no competing financial interest.

450

REFERENCES

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(1) Vetter, J. L. Fiber as a food ingredient. J. Food Technol. 1984, 38, 64.

452

(2) Zhang, D. C.; Moore, W. R. Wheat bran particle size effects on bread baking performance and

453 454 455 456 457 458 459 460 461 462 463

quality. J. Sci. Food Agr. 1999, 79, 805–809. (3) Albers, S.; Muchová, Z.; Fikselová, M. The effects of different treated brans additions on bread quality. Scienta Agriculturae Bohemica 2009, 40, 67–72. (4) Hemdane, S.; Jacobs, P. J.; Dornez, E.; Verspreet, J.; Delcour, J. A.; Courtin, C. M. Wheat (Triticum aestivum L.) Bran in Bread Making: A Critical Review. Compr. Rev. Food Sci. Food Saf. 2015. (5) Jacobs, P. J.; Hemdane, S.; Dornez, E.; Delcour, J. A.; Courtin, C. M. Study of hydration properties of wheat bran as a function of particle size. Food Chem. 2015, 179, 296–304. (6) Roozendaal, H.; Abu-Hardan, M.; Frazier, R. A. Thermogravimetric analysis of water release from wheat flour and wheat bran suspensions. J. Food Eng. 2012, 111, 606–611. (7) Sanz Penella, J. M.; Collar, C.; Haros, M. Effect of wheat bran and enzyme addition on dough functional performance and phytic acid levels in bread. J. Cereal Sci. 2008, 48, 715–721.



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(8) Moder, G. J.; Finney, K. F.; Bruinsma, B. L.; Ponte, J. G.; Bolte, L. C. Bread-making potential of

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straight-grade and whole-wheat flours of triumph and Eagle Plainsman V hard red winter

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wheats. Cereal Chem. 1984, 61, 269–273.

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(9) Zhang, D. C.; Moore, W. R. Effect of wheat bran particle size on dough rheological properties. J. Sci. Food Agr. 1997, 74, 490–496. (10) Dornez, E.; Cuyvers, S.; Gebruers, K.; Delcour, J. A.; Courtin, C. M. Contribution of wheat

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endogenous and wheat kernel associated microbial endoxylanases to changes in the

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arabinoxylan population during breadmaking. J. Agric. Food Chem. 2008, 56, 2246–2253.

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(11) Lunn, G.; Kettlewell, P.; Major, B.; Scott, R. Effects of pericarp alpha-amylase activity on wheat (Triticum aestivum) Hagberg falling number. Ann. Appl. Biol. 2001, 138, 207–214. (12) Kaprelyants, L.; Fedosov, S.; Zhygunov, D. Baking properties and biochemical composition of wheat flour with bran and shorts. J. Sci. Food Agr. 2013, 93, 3611–3616. (13) Rani, K.; Rao, U. P.; Leelavathi, K.; Rao, P. H. Distribution of enzymes in wheat flour mill streams. J. Cereal Sci. 2001, 34, 233–242.

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(14) Bonnin, E.; Le Goff, A.; Saulnier, L.; Chaurand, M.; Thibault, J. F. Preliminary characterisation of

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endogenous wheat arabinoxylan-degrading enzymic extracts. J. Cereal Sci. 1998, 28, 53–62.

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(15) Every, D.; Simmons, L. D.; Ross, M. P. Distribution of redox enzymes in millstreams and relationships to chemical and baking properties of flour. Cereal Chem. 2006, 83, 62–68. (16) Poutanen, K. Enzymes: An important tool in the improvement of the quality of cereal foods. Trends Food Sci. Technol. 1997, 8, 300–306. (17) Joye, I. J.; Lagrain, B.; Delcour, J. A. Use of chemical redox agents and exogenous enzymes to

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modify the protein network during breadmaking–a review. J. Cereal Sci. 2009, 50, 11–21.

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(18) Lai, C. S.; Hoseney, R. C.; Davis, A. B. Effects of wheat bran in breadmaking. Cereal Chem. 1989, 66,

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217–219.


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(19) Chen, H.; Rubenthaler, G. L.; Leung, H. K.; Baranowski, J. D. Chemical, physical, and baking properties of apple fiber compared with wheat and oat bran. Cereal Chem. 1988, 65, 244–247. (20) Özboy, O.; Köksel, H. Unexpected strengthening effects of a coarse wheat bran on dough rheological properties and baking quality. J. Cereal Sci. 1997, 25, 77–82. (21) de Kock, S.; Taylor, J.; Taylor, J. R. N. Effect of heat treatment and particle size of different brans on loaf volume of brown bread. Lebensm.-Wiss. Technol. 1999, 32, 349–356.

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(22) Campbell, G. M.; Ross, M.; Motoi, L., Bran in bread: Effects of particle size and level of wheat and

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oat bran on mixing, proving and baking, in Bubbles in Food 2: Novelty, Health and Luxury, G.M.

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Campbell, M.G. Scanlon, and D.L. Pyle, Editors., Eagan Press: Eagan, 2008, 337–354.

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(23) Noort, M. W. J.; van Haaster, D.; Hemery, Y.; Schols, H. A.; Hamer, R. J. The effect of particle size of

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wheat bran fractions on bread quality - Evidence for fibre protein interactions. J. Cereal Sci. 2010,

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52, 59–64.

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(24) Cai, L.; Choi, I.; Hyun, J. N.; Jeong, Y. K.; Baik, B. K. Influence of bran particle size on bread-baking quality of whole grain wheat flour and starch retrogradation. Cereal Chem. 2014, 91, 65−71. (25) Pomeranz, Y.; Shogren, M. D.; Finney, K. F.; Bechtel, D. B. Fiber in breadmaking - Effects on functional properties. Cereal Chem. 1977, 54, 25–41. (26) Coda, R.; Kärki, I.; Nordlund, E.; Heiniö, R. L.; Poutanen, K.; Katina, K. Influence of particle size on

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bioprocess induced changes on technological functionality of wheat bran. Food Microbiol. 2014,

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37, 69–77.

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(27) Galliard, T.; Gallagher, D. The effects of wheat bran particle size and storage period on bran flavour and baking quality of bran/flour blends. J. Cereal Sci. 1988, 8, 147−154. (28) Curti, E.; Carini, E.; Bonacini, G.; Tribuzio, G.; Vittadini, E. Effect of the addition of bran fractions on bread properties. J. Cereal Sci. 2013, 57, 325−332.



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(29) Nelles, E. M.; Randall, P. G.; Taylor, J. R. N. Improvement of brown bread quality by prehydration treatment and cultivar selection of bran. Cereal Chem. 1998, 75, 536−540. (30) Wang, W. M.; Klopfenstein, C. F.; Ponte, J. G. Effects of twin-screw extrusion on the physical

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properties of dietary fiber and other components of whole wheat and wheat bran and on the

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baking quality of the wheat bran. Cereal Chem. 1993, 70, 707−711.

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(31) Gómez, M.; Jimenez, S.; Ruiz, E.; Oliete, B. Effect of extruded wheat bran on dough rheology and bread quality. Lebensm.-Wiss. Technol. 2011, 44, 2231–2237.

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(32) Caprez, A.; Arrigoni, E.; Amado, R.; Neukom, H. Influence of different types of thermal treatment

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on the chemical composition and physical properties of wheat bran. J. Cereal Sci. 1986, 4, 233–

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(33) Jacobs, P. J.; Hemdane, S.; Delcour, J. A.; Courtin, C. M. Dry heat treatment affects wheat bran surface properties and hydration kinetics. Food Chem. 2016, 203, 513–520.

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(34) AOAC In Official methods of analysis, 16th ed., AOAC: Arlington, 1995.

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(35) Courtin, C. M.; Van den Broeck, H.; Delcour, J. A. Determination of reducing end sugar residues in

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oligo- and polysaccharides by gas-liquid chromatography. J. Chromatogr. A 2000, 866, 97−104.

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(36) AACC International In Approved methods of analysis, 11th ed., AACC International: St. Paul.

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(37) Jones, D. B. Factors for converting percentatges of nitrogen in foods and feeds into percentages of

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proteins. USDA Circular Series 1941, 183, 1–21. (38) Gerits, L. R.; Pareyt, B.; Delcour, J. A. Single run HPLC separation coupled to evaporative light

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scattering detection unravels wheat flour endogenous lipid redistribution during bread dough

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making. Lebensm.-Wiss. Technol. 2013, 53, 426–433.

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(39) Bergmeyer, H. U. In Methods of enzymatic analysis. Verlag Chemie, 1974.


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enzyme während der seneszenz von weizenblättern (Triticum aestivum L.). Z. Pflanzenphysiol.

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1978, 90, 235−244.

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(41) Hemdane, S.; Leys, S.; Jacobs, P. J.; Dornez, E.; Delcour, J. A.; Courtin, C. M. Wheat milling byproducts and their impact on bread making. Food Chem. 2015, 187, 280−289.

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(42) Enslin, O. Über einen apparatzur messung der flüssigkeitsaufnahme von quellbaren und porösen

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stoffen und zur charakterisierung der benetzbarkeit. Chem. Fabrik 1933, 13, 147–148.

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(43) Kuniak, L.; Marchess, R. H. Study of crosslinking reaction between epichlorohydrin and starch.

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Starch 1972, 24, 110–116. (44) Shogren, M. D.; Finney, K. F. Bread-making test for 10 grams of flour. Cereal Chem. 1984, 61, 418−423. (45) Ralet, M. C.; Thibault, J. F.; Della Valle, G. Influence of extrusion-cooking on the physico-chemical properties of wheat bran. J. Cereal Sci. 1990, 11, 249−259.

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(46) Roels, S.; Cleemput, G.; Vandewalle, X.; Nys, M.; Delcour, J. Bread volume potential of variable-

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baking absorption levels. Cereal Chem. 1993, 70, 318−318.

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(47) Oliver, J.; Allen, H. The mixing requirement of the Australian hard wheat cultivar Dollarbird. Cereal Chem. 1994, 71, 51−54. (48) Hareland, G. Evaluation of flour particle size distribution by laser diffraction, sieve analysis and near-infrared reflectance spectroscopy. J. Cereal Sci. 1994, 20, 183−190.



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Figure captions Figure 1: Farinograms of bran enriched meals (75% flour, 20% bran, 5% vital gluten) with different average particle sizes (dav) before and after toasting (T). Farinograms of bran enriched meals (black) are shown on top of control meal (95% flour, 5% vital gluten) (grey). (A) dav: 1687 µm, (B) dav: 520 µm, (C) dav: 77 µm, (D) dav: 1687 µm T, (E) dav: 77 µm T. Bran enriched meals required a water addition of approximately 70% to reach 500 Farinograph units while control meal required 60%.

Figure 2. Loaf volumes of bran enriched breads (75% flour, 20% bran, 5% vital gluten) with different dav before and after toasting (T) as a function of mixing time and water absorption. (A) dav: 1687 µm, (B) dav: 520 µm, (C) dav: 77 µm, (D) dav: 1687 µm T, (E) 77 µm T. The optimal water absorption for all samples was 80%.

Figure 3. Loaf volumes of bran enriched breads (75% flour, 20% bran, 5% vital gluten) containing differently treated bran samples as a function of mixing time at an optimal water absorption of 80%. (A) Untreated and presoaked bran with an average particle size (dav) of 1687 µm. (B) Toasted and presoaked toasted bran with a dav of 1687 µm. (C) Untreated and presoaked bran with a dav of 77 µm. (D) Toasted an presoaked toasted bran with a dav of 77 µm. Figure 4. Loaf volumes of control bread (95% flour, 5% vital gluten) and bran enriched breads (75% flour, 20% bran, 5% vital gluten). The latter were prepared with untreated or toasted (T)


Page 29 of 37


bran with varying average particle sizes at optimal water absorption and mixing time. The water absorption and mixing time used for control meal were 60% and 4 min, respectively.

Figure 5. Dependency of optimal dough development time of bran enriched dough on bran hydration rate and bran particle size. A short dough development time is obtained in case of bran which is characterized by a fast hydration rate and small particle size.

553



Page 30 of 37

Tables Table 1. Hydration properties and enzyme activities of wheat bran samples with average particle

555

sizes (dav) of 1687 µm, 520 µm, and 77 µm and toasted (T) wheat bran with a dav of 1687 µm

556

and 77 µm. Values within the same row not sharing a same letter are significantly different (P

Impact of Wheat Bran Hydration Properties As Affected by Toasting

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