Rheological and stability aspects of dry and hydrothermally heat treated aleurone-rich wheat milling fraction

Food Chemistry 220 (2017) 9–17

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Rheological and stability aspects of dry and hydrothermally heat treated aleurone-rich wheat milling fraction Blanka Bucsella a,d,⇑, Ágnes Takács a, Walter von Reding b, Urs Schwendener c, Franka Kálmán d, Sándor Tömösközi a a Department of Applied Biotechnology and Food Science, Faculty of Chemical Engineering and Bioengineering, Budapest University of Technology and Economics, Szent Gellért tér 4. H-1111, Budapest, Hungary b Business Unit Grain Milling Flour Services, Gupfenstrasse 5, CH-9240 Uzwil, Switzerland c Value Added Processing Bühler AG, Gupfenstrasse 5, CH-9240 Uzwil, Switzerland d Institute of Life Technologies, University of Applied Sciences Western Switzerland, Route du Rawyl 47, CH-1950 Sion, Switzerland

a r t i c l e

i n f o

Article history: Received 29 May 2016 Received in revised form 25 September 2016 Accepted 29 September 2016 Available online 30 September 2016 Keywords: Heat treatment Aleuron Mixolab RVA Phenolic compound Fiber

a b s t r a c t Novel aleurone-rich wheat milling fraction developed and produced on industry scale is investigated. The special composition of the novel flour with high protein, dietary fiber and fat content results in a unique combination of the mixing and viscosity properties. Due to the high lipid concentration, the fraction is exposed to fast rancidity. Dry heat (100 °C for 12 min) and hydrothermal treatment processes (96 °C for 6 min with 0–20 L/h steam) were applied on the aleurone-rich flour to modify the technological properties. The chemical, structural changes; the extractability of protein, carbohydrate and phenolic components and the rheological characteristics of the flours were evaluated. The dry treated flour decreased protein and carbohydrate extractability, shortened dough development time, reduced gel strength and enhanced the gelling ability. Hydrothermal treatment caused changes in the phenolic content improved the dough stability and -resistance. Heat treatment processes were able to extend the stability of the flour. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction The consumption of the bran and fiber enriched food products has increased over the last years (King, Mainous, & Lambourne, 2012). There is still a need for new applications to increase further the sensorial acceptance and the available selection of fiber-rich cereal based food. Currently, the traditional whole grain fractions are commonly used to increase the nutritional value of the cereal based products. The whole grain cereal fractions with the bran and the germ contain fat in a higher amount (2–3%) than white flour (0.5–1%) (Jaekel, Batista, Steel, & Chang, 2012). Thus, whole grain flours are more exposed to rancidity during storage than white flours. The shelf-life of whole grain wheat flour is 3–9 months and the viability of white wheat flour is extended 9–15 months after milling indicated by producers on the packages. In the cereal industry hydrothermal and dry heat treatment processes (Zhao et al., ⇑ Corresponding author at: Department of Applied Biotechnology and Food Science, Faculty of Chemical Engineering and Bioengineering, Budapest University of Technology and Economics, Szent Gellért tér 4. H-1111, Budapest, Hungary. E-mail address: [email protected] (B. Bucsella). http://dx.doi.org/10.1016/j.foodchem.2016.09.198 0308-8146/Ó 2016 Elsevier Ltd. All rights reserved.

2014) are applied mainly for extending the shelf-life and modifying the techno-functional properties of the flours during food production (Ozawa, Kato, & Seguchi, 2009). The dry heat treatment processes (Zhao et al., 2014) are cost effective methods for extending the shelf-life of whole meal flours via microbial activity reduction, lipase and lipoxygenase enzyme inactivation. In these processes only the separated bran and germ part are treated to avoid structural changes of the endosperm. On the other hand, dry heat treatment on endosperm based white wheat flour is a tool for improving the flour quality (extend dough stability) via the reorganization of the intermolecular linkages among the polymer proteins (Jeanjean, Damidaux, & Feillet, 1980). The dry heat treatment processes are appropriate to change technological properties without significant nutritional losses (Dimberg, Molteberg, Solheim, & Frølich, 1996). Furthermore, dry heat treatment processes do not cause substantial gelatinization of the starch (Ozawa et al., 2009). Little has been published regarding dry heat treated whole wheat flours with different treatment settings. The dry heat treatment of bran fractions has been shown to be appropriate for enhancing the end-product performance. Thus, compared to untreated bran, adding dry heat treated bran

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to white flour resulted in smaller decrease in the loaf volume (Gan, Galliard, Ellis, Angold, & Vaughan, 1992). The rheological properties of dosed bran after different heat treatment processes (boiled, steam-cooked, autoclaved, roast, etc.) in flour blends have been investigated. The physical properties such as water absorption and mixing time did not show substantial differences from the untreated bran fraction since the treatment has no or little effect on the starch granules and viscosity properties (Caprez, Arrigoni, Amado, & Neukom, 1986). Available literature is limited for hydrothermal treatment processes of flour. Hydrothermal treatments are applied to (1) inactivate enzymes therefore, it is able to reduce hydrolytic rancidity (Ekstrand, Gangby, & Akesson, 1992) and (2) to produce matrices with higher viscosity for thickening agents in soups, sauces etc. (Prakash & Rao, 1999). The hydrothermal treatment processes modify the starch properties by pre-gelatinization and denature the proteins, which become unable to form a gluten network (Bucsella, Takács, Vizer, Schwendener, & Tömösközi, 2016; Prakash & Rao, 1999). Thus, a high viscosity suspension can be prepared. Hydrothermal treatment of whole grain rice flour results in lower viscosity values and pasting properties than extracted starch measured by Rapid Visco Analyzer (RVA) (Sun, Han, Wang, & Xiong, 2014). Moreover, better techno-functional properties (higher dough stability with longer development time, higher resistance to mechanical stress) have been observed after the dosage of the hydrothermally treated (acetate buffer (pH 4.8) at 55 °C for 24 h) wheat bran fractions to the former separated endosperm based fraction (Mosharraf, Kadivar, & Shahedi, 2009). The hydrothermal treatment has a significant effect on the nutritional value. The treatment results in a reduction in concentration of bioactive components, such as phytate and vitamins (i.e. heat labile vitamin C and B-group vitamins) (Caprez et al., 1986). The wheat grain can be utilized more effectively in order to gain flour with enhanced nutritional value. The aleurone layer is the most valuable part of the grain outer layers because it is an abundant source of protein (31%), dietary fiber (28%), lipids (9%), minerals (8%), vitamins, bioactive compounds and other micro- and macro- components with health benefits (Brouns, Hemery, Price, & Anson, 2012; Zhou, Su, & Yu, 2004). During the widely used large scale industrial milling processes, most of the aleurone layer is separated with the by-product, the bran. Previously an aleurone rich wheat milling fraction was developed at industrial scale (Bagdi et al., 2014; Bucsella, Molnár, Harasztos, & Tömösközi, 2016). The novel aleurone-rich flour is produced from bran rich milling fractions and lacks the outer layers of the grain. The aleurone-rich flour has a different composition (20% protein, 15% dietary fiber) to that of commercial fiber rich wheat fractions (9–13% protein, 9% dietary fiber). Furthermore, it has irregular techno-functional properties (Bagdi et al., 2014; Bucsella, Molnár et al., 2016). Since the product contains higher amount of inner layers of the seed coat than white and whole grain flour, the higher fat content (4%) may cause a decrease in the shelf-life properties. Dry and hydrothermal processes were applied to this novel aleurone-rich flour. The aim of this study is to characterize the heat treatment induced changes on the stability-, mixing- and viscous properties for further product development. The results are compared to our previous work wherein dry and hydrothermal heat processes were applied on cake and standard white wheat flour (Bucsella, Takács et al., 2016). 2. Materials and methods 2.1. Materials The novel aleurone-rich wheat flour (ARF) was developed at industrial scale by the Budapest University of Technology and

Economics, the Gyermelyi Zrt. Hungary and the Bühler AG, Switzerland (Bagdi et al., 2014; Bucsella, Molnár et al., 2016) from Triticum aestivum wheat. The investigated ARF is an intermediate product of the process development. 2.2. Heat treatment processes The dry heat and hydrothermal procedures were carried out in the pilot plant laboratory of Bühler AG (Uzwil, Switzerland) on a continuous process. The experimental design including the coding of the flour products are displayed in Table 1. During the dry heat treatment, the sample (ARF th) was first heated with the thermopneumatics and was then fed into the conditioner and the retention screws where it was held at 100 °C for 12 min. The throughput capacity of the procedure was 150 kg product/h. During the hydrothermal process, the flours (ARF hyd) were heated with steam in the conditioner and then were dried with thermo-pneumatics after the retention screws. The production capacity was 150 kg/h. At the end of the processes the moisture content of the products were adjusted to 5% at dry treatment and 10% at hydrothermal treatment by drying. Afterwards, the samples were sieved to homogenize the material and to remove aggregates. 25 kg flour product was prepared for each setting. The samples were stored at 18 °C until further analysis. 2.3. Chemical analysis 2.3.1. Determining the chemical composition The chemical composition of the untreated flour samples was analyzed. Ash, moisture, crude protein, crude fiber and the wet gluten contents were measured according to the international standard methods (ICC., 1996b). The dry gluten content was determined according to the standard method (ISO, 2006). Finally, the dry gluten samples were ground and sieved. 2.3.2. Determining the un-extractable polymeric protein fraction (%UPP) by size-exclusion chromatography (SE-HPLC) The effect of the heat treatment processes on the protein extractability was investigated by high performance sizeexclusion chromatography on an HP1100 HPLC system with a diode array detector (detection at 214 nm) and Agilent ChemStation software (Agilent Technologies Inc. Palo Alto, CA). The device was equipped with Zorbax GF-250 HPLC column (9.4 mm  250 mm, Agilent Technologies Inc. Palo Alto, CA.). The analysis was carried out according to the method of presented in Larroque and Bekes (2000). The injection volume was 20 ll, the flow rate was 1 ml/min, and the column was thermostated at 25 °C. This procedure was executed three times on each sample. 2.3.3. Determination of monosaccharide composition by capillary zone electrophoresis 2.3.3.1. Preparation of the flour water extracts (WEX). Water extracts were prepared for each sample twice according to the procedure of Agil and Hosseinian (2014). The flour samples were extracted with distilled water (1:50 w/v), vortexed and thermostated at 65 °C for 4 h (mixing in each 30 min). After cooling, the samples were centrifuged for 20 min at 4000 rpm. The supernatants were collected and the above mentioned extraction method was repeated on the pellet. Afterwards, the supernatants from the two extractions were combined; the extracts were freeze-dried and stored at 20 °C until further analysis. 2.3.3.2. Preparation of samples for monosaccharide analysis. Hydrolysis was performed according to the Healthgrain method (Gebruers, Courtin, & Delcour, 2009). From the freeze-dried water extracts and dry gluten samples, 5 mg/ml solutions were prepared

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B. Bucsella et al. / Food Chemistry 220 (2017) 9–17 Table 1 Applied parameters of dry heat (signed by th) and hydrothermal (signed by hyd) treatments on the aleurone-rich flour (ARF) flour with the sample codes. Sample code

Type of treatment

Product temperature (°C)

Holding time (min)

Steam (kg/h)

H2O (l/h)

Total H2O (%)

ARF ARF ARF ARF ARF

Dry Hydrothermal

100 95 96 96 96

12 5 5 5 5

– 13.5 13.5 15.0 17.0

– 0 5 10 20

– 9.0 12.3 16.7 24.7

th hyd0 hyd5 hyd10 hyd20

Numbers after ARF hyd codes indicate the water content (l/h) of the applied steam.

in distilled water. Hydrolysis was performed with trifluoroacetic acid (TFA) to liberate the monosaccharaides from the polymeric carbohydrate content. Hydrolysis was carried out in 2 M TFA for 1 h at 110 °C, followed by nitrogen evaporation to remove the TFA. Afterwards, the dry sample was diluted with distilled water to 5 mg/mL WEX concentration and analyzed immediately. 2.3.3.3. Determination of the monosaccharide composition by capillary zone electrophoresis. After quantitative hydrolysis, released monosaccharaides from the water extracts and the dry gluten samples were identified and quantified. The carbohydrates were separated in a high pH (12.6) buffer system with capillary zone electrophoresis. Employing a diode array detector (DAD) in the capillary detection window, the separated carbohydrates underwent an on-column reaction and they could be detected directly at 270 nm with a LOQ of about 10 lg/ml. Two measurements were performed from one sample. High performance capillary electrophoresis (HP 3D CE, Agilent Technologies Inc. Palo Alto, CA) equipped with a DAD and an uncoated capillary with 60 cm effective length and 50 lm inner diameters (BGB Analytics, Geneva, Switzerland) were applied. The analysis was performed according to the method of Rovio, Simolin, Koljonen, and Sirén (2008). The background electrolyte buffer (BGE) contained 90 mM NaOH, 36 mM Na2HPO4 (pH = 12.6) in milliq-water. BGE was filtered through a 40 lm filter and sonicated (Sonorex RK 100 H, Bandelini, Berlin, Germany) for 10 min before use. From each sample 3 injections were performed. The calculation of the water extractable arabinoxylan (WEAX) content were performed according to the Healthgrain method (Gebruers et al., 2009) 2.3.4. Total phenolic content (TPC) of the ethanol and alkaline extracts 2.3.4.1. Extraction of free phenolic compounds. The free phenolic compounds of the ARF samples were extracted using a modified version of the method of Adom, Sorrells, and Liu (2005). Two replicates (0.1 g each) of each flour and dry gluten samples were sonicated (Sonorex RK 100 H, Bandelini, Berlin, Germany) for 60 min with 2 ml 85% (v/v) cold ethanol in the dark and then centrifuged at 4000 rpm for 20 min. The extraction process was repeated, the supernatants pooled and freeze dried in dark. The residues were then dissolved in 0.5 mL 50% MEOH and analyzed immediately. The residues were kept for the alkali hydrolysis. 2.3.4.2. Extraction of the alkaline hydrolyzed bonded phenolic compounds. The residues from the ethanol extraction were further processed for the ester bonded phenolic content according to (Nardini et al., 2002) with modifications. The procedure for alkaline hydrolysis of 1 ml 1 M NaOH was performed for 30 min in the dark. Following this, the solutions were centrifuged at 14,000 rpm for 20 min and the extraction procedure was repeated. The supernatants were pooled and the pH was adjusted to pH = 2 with 6 M HCl. Samples were extracted three times with ethyl acetate ( 2 volumes) by vortexing for 5 min. After each extraction, samples were centrifuged (4000 rpm, 30 min) and supernatants collected.

The organic phase was freeze dried. The residue was dissolved in a final volume of 50% 0.5 ml MeOH and analyzed immediately. Two measurements were carried out per each sample. 2.3.4.3. Total phenolic content (TPC). Total phenolic content (TPC) of extracts was determined using the Folin–Ciocalteau reagent according to a modified procedure of Beta, Nam, Dexter, and Sapirstein (2005). 200 ll sample of the 0.5 mL (free or alkaline) extracts in 50% MEOH was added to 1.9 ml of freshly diluted 10fold Folin–Ciocalteau reagent (Sigma-Aldrich Ltd.). Sodium carbonate solution (1.9 ml) (60 g/L) was then added to the mixture and mixed. After 120 min of reaction at room temperature, the absorbance was measured at 725 nm against a blank of distilled water (Cary 8454 UV–vis, Agilent Technologies Inc. Palo Alto, CA). Ferulic acid (Sigma-Aldrich Ltd.) was used as an equivalent standard. The results are expressed in ferulic acid equivalent (FAE). The analyses were performed twice per sample. 2.3.5. Determining the acid number The hydrolytic rancidity process can be measured by the acid value. The acid value is the amount of 0.1 M potassium hydroxide required to neutralize the free acids released by lipase enzyme activity and to saponify the esters in 1 g of the substance. Acidity was measured by titration of the crude oil samples (0.1 g) with potassium hydroxide and the result is expressed by the acid value (mg KOH/g flour) according to the standard method (AOCS., 2009). The measurements were performed three times for each sample. 2.4. Rheological methods 2.4.1. Micro-Zeleny sedimentation test In order to gain more information about the heat process caused complex changes in the fiber rich ARF flours, Zeleny sedimentation test was considered as rheological tool. In this case Zeleny sedimentation value is not only determined by the gluten swelling properties but the complex network developed by the proteinfiber-lipid complex. During the sedimentation test, the flour samples were suspended in lactic acid and their degree of sedimentation was detected after a standard time. The Zeleny sedimentation values were determined according to the standard method (ICC., 1994) with flour repetitions. 2.4.2. Evaluation of mixing and pasting properties by Mixolab The water absorption capacity and the dough properties, such as dough development time (DDT), dough stability (C1), protein weakening (C2), starch gelatinization (C3), amylase activity (C4) and starch gelling (C5) were determined by Mixolab (Chopin, Tripette et Renaud, Paris, France). The measurements were carried out according to the Mixolab manual. The tests were performed for each sample with the addition of certain amount of water (water absorption) to reach the maximal 1.1 Nm. The Chopin protocol, called Chopin + a was applied for studying both the mixing and the pasting behaviors (CHOPIN., 2009). Three parallel measurements were performed for each sample.

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2.4.3. Viscosity properties by RVA and falling Number The viscosity properties were also studied in slurry using the Rapid Visco Analyzer (RVA, New Port Scientific, Sydney, Australia) and also by measuring the falling number. In case of RVA the peak-, through-, final-, breakdown-, setback viscosity values, the pasting temperature and the peak time were determined according to the standard method (ICC., 1996a). The falling numbers were measured by a standard method (AACC., 2003). Both RVA and falling number measurements were repeated three times for each sample. 2.5. Statistical analysis Statistical analysis was carried out by the STATISTICA 11 software (StatSoft, Inc., Tulsa, Oklahoma, USA). For each sample the mean value and standard deviation were determined of the replicate measurements. The effects of different factors (applied heat process parameter) on the composition and rheological parameters of the samples were analyzed with one-way ANOVA calculated by the Tukey-test with a significance level of p < 0.05.

3. Results and discussion 3.1. Chemical composition of the aleurone-rich flours (ARF) 3.1.1. Chemical composition of the untreated ARF sample Untreated aleurone-rich flour (ARF) is an abundant source of protein. Crude protein forms 26.98 ± 0.21% of ARF. This is more than twice as much as in white flour (approx. 12%), which itself contains more than whole grain flours. The total dietary fiber content of ARF is 19.35 ± 1.20%; soluble dietary fiber is 1.59 ± 0.81%. These also exceed the amounts currently found in available wheat fractions of a similar nature like whole grain wheat and rye flour (Bucsella, Molnár et al., 2016). Furthermore, ARF contains 5.71 ± 0.42% crude fiber, 3.31 ± 0.07% ash and 36.66 ± 1.23% wet gluten. The increased presence of the crude protein and dietary fiber indicates the reduced calculated starch content of 46.16. The determined high percentage of crude protein includes the endosperm originated gluten proteins, the albumins and globulins from the aleurone and sub-aleurone layer (Brouns et al., 2012). The content of the washed wet gluten is 36.66 ± 1.23%, which is similar to white flours: 20–40% and whole wheat flours: 16–40% (Bucsella, Molnár et al., 2016). The measured values refer to a complex network system containing fibers, which poses questions about the gluten content determination by fiber rich fractions. 3.1.2. Effect of heat treatment on the extractability of polymeric proteins, %UPP The impact of heat treatment processes on the polymeric protein extractability is evaluated by the% unextractable polymeric protein (%UPP) values. ARF contains 32.3% unextractable polymeric protein (Fig. 1.). By the dry heat treatment process, the %UPP increased with 23% which means a significant decrease in the polymer protein extractability. The observed phenomenon is mainly due to the heat induced changes in the protein-protein interactions and is also due to formation of the carbohydrate and lipid complex formation. Generally, the applied dry, high temperature during the processes is indicated in the unfolding of gluten proteins, the hydrophobic parts are more exposed and allows the rearrangement of disulfide bonds (Jeanjean et al., 1980). This results in the formation of gluten aggregates, the decreased extractability and changed molecular weight distribution of the gluten proteins (Brouns et al., 2012). Moreover, in ARF, besides the gluten protein, the higher amounts of albumin and globulin also participate in the new, aggregated protein and carbohydrate – fat complex matrix.

Fig. 1. Impact of heat treatment processes on the polymeric protein extractability (%UPP) and the Zeleny sedimentation values. Values are the means of replicates (N = 3); error bars are represent the standard deviation ARF: aleurone-rich flour, th: dry heat treated, hyd: hydrothermally treated, numbers after ARF hyd codes indicate the water content (l/h) of the applied steam.

The protein-carbohydrate interactions are established via the phenolics. The level of the %UPP in the hydrothermally treated samples is higher than in the ARF. The %UPP values varied between 56.7– 61.2% with an increasing level from 5 L/h to 20 L/h applied steam moisture content. It is worth noting that the differences between the dry and hydrothermal treatment were also visible during the washing of the gluten yield. The gluten of the ARF th is a continuous and consistent texture meanwhile the ARF hyd samples have separate aggregates without coherency.

3.1.3. Effect of heat processes on the water extractable carbohydrate composition The water soluble carbohydrate composition and the measured water extract (WEX) weight values of the heat treated samples are shown in Table 2. Both, dry and hydrothermal heat treatments caused a decrease in the water extractable materials. The ARF contains 20% water extractable material while the treated flours contain only 12–15%. The glucose monomers are mainly composed of the water soluble starch molecules. The effects of the thermal and hydrothermal treatments result in significant decrease of the soluble glucose level in comparison to in the untreated flour (2.88%). The dry heat process indicated reduction is lower (2.31% glucose content) than the hydrothermal treatment caused decrease in the glucose content (1.5%). This suggests that the chemical interactions among proteins, carbohydrates and lipids are more intensive following hydrothermal treatment than after dry treatment. However, both have significant reducing impact on the starch solubilisation (Lásztity, Békés, Örsi, Smied, & Ember-Kárpáti, 1996). The pentosan fiber components: the arabinose, xylose and galactose sugars in the water extracts were also investigated. The heat treatment processes also resulted in significant decrease in the content of them compared to the ARF. Galactose content in ARF was 0.78% in ARF th 0.54% and in the hydrothermally treated samples varied 0.24–0.54% showing steam moisture content increase. The calculated water soluble arabinoxylan (WEAX) content of the ARF is 1.5%. The dry treatment causes reduction (0.95%) in the WEAX content of ARF th. Meanwhile, the WEAX contents vary between 0.69–1.46% among the hydrothermally treated samples irrespective of the treatment parameters. The heat processes had no effect on the A/X ratio. The same reduction in water soluble dietary fiber content caused by heat was observed by Azizah and Zainon (1997) after roasting and boiling the whole

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B. Bucsella et al. / Food Chemistry 220 (2017) 9–17 Table 2 Impact of heat treatment processes on monosaccharide composition and phenolic content (PC) of water extracts (WEX) and the dry gluten of the aleuron-rich flour. Sample code

Type

WEX (g/ 100 g)

ARF ARF ARF ARF ARF ARF

Flour

20 ± 4 15 ± 2 12 ± 3 15 ± 3 14 ± 4 12 ± 2 Dry gluten (g/ 100 g) 20 ± 3 26 ± 4

Glucose

Arabinose

Xylose

Galactose

A/X

AX (%)

ARF ARF th

Dry gluten

Free + Alkaline hydrolyzed PC

lg FAE/g flour

% (g /100 g flour) th hyd0 hyd5 hyd10 hyd20

Alkaline hydrolyzed PC

2.88 ± 0.17a 2.31 ± 0.17b 1.24 ± 0.11c 1.55 ± 0.12c 1.45 ± 0.05c 1.4 ± 0.05c % (g /100 g dry

0.78 ± 0.05a 0.48 ± 0.03b 0.35 ± 0.06c 0.55 ± 0.03b 0.49 ± 0.05b 0.76 ± 0.07b gluten)

0.93 ± 0.11a 0.60 ± 0.04b 0.43 ± 0.02c 0.74 ± 0.02bcd 0.59 ± 0.04cd 0.9 ± 0.02bd

0.78 ± 0.05a 0.54 ± 0.02ab 0.24 ± 0.02c 0.40 ± 0.03bcd 0.42 ± 0.01bcd 0.57 ± 0.1ad

0.84 0.8 0.83 0.75 0.84 0.85

1.5 0.95 0.69 1.14 0.96 1.46

4632 ± 32a 5022 ± 26ab 6425 ± 33b 4479 ± 41a 3680 ± 57c 2519 ± 43c lg FAE/g dry gluten

5467 ± 56a 5745 ± 24a 7083 ± 98b 5164 ± 31a 4406 ± 37ac 3573 ± 65c

32.36 ± 1.6e 31.71 ± 3.85e

0.68 ± 0.17e 1.27 ± 0.22f

4.68 ± 0.76e 7.73 ± 0.86f

1.5 ± 0.52e 3.31 ± 1.11f

0.15 0.16

4.72 7.92

9262 ± 32e 11868 ± 20f

13400 ± 62e 15220 ± 98f

ARF: aleurone-rich flour, th: dry heat treated, hyd: hydrothermally treated, numbers after ARF hyd codes indicate the water content (l/h) of the applied steam. AX: arabinoxylan, A/X: ratio of arabinose to xylose content, FAE: ferulic acid equivalent. Values are the mean value and standard deviation (N = 3). The values followed by the same letters are not different significantly at 0.05 probability level (N = 3).

wheat fraction. However, the heat treatment processes resulted in an increased concentration of the soluble dietary fiber content in the wheat bran showed increased concentration (Caprez et al., 1986). Therefore, the decrease in the soluble dietary fiber components might be contributed to the endosperm constituents. The large amount of protein and starch reduce the solubilisation via the reordered bonds/interactions among them. Since water soluble dietary fiber is attributed to an important role in human nutrition, this decrease is a rather undesirable effect. 3.1.4. Effect of heat treatment processes on the alkaline hydrolyzed and free phenolic content The ARF contains higher amount of ester bonded (4632 lg FAE/g) and total (free + alkaline hydrolyzed) (5467 lg FAE/g) phenolic components (Table 2.) than whole grain and white flours (Irmak, Jonnala, & MacRitchie, 2008). Moreover, the phenolic content of ARF is comparable to that of the wheat bran fractions (Abozed, El-kalyoubi, Abdelrashid, & Salama, 2014). The dry heat process has no significant effect on the phenolic content. In case of hydrothermal treatment with increasing steam water content, a reduction is observed in the phenolic content in the ARF hyd samples: ester bonded phenolic content changed between 6425 lg FAE/g and 2519 lg FAE/g. The total phenolic content of ARF hyd followed the same pattern. Thus, the phenolic content of hydrothermally treated samples show process dependency. ARF hyd0 has the highest phenolic content among the examined samples both in bonded and free + bonded forms. This might be caused by the mild conditions that made the phenolic compounds more accessible during the extraction. The observed phenolic content decrease after hydrothermal treatment referred to an increase in the number of interactions between proteins and phenolics via hydrogen bonds, ionic-, covalent- and hydrophobic interactions and with carbohydrates via Maillard reactions and polyphenol-carbohydrate reactions (Renard, Baron, Guyot, & Drilleau, 2001). The chosen steam conditions have a significant effect on the intensity of the interactions. All these interactions result in complexes that have lower ability for solubilisation of the phenolic compounds and affect the dough structure. 3.1.5. Impact of heat treatment processes on the stability properties by acidity values The ARF high crude fat content at 4.2 ± 0.50%, which could reduce the shelf-life of the flour. The different heat procedures with impact on the lipase dependent storage properties are evaluated with the acidity values in a 9-month interval (depicted in Fig. 1).

The acidity numbers of the untreated sample show a significant increase after 3 months of storage. At the 6th month, 7.9 mg KOH/g flour is reported, which is followed by 14.4 mg KOH/g flour in the 9th month. The growing values refer to the rising amount of liberate and free fatty acids in the flours that means 0.17 mmol/g flour liberated free fatty acids in the 9 month interval. An increase in the acidity values of the heat treated samples is also observed, with lower values than for the ARF. This indicates that the heat processes changed the flour’s storage stability significantly. The dry heat treated ARF th demonstrates increase from 2.0 to 4.3 mg KOH/g in the 9-month-long interval that indicates 0.04 mmol/g flour liberated free fatty acid in the 9 month interval. The slope of the acidity numbers increases in the hydrothermally treated samples. It is gentler in the first 6 months (from 1.6 to 2.5 mg KOH/g) and in the 9th month the acidity exceeds 4.5 mg KOH/g. The ARF hyd20 show different trend and the value of the 9th month is the lowest among the ARF hyd samples. The heat treatments have a great impact on the hydrolytic rancidity, via the reduced amount of liberated free fatty acids which suggests reduced enzymatic activity. Therefore, the shelf life stability of the ARF can be modified with the heat treatment processes. 3.2. Impact of heat treatment processes on the rheological properties 3.2.1. Zeleny sedimentation The Zeleny values describe the changes in the gluten protein swelling behavior. The untreated ARF provides 5.26 ml Zeleny value which suggests acceptable baking quality and exceeds the value of the commercial white bread flour (Fig. 2) (Bucsella, Takács et al., 2016). Dry heat treatment caused no significant

Fig. 2. Effect of heat treatment processes on the acidity values of aleurone-rich flour (ARF) samples after 1, 3, 6, 9 months. Bars represent the mean values of replicates (N = 3); error bars represent standard deviation. th: dry heat treated, hyd: hydrothermally treated, numbers after ARF hyd codes indicate the water content (l/h) of the applied steam.

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difference in the Zeleny value, which means the absorbed water content of the material is similar to the ARF. In contrast, dry heat treatment generates a significant decrease in the Zeleny value at the bread wheat flour (Bucsella, Takács et al., 2016). The hydrothermal treatment denatured the proteins and leads to function loss that caused low 1.7 ml values by each ARF hyd sample. The same tendency is reported in case of the hydrothermally treated bread wheat flour (Bucsella, Takács et al., 2016).

3.2.2. Impact of heat treatment processes on the mixing and pasting properties by Mixolab The ARF absorbs 71% water (Fig. 3a). For the proper dough development the ARF needs 6.9 min and the stability of the dough is 7.5 min with 0.56 Nm dough weakening (Fig. 3b, c, d). In comparison to bread wheat (water absorption: 60%, DDT: 4.3 min, dough stability: 7.9 min) flour ARF has larger water absorption, longer DDT and similar dough stability. The DDT values of the ARF suggest the delayed development of a strong and resistant dough structure via the irregular composition of the fraction with high ability for water uptake. The ARF dry gluten contains a high quantity of fiber constituent carbohydrates and phenolic components (Table 2.). This means that the fiber and extra protein constituents are able to incorporate to the gluten network and support the network structure of the dough (Sudha, Vetrimani, & Leelavathi, 2007). The dry heat treatment has significant effect on the ARF th mixing behaviors, although water absorption which is not affected by the applied heat treatment process. For the proper dough development ARF th needs 1.5 min less time than ARF, and the formed structure has the same stability as ARF. The rather high weakening values are the result of the network containing higher amount of fiber constituents as mentioned in Table 2. The bread wheat flour treated with dry heat in the same (Bucsella, Takács et al., 2016) way to ARF th provided longer DDT (5.7 min) and higher stability (8.8 min) than ARF th. In case of the ARF th these inflexible non-starch polysaccharides are able to interact with the enlarged surface of the proteins via the ester bonded phenolic acids that leads also to decrease in the amount of solubilized carbohydrate (Table 2). The increased number of cross links between the gluten and fibers allows the formation of a strong gel structure (Noort, van Haaster, Hemery, Schols, & Hamer, 2010). However, the physical properties of the network also

change and the structure becomes more rigid and less resistant to heating and mixing stress. In case of the hydrothermal treatment, only the ARF hyd0 and hyd5 samples provide measurable results, however gluten yields were not possible to wash from ARF hyd samples. The ARF hyd10 and hyd20 samples are stacked to the mixer and are unable to form dough. The ARF hyd0 sample has significantly lower water absorption (67%) and dough development time (1.0 min) but has longer stability (12.3 min) than the untreated ARF. In the hydrothermally treated bread wheat flour the water absorption was significantly higher and the dough stability significantly lower than the untreated flour (Bucsella, Takács et al., 2016). Interestingly, the ARF hyd5 sample showed similar water absorbing and mixing behaviors as the ARF except its significantly shorter, 1.2 min DDT value. The partially denatured proteins and pre-gelatinized starch are able to uptake water more quickly since the proteins are not able to retain the water (see Zeleny results 3.4.1.) in the swelling period. Although, the Zeleny results show the same low swelling volume for each ARF hyd sample; the complete function loss of the ARF hyd10 and hyd20 was not predicted. A more detailed evaluation can be performed by the Mixolab parameters for the effects of the process. After heat-induced protein denaturation, typically, the carbohydrate dependent starch gelatinization (C3), amylase activity (C4) and starch gelling (C5) behaviors dominate. ARF has acceptable C3 (1.6 Nm) and retrogradation C5 (0.32 Nm) values (Fig. 3e, f) that are similar to the white flour (Bucsella, Takács et al., 2016). The C3 torque value ARF th (1.3 Nm) is lower than the C3 value of the ARF, which means a reduction in the gelling ability. The retrogradation of the sample is not affected by the treatment process. Generally, the dry heat has no or negligible effect on the starch granules (Ozawa et al., 2009) and the same is reported for the C3 and C4 values of the dry heat treated bread wheat flour (Bucsella, Takács et al., 2016). Therefore, these observations suggest that the altered protein-pentosan-lipid complexes cause reduction in the gelling ability (C3 parameter). However, the 95 °C tempering completely denatures and depolymerizes the protein moiety and the unchanged starch behaved the same as the ARF which resulted in the similar trough (C4 parameter) and retrogradation value (C5). The observed C3 values are significantly different between the hydrothermally treated ARF hyd0 and hyd5 samples. However, taking into account the previous dough weakening differences (C3-C2 parameter difference) (Fig. 3d), the gelling abilities are similar to

Fig. 3. Thermal (ARF th) and hydrothermal (ARF hyd) processes impact on the Mixolab values: (A) water absorption, (B) DDT (dough development time), (C) dough stability, (D) dough weakening (1.1 Nm-C2), (E) viscosity (C3) and (F) retrogradation (C5-C4) of the ARF Values are the mean ± SD Identical letters above the bars indicate no significant difference at 0.05 probability level (N = 3) ARF: aleurone-rich flour, numbers after ARF hyd codes indicate the water content (l/h) of the applied steam.

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each other and to the ARF. The differences caused by hydrothermal treatment are measurable at the cooling phase of the measurement. The C5-C4 retrogradations of the ARF hyd samples (0.9 and 0.75 Nm) are significantly higher than for ARF. ARF hyd0 sample treated by steam without additional water has a significantly higher C5 value than ARF hyd5. Thus, with low moisture content steam treatment processing of ARF, a quick dough development and stable, resistant structure can be gained that has high retrogradation. Meanwhile the hydrothermally treated bread wheat flour samples showed reduction in the C5 values as a function of the steam moisture content. These results show that the hydrothermally treated fiber rich wheat flour is able to form a strong gel after cooking during the cooling phase in limited water availability. The arabinoxylan, galactomannan non-starch polysaccharides in the new macromolecular complexes are able to uptake and hold the available water. The phenomenon is also observed by (Brennan & Cleary, 2007). 3.2.3. Impact of heat processes on the viscosity properties by falling number and RVA The ARF has 505 s falling number and the bread wheat flour has 790 s (Bucsella, Takács et al., 2016). Thus, falling number value (505 s) of the ARF suggests the development of a strong gel at high temperature (Fig. 4a). Since ARF contains less starch than white flour and whole wheat fractions, the high value does not only refer to the result of the enzyme activity but the consistency of the protein-carbohydrate-lipid based viscous material. The dry heat treatment increased the falling number value significantly in the ARF th despite the structural change in the starch particles. The same effect was reported for the dry heat treated bread flour (Bucsella, Takács et al., 2016). Therefore, the dry heat treatment induces similar modifications in the white flour, and the presence of pentosans has less impact on the measured changes. The hydrothermally treated samples have low values of falling number that show inverse proportionality to the applied steam moisture content. Thus, ARF samples after hydrothermal treatment

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are not able to form dense material with high viscosity at 100 °C in contrast to the hydrothermally treated bread wheat flour (Bucsella, Takács et al., 2016). The RVA provided typical curves and parameters as depicted in Fig. 4. The untreated ARF has 90 °C pasting temperature, 1010 cP peak viscosity, 268 cP breakdown and 569 cP setback viscosity values. The viscosity values of the ARF are almost as low as one third of the RVA values of white flour (Bucsella, Takács et al., 2016). The values correlate wit the lower starch content of the ARF. After exposing the ARF to dry heat, the pasting temperature propped to 88 °C and the peak viscosity value was not significantly different from the value of the ARF. The breakdown value of ARF th was 391 cP, thus, the developed relatively strong but rigid gel structure suffered significantly larger collapse at the tempering period than the ARF. During the cooling phase the dry heat treated sample provides a 755 cP setback value that refers to the development of a strong gel structure in the retrogradation phase. The same tendency was reported for the dry heat treated bread wheat flour but with significantly higher viscosity values than ARF th (Bucsella, Takács et al., 2016). The RVA method with its applied calculation of the additional water was developed for commercial flour types that have 60–70% starch content and 10–14% moisture content. In case of the heat treated ARF samples the moisture content is readjusted to 5% after the dry treatment and 10% after the hydrothermal. Furthermore, ARF has less starch than the white or the whole grain flour. These factors might influence the results of the measurements. It is well known that the wheat starch gelling properties show gluten protein dependency since the protein is able to control water uptake and the moisture transfer of the starch. Moreover, interactions can develop between them during the process and starch showed decreased viscosity values in the presence of gluten proteins compared with the behavior of the pure starch (Eliasson, 1983). The dietary fiber polysaccharides – mainly the arabinoxylans, galactomannans and b-glucans – can uptake water faster and impair the gelling properties of the starch via blocking

Fig. 4. Dry (ARF th) and hydrothermal (ARF hyd) processes impact on viscosity properties: (A) falling number, (B) typical RVA curves, (C) pasting temperature, (D) breakdown and (E) setback values of the aleurone-rich flour Values are the mean ± SD Identical letters above the bars indicate no significant difference at 0.05 probability level (N = 3) Numbers after ARF hyd codes indicate the water content (l/h) of the applied steam.

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the water accessibility (Brennan & Cleary, 2007). In our case, the viscosity reducing effect of the protein-pentosan polysaccharide complexes is larger. The ARF th has low starch content in the presence of large amounts of protein-pentosan complexes. With their enlarged surface they express increased retarding effect on the gelling properties. In slurry matrix the hydrothermally treated samples behave similarly to each other. Their pasting temperature values of 91–92 °C are higher than for ARF. Therefore, the pre-gelatinized starch constituents need a higher temperature for gelling. The swelling of the intact starch granules in ARF causes the viscosity increase at lower temperature. Hydrothermal treatment induced low peak viscosity (Fig. 4b) and the breakdown values are observed by the ARF hyd samples. Their values are significantly lower than those of the ARF. The hydrothermal treatment has impact on the setback value, the detected value of the ARF hyd5 is significantly lower and setback of hyd 20 sample is significantly higher than the ARF. The setback values of the ARF hyd10 and ARF hyd20 are not significantly different from the ARF th. Hydrothermal treatment on the bread flour resulted in increase in the peak viscosity and breakdown and has no effect on the setback values related to the ARF hyd results. The decreasing effect of the hydrothermal treatment on the peak viscosity values has been already observed of whole grain fractions. According to theory of Sun et al. (2014), the resulting physical and chemical alteration both in the protein and carbohydrate moieties following treatment reduced the leaching of the amylose molecules that would have been able to increase the viscosity (Sun et al., 2014). Furthermore, observation of the reduced carbohydrate solubility (Table 2) and protein extractability (Fig. 2) refer to the formation of a large amount of insoluble matrix with lower swelling properties at high temperature (see falling numbers Fig. 4a). The lower breakdown values of the ARF hyd samples suggest the hydrothermal treatment improved the shear stability, which can be caused by the presence of rigid nonfragmented swollen starch granules (Yadav, Guleria, & Yadav, 2013) and the dietary fiber pentosan constituents that do not change structurally after the tempering period. It is also noticeable that the falling number and the breakdown values follow the same pattern. This might be due to the fact that both parameters indicated the viscosity of the materials after tempering and therefore, the same structural modification occurred. The investigation of the effect of heat treatment on starch/ carbohydrate properties highlighted the matrix based differences originating from different measuring procedures. In dough matrix investigated with Mixolab the increased retrogradation ability is not detectable contrary to the slurry matrix of the RVA method. The dry heat treated sample provides increased viscosity only in slurry. The material needs moisture to develop the high viscosity gel structure that could be attributed to the swelling dominance of the carbohydrates. Meanwhile, the alteration of viscosity properties caused by hydrothermal treatment can be observed similarly in dough and also in slurry. This difference suggests that by the hydrothermally treated samples have increased gelling ability at the cooling phase. The denatured protein, pre-gelatinized starch and the inflexible pentosan polysaccharides might stiffen to a highly viscous material.

4. Conclusion The effects of different heat treatment processes on the quality of a novel, aleurone-rich wheat milling special flour (ARF) were investigated. ARF is an abundant source of protein (26%), dietary fiber (19%) and contains increased fat (4%). Due to its irregular

composition, the new product shows particular combinations of rheological properties and it is exposed to rancidity. To modify the expiration properties and explore the possible applications of this special flour (ARF), dry heat and hydrothermal treatment processes were applied. Both heat treatment processes proved to be capable of extending the shelf-life and providing significant changes to the rheological properties. Dry treatment of the aleurone-rich flour provided similar mixing properties to the commercial white flour. This treatment is suitable for reducing the mixing time without dough stability loss via the developed protein-carbohydrate-lipid gluten network. However, although the novel flour has lower gelling ability than the white flour, the pasting properties are still acceptable. The dry heat treatment increases the viscosity of the flour slurry after cooling with prolonged shelf-life. Thus, for bakery products, dry heat treated aleurone-rich flour can be a very suitable raw material. With hydrothermal treatment a wide range of product can be produced with the application of different moisture content steam. The gelling ability is also modified by applying steam. A fraction with increased final viscosity lacking dough forming ability can be produced but with significantly lower pasting behavior to that of the white flour. The dry heat and hydrothermal processes can be used as a powerful tool in modifying relevant properties of fiber-rich wheat flours for targeted final application in food products such as bread, biscuits etc. Thus, these results contribute to the development of cereal based food products with enhanced nutritional values and functional properties.

Acknowledgements This work was supported by the Hungarian national projects titled, Healthcare and tradition: development of raw materials, products and technology in cereal industry” (TECH_08_A/2-20080425) and ‘‘New aspects in wheat breading: improvement of the bioactive component composition and its effects” (OTKA 112179) and by Gyermely Zrt. Hungary who provided the material for the research. This research activity is also connected to the scientific program of the project titled ‘‘Development of quality orientated, harmonized educational and R+D+I strategy and operational model at the Budapest University of Technology and Economics” (TÁMOP4.2.1/B-09/1/KMR-2010-0002). Blanka Bucsella was generally supported by the Swiss SCIEX-NMS exchange program No.13.080 titled, GLUC-AN: Development of analytical tools for the characterization of complex functional fiber glucans in wheat based products, establishment of quantitative structure-function relationships”.

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