thermogravimetric analysis of water release from wheat flour and wheat bran suspensions

Journal of Food Engineering 111 (2012) 606–611

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Journal of Food Engineering

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Thermogravimetric analysis of water release from wheat flour and wheatbran suspensions

Hajo Roozendaal a, Madian Abu-hardan b, Richard A. Frazier a,⇑a Food and Bioprocessing Sciences Group, Department of Food and Nutritional Sciences, University of Reading, Reading, Berkshire RG6 6AP, United Kingdomb Applied Science Department, Nestlé Product Technology Centre, York, UK

a r t i c l e i n f o a b s t r a c t

Article history:Received 15 November 2011Received in revised form 7 March 2012Accepted 10 March 2012Available online 19 March 2012

Keywords:WaterWheat branThermogravimetric analysisBran fractions

0260-8774/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.jfoodeng.2012.03.009

⇑ Corresponding author. Tel.: +44 (0) 118 378 8709E-mail address: r.a.frazier@reading.ac.uk (R.A. Fraz

Bran is hygroscopic and competes actively for water with other key components in baked cereal productslike starch and gluten. Thermogravimetric analysis (TGA) of flour–water mixtures enriched with bran atdifferent incorporation levels was performed to characterise the release of compartmentalised water.TGA investigations showed that the presence of bran increased compartmentalised water, with the mea-surement of an increase of total water loss from 58.30 ± 1.93% for flour only systems to 71.80 ± 0.37% informulations comprising 25% w/w bran. Deconvolution of TGA profiles showed an alteration of the dis-tribution of free and bound water, and its interaction with starch and gluten, within the formulations.TGA profiles showed that water release from bran-enriched flour is a prolonged event with respect tothe release from non-enriched flour, which suggests the possibility that bran may interrupt the normalcharacteristic processes of texture formation that occur in non-enriched products.

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1. Introduction

Baking involves a process of an irreversible series of heatinduced chemical, physiological and biochemical changes (Chang,2006) and is normally the final stage of processing a cereal endproduct (i.e. bread, cookies etc.). During baking, the three mainingredients: water, starch and gluten, interact to transform theproduct from a foam-like structure (dough) to a sponge-like,porous structured end product (e.g. bread) (Hug-Iten et al.,1999). During this transformation, the product undergoes a seriesof changes that start with; (1) the formation of a viscoelastic glutennetwork during mixing at room temperature, (2) the gelatinisationof starch during the early stages of baking, (3) the coagulation ofthe gluten network during the latter stages of baking, and (4) thegelation and crystallization of starch during cooling. Theseprocesses are all governed by water.

Water, in the presence of heat, establishes a high vapour pres-sure gradient within dough and becomes the main driving forcefor the chemical and physical changes, i.e. acting as a plasticiseron proteins and a solubiliser of the starch component. Both thestarch and the gluten compete actively for the available water(Grinberg and Tolstoguzov, 1997) and retain the captured waterin different ways. Starch being a polysaccharide, holds onto thiswater through hydrogen bonding between the amylose and amylo-pectin branches and inter amylopectin helices (Orlowska et al.,

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2009). These helices have an ability to form junction zones inwhich large amounts of water can be stored (Chaplin, 2003). Glu-ten protein on the other hand favours the formation of covalentdisulfide bonds via the cysteine groups of the glutenin. In additionit forms hydrogen bonds via the glutamine residues (Belton et al.,1998). These will bind water tightly and will resist the removalof this water for an extended period of time (Durchschlag andZipper, 2001).

Bran is viewed mostly as a milling by-product of the wheat mill-ing industry (Dexter and Wood, 1996; Antoine et al., 2004) and con-sists mainly of the dead outer layers of the wheat kernel. However,incorporation of cereal bran and use of wholegrain flours in com-mercial food products are driven by their widely reported andrecognised health benefits for humans. However, this poses techno-logical challenges. Bran incorporation increases the mass of the endproduct due to the additional water needs, decreases loaf heightand cookie spread, darkens colour and decreases sensory accep-tance of the end product by the consumer (Vratanina and Zabik,1978; Krishnan et al., 1987; Chen et al., 1988; Sievert et al., 1990;Park et al., 1997; Zhang and Moore, 1997; Abdul-Hamid and Luan,2000; Lang and Jebba, 2003; Ragaee and Abdel-Aal, 2006; Seyerand Gélinas, 2009). Bran tends to be highly hygroscopic and onaddition to a formulation results in an extra water need, whichneeds to be added in order to compensate. On the other hand branhas a low affinity for water (Robertson and Eastwood, 1981) andthis results in it releasing most of its absorbed water when placedunder stress (mechanical, gravimetrical or heat), hence causing itsundesirable side effects.

H. Roozendaal et al. / Journal of Food Engineering 111 (2012) 606–611 607

Thermogravimetric analysis (TGA) of flour–water mixtures havebeen undertaken by previous researchers (Fessas and Schiraldi,2001, 2004; Lodi and Vodovotz, 2008; Orlowska et al., 2009). Theyhave shown how water is held within a simple water–flour mix-ture and through the deconvolution of peaks, they could discrimi-nate different water fractions during baking. Fessas and Schiraldi(2001) showed through the first derivative of the TGA mass losscurve (DTG), that water in both the starch fraction and the glutenfraction could be discriminated. The water in the gluten traceshowed two peaks, with the first early peak (at low T), attributedto the mobile water (free water), and the second peak identifiedwas attributed to the tightly bound water (at high T) (Durchschlagand Zipper, 2001). Starch on the other hand only showed a singleearly large peak (greatly overlapping the first low temperaturepeak of the gluten), which shows that water associated with thepolysaccharides are held by weak bonding. This weak bonding lar-gely comprises of the polysaccharides’ hydrogen bonds, but also in-cludes its ability to form junction zones (Chaplin, 2003). This is oneof the reasons that the starch peak, shown in the TGA mass losscurve (Fessas and Schiraldi, 2001) is larger than that of the glutenpeak. Further investigation by Orlowska et al. (2009) using NMRand TGA, showed that within the single peak of a wheat starch–water suspension, free and bound water phases do exist, but over-lap each other and as a result show as one peak in the TGA.

The aim of this study was to investigate the effect of the addi-tion of wheat bran, to a flour–water mixture, on how water is dis-tributed between the different components (bran, starch andgluten), and the release of water at baking temperatures.

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Fig. 1. DTG of 100% flour, 50% flour/bran and 100% bran. The replacement of 50% offlour with 50% bran has a profound effect on the peak shape, with an increase inpeak height (B) as a transition occurs away from the starch and into the bran, and ashift to the left (A) of the gluten shoulder, as a result of bran dilution on both thestarch and flour components. Extra additional incorporation of bran, above 25%does not have such a dramatic effect.

2. Materials and methods

2.1. Materials

Both wheat bran (wheatings) and wheat flour samples (Claire, aUK soft wheat variety) were kindly supplied by Premier Foods,Rank Hovis (UK).

2.2. Methods

2.2.1. HydrationFlour, bran and flour–bran suspensions were produced by the

addition of 1 g of either flour, bran or flour–bran mixture, to15 mL of distilled water and left over night to allow them to becomefully hydrated (18 h). After soaking the suspensions were drainedunder gravity and 20 mg used for TGA analysis.

2.2.2. Thermal gravimetric analyzer (TGA)Using a TGA Q50 (TA instruments, Crawley, West Sussex, UK)

the sample was heated in a aluminium pan from room tempera-ture (±25 �C) to 120 �C, using a heating profile of 5 �C per minuteand run in triplicate.

The resulting TGA trace of mass loss (%) (derived from mass lossover temperature (�C)) was then analysed for its first derivative(Derivative Thermogravimetry (DTG) (%/�C)) and its second deriv-ative (2nd DTG (%/�C2)) using Universal Analysis Software V 4.7A(TA Instruments, Crawley, West Sussex, UK) with subsequentdeconvolution of peaks using PeakFit V 4.12 (Systat Software, SanJose, CA, USA).

Mass loss experiments were performed on 100% flour, and 100%bran samples. Additional experiments were conducted with sam-ples in which the bran–flour ratio was altered from 100% flour to100% bran on a gradient scale by mass which decreased 5% for flourand increased 5% for bran, up to 75% flour–25% bran mixture, fol-lowed by 50–50% flour–bran mixture, and then continued from25% flour–75% bran to 100% bran.

For the mass loss traces, the DTG and 2nd DTG were calculatedand the deconvolution of peaks under the DTG was determined inorder to establish their different water types (i.e. free, bound, etc.),with the 2nd DTG used to identify specific water loss events andused to check the validity of the deconvoluted peaks.

2.2.3. Statistical analysisThe TGA experiments were performed and analysed in dupli-

cate. Statistical investigations were performed using SPSSV.17.0.2 (Chicago, Illinois, USA).

3. Results

3.1. Derivative thermogravimetry (DTG)

Fig. 1 shows the first derivative DTG plots derived from the rawTGA data of %mass loss vs. temperature. The DTG plots are onlyshown for selected flour/bran mixtures for clarity. Examination ofthe DTG plots reveal that the flour rich mixtures exhibit two distinctfeatures with the initial peak attributed to starch and a secondaryshoulder (at approximately 80–90 degrees Celsius (labelled A inFig. 1)) attributed to gluten, as described by Fessas and Schiraldi(2001). A gradual shift occurs in the gluten shoulder (A), in conjunc-tion with the addition of bran to the mixture. Whilst still being vis-ible in the flour 50–bran 50% mixture, the gluten shoulder (A) isabsent in the bran rich mixtures (bran 100%). The introduction ofbran not only forces the gluten shoulder (A) to shift towards a lowertemperature, but on further increase of the bran (up to 100%), an in-crease in peak height (B), as well as a shift of the complete peak to ahigher temperature range was observed.

To calculate the amount of water lost associated with each peak(gluten and starch peaks in the bran poor mixtures and bran peakin bran rich mixtures), the maximum peak heights were calculatedusing the DTG and overlaid onto the TGA signal (Table 1). Thisshowed that an increase of bran resulted in an increase of totalwater loss (%), from 58.30 ± 1.93% in the presence of flour (100%)to 75.64 ± 1.34% bran (100%). Mass loss of the starch peak, whichshifts towards the bran peak, also increased from 68.96 ± 0.60%to 76.65 ± 1.20%. The gluten peak was unchanged by the additionof bran until 50% bran was added, above which the gluten peakcould no longer be detected.

Table 1Maximum peak height temperatures (�C) and associated water loss (%) of the two peaks (if present) derived from the DTG, including total water loss of the complete sample for100% flour and 75% flour–25% bran and 50% flour–bran mixture. A small increase (as little as 5%) in bran results in an increase of over 5% extra water loss. In contrast a 5% branincrease of over 25% bran inclusion, results only in 1% water increase per bran increment.

Sample 1st Peak 2nd Peak Total weight loss (%)

Max. peak height temp (�C) Weight loss (%) Max. peak height temp (�C) Weight loss (%)

Flour 100% 68.96 ± 0.60 29.22 ± 1.27 94.26 ± 3.55 19.76 ± 2.03 58.30 ± 1.93Flour 75% 75.92 ± 0.95 44.72 ± 0.83 89.69 ± 1.78 19.86 ± 1.37 71.80 ± 0.37Flour 50% 80.86 ± 1.44 50.62 ± 1.71 94.13 ± 3.66 19.74 ± 1.79 77.20 ± 1.10Flour 25% 82.92 ± 1.23 60.72 ± 1.70 – – 83.04 ± 1.64Bran 100% 76.65 ± 1.20 49.74 ± 1.61 – – 75.64 ± 1.34

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3.2. Second TGA derivative (2nd DTG)

The 2nd DTG for the samples were determined (Fig. 2) showingdistinctive inflexion points (DW), which marked the transitionalboundary between two distinctive water phases (water lossevents). The distinct features seen in the samples are attributedto the mixture formulation and ingredient composition. Threeinflexion points (DW1, DW2 and DW3) were identified within theflour. These inflexion points show the boundary between twowater loss events and are used to separate and identify different

Fig. 2. DTG and 2nd DTG of flour (A) and bran (B). Flour shows the starch (A) andgluten (B) with their corresponding inflexion points (end of water loss phases)(DW1–3), with DW1 associated with excess water, DW2 associated with the glutenmobile water and DW3 associated with the bound gluten. Bran only shows twowater loss events, DW1 and DW2, with DW1 associated with large amounts ofexcess and superficial and outer fringed water and DW2 associated with the loss ofthe deep intrinsic water.

phases of water losses. The first inflexion point (DW1, Fig. 2A) indi-cated the end of the first phase of water release and was linked tothe amount of excess water being evaporated from the samples. Onthe other hand, DW2 and DW3 were associated with the release ofwater from the gluten component of the flour, with DW2 linked tothe end phase of the free water of the gluten and DW3 signals theend phase of the bound water associated with the gluten. Thewater associated with the starch component as either mobile, cap-illary or condensed water, could not be resolved by DTG or 2ndDTG(Fessas and Schiraldi, 2001), due to the amount of excess waterwhich occupies the spaces between the starch granules and/orbran particles, being released upon heating of the mixtures in theTGA, overshadowing the release of the water associated starch.

In bran (100%) (Fig. 2B), DW1 is highly dominant, indicating aloss of large amounts of water from the system, while DW2 indi-cates a shift away from the large amounts of excess and superficialwater, to the loss of the deeper intrinsic water.

3.3. Deconvolution of DTG data

The deconvolution of the flour, flour–bran intermediates andbran samples were performed to resolve the different states ofwater held under the DTG curve. Both flour and bran possess uniqueDTG profiles which are a combination of different deconvolutedpeaks present within that profile and ultimately are determinedby the water state of the sample’s specific compositional matrix.

3.3.1. FlourDeconvolution was carried out on the flour sample to a 5 peak

model, to resolve the missing starch components, the deconvolu-tion of flour (Fig. 3) clearly shows the 3 components of the flour–water mixture; excess water (f (12%)), starch (a + b (57%)) andgluten (c + d (31%)). It also showed the different water types heldby the starch and gluten, as free (a and c) or bound (b and d) water,with water associated with the starch being held in a more freestate (a (41%)) compared to the bound state (b (16%)). This wasthe opposite for the gluten component, in which the free water(c) only occupies 2% while the bound water (d) hold 27%. Deconvo-lution of a 4 or 6 peak model resulted in low agreements with DTGr2 model fits compared to the 5 peak r2 fit.

3.3.2. BranThe deconvolution peaks of bran and its mixtures can be re-

solved in 4, 5 or 6 peaks, all with high fit agreement to the DTGand high correlations (r2 values). To investigate which peak modelwas more robust we looked first of all at the application of 6 decon-voluted peaks. This 6 peak model, in any bran and/or flour–branmix sample, led to the depression of the first deconvoluted peak.The first deconvoluted peaks are associated with the excess waterfound in the samples (Fig. 3 (f)). Obtaining the 6 peak model meantthat the first peak was being overlapped by the second deconvo-luted peak (Fig. 3 (g1)) depressing the first peak. While, the 2ndDTG did not show any inflexion point (DW) for the first, now,

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Fig. 3. In (A) the deconvolution of flour shows the excess water (12%), starch (57%(a + b)) and gluten (31% (c + d)). Deconvolution shows the different water segmentsheld by the starch and gluten, as free (a) and bound water (b) with water associatedto the starch is held more in a free state (41%), compared to the bound state (16%)while this is reversed for the gluten in which the free water (c) only occupies 2%while the bound water (d) hold 27%. In (B) the deconvolution of the first derivative(DTG) of 100% bran shows the multilayered histological design of bran, each withtheir own associated water fraction. The first deconvoluted peak (f) is excess water,after which large amounts of superficial (outer fringed) water (g1) is lost; thefollowing peaks (g1–g4) are associated with the loss of deep intrinsic water.

H. Roozendaal et al. / Journal of Food Engineering 111 (2012) 606–611 609

depressed peak. Statistical comparison between the 1st peak of the100% flour (5 peak deconvoluted results) and the 1st peak of the95% flour–5% bran (6 peaks deconvoluted results), showed a signif-icant statistical difference (p = 0.04) indicating that the 6 deconvo-luted peak model was not favourable. Sequential statisticalinvestigation via correlation, covariance and distant proximitiesall showed high agreement of a 5 peak deconvolution modelthroughout, from the initial 100% flour 5 peak deconvolution tothe 100% bran 5 peak deconvolution.

4. Discussion

4.1. DTG and 2nd DTG

The peak shift (B) (Fig. 1) observed when moving from flour richmixtures to bran rich mixtures and the shift of the DW1 observedin Fig. 2, when moving from the flour rich system to the bran richsystem, is attributed to the increased amount of excess water beingrelease from the bran particles into the flour–bran system. Thisincrease does not indicate that the water held by the bran is

increasingly held in a bound state as it does with the flour gluten(A in Fig. 1), but rather is attributed to the multilayered structureof the bran, in which the superficial (outer fringed) water of thebran particles is undergoing its first water loss.

The water loss gradient (as observed in Fig. 1) slowly movesfrom inflexion DW1 towards the inside of the bran particles ofinflexion DW2 (were the deep intrinsic water is located), over thecourse of the heating profile. Literature shows that bran, due toits hygroscopicity, has the capacity to take up approximately200–500 times its own mass in adsorbed water (Holloway andGreig, 1984), but due to its low affinity can release large amountsof captured water when placed under stress, for example heating.This increase in stress, as a result of the TGA heating profile, resultsin an increase in peak height and a prolonged release of water, aswater is being released from deep within the bran particles, result-ing in a creep along the temperature axis to a higher temperature(Fig. 1(B)).

4.1.1. FlourThe flour 2nd DTG trace (Fig. 2(A)) shows high agreement be-

tween the inflexion points and the deconvoluted peaks of theDTG, confirming that that the 5 peaks found during deconvolutionare peaks that can be attributed to the flour composition and itsrehydration state. The first peak, attributed to excess water, fol-lows the 2nd DTG until the first inflexion point. Both the excesswater and the starch free water, showed in the 2nd DTG as a grad-ual increased slope, indicating large amounts of highly mobile freewater being lost. The slope of the first inflexion point shows theboundary between this highly mobile free water, and the tighterbound water that exist within the starch compartment in the formof hydrogen bonding of water to the monomers of the starch. Thisis then followed on by the free water associated with gluten, whichshows as a left side of the shoulder with the large amount of boundwater of the gluten on the right side of the shoulder, which is char-acterised by its long resistance to release water, increasing the bak-ing time (Durchschlag and Zipper, 2001) thus being one of the lastwater fractions to be removed.

4.1.2. BranSaldo et al. (2002) showed that the inflexion points as bound-

aries between different types of water. The 2nd DTG Bran DW1

inflexion point (Fig. 2B) indicates high water loss at low tempera-ture (<60 �C). The DW2 inflexion point shows the point at whichthe high water evaporation (a combination of excess water andfree water) ends and signals the start of the deep intrinsic waterevaporation. The large amount of water being evaporated is linkedto its histological structure which can hold large amounts of waterwithin the structural matrix of the bran. Release of this water re-sults in the high 2nd DTG DW1 compared to the flour DW1.

4.2. Deconvolution

Deconvolution of peaks present under the DTG, was performedin order to resolve the issue of the missing flour component inFig. 2A and to investigate the distribution of water in the sampleswith higher bran enrichment.

4.2.1. FlourThe deconvolution of flour through the 5 peak model shows

that starch and gluten hold water through different mechanisms.Starch granules are characterised by a high number of surfacemicro-capillaries, giving them the ability to store large amountsof mobile water. They also hold water through hydrogen bondinggiving rise to the bound water fraction of the starch (Chaplin,2003), resulting in a total of 26% increase in water bound to starchcompared to gluten.

Table 2Areas under the curve for the 5 deconvoluted peaks of flour and bran show that starch and gluten play a significant role in water compartmentalisation of the system as high as50%. The subsequent increase in bran shows a more homogenous water compartmentalisation.

Peak Flour 100% Flour 75% bran 25% Flour 50% bran 50% Flour 25% bran 75% Bran 100%

1 42.56 ± 14.99 6.20 ± 3.66 5.58 ± 2.58 24.51 ± 1.13 25.50 ± 3.922 23.53 ± 8.68 36.63 ± 9.43 36.72 ± 7.26 27.62 ± 1.24 30.45 ± 3.143 7.08 ± 4.62 40.19 ± 6.54 32.25 ± 3.34 23.24 ± 0.45 23.11 ± 1.314 9.31 ± 3.40 6.75 ± 3.91 17.68 ± 7.26 17.54 ± 0.44 13.81 ± 0.975 17.52 ± 5.19 10.25 ± 2.91 7.79 ± 3.17 7.11 ± 1.32 7.13 ± 0.74

610 H. Roozendaal et al. / Journal of Food Engineering 111 (2012) 606–611

The gluten compartment can hold more water in the boundstate compared to the free state (27% over 2%). This is in agreementwith Fessas and Schiraldi (2001) who showed that gluten holdsmore water in a bound state, when non-worked. Mechanicallyworked gluten favours the formation of the covalent disulfidebonds via the cysteine groups of the glutenin residues over thewater–gluten hydrogen bonds via the glutamine residues (Lodiand Vodovotz, 2008), thus reducing the amount of water held inthe system. The positioning of the gluten as the last compartment(Figs. 2A and 3A) is the result of resistance to the removal of thiswater from the glutamine residues for an extended period of time(Durchschlag and Zipper, 2001).

4.2.2. BranThe histological features of bran, comprising mostly of a dead

cellular matrix, with intra cellular pore matrix (micro-capillaries)situated throughout the bran which act as flow regulators(Robertson et al., 2000), coupled with the unique ability of the branto take up 200–500% of its own body mass, result in a slow but stea-dy release of water back into the system during baking. This steadystate release can be seen in the 2nd DTG in which the first inflexionpoint seen in the flour samples is absence in the bran. As a result the5 deconvoluted peaks associated with the bran, shows a moreuniform distribution of water loss compared to the flour samples(Table 2). The first deconvoluted peak (f) in Fig. 3 (B) is againassociated with external surface water loss, whilst the other 4 areassociated with the histological trapped water. In Fig. 3, the seconddeconvoluted peak (g1) shows high water loss, associated with themobile water found at the more outer layers of the bran particlewhile the third deconvoluted peak (g2) being the deep mobilewater. Finally, the fourth peak (g3) is crossover between the mobilewater and the bound water of the fifth peak (g4) which is associatedwith the bound water components. This is in agreement with the2nd DTG which shows large amount of mobile water being lost overthe first 3 peaks after which the inflexion point showing a two stageevent, agreeing with the 4th and 5th peaks. The mobile watersupply becomes exhausted during the 4th peak (13.81 ± 0.97%)and a change over occurs between the free and bound waterboundaries and the 5th peak release only 7.12 ± 0.74%.

4.3. Bran and flour interaction on water release

A significant increase (p < 0.05) in water release can be seenwhen bran is incorporated as little as 5%. However subsequent in-crease of bran did not result in a similar increase of water being re-leased from the flour–bran mixture which is due to an interactionbetween the histological features of the bran particle and theexperimental sample preparation process. As part of the samplepreparation process, the bran is left to drain under gravity. Duringthis, a 25% increase in bran leads to a 13% increase in water lossduring drying. Subsequent increases of bran result only in an in-crease of 5% per 25% bran increase. The reason why there is onlya 5% increase and not the 13% anticipated increase is due to thebran’s secondary ability, with the first being its hygroscopic abilityand the second its low affinity towards water. It readily gives up its

captured water when placed under stress. The water holding andwater binding capacity experiments performed by (Holloway andGreig, 1984; Mongeau and Brassard, 1982) and others, are proofsof this concept. The bran used in the experiments, albeit in a wetsystem, has actually most of its mobile water removed throughdraining. Therefore, the first deconvoluted peaks consist of waterthat has coated the bran’s structural surfaces.

This on its own does not fully explain why there is such a differ-ence, until we also include the flour and its ability to capture andhold onto its water. A 100% flour sample releases a total of58.30 ± 1.93% of water upon heating, while the addition of 25%bran to the flour mix, results in an increase of total water being re-leased to 71.80 ± 0.37%, which is a significant increase of 13.5%.Increasing the bran concentration to 50%, results in a water releaseof 77.20 ± 1.10% while and an increase of bran to 75% results in awater release of 83.04 ± 1.64% which is only an increase of ±5% inboth cases. This indicates that doubling the amount of bran doesnot result in a doubling of the amount of water released. There isthus a fine balance between the amount of bran present in the sys-tem and its effect on the amount of water released.

5. Conclusions

Deconvolution of the water peaks in TGA data of flour, flour–branmixtures and bran revealed a high degree of influence of the bran onthe distribution of water. The total water loss from analysed sys-tems during TGA experiments ranged from 58.30 ± 1.93% for flouronly systems to 71.80 ± 0.37% in the presence of 25% w/w bran,showing that bran releases large amounts of water during heating,which increases the water content of the overall system. A five-peakdeconvolution model allowed discrimination of free and boundwater associated with flour starch and gluten, the ratios of whichwere significantly affected by the presence of bran. This finding sug-gests that the presence of bran in cereal dough and batter formula-tions may influence final baked product quality by disrupting theformation of gluten networks, gelatinisation of starch, the aggrega-tion of the gluten and finally the gelation and crystallization ofstarch during cooling, events which are all governed in some partby water. Although small additions of bran were not observed to re-sult in a major effect on the starch and gluten deconvoluted peaks,large amounts of bran do; 20% addition of bran still shows the glutenpeak on the TGA, while 25% increase in bran, suppresses this. Themajor water increase into the system occurs between 0 and 25%bran addition and a subsequent increase above 25% leads only to5% per 25% bran. Thus the first 25% bran can be seen as the most crit-ical stage of bran addition to a cereal based product, after which anysubsequent addition does not have a major incremental impact.

Acknowledgements

We gratefully acknowledge the following Grants; the BBSRCDoctoral Training Grant (BB/E527920/1) and the Nestlè IndustrialCASE Studentship for funding this project.

Also the use of the Chemical Analysis Facility (CAF) at theUniversity of Reading is gratefully acknowledged.

H. Roozendaal et al. / Journal of Food Engineering 111 (2012) 606–611 611

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