Optimization of ingredients and baking process for improved wholemeal oat bread quality

ARTICLE IN PRESS

LWT 40 (2007) 860–870 www.elsevier.com/locate/lwt

Optimization of ingredients and baking process for improved wholemeal oat bread quality L. Flander, M. Salmenkallio-Marttila, T. Suortti, K. Autio VTT Biotechnology, P.O. Box 1500, 02044 VTT, Finland Received 24 October 2005; received in revised form 28 April 2006; accepted 2 May 2006

Abstract Baking technology for tasty bread with high wholemeal oat content and good texture was developed. Bread was baked with a straight baking process using whole grain oat (51/100 g flour) and white wheat (49/100 g four). The effects of gluten and water content, dough mixing time, proofing temperature and time, and baking conditions on bread quality were investigated using response surface methodology with a central composite design. Response variables measured were specific volume, instrumental crumb hardness, and sensory texture, mouthfeel, and flavour. The concentration and molecular weight distribution of b-glucan were analysed both from the flours and the bread. Light microscopy was used to locate b-glucan in the bread. Proofing conditions, gluten, and water content had a major effect on specific volume and hardness of the oat bread. The sensory crumb properties were mainly affected by ingredients, whereas processing conditions exhibited their main effects on crust properties and richness of the crumb flavour. b-glucan content of oat bread was 1.3/100 g bread. The proportion of the highest molecular weight fraction of b-glucan was decreased as compared with the original b-glucan content of oat/wheat flour. A great part of b-glucan in bread was located in the large bran pieces. r 2006 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. Keywords: Oat bread; Baking; Optimization; b-glucan

1. Introduction Bread is an ideal functional food product, since it is an important part of our daily diet. The taste of oat bread is nutty, mild, and pleasant, and it could compete successfully as a healthy alternative to consumers, who are used to eating white wheat bread. Oat has excellent moisture retention properties that keep breads fresher for longer periods of time (McKechnie, 1983). Addition of oat, oat starch, or oat lecithin to wheat bread might retard also the staling rate of the bread (Forssell, Shamek, Ha¨rko¨nen, & Poutanen, 1998; Prentice, Cuendet, & Geddes, 1954; Zhang, Moore, & Doehlert, 1998). The main problem in the use of oat in higher quantities is the inferior baking quality (Bru¨mmer, Morgenstern, & Neumann, 1988; Gormley & Morrissey, 1993; Oomah, 1983), because oat proteins, normally denaturated by a Corresponding author. Tel.: +358 20 722 5842; fax: +358 20 722 7071.

E-mail address: laura.flander@vtt.fi (L. Flander).

heat treatment, do not possess the unique visco-elastic properties of wheat gluten. An addition of 20 g oat/100 g wheat flour allows the bread to be labelled as ‘‘oat bread’’ in Germany (Bru¨mmer et al., 1988). Exceeding this amount of oat leads easily to tight, moist, and gummy breads. The effect of oat on dough properties and bread quality have been studied so far with addition of oat bran, flakes or flour from 10 to 25/100 g wheat flour (Degutyte-Fomins, Sontag-Strohm, & Salovaara, 2002; Krishnan, Chang, & Brown, 1987; Oomah, 1983; Zhang et al., 1998). In all these cases, breads with 10 g oat/100 g wheat flour had better loaf volume, crumb grain, and texture than breads with 15–25 g oat/100 g wheat flour. Bru¨mmer et al. (1988) attained good quality of oat bread by adding 20 g oat flakes/100 g wheat flour, although the bread volume was 10% smaller than volume of the control white wheat bread. The poor baking performance of oat can be compensated for by adding dry gluten into the dough (Gormley & Morrissey, 1993). If the amount of added fibre is higher than 10 g oat flour/100 g wheat flour, a flour protein

0023-6438/$30.00 r 2006 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2006.05.004

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content of about 16/100 g flour is recommended and the amount of water used should be sufficient to properly hydrate both the added gluten and the fibre components (Stear, 1990). Gluten strengthens the protein matrix and enhances the structure of oat bread. According to Oomah and Lefkovitch (1988), loaf volume of wheat breads containing up to 15 g oat flour/100 g flour can be optimized by a sufficiently high water level (68–72/100 g flour) in the dough. Whole grain oat contains high amounts of valuable nutrients such as soluble fibres, proteins, unsaturated fatty acids, vitamins, minerals, and phytochemicals. The dietary fibre complex with its antioxidants and other phytochemicals may protect us from cardiovascular disease and some types of cancer (Jacobs, Marquart, Slavin, & Kushi, 1998a, b; Slavin, Marquart, & Jacobs, 2000; Thompson, 1994). Whole grain oat contains significant amounts of dietary fibre and especially water soluble (1-3), (1-4)-b-D-glucan. The b-glucan content in oat (Avena sativa) varies between 2.3 and 8.5/100 g (Welch, Brown, & Leggett, 2000). On the basis of numerous clinical studies, the US Food and Drug Administration (FDA) permitted the use of a claim that oat-soluble fibre has the ability to reduce the risk of coronary hearth disease (FDA, 1996). The required dose of b-glucan for a single food is 0.75 g/serving. The highly viscous b-glucan fraction of oat has been related to the ability to lower blood cholesterol and the intestinal absorption of glucose (Ma¨lkki, 2001; Wood, 1993). In order to be physiologically active and form viscous solutions in the gut, b-glucan must be soluble, and the concentration and molecular weight must be sufficiently high (A˚man, Rimsten, & Andersson, 2004; Autio, Myllyma¨ki, & Ma¨lkki, 1987; Doublier & Wood, 1995). The molecular weight of b-glucan in oat/barley products has been reported to be smaller than the molecular weight of b-glucan in the raw material (A˚man et al., 2004; Beer, Wood, Weisz, & Fillion, 1997; Kerckhoffs, Hornstra, & Mensink, 2003; Sundberg et al., 1996). The molecular weight of b-glucan in oat bread was reduced as compared with the molecular weight of b-glucan in oat bran, and no significant changes in LDLcholesterol levels of hypercholesterolemic subjects were detected (Kerckhoffs et al., 2003; To¨rro¨nen et al., 1992). Raw material, endogenous b-glucanase activity, processing, and storage conditions exhibit an effect on the amount, solubility, molecular weight, and structure of b-glucan in the products (Beer et al., 1997; DegutyteFomins et al., 2002; Zhang, Moore, & Doehlert, 1998). The aim of this study was to develop wholemeal oat bread baking technology by using experimental design and response surface model (RSM) to attain a bread with good quality, high wholemeal oat content (51 g whole grain oat flour/100 g wheat flour), and high b-glucan content (0.75 g/portion). The possible depolymerization of oat b-glucan in bread was also studied and light microscopy was used to locate oat b-glucan in the bread matrix.

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2. Materials and methods 2.1. Flour properties Oat flour (Helsingin Mylly Ltd., Ja¨rvenpa¨a¨) and white wheat flour (Raisio Group plc, Raisio) were obtained from Finnish mills. White wheat flour contained ascorbic acid. All chemical analyses of the flours were made in duplicate (Table 1). Moisture content was determined according to standard method 44/15A, and wet gluten with method 38/12A (AACC, 2000). Protein content was determined by the Kjeldahl method (AACC standard 46/11A), and ash content was analysed according to standard method 08-01 (AACC, 2000). The sieve analysis of oat flour was carried out by sieving two 100 g portions of the flour for 10 min. 2.2. Experimental design A fractional factorial design was used to screen the most important factors (ingredients and processing conditions) affecting the specific volume, instrumental crumb hardness and sensory properties of the breads and to choose the most significant ones and their appropriate range for optimization tests (data not shown). The specific volumes of these breads varied from 1.9 to 3.1 cm3/g and their instrumental crumb hardness after 2 and 72 h varied between 0.2 and 0.4 kg, and between 0.2 and 0.7 kg, respectively. 2.2.1. Optimization of ingredients A central composite face-centered design (CCF) was used with two variables and four replicates at the centre point, for a total of 12 experiments (Table 2). The two recipe variables optimized were the gluten (G, g/100 g flour) and water content (W, g/100 g flour). Experimental conditions at the centre point were G ¼ 11.8 g/100 g and W ¼ 88/100 g. The scaled values were x1 ¼ (G–11.8)/3.45,

Table 1 Chemical analyses of flours Attribute

Oat flour, Helsingin Mylly Ltd.

Wheat flour, Raisio Group plc

Moisture (g/100 g flour) Protein (g/100 g, db)a Ash (g/100 g, db) Wet gluten (g/100 g) Sieves, mm (%) 630 475 355 250 132 o95

10.6 19.0 2.8 —

12.1 12.9 0.7 28.1

21 12 8 7 50 0.5

— — — — — —

a

Nx5.7 for wheat and Nx6.26 for oat.

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where G ranged from 8.3 to 15.2/100 g flour; x2 ¼ (W–88)/ 10, where W ranged from 78 to 98/100 g flour. 2.2.2. Optimization of baking process A CCF was used with five process variables and four replicates at the centre point, for a total of 30 experiments (Table 3). The five process variables studied were the mixing time (tm, min), the intermediate proofing time (floor time) (ti, min), the final proofing time (tf, min), the final proofing temperature of the cabinet (Tf), and the baking temperature (Tb). Experimental conditions at the centre point were tm ¼ 6 min, ti ¼ 12 min, tf ¼ 65 min, Tf ¼ 35 1C, and Tb ¼ 195 1C. The experimental number and real values

Table 2 Optimization of the ingredientsa Run

Scaled value

1 2 3 4 5 6 7 8 9 10 11 12

Real value

X1

X2

Gluten (g/100 g Water (g/100 g flour) flour)

0.0 0.0 1.0 0.0 0.0 1.0 +1.0 0.0 1.0 0.0 +1.0 +1.0

0.0 1.0 1.0 +1.0 0.0 0.0 +1.0 0.0 +1.0 0.0 0.0 1.0

11.8 11.8 8.3 11.8 11.8 8.3 15.2 11.8 8.3 11.8 15.2 15.2

88.0 78.0 78.0 98.0 88.0 88.0 98.0 88.0 98.0 88.0 88.0 78.0

Amount of water and gluten in oat breads in scaled and real values. a x1 ¼ (G–11.8)/3.4, where G ranged from 8.3 to 15.2/100 g flour; x2 ¼ (W–88.0)/10, where W ranged from 78.0 to 98.0/100 g flour.

are given in Table 3. The scaled values (1, 0 and +1) were x1 ¼ (tm–6)/2, where tm ranged from 4 to 8 min; x2 ¼ (ti–12)/7.5, where ti ranged from 5 to 20 min; x3 ¼ (tf–65)/ 10, where tf ranged from 55 to 75 min; x4 ¼ (Tf–35)/5, where Tf ranged from 30 to 40 1C; and x5 ¼ (Tb–195)/15, where Tb ranged from 180 to 210 1C. A verification experiment was performed in the experimental domain (experiment 31). 2.3. Baking 2.3.1. Optimization of ingredients The amounts of tap water and gluten (Raisio Group plc, Raisio, Finland) were according to the experimental design (Table 2). The formula consisted of oat flour (51 g), wheat flour (49 g), sugar (3.2 g), salt (2.3 g), shortening (3.2 g) (Sunnuntai, Raisio Group plc, Raisio, Finland), and pressed baking yeast (3.2 g) (Finnish Yeast Ltd., Lahti, Finland). Amounts of the ingredients were based on the weight of oat and wheat flour mixture (100 g). Total weight of the dough batch was 2500 g. Wheat flour was blended thoroughly with the sugar and salt and placed in a spiral mixer (Diosna SP 12 F, Dierks and So¨hne GmbH, Osnabru¨ck, Germany). The yeast was suspended in water (24 1C) and added to the mixture with the tempered shortening. The optimal mixing time of the dough was based on the results of screening tests. The dough was mixed with fast speed (200 rpm) for 6 min and the oat flour with the rest of the water was added to the dough and mixed at low speed (100 rpm) for 6 min. By this method it was possible to minimize the detrimental effect of oat on the formation of gluten network. The temperature of dough at the end of mixing was kept at 30 1C by controlling the temperature of the added water. After intermediate proofing at 28 1C, 80% rh for 12 min, the dough was

Table 3 Optimization of processing conditions Run

Mixing time (min)

Int. proofing (min)

Proofing time (min)

Proofing temp. (1C)

Baking temp. (1C)

Run

Mixing time (min)

Int. proofing (min)

Proofing time (min)

Proofing temp. (1C)

Baking temp. (1C)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

8 6 4 6 4 8 4 4 4 6 6 8 6 6 6

5 12 5 12 20 20 20 5 5 12 12 20 12 12 20

55 75 55 65 55 75 75 55 75 65 65 55 65 65 65

30 35 30 35 40 40 40 40 40 35 30 30 35 35 35

180 195 210 210 210 210 180 180 210 195 195 210 180 195 195

16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

8 6 6 8 4 6 4 8 8 8 4 4 6 8 6 6

12 12 12 5 20 5 20 20 20 5 12 5 12 5 12 12

65 65 65 75 55 65 75 75 55 55 65 75 55 75 65 65

35 35 40 30 30 35 30 30 40 40 35 30 35 40 35 39

195 195 195 210 180 195 210 180 180 210 195 180 195 180 195 210

Processing conditions of oat breads in real values.

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divided into six 400 g pieces, rounded, and moulded by hand to tempered pans which were sprayed with pan grease and proofed at 80% rh, 35 1C for 65 min. The breads were baked at 195 1C for 30 min (Rack Oven 9000, Sveba Dahlen Ab, Sweden) and with 5 s of steam in the beginning.

bread were analysed after stirring 1 g of the sample overnight with magnetic stirrer in 1 l of 0.1 N NaOH containing 0.1% NaBH4. The samples were analysed by HPLC-SEC with calcofluor staining by using right-angle laser light scattering for detection (Suortti, 1993).

2.3.2. Optimization of baking process Water and gluten content of the dough were fixed according to the results attained by optimization of the recipe to 91.5 and 15.2/100 g flour, respectively. The experimental design for the processing parameters are presented in Table 3.

2.6. Microscopy

2.4. Analyses of bread characteristics After baking, the loaves were cooled for 2 h before being weighed. Loaf volume was determined by the rapeseed displacement method (Siebert, 1971). Crumb hardness was measured at 2 and 72 h after baking by the TA-XT2 Texture Analyser (Stable Micro Systems, Godalming, UK) using the Texture Profile Analysis test. Six 25 mm thick slices were used for the analysis, two slices were taken from the middle of each of the three different breads. The crust of the slices was removed so that only textural parameters from the crumb were measured. The slices were compressed by 10 mm (40%) with a speed of 1.7 mm/s. A trained descriptive sensory panel (n ¼ 5) evaluated the characteristics of the breads. Attribute intensities were rated on 5-unit, verbally anchored intensity scales (Table 4). Altogether, nine attributes were selected to describe texture, mouthfeel, and flavour of the breads. 2.5. b-glucan content and molecular weight distribution b-glucan was determined by the enzymatic method of McCleary and Codd (1991) using an assay kit obtained from Megazyme International Ltd. (Bray, Ireland). The average molecular weights (Mw) of b-glucan of flours and

Pieces of bread crumb (0.5 cm) were taken from the middle of the loaf, embedded in 1% agarose, fixed in 1% glutaraldehyde in 0.1 mol/l phosphate buffer, pH 7.0, dehydrated with ethanol, embedded in Historesin (Leica, Heidelberg), and sectioned (4 mm) with a Leica microtome (Heidelberg, Germany). For the fluorescence microscopic examination, the bread sections were stained with specific fluorochromes (Fulcher & Wong, 1980; Parkkonen, Ha¨rko¨nen, & Autio, 1994; Wood, Fulcher, & Stone, 1983). Protein was stained with aqueous 0.1% (w/v) Fuchsin acid for 1 min (Gurr, BDH Ltd., Poole, England), and b-glucan was stained with aqueous 0.01% (w/v) calcofluor White for 1 min (Fluorescent brightener 28, Aldrich, Germany). Calcofluor stains intact cell walls blue. Fuchsin acid stains proteins red. Starch remains unstained and appears black. 2.7. Data analyses Maximum and minimum ingredient and process variable levels for the optimization tests were chosen by carrying out preliminary screening tests (data not shown). A central composite design made it possible to approximate the measured data (yobs) using an RSM (Eq. (1)) expressed in unscaled variables: Y obs ¼ b0 þ b1 x1 þ b2 x2 þ b3 x3 þ b11 x1 x1 þ b22 x2 x2 þ b33 x3 x3 þ b12 x1 x2 þ b13 x1 x3 þ b23 x2 x3 þ e, e ¼ yobs  ycalc ,

Table 4 Sensory attributes and verbal anchors of the rating scales Attribute Bread crust Evenness Intensity of the colour Thickness Intensity of the flavour Crispness Bread crumb Softness Elasticity Moistness Richness of the flavour

Anchors

Not at all even–very even Very light–very dark Very thin (1–2 mm)–very thick (45 mm) No flavour–very intense flavour Not at all crispy–very crispy (a crispy sound during biting) Not at all soft–very soft Not at all elastic (slice breaks immediately, when bended)–very elastic Not at all moist (in the mouth)–very moist Very lean flavour–very rich flavour

ð1Þ (2)

where b0 is a constant; b1, b2, and b3 express the main effect of each process variable b12, b13, and b23 show the interaction effects between the variables and the square coefficients; and b11, b22, and b33 reveal whether any of the variables give a maximum or minimum within the experimental domain. The difference between the experimental data (yobs) and the model (ycalc) gives the residual (e) in Eq. (2) (Lindgren, Sjo¨stro¨m, Hellsten, & Lif, 1995). The results were examined by the computer program MODDE version 4.0 (Umetrics Ab, Umea˚ Sweden). The RSM were estimated by partial least squares (PLS) for the 12 and 30 experiments in the CCF design. The centre point made it possible to estimate the pure error of the analyses, which was used to predict whether the models gave significant lack of fit (Carlsson, 1992). The reliability of the models was evaluated by calculating the R2 and Q2 values for each model, where R2 is the variation of the response explained

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by the model and Q2 is the fraction of the variation of the response that can be predicted by the model (MODDE version 4.0). Q2 should be 40.5 if conclusions are to be drawn from the model (Lindgren, 1995). Generally, a model is considered excellent if R2 and Q2 exceed 0.9 (Lindgren et al., 1995). A verification experiment was performed to estimate the predictive capacity of the models. Tables 2 and 3 show the combination of predictor variable levels used in the central composite design. To study five factors (predictor variables) at three levels would require 35, i.e., 243 experiments, whereas use of the central composite design required 30 runs of experiments. The centre point in the design was repeated four times to calculate the reproducibility of the method. The response variables measuring baking performance were specific volume, hardness after 2 and 72 h and sensory attributes of the bread crust (evenness, colour, thickness, intensity of the flavour, and crispness) and crumb (softness, elasticity, moistness, richness of the flavour) (Table 4). For each of the response variables, model summaries and lack of fit tests were analysed for linear, quadratic, and cubic models. From this information, the most accurate model was chosen, which in all cases was quadratic. Two-dimensional response surface plots were generated for each quality parameter. Calculation of optimal processing conditions for baking performance of oat bread was performed using a multiple response method called desirability. This optimization method incorporates desires and priorities for each of the variables. Specific volume, evenness, and crispness of the crust, and softness, elasticity, and richness of the bread crumb were specified as maximum level desirable. Hardness was specified as minimum desirable. The desirable levels of intensity of the colour and flavour as well as thickness of the crust and moistness of the crumb was fixed to intermediate level (score 3 on the sensory scale) (Table 4). Optimization was carried out at recipe first and the optimized recipe was used to carry out the optimization of the process.

3. Results and discussion 3.1. Baking quality 3.1.1. Optimization of ingredients The results of the 12 experiments were evaluated statistically by PLS method. Complete RSM were estimated. The achieved mathematical models, expressed in unscaled variables are presented in Table 5. Using these tables, the specific volume of the bread can be predicted by the equation for the experimental area under consideration, e.g., Specific volume ¼  83:2 þ 2:8G þ 3:6W  0:044W 2  0:06GW . The gluten and water significantly influenced specific volume and hardness of the oat bread crumb. The evenness of the bread crust as well as sensory softness, elasticity, and moistness of the bread crumb were also affected significantly by gluten and water contents. Gluten and water contents did not affect significantly to the intensity of the crust colour, thickness or crispness of the crust, or intensity of the crust flavour. Response surface plots of specific volume and hardness of the breads are shown in Fig. 1A–C. As can be seen in Fig. 1A–C, water had a slightly more pronounced effect on these quality attributes than gluten due to a wider range. According to the response surface plots, a water content of 90–92.5 g and a gluten content of 14.2–15.2/100 g flour were required for maximal specific volume and minimal instrumental hardness measured after 2 and 72 h, respectively. The maximal specific volume (3.6 cm3/g) and minimal hardness (0.1 kg after 2 h, and 0.2 kg after 72 h) were attained by adding gluten 15.2 g and water 91.5/100 g of flour weight to the dough. From the sensory attributes tested, the gluten and water contents mainly affected crumb properties, whereas processing conditions exhibited their main effects on crust properties. Optimal evenness of the crust and optimal

Table 5 Effects of ingredient factors, expressed as their corresponding coefficients obtained in the models for texture and sensory attributesa Factorb

Specific volume

Hardness, 2h

Hardness, 72 h

Evenness

Softness

Elasticity

Moistness

Constant G W GW G2 W2 R2 Q2

83.2 2.8 3.6 0.06 ns 0.04 0.93 0.66

23.1 0.6 1.0 0.02 ns 0.01 0.97 0.73

59.4 1.7 2.5 0.04 ns 0.03 0.96 0.68

31.1 2.6 1.2 0.06 ns 0.01 0.85 0.62

84.9 3.2 3.6 0.04 0.11 0.04 0.87 0.57

17.1 1.1 0.4 0.05 0.09 ns 0.89 0.60

92.3 4.5 ns ns 0.05 ns 0.80 0.74

a

Only values of significant coefficients are presented (95% confidence level); ns, no significant effect at the 5% level. G, gluten; W, water; G  W, interaction between gluten and water; G2, quadratic effect of gluten; W2, quadratic effect of water; R2, measure of fit of the model: Q2, predictive power of the model. b

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98

94

94 Water (g/100 g flour.)

Water (g/100g flour).

L. Flander et al. / LWT 40 (2007) 860–870

3.6

90 3.4 86 3.20 3.0

82

2.8 2.6 8.3

9.4

90 0.15 0.20

86

0.25 0.3

82

0.35

0.4 78

78

(A)

865

10.6 11.8 12.9 14.0 Gluten (g/100 g flour)

15.2

8.3

(B)

9.4

10.6 11.8 12.9 14.0 Gluten (g/100 g flour)

15.2

98 0.24

Water (g/100 g flour)

94 0.24 90 0.37 86

0.50 0.64

82

78

0.78 0.92 1.04 8.3

9.4

(C)

10.6 11.8 12.9 Gluten (g/100 g flour)

14.0

15.2

Fig. 1. Response surface plots of recipe optimization. Effects of gluten and water on (A) specific volume (cm3/g) of the bread, (B) instrumental hardness (kg) of the crumb after storage of 2 h, (C) instrumental hardness (kg) of the crumb after storage of 72 h.

moistness of the crumb were achieved with the same concentrations of water and gluten as the optimal volume and hardness of the oat bread. The softest bread was obtained when the gluten content of the bread was 12/100 g flour and the water content was 90/100 g flour. Most elastic bread was attained with the smallest gluten and water contents (8 and 84/100 g flour, respectively). According to Oomah and Lefkovitch (1988), loaf volumes of wheat–oat breads can be optimized by a sufficiently high amount of water. Also, Gormley and Morrissey (1993) obtained the largest bread volumes by the addition of gluten and extra water to bread containing 5–20 g oat flakes/100 g flour. The suppression of loaf volume by soluble oat dietary fibre is probably related to the inhibition of gluten strength. Increasing its content without a concomitant increase in vital gluten content results in a reduction in loaf volume and even in unsatisfactory loaves (Rudel, 1990). Barley is another cereal with a high content of soluble b-glucan. Cavallero, Empilli, Brighenti, and Stanca (2002) evaluated the breadmaking quality of mixed barley breads containing 50 g whole grain barley flour/100 g wheat flour by evaluations of the bread volume and sensory acceptance in order to get test meals for glycemic index analysis. The volume of the bread was low (specific volume was about 2.5 ml/g) and the bread received quite low flavour/aroma scores by the panel. The barley bread had lower water contents than our oat

bread (64.9/100 and 87/100 g flour, respectively). All of the ingredients in barley bread were blended with a slow-speed mixer with shorter fermentation time and at a lower temperature than our breads. 3.1.2. Optimization of baking process The processing conditions were optimized by using 15.2 g gluten and 91.5 g water/100 g flour to the dough. The results from the measurements were evaluated statistically by PLS. Complete RSMs, including the 30 experiments in the design, were estimated. The achieved mathematical models for texture and sensory attributes are presented in Table 6. The final proofing temperature and time, as well as baking temperature significantly influenced the specific volume of the oat bread. The final proofing temperature and time as well as intermediate proofing time together with final proofing temperature had significant effects on the hardness of the oat bread. Also, mixing time affected the crumb hardness significantly. The significant effect of proofing time on specific volume and hardness of wheat sourdough bread has also been reported by Clarke, Schober, Angst, and Arendt (2003). The intensity of the crust colour and richness of the crumb flavour was affected most by baking temperature. Thickest crust with most intensive flavour was obtained with highest baking temperature. The most significant variables affecting the crispness of the crust, were final

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Table 6 Effects of processing factors, expressed as their corresponding coefficients obtained in the models for texture and sensory attributesa Factorb

Texture attributes Specific volume

Constant M PI PTi PTe B M  PI M  PTi M  PTe MB PI  M PI  PTi PI  PTe PI  B PTi  PTe PTi  B PTe  B M2 PI2 PTi2 PTe2 B2 R2 Q2

Sensory attributes Hardness, 2 h

Hardness, 72 h

Crust

Crumb

Colour

Thickness

Flavour

Crispness

Richness

2.963 1.111 0.294 0.050 0.681 0.094 0.004 0.003 0.004 0.003 0.009 0.001 0.004 0.001 0.005 ns 0.001 0.015 0.001 0.001 0.002 0.000 0.93 0.72

6.058 0.715 0.060 0.067 0.005 0.031 0.009 0.013 ns ns ns ns ns

52.554 0.245 0.197 0.095 0.132 0.504 0.018 ns ns ns ns 0.002 ns

5.364 0.771 0.193 0.105 0.141 0.074 ns ns ns 0.003 ns 0.002 0.001

ns ns ns ns ns ns ns ns 0.84 0.66

0.003 ns ns ns ns ns ns 0.001 0.84 0.57

0.001 0.001 0.001 0.010 0.001 0.002 0.001 0.000 0.84 0.61

5.457 0.020 0.004 0.085 0.044 0.026 ns ns ns ns ns ns ns

496.164 89.093 31.769 10.960 11.066 6.974 ns ns ns 0.426 ns 0.131 0.464

1142.089 130.410 39.924 25.486 25.801 15.338 ns ns ns 0.587 ns 0.053 0.839

3.746 0.981 0.000 0.159 0.272 0.032 0.009 ns 0.009 0.002 ns 0.001 0.003

ns 0.001 ns ns ns ns ns ns 0.85 0.66

ns 0.076 ns ns 0.267 ns ns ns 0.83 0.52

ns 0.170 ns ns 0.237 ns ns ns 0.86 0.50

ns 0.001 0.001 0.009 0.001 1.814 0.001 0.000 0.85 0.58

a

Only values of significant coefficients are presented (95% confidence level). M, mixing time; PI, intermediate proofing time; PTi, proofing time; PTe, proofing temperature; B, baking temperature; M2, quadratic effect of mixing time; M  PI, interaction between mixing time and intermediate proofing time; R2, measure of fit of the model: Q2, predictive power of the model. b

proofing time, temperature, and baking temperature. Processing did not significantly affect the evenness of the crust, softness, elasticity and moistness of the breads. Of the five processing factors, proofing temperature and time had the greatest effects on bread quality. Response surface plots for specific volume and hardness after 2 and 72 h storage are shown in Fig. 2A–C. Proofing time had a slightly more pronounced effect than proofing temperature on the specific volume and hardness of the breads. According to the response surface plot, the maximal specific volume 3.7 (cm3/g) and minimal hardness (0.1 kg after 2 h, and 0.3 kg after 72 h) could be achieved by longest proofing times of 71–75 min and highest temperatures of 39–40 1C, respectively. Of the sensory attributes evaluated, the processing conditions significantly affected the crust properties and richness of the crumb flavour. The thickness, intensity of flavour and crispness of the crust were attained in conditions which were the same as the optimal conditions for bread volume and hardness. The optimal colour of the crust and richness of the crumb flavour were attained in a slightly shorter proofing time (64 min) than other sensory attributes.

3.1.3. Optimized oat bread The water content and the gluten content for the optimized bread were 91.5 and 15.2/100 g flour, respectively. The dough was mixed for 6 min and the intermediate proofing time was 12 min. The final proofing time was slightly reduced from 70 to 65 min in order to obtain optimum richness of the crumb flavour and crust colour to the bread. The final proofing temperature was 39 1C and the baking temperature was 210 1C. The specific volume of the bread baked for the verification was somewhat higher than the predicted value, but fell within the confidence interval (Table 7). Because of the higher specific volume, the hardness of the stored bread in the verification experiment was lower than the predicted value. Fig. 3 shows the difference between the oat breads before and after optimization of the bread quality. Tasty breads with high quality are most important factors to increase the popularity of healthier breads among consumers. 3.2. b-glucan content and molecular weight distribution The b-glucan content of the bread was 2.4/100 g bread (db) (Table 8), so the amount of b-glucan in fresh bread

ARTICLE IN PRESS L. Flander et al. / LWT 40 (2007) 860–870 40 3.7 38

Proof temperature ( C)

Proof temperature ( C)

40 3.6 3.4

36

3.3 3.2

34 3.1 32 30

867

2.9 2.8 55

0.16 38 0.18 36

0.20

34

0.21 0.23 0.24

32

0.26

30 60

(A)

65 70 Proof time(min)

55

75

60

(B)

Proof temperature( C)

40

65 Proof time (min)

70

75

0.34

38

0.38

36

0.43

34

0.47 0.52

32

0.56 0.6

30 55

60

(C)

65 70 Proof time (min)

75

Fig. 2. Optimization of the process conditions. Response surface plots at 14.4 g gluten/100 g flour and 87 g water/100 g flour, 4 min mixing time, 20 min intermediate proofing time, and 210 1C baking temperature. Effects of final proofing time and temperature on (A) specific volume (cm3/g) of the bread, (B) instrumental hardness (kg) of the crumb after storage of 2 h, (C) instrumental hardness (kg) of the crumb after storage of 72 h.

Table 7 Measured and predicted valuesa for specific volume, hardness and sensory attributes for the verification experimentb

Specific volume (cm3/g) Hardness, 2 h Hardness, 72 h

Measured value

Predicted value

3.6070.07 0.1470.02 0.2970.04

3.4070.1 0.1970.02 0.4470.04

a The values were calculated by response surface modelling using the computer program MODDE 4.0 (Umetri AB, Umea˚, Sweden). b Experiment 31: mixing time 6 min, intermediate proof 12 min, proofing time 65 min at 39 1C, baking temperature 210 1C.

was 1.3/100 g. This means that a portion (two slices a´ 30 g) of the bread contains 0.78 g b-glucan. FDA allows the health claim for products containing a minimum of 0.75 g of b-glucan per portion. The lowest suggested daily intake of b-glucan for achieving the health effects is 3 g per day, which requires four portions with 0.75 g of b-glucan. The molecular weight distribution of b-glucan indicated that the proportion of very high molecular weight b-glucan (Mw41  106) had decreased and the proportion of the lower molecular weight b-glucan had increased during the baking process (Table 8). The reason for the partial degradation of b-glucan in oat bread may be the b-glucanase activity of the wheat flours. Several studies have shown that endogenous b-glucanase activity will decrease the content (Degutyte-Fomins et al., 2002;

Ellis et al., 1997; Henry, Martin, & Stewart, 1989) and average molecular weight of barley b-glucan (Rimsten, 2003). A˚man et al. (2004) found that large particle size of the oat bran and short fermentation time limited the b-glucan degradation during baking. Molecular weights of b-glucan in oat breads and muffins have shown to be smaller than in oat flour or bran (Beer et al., 1997; Kerckhoffs et al., 2003; Sundberg et al., 1996). Kerckhoffs et al. (2003) analysed the molecular weight distribution by HPLC-SEC. The proportion of the highest molecular weight (over 1 000 000) of b-glucan was only 30% and 20% in the oat bran concentrate and oat bran. About 50% of the b-glucan exceeded this size in oat flours used in this study. Possible differences in variety, crop year, and/or processing of the oat may have caused these differences in molecular weight distribution. The amount of b-glucan in the oat bran–wheat bread of Kerckhoffs et al. (2003) was 3.3/100 g and in our oat flour-wheat bread 1.3/100 g. In both breads, only about half of the original proportion of b-glucan with the highest molecular weight remained after baking; 10–15% in oat bran–wheat breads and 30% in oat flour-wheat breads, respectively. This is in accordance with other studies on barley and oat bran breads (Andersson et al., 2004; A˚man et al., 2004). The amount of high molecular weight b-glucan (41 000 000) was about the same; 0.3–0.5/100 g in oat bran–wheat bread and 0.4/100 g oat flour-wheat bread. The amount of middle-size molecular weight b-glucan (200 000–1 000 000) was 30% in both breads. The middle-size b-glucans were higher in oat

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Fig. 3. Oat bread from preliminary screening test (A), after optimization of the recipe (B) and after optimization of the process (C).

Table 8 b-glucan analyses of oat flour and bread Whole grain oat flour

White wheat flour

b-glucan content (g/ 5.9870.04 0.2670.01 100 g dry weight) 5.35 0.23 b-glucan content (g/ 100 g fresh weight) Molecular weight distribution of b-glucan Mw41 000 000 60 25 Mw, 200 000–1 000 000 30 30 Mwo200 000 10 45

Oat bread

2.4070.18 1.34

30 30 45

 Moisture contents: oat flour 10.6/100 g, white wheat flour 12.1/100 g,

bread 44.3/100 g.

bran–wheat bread 1.0/100 g than in our bread 0.4/100 g. To¨rro¨nen et al. (1992) prepared oat breads without wheat for clinical studies. They did not detect any changes in molecular weight of b-glucan during baking or storage of those oat breads. This indicates that b-glucanase from wheat could be the main reason for degradation of high molecular weight b-glucan during baking (A˚man et al., 2004; Andersson et al., 2004). Microstructural study of the oat breads showed that the b-glucan was located mainly in insoluble form in the cell walls of large bran particles (Fig. 4). b-glucan is the major endospermic cell wall polysaccharide in oat, constituting approximately 85% of the cell wall (Miller, Fulcher, Sen, & Arnason, 1995). The bran fraction of the grain is rich in b-glucan, as the cell walls of the subaleurone layer are very thick (Fig. 4). It appears that the use of coarse flour is advantageous for protection of b-glucan from enzymatic degradation. Hydration of large particles is slower than hydration of small particles, and the complex structure and thickness of the cell walls slow down the solubilization of b-glucan and other cell wall polymers. The mixing method probably affects the distribution of water between wheat and oat flour components and especially the added gluten in the dough. This may have had protective effect against degradation of high molecular level b-glucans, because the

Fig. 4. Microstructure of oat bread. The b-glucan in the cell walls has been stained with calcofluor and appears blue.

oat flour was incorporated into the dough with slow mixing speed after formation of a proper gluten network with fast mixing speed. The degrading effect of b-glucanase and mixing might have been stronger, if all of the ingredients had been mixed at the same time with fast speed. Long fermentation of the dough at high temperature could have activated the b-glucanase of the wheat flour and degraded part of the b-glucan. The incorporation of oat groat or grain instead of oat flour to the bread dough, or inactivation of b-glucanase of wheat flour could be the solutions to reduce the degradation of b-glucan during processing of the oat bread. 4. Conclusions The concentrations of gluten and water in oat breads were optimized first and these concentrations were used in

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the optimization test for process conditions. Maximal specific volume 3.7 (cm3/g) and minimal hardness (0.1 kg after 2 h, and 0.2 kg after 72 h) were attained by adding gluten (15.2/100 g flour) and water (91.5/100 g flour) to the dough. The optimal evenness of the crust and moisture of the crumb were attained with the same concentrations of gluten and water as those used for maximal volume and minimal hardness. Of the five processing conditions, baking temperature, proofing time and temperature exhibited the greatest effects on bread quality. The maximal specific volume 3.7 (cm3/g) and minimal hardness (0.1 kg after 2 h, and 0.3 kg after 72 h) were attained by proofing the bread at 40 1C for 75 min and baking it at 210 1C. Of the sensory attributes evaluated, the processing conditions significantly affected the crust properties and richness of the crumb flavour. The optimal thickness, flavour, and crispness of the crust were attained in the same conditions as maximal volume and minimal hardness of the bread. The b-glucan content of oat bread was 2.4/100 g bread (db) corresponding to the amount 1.3 g b-glucan/100 g of fresh bread. This means that a portion (two slices a´ 30 g) of the bread contains 0.78 g of b-glucan, which meets the required amount of 0.75 g b-glucan per portion for a health claim (FDA, 1996). A slight decrease in molecular weight of b-glucan was observed. It is probable that the b-glucan hydrolysis was caused mainly by endogenous enzymes present in wheat flour. From the data presented, it is evident that bread with 51/100 g flour could be baked and that good taste and structure as well as long shelf-life could be obtained by optimizing recipe and processing parameters. These breads with elevated levels of fibres, nutrients and b-glucan can be produced on an industrial scale.

Acknowledgments We thank the Ministry of Agriculture and Forestry of Finland for financial support and Arja Viljamaa for her skilful technical assistance.

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