Rheological properties of biscuit dough from different cultivars, and relationship to baking characteristics

Journal of Cereal Science 39 (2004) 37–46 www.elsevier.com/locate/jnlabr/yjcrs

Rheological properties of biscuit dough from different cultivars, and relationship to baking characteristics Lene Pedersena,*, Karl Kaacka, Merete N. Bergsøeb, Jens Adler-Nissenb a

Department of Food Science, Danish Institute of Agricultural Sciences, Kirstinebjergvej 10,DK-5792 Aarslev, Denmark b BioCentrum-DTU, Technical University of Denmark, Søltofts Plads, DK-2800 Lyngby, Denmark Received 25 November 2002; revised 19 June 2003; accepted 16 July 2003

Abstract Rheological properties of semi-sweet biscuit doughs from eight wheat cultivars were studied, and related to the dimensional changes of biscuits after cutting and baking. The tested cultivars were selected in order to represent a wide diversity in biscuit baking performance, and were grown with low use of N-fertiliser in three successive years. A standard recipe for semi-sweet biscuit dough was used, and the amount of water added was adjusted to the water absorption capacity. The rheological properties of the dough were characterised by creep recovery and oscillation. The fundamental methods showed that maximum strain at creep, recovery, storage modulus G0 ; and phase angle d were significantly influenced by the tested cultivars. The ranking of the cultivars according to phase angle d was identical in each of the years investigated 3 which indicates that phase angle d reflects differences in structural properties with genetic control. Multivariate regression of flour physiochemical, dough rheological, and biscuit baking characteristics showed that a decrease in biscuit length was correlated under several rheological parameters, including phase angle d; Farinograph and creep recovery parameters. Sedimentation value was the only physiochemical flour characteristic with considerable influence on the model. Validation of the partial least squares-model including all samples from the 3 years gave only a weak correlation ðr ¼ 0:58Þ; whereas when each single year was evaluated separately, the correlation increased considerably (r ¼ 0:71 and 0.87). q 2003 Elsevier Ltd. All rights reserved. Keywords: Biscuit; Dough rheology; Viscoelasticity

1. Introduction Semi-sweet biscuits are produced from wheat flour dough with a moderate level of fat and sugar, approximately 20 and 15 wt%, respectively. During mixing of the ingredients with a restricted amount of water, a gluten network is developed (Levine and Drew, 1994). Due to the lower water level, biscuit dough is less extensible and more elastic than bread dough. During the biscuit manufacturing process the dough is sheeted and laminated in several reduction steps, which causes the gluten network to be Abbreviations: G 0 , storage modulus; G 00 , loss modulus; H, height of biscuit; HMW, high molecular weight; L, length of biscuit; PC, principal component; PCA, principal component analysis; PLSR, partial least squares regression; r, correlation coefficient; SDS, sodium dodecylsulfate; W, width of biscuit; WA, water absorption; d, phase angle. * Corresponding author. E-mail address: [email protected] (L. Pedersen). 0733-5210/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0733-5210(03)00064-X

aligned in the direction of machining (Levine and Drew, 1994). The sheeting applies significant stresses to the dough, and the elastic components in the dough cause a gradual contraction of the dough sheet, which may give an oval biscuit after baking (Thacker, 1993). Variability in the elastic recovery and thereby in the dimensions and weight of the biscuits causes considerable problems in fully automated packaging systems. Dough rheology characterisation, which relates to dough handling properties and the tendency of the dough to contract is an important parameter in the evaluation of biscuit wheat quality. Several methods are used to characterise the rheological properties of biscuit dough, including the Farinograph and Extensograph methods (ICC, 1996; Bloksma and Bushuk, 1988). These methods are empirical in nature, which makes a fundamental interpretation difficult. Moreover, these methods are mostly used to characterise rheological properties of bread doughs

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(Janssen et al., 1996), which have a strong gluten structure and a high resistance to deformation. Low content of protein (8 –10% in the grain), low water absorption (WA), and low resistance to deformation, are the characteristics used to describe the suitability of wheat for biscuit production. Fundamental rheological testing at small deformations are non-destructive, and the methods used for dough characterisation can be transient such as creep recovery or stress relaxation, or dynamic such as oscillatory measurements. Several studies have been carried out to evaluate the viscoelastic properties of wheat flour dough, with the aim to study the influence of wheat quality, dough ingredients, and processing conditions on the fundamental rheological properties. Bloksma (1962) introduced creep recovery to study the shear flow of wheat flour dough, and the method has been used to characterise deformation and recovery of wheat flour dough (Hibberd and Parker, 1979; Danilo et al., 1997; Edwards and Dexter, 1999). Studies on weak and strong wheat flour doughs showed that stress relaxation tests at high strain-values (Safari-Ardi and Phan-Thien, 1998) and creep recovery (Edwards and Dexter, 1999) could differentiate between doughs from high protein and low-protein wheat cultivars. Undeveloped doughs showed lower values of creep strain than fully developed doughs (Danilo et al., 1997). Dynamic oscillatory methods have been used to characterise the fundamental viscoelastic behaviour of dough, mainly in relation to protein content, gluten strength, and glutenin/gliadin ratio (Edwards and Dexter, 1999; Khatkar et al., 1995; Uthayakumaran et al., 1999). Storage modulus ðG0 Þ and loss modulus ðG00 Þ are strongly affected by water content (Navickis et al., 1982). Regarding the influence of protein content, different results have been reported. According to Safari-Ardi and Phan-Thien (1998), oscillatory tests could not differentiate between doughs prepared from weak and strong wheat flour, but Rao et al. (2000) demonstrated differences in G0 and tan d between extra strong and medium bread wheat. Comparing results from Extensograph, Alveograph, and dynamic oscillatory testing of flour of different gluten strength (Janssen et al., 1996) showed that the three methods were complementary and in good agreement with each other. Studies on bread flour dough and biscuit flour dough (Amemiya and Menjivar, 1992) concluded that oscillatory measurements reflect interactions in the protein phase as well as starch – starch and protein –starch interactions. Relatively few studies have been performed on biscuit doughs with fat and sugar. Comparing cookie dough and cracker dough (Menjivar and Faridi, 1994), approximately the same value of G0 was found in the two types of dough, which indicates that there is no influence of the gluten network formed in the cracker dough. The type and amount of fat added to the dough has a strong effect on the viscoelastic properties, and reduction in the fat content changes the system from bicontinous to a dispersed system (Baltsavias et al., 1997).

Relating rheological measurements and biscuit baking performance, Oliver et al. (1995) found that dynamic rheological measurements gave a better prediction of the tendency of the dough to contract than the protein content and the protein quality measured by the sodium dodecylsulfate (SDS) sedimentation test. The present study was performed with the aim to characterise the fundamental rheological properties of semi-sweet biscuit dough from wheat cultivars differing in biscuit baking performance, and to evaluate the capability of the fundamental and empirical rheological characteristics to (1) differentiate between different biscuit wheat cultivars and (2) to predict the contraction of the dough after processing. In relation to (2), results from fundamental rheological testing are related to quality measurements on flour and dough in order to indicate which methods provide the best information of the tendency of the dough to contract after dough processing.

2. Experimental 2.1. Wheat material The wheat material used in the present study included six cultivars (Banker, Encore, Claire, Galatea, Reaper, and Ritmo), and two breeding lines (SJ 977435 and NSL 959183). These cultivars were selected with the aim to obtain a wide diversity in biscuit-making properties. Ritmo and Reaper are hard endosperm cultivars, and the remaining cultivars and lines are soft endosperm cultivars. Galatea has no high molecular weight (HMW) glutenins, hence it produces dough with almost no gluten structure. Ritmo is classified as a bread wheat, but it is frequently used as biscuit wheat. Samples were harvested in 1998, 1999 and 2000. In 1998 and 2000, they were harvested from one location (Ab), and in 1999 from two locations (Ab and Sj) in Denmark. All samples were grown in triplicate using mineral fertiliser and pesticides in accordance with normal practice at each location. Samples from replicates were mixed and stored dry for two months before milling. Milling was done on a Brabender Quadromat Seniorw. Before being milled, the samples were conditioned to 15.0% moisture for 2 h. 2.2. Flour quality tests All the quality testing was performed in accordance with established procedures, which are frequently used to characterise wheat flour quality. Protein content was determined by Near Infrared Reflectance, which was calibrated to Kjeldahl nitrogen. The gluten content was determined according to ICC (1996) standard No. 137 using a Glutomatic 2100 (Perten Instruments). Protein quality was determined by the sedimentation test (ICC 116; ICC, 1996). These tests were repeated once.

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Standard testing on dough included the Extensograph (ICC 114; ICC, 1996), which measures the extensibility and the resistance, and the Farinograph (ICC 115; ICC, 1996), which determines the WA and the mixing characteristics of the flour. Dough tests were performed as single test. 2.3. Dough procedure for rheological testing A standard dough recipe was used, consisting of 200 g flour, 40 g granulated sugar, 20 g hardened vegetable fat, melted at 50 8C, and tap water at 20 8C. The amount of water added was adjusted to WA measured on the Farinograph, with 80 ml corresponding to 55% WA. This was done in order to equalise the consistency of the doughs from cultivars with different WA. Doughs were mixed in a 300 g Farinograph mixing bowl for 6 min at a speed of 126 rpm. In order to obtain homogenous dough after mixing, the water content of the dough for rheological testing was higher (approximately 24%) compared with the dough recipe for biscuits (19%). Before testing the dough rested in a container at room temperature for 10 min, the dough temperature was 23 –24.5 8C. 2.4. Rheological testing A controlled stress rheometer (Bohlin, CVO) was used in both oscillatory and creep recovery tests. The rheometer was equipped with a 40 mm parallel plate measuring geometry. Both plates were serrated in order to prevent the dough from slipping. A dough sample of 4.5 ml was extracted with a cylinder and placed on the lower plate. The upper plate was lowered until the gap was 2.0 mm. To prevent the dough from drying during testing, the dough edges were sealed with a polymer resin (Plastybycol), which has no effect on the rheological measurements. The sample rested 3 min before measurements were conducted, and all experiments were done at 30 8C. A strain sweep at a frequency of 1 Hz was made to determine the linear viscoelastic region. This was determined to be up to 0.15%, and a target strain of 0.1%, corresponding to a stress value of 10 Pa, was used in all the experiments. A frequency sweep was performed in the range from 0.1 to 60 Hz. At frequencies above 30 Hz, recordings showed scattering, therefore, only recordings up to 20 Hz were included. Results were expressed in terms of the storage modulus G0 ; the loss modulus G00 ; and the phase angle d (tan21 G00 =G0 ), although only G0 and d will be discussed. Initially it was found that the slope of G0 and d in the frequency sweep was similar for the different cultivars, and mean values from 0.1 to 10 Hz were used in the statistical analysis. Creep recovery measurement was performed with creepand recovery time of 300 s, and a stress value of 10 Pa. Initial experiments showed that the biscuit dough reached a steady viscous flow within this time range, which makes it possible to measure and compare the elastic recovery. Creep

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recovery parameters included maximum strain, recovery, expressed as the difference between maximum strain and the final strain, and % recovery, which is recovery expressed in percentage of the maximum strain. Creep recovery at 10 Pa and oscillatory measurement were made consecutively on the same dough sample. From each flour sample, two dough samples were tested. The reproducibility of the dough mixing and rheological testing was determined, by measuring 10 dough samples from one cultivar. The mean values, and the coefficient of variation were calculated for both creep and oscillation parameters. The coefficients of variation varied between 7.7 and 12.0%, which agreed well with results from Baltsavias et al. (1997). However, the coefficient of variation for d was as low as 2%. In this work, the ageing time was 10 min, which is within the same time range as the commercial baking procedure. After 10 min, the dough will still be in a dynamic state, but when all dough samples are measured within the exact same time range, recordings from different cultivars can be compared. 2.5. Biscuit-making procedure Semi-sweet Marie type biscuits were produced according to a commercial formulation and baking practice. The basic recipe is given in Table 1. All dry ingredients were at room temperature, fat was added at 50 8C, and the water at 40 8C. The standard amount of water used was 32.5% of flour, but doughs from cultivars with increased WA were added up to 35% water. The doughs were mixed in a D-300 Hobart mixer for 7 min (1 min at slow speed), and after mixing the dough rested for 10 min. Dough temperature varied between 29 and 33 8C. After resting, the dough was sheeted and laminated in eight layers in three reduction steps, with a final gauge roll gap of 1 mm. There was a one-minute rest between each reduction, and the dough piece was rotated 908 before the second reduction step. Biscuits were cut using a circular mould (56 mm in diameter) and baked immediately in a 205 8C oven for 6 min. Biscuits from doughs with a high degree of contraction and an increased biscuit height were baked for 7 min, in order to obtain the same moisture content for all the biscuits. After baking, the biscuits were cooled at room temperature, packed in sealed bags, and Table 1 Semi-sweet biscuit dough recipe Flour Total sugarsa Fatb Salt Na2CO3 (NH4)2CO3 Waterc a b c

1000 g 224 g 136 g 10 g 7g 13 g 325 g

Include a mixture of sucrose, glucose and lactose (dry products). Hardened vegetable fat. Adjusted to the water absorption.

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stored at room temperature. Two batches of biscuits were produced for each cultivar and biscuits were mixed before test samples were taken. The testing of the biscuits included length ðLÞ; width ðWÞ and height ðHÞ of 20 biscuits taken randomly from the mixed batches. In all experiments, L was defined in the direction of sheeting, and W was the dimension perpendicular to L: Changes in dimensions after cutting and baking were calculated as %decrease in L; %increase in W; and eccentricity ðW=LÞ: Additionally, area and volume were calculated with the assumption of ellipsoidal form of the biscuits. 2.6. Statistical analysis A General Linear Model procedure in the Statistical Analyses System (SAS, version 8.0, 1999) was used for the statistical analyses of the rheological characteristics from different wheat cultivars. The following notation *, **, *** means significant at P # 0:05; P # 0:01 and P # 0:001; respectively. Variation and relationships among the flour and biscuit characteristics were studied by the use of the multivariate methods: Principal Component Analysis, PCA and Partial Least Squares Regression, PLSR (Unscrambler, version 7.5, CAMO, Trondheim, Norway). Using PCA, the relationships among many variables are simplified by the projection of the data to a smaller number of uncorrelated variables called Principal Components (PCs; Esbensen, 1998). PLSR was performed to study relationships between flour and dough rheological characteristics (x-variables) and biscuit characteristics (y-variables). The information in the data is projected down to a small number of new variables, the PLS-factors that are estimated to give the best prediction of y-variables from the x-variables (Martens and Næs, 1989). PCA and PLSR have been used to study the relationships between chemical flour composition, physical dough properties, baking process and the characteristics of bread (Færgestad et al., 2000; Magnus et al., 2000).

3. Results and discussion 3.1. Physical flour characteristics The mean values for analysis of all samples are shown in Table 2. In general, all flours could be characterized as low-protein, weak flours. The protein content of grain and flour was within the range 10.2 –11.3% and 8.7 –9.7%, respectively. Some variation was observed, however, most of this variation can be explained by the difference in the expenditure of N-fertiliser in the field trials (data not shown). The gluten content of the cultivars was all within the low range, 18 – 23% of the flour. Differences in gluten structure were reflected in the sedimentation values, where Ritmo, Reaper and the breeding line SJ 977435 had higher values than the other cultivars tested. The Farinograph data demonstrated some variation in dough mixing characteristics, but in general all the flours behaved as weak flours with short mixing times, poor stability, and a high degree of break down (data not shown). Flour from Reaper and Ritmo had higher WA than soft wheat cultivars. Regarding Extensograph data, some variation was observed in both extensibility and in resistance. Reaper differed from the other cultivars with a high extensibility and a low resistance. A fairly high variation in resistance was observed between the years, and between samples from different locations. 3.2. Ageing time Two representative examples of the creep recovery behaviour when testing was performed at 10, 25 and 35 min after dough mixing are shown in Fig. 1. The behaviour of the doughs showed that during a creep time of 300 s, a steady-state viscous flow occurred, which agreed with previous studies (Edwards and Dexter, 1999). The maximum strain after 300 s represents the extensibility of the dough at small shear deformations, and % recovery represents the degree of recovery after relaxation. For all cultivars, a decrease in maximum strain and an increase in

Table 2 Physiochemical characteristics of wheat and flour from 1998, 1999 and 2000, n ¼ 4 Cultivar

Protein in grain (% of DM)

Protein in flour (% of DM)

Gluten (% of flour)

SED (ml)

WA (% of flour)

E (mm)

R (BU)

Encore Claire Banker Ritmo Reaper Galatea SJ 977435c NSL 959183c

11.0 ^ 0.8a 10.7 ^ 0.6 10.9 ^ 1.1 10.2 ^ 1.5 11.2 ^ 1.2 11.3 ^ 0.7 10.7 ^ 0.4 10.7 ^ 1.0

9.0 ^ 0.7 9.2 ^ 0.4 9.4 ^ 0.6 9.1 ^ 0.9 9.7 ^ 0.9 9.2 ^ 0.5 8.7 ^ 0.2 8.9 ^ 0.9

17.7 ^ 0.3 21.2 ^ 2.7 21.6 ^ 4.3 21.2 ^ 3.7 23.4 ^ 3.7 20.5 ^ 1.5 18.9 ^ 1.8 20.5 ^ 2.7

21 ^ 5 19 ^ 2 21 ^ 3 32 ^ 6 28 ^ 5 ,10 29 ^ 5 17 ^ 5

54.8 ^ 2.0 51.5 ^ 2.7 53.7 ^ 3.3 56.8 ^ 3.0 59.0 ^ 4.3 53.7 ^ 3.5 53.2 ^ 2.7 52.3 ^ 2.5

117 ^ 11 135 ^ 10 128 ^ 4 128 ^ 16 147 ^ 18 –b 135 ^ 19 128 ^ 17

187 ^ 59 262 ^ 68 177 ^ 49 232 ^ 108 133 ^ 30 –b 264 ^ 80 187 ^ 35

a b c

SED, sedimentation value; WA, water absorption; E; extensibility after 45 min dough resting; R; resistance after 45 min dough resting; DM, dry mass Mean value ^ std deviation. Analysis could not be performed due to a very soft dough Results from 2 years, n ¼ 3:

L. Pedersen et al. / Journal of Cereal Science 39 (2004) 37–46

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the dough is between 10 and 20 min, and therefore, all rheological testing and baking tests were done with an ageing time of 10 min. Furthermore, when measuring after 10 min of ageing, the variation between the cultivars seemed to be more distinct than after 25 and 35 min. 3.3. Rheological properties of dough from different cultivars

Fig. 1. Creep recovery curves from two cultivars with different resting time: (W) 10 min; (A) 25 min; (K) 35 min.

% recovery for increasing ageing time were observed. This agreed with earlier observations (Hibberd and Parker, 1979), which means that the dough is getting less extensible, but more recoverable. Previous studies of relationship between ageing time, G0 ; and d (Kidmose et al., 2001; Lindahl and Eliasson, 1992) showed an increase in G0 and a decrease in d up to 30 min of ageing. For durum wheat dough (Edwards and Dexter, 1999), 15 min of ageing ensured stability in the rheological testing. Both in a small baking test and in biscuit manufacturing, ageing time of

Statistical testing was done separately for each year, due to a significant interaction between environment (harvest year) and the cultivars tested. Data from the two locations in 1999 were treated separately due to the difference in protein content. Finally, data from all samples were analysed to characterise the overall differences among the cultivars. Creep recovery results from the three years are shown in Table 3. Maximum strain and recovery were strongly affected by the cultivar ðP # 0:001Þ; whereas % recovery was only slightly affected. Significant differences in extensibility measured by the maximum strain were observed among the soft wheat cultivars and lines, even though they had nearly the same WA and protein content. This indicates that differences in the structure of the gluten or other components also contribute to the extensibility. Due to a high WA, there was a higher water content of the dough from the hard wheat cultivars Reaper and Ritmo, but this extra water was only reflected in the high extensibility of Reaper. Ritmo showed the same level of extensibility as the soft wheat cultivars. The two locations used in 1999 (Ab and Sj) were significantly different regarding maximum strain and recovery ðP # 0:001Þ; whereas % recovery was not affected. Mean values of maximum strain and recovery were enhanced for the samples from 1999, Ab compared with 1999, Sj. As the difference between the two locations was mainly associated to a higher protein content for Ab, the results indicate that an increase in protein (and gluten) increases both extensibility and recovery, but % recovery is not affected. However, for some cultivars, i.e. Banker and Claire, extensibility and recovery were not affected, or

Table 3 Creep and recovery characteristics of cultivars and lines from 1998, 1999 and 2000 Cultivar

‘ Encore Galatea Claire Ritmo Reaper NSL 959183 SJ 977435 a b

1998 Ab

1999 Sj

1999 Ab

2000 Ab

All years

MSNS (%)

R*** (%)

%R**

MS*** (%)

R*** (%)

%R**

MS*** (%)

R*** (%)

%R*

MS*** (%)

%R***

%R*

MS*** (%)

R*** (%)

%R***

1.53 1.15 1.27 0.84 1.01 1.20 1.63 1.44

0.50aba 0.38c 0.47b 0.33c 0.40c 0.49ab 0.55a 0.52ab

40.6b 35.7b 34.6b 40.1b 63.4a 43.2b 41.2b 41.0b

1.29a 1.16a 1.32a 0.78b 0.43c 1.19a 0.71b 0.59bc

0.52a 0.41b 0.46ab 0.31c 0.27c 0.51a 0.29c 0.24c

40.6b 35.7b 34.6b 40.1b 63.4a 43.2b 41.2b 41.0b

1.06c 1.24bc 1.77a 0.71d 1.07bc 1.26b 1.24bc –b

0.42c 0.46c 0.63a 0.29d 0.48c 0.56b 0.55b –b

39.5ab 37.2b 35.7b 41.3ab 44.8a 44.7a 44.9a –b

1.10e 1.60bc 1.72ab 1.24de 1.52bcd 2.00a 1.34cde 1.11e

0.40ef 0.69b 0.60c 0.49d 0.49d 0.81a 0.46de 0.46de

36.6b 43.2ab 35.4b 39.3b 32.5b 40.5b 34.1b 42.7ab

1.26b 1.19b 1.48a 0.77c 0.87c 1.22b

0.48ab 0.42bc 0.53a 0.31d 0.40c 0.52a

38.3bc 35.7c 35.7c 40.3bc 48.5a 43.4ab

MS, maximum strain; R; recovery; %R ¼ %recovery. NS, non-significant. ***,**,*: significant at P , 0:001; 0.01 and 0.05, respectively. Mean values within a column followed by the same letter are not significantly different. No samples available.

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a negative effect was observed, when the protein content was increased. Creep testing of dough from durum wheat with different protein levels also showed a high correlation between protein content and maximum strain (Edwards and Dexter, 1999). When data from all years are analysed (Table 3), Galatea was significantly different from all other cultivars ðP # 0:001Þ regarding extensibility. This high extensibility could be explained by the fact that Galatea has no HMWglutenins, which results in a higher proportion of gliadins. It is well established that gliadins contribute to the extensibility and viscous properties of wheat flour dough (Uthayakumaran et al., 2000). Extensibility was not significantly different for Banker, Encore, and Reaper, and for Claire and Ritmo. The two hard endosperm cultivars Ritmo and Reaper did not differ from the soft endosperm cultivars. Cultivars with high values for extensibility also showed high values for recovery. Measuring recovery as % recovery gave another ranking of the cultivars. The hard endosperm cultivars, Reaper and Ritmo, showed the highest value, being more elastic due to the elasticity in their gluten network. The cultivars Galatea and Encore, with very weak gluten structure, recovered less than the others did. Claire was less extensible than the other soft endosperm cultivars, but recovered to a high degree. Results of frequency sweep tests are shown in Fig. 2. Increasing frequency increased both G0 and G00 : Correlation between frequency and d depended on the frequency range. At very low frequencies, d decreased when frequency was increased; from 0.5 to 1 Hz, d was nearly constant, and at high frequencies, d increased. These differences imply that the dough acts more like a solid, when imposed to slow changes in stresses, but very fast changes will make the dough act more as a liquid. A similar frequency

Fig. 2. Frequency dependence of storage modulus G0 and phase angle d for two cultivars.

dependency was found for cookie dough (Baltsavias et al., 1997), and increasing viscous properties at high frequencies are suggested to be determined by the fat phase in the dough. Mean values of G0 and d from 0.1 to 10 Hz for 3 years and locations are shown in Table 4. As for creep recovery environment (harvest year) affected the oscillation results, where G0 was significantly affected ðP # 0:001Þ: For each set of samples (year, location), cultivars strongly affected G0 and d ðP # 0:001Þ: Investigation of the ranking of cultivars expressed by G0 and d showed that d gave nearly identical ranking of the cultivars for all sample sets. Especially in samples from 1999, a very distinct separation of each cultivar was observed by the value of d: The different cultivars could be ranked as A (Reaper and Galatea), . B (Banker, Encore, and Ritmo) and . C (Claire, NSL 959183, SJ 977435). From this, it can be concluded that differences in d; which means differences in viscoelastic properties of the dough, are related to structures in the wheat, which are distinctive for the cultivar. By adding water on the basis of WA, our approach was to eliminate large differences in dough consistency, in order to get a better resolution between the tested cultivars. It is well established that increasing water content leads to a decrease in G0 and G00 ; but Berland and Launay (1995) concluded that the overall dough structure and the structure of the gluten network are not altered. Therefore, d will be almost constant at different water levels, and thus, it reflects the differences in the structure of the doughs. From rheological studies of gluten (Khatkar et al., 1995), it was concluded that increasing the gliadin/glutenin ratio significantly increased d for the gluten. Therefore it is likely that the differences in d between cultivars are associated mainly with differences in the gliadin/glutenin ratio. This agreed well with the high ranking of Galatea, which have a high proportion of gliadins. However, interactions between the gluten network and starch or non-starch polysaccharides may also influence the value of d (Amemiya and Menjivar, 1992). The values of d in cultivars from 1999, Ab were significantly higher compared to 99, Sj ðP # 0:001Þ: Cultivars from 1999, Ab had higher protein content than 1999, Sj, indicating that the dough from a certain cultivar gets more viscous, when protein content increases. This agreed with results from Edwards et al. (1999), who also found increasing d with increasing protein content in doughs from durum wheat. The ranking of cultivars with respect to G0 was less distinct compared to the ranking by d: Reaper had the lowest G0 during the 3 years, but the ranking of the other cultivars varied among the years. Although the water content of the dough was adjusted, there were no clear relationship between G0 and the cultivars. This agreed with previous results (Safari-Ardi and Phan-Thien, 1998; Menjivar and Faridi, 1994), which found that measurements of G0 were unable to distinguish between doughs, which have different strength of the gluten network.

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Table 4 Mean values (0.1– 10 Hz) for G0 (storage modulus) and d (phase angle) for cultivars and lines from 1998, 1999 and 2000 Year

1998

1999

1999

2000

Location

Ab

Sj

Ab

Ab

Banker Encore Galatea Claire Ritmo Reaper NSL 959183 SJ 977435 a b

G0 NS (kPa)

d*** (8)

G0 *** (kPa)

d*** (8)

G0 *** (kPa)

d*** (8)

G0 *** (kPa)

d*** (8)

16.7aa 19.6a 16.8a 18.0a 16.9a 15.9a 14.8a 13.6a

22.5b 21.7c 23.2a 20.9d 22.7b 23.4a 22.3b 21.6c

13.4e 15.3de 18.9c 18.0cd 27.6a 14.1e 23.0b 26.7a

22.3b 21.3c 23.4a 19.1f 21.5c 24.2a 20.8d 19.9e

19.4b 16.7c 16.0c 23.1a 15.2d 13.8de 13.4e –b

25.1c 24.6d 26.4a 22.2g 23.9e 25.6b 23.5f –b

15.6b 12.6cd 14.4bc 12.2d 12.4d 9.5e 12.9cd 19.3a

21.9cd 21.4de 23.2b 21.0ef 22.3c 24.0a 20.9f 19.8g

NS ¼ non-significant. ***, **, *: Significant at P , 0:001; 0.01 and 0.05, respectively. Mean values within a column followed by the same letter are not significantly different. No samples available.

3.4. Biscuit-baking characteristics For all biscuits, the eccentricity was . 1, which means that W . L: L was reduced for all samples, i.e. the dough contracts in the direction of sheeting. For all samples, a small spread was measured in the direction perpendicular to the sheeting. The eccentricities of some cultivars increased during the 3 years (Table 5). Generally, the eccentricity coefficient of variation for each cultivar was fairly high (up to 60% calculated on the mean value exceeding 1) due to differences among the 3 years tested. Mean values for eccentricity for each cultivar varied between 1.05 for Galatea, and 1.28 for SJ 977435, which showed very high values for eccentricity in 2000. A PCA was performed on all baking characteristics (seven variables) to see the variation among the measured samples. Three PCs explained 95% of the variation. The plot of scores and loadings (Fig. 3) showed that PC1 spans out differences in eccentricity, %length, %width, and PC2 variations in height and volume (Fig. 3a). In PC3 variation in %width is represented (Fig. 3b). Volume and weight, and eccentricity and %length are highly correlated (PC1 and Table 5 Eccentricity of biscuits from 1998, 1999 and 2000 Cultivar

1998a

1999b

2000b

Mean ^ std deviation

Encore Claire Banker Ritmo Reaper Galatea SJ 977435 NSL 959183 Mean value

1.07 –c 1.06 1.09 1.06 1.02 –c –c 1.06

1.10 1.16 1.08 1.15 1.12 1.06 1.12 1.08 1.11

1.19 1.09 1.15 1.13 1.12 1.06 1.28 1.16 1.15

1.13 ^ 0.06 1.12 ^ 0.07 1.10 ^ 0.06 1.13 ^ 0.04 1.11 ^ 0.03 1.05 ^ 0.02 1.23 ^ 0.12 1.11 ^ 0.06

a b c

Data from one location. Mean from two locations. Cultivar not available.

Fig. 3. PCA loadings and scores of baking characteristics. (a) PC1 and PC2 loadings. (b) PC1 and PC3 loadings. (c) PC1 and PC2 scores for the cultivars.

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Fig. 4. PLSR x-loadings and y-loadings of flour and dough properties, and biscuit characteristics.

PC2), whereas eccentricity and area are inversely correlated. From the correlation between volume and weight, it can be concluded that the density of the biscuits from different cultivars was equal. Decrease in length, %length, is mainly correlated to eccentricity, which means that decrease in length mainly accounts for the eccentricity calculated (Fig. 3a). For some samples, %length was correlated to height (Fig. 3b). No correlation was observed between %length and %width, but %width showed some correlation to height (Fig. 3a). Therefore, when biscuits contract in the direction of sheeting, the main effect is an increased height, which result in a smaller spread of the biscuits (height and %width are inversely correlated). Increase in height could also be due to a very fast contraction of the dough sheet before cutting, a mechanism that could explain the weak correlation between height and %length. Variability in height is also shown by the influence of volume and weight in the model. From the scores plot (Fig. 3c), the samples seemed to be evenly distributed, only the cultivar Galatea was clearly separated from the other cultivars along the PC1, related to low values of eccentricity, low height, and high area. 3.5. Relationships between flour and dough properties, and biscuit-baking characteristics Initially a PLSR was performed on the physiochemical flour analyses and rheological dough characteristics as x-variables, and the biscuit characteristics as y-variables. The PLSR included 43 samples from 1998, 1999 and 2000. The plot of loadings is presented in Fig. 4, and the symbols used are listed in Table 6. The PLSR showed that 33% of the variability in biscuit characteristics was explained from the flour and dough measurements, using a PLSR-model with

two PLS-factors. This coarse map of relationships indicates that the biscuit characteristics, with exception of %width, are related to several of the flour and dough characteristics. Volume, weight, height, %length, and eccentricity are related to the sedimentation value, Farinograph values (-WA), d; and % recovery, and negatively related to maximum strain, recovery, and extensibility. Area is related to break down, and inversely related to %length and the parameters associated with %length. Additionally, the plot indicates that protein and gluten content of the flour have only a weak influence on the biscuit characteristics. The low correlation indicates that the flour and dough characteristics could be used only to a limited extent to predict biscuit characteristics by using a linear model as PLSR. The highest value of correlation between predicted and measured values of the biscuit characteristics was found for %length and eccentricity, whereas the PLSR-model did not fit %width at Table 6 Quality characteristics and abbreviations used in the PLSR Quality characteristic

Abbreviation in PLSR

Protein content (% of flour) Wet gluten (% of flour) Sedimentation value (ICC 116) Water absorption (Farinograph) Development time (Farinograph) Stability (Farinograph) Break down (Farinograph) Extensibility (Extensograph) Resistance (Extensograph) Maximum strain (creep) Recovery (creep recovery) % Recovery (creep recovery) Storage modulus (oscillation) Phase angle (oscillation)

prot glu sedi wa abs devel stab break exten res max rec % rec G0 delta

L. Pedersen et al. / Journal of Cereal Science 39 (2004) 37–46

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Table 7 Correlation between predicted and measured value of %length (decrease in length), and important variables, using PLSR with two PLS-factors Year

%Explained Y-variance

Correlation coefficient

Important variables

1998, 1999 and 2000 1999 and 2000 1999 2000

58 58a 88 79

0.69 0.64 0.87 0.71

Sedimentation, Farinograph variables (-WA), and d Sedimentation, Farinograph variables, maximum strain, % recovery, and d Sedimentation, Farinograph variables (-WA), maximum strain, % recovery Sedimentation, development (Farinograph), maximum strain, % recovery, and d

a

Only 1 PLS factor.

all. In the following, PLSR %length was used as a single y-variable. Results of PLSR on samples from all years, from 1999 to 2000 and from 1999 or 2000, respectively, are presented in Table 7. Models from single years (1999 or 2000) showed higher %explanation for %length and better correlation than models from 3 or 2 years. The results indicate that Extensograph variables, G0 ; and protein and gluten contents have almost no influence on %length. The contraction in the direction of sheeting is mainly related to the sedimentation value, the Farinograph data, creep parameters, and to some extent to the phase angle d: Thus, both large deformation and small deformation rheological measurements could be used to make an estimate of the decrease in length.

4. Conclusions The tested cultivars were well suited for studies of rheological properties and biscuit baking properties, as they showed a great variability in properties, but are still characterised as biscuit wheat. Creep recovery and oscillation measurement of biscuit dough from the tested cultivars reflected differences, which are likely to be related to dough structural differences. The phase angle d gave the best resolution between the cultivars tested, and the ranking was nearly identical for each year tested. Results from baking tests showed that contraction in the direction of sheeting mainly affected the height of the biscuit. The increase in width of the biscuits was not related to the contraction in the direction of sheeting. For the present material, the Farinograph parameters, sedimentation value, creep parameters, and phase angle d contributed more to the explanation of the variability in length, than protein and gluten content, and Extensograph parameters. The results demonstrate the difficulties in determining a few rheological dough parameters, which are optimal for prediction of the dimensional changes during biscuit manufacturing, when different flour qualities are used.

Acknowledgements The present work was funded by the 1st Framework Programme of the Cereal Network (the Danish Ministry of

Food, Agriculture and Fisheries). The authors wish to thank Pajbjergfonden and Sejet Plantbreeding for providing the wheat material used in the study. We also acknowledge Cerealia Danmark and KelsenBisca for the technical assistance with quality analyses and baking experiments.

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