Durum wheat breadmaking quality: Effects of gluten strength, protein composition, semolina particle size and fermentation time

ARTICLE IN PRESS

Journal of Cereal Science 45 (2007) 150–161 www.elsevier.com/locate/yjcrs

Durum wheat breadmaking quality: Effects of gluten strength, protein composition, semolina particle size and fermentation time H.D. Sapirsteina,, P. Davida, K.R. Prestonb,1, J.E. Dexterb a

Department of Food Science, University of Manitoba, Winnipeg, MB, Canada R3T 2N2 Grain Research Laboratory, Canadian Grain Commission, 1404-303 Main Street Winnipeg, MB, Canada R3C 3G8

b

Received 11 May 2006; received in revised form 22 August 2006; accepted 25 August 2006

Abstract The effects of particle size of granulars (semolina and flour combined), gluten strength, protein composition and fermentation time on the breadmaking performance were compared for eleven durum wheat genotypes of diverse strength from North America and Italy grown in the same environment. All genotypes were g-gliadin 45 types (low-molecular weight glutenin subunit 2 patterns) associated with superior pasta-making quality. Three cultivars with high-molecular weight glutenin subunit 20 exhibited relatively weak gluten, confirming that this subunit is associated with weakness in durum wheat. Gluten strength as measured by a range of technological tests was directly and strongly related to the proportion of insoluble glutenin (IG) in granulars protein as determined by a spectrophotometric procedure. Reducing the particle size of granulars by gradual reduction shortened development time in both the farinograph and mixograph. Reducing granulars also increased starch damage and, accordingly, farinograph water absorption, but remix-to-peak baking absorption was unaffected due to increased fermentation loss for finer granulars. Neither loaf volume, nor remix-to-peak mixing time were affected by the particle size of the granulars indicating that regrinding is not an asset for baking provided there is adequate gassing power. Loaf volume was directly related to gluten strength and IG content, and inversely related to residue protein, a non-gluten containing fraction. When fermentation time was reduced from the standard 165 to 90 min and 15 min, all genotypes exhibited a progressive increase in loaf volume. Therefore, regardless of strength, short fermentation time is preferred when high volume durum wheat bread is desired. Some of the stronger durum genotypes exhibited remix-to-peak bread volume comparable to that expected of good quality bread wheat, indicating that there is potential to select for genotypes with improved baking quality in conventional breeding programs by screening for high content of insoluble glutenin. r 2006 Elsevier Ltd. All rights reserved. Keywords: Durum wheat semolina; Particle size; Insoluble glutenin; Fermentation; Breadmaking

1. Introduction Durum wheat (Triticum durum Desf.) is the preferred raw material for pasta, which is made by extruding a stiff semolina water dough (Feillet and Dexter, 1996), and for couscous, which is made by agglomeration of semolina (Quaglia, 1988). Durum wheat has found traditional use in flat breads and specialty breads, particularly in MediterraAbbreviations: HMW-GS, high molecular weight glutenin subunit; IG, insoluble glutenin; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, soluble protein; RP, residue protein Corresponding author. Tel.: +1 204 474 6481; fax: +1 204 474 7630. E-mail address: [email protected] (H.D. Sapirstein). 1 Retired. 0733-5210/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jcs.2006.08.006

nean countries (Quaglia, 1988) but now is also experiencing increasing application in the Mediterranean region for breads of all types (Palumbo et al., 2000). There is considerable interest in developing durum wheat suited to more general use for bread-making (Liu et al., 1996). Durum wheat with good baking quality is a desirable goal because such cultivars would have alternative markets in years of high production, by being used in place of bread wheat, either alone or in blends with bread wheat flour (Boggini and Pogna, 1989). There have been a number of studies related to the suitability of durum wheat for making high volume hearth bread and pan bread (Boggini and Pogna, 1989; Boggini et al., 1995; Boyac- ioglu and D’Appolonia, 1994; Dexter

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et al., 1981, 1994; Hareland and Puhr, 1999; Josephides et al., 1987; Lopez-Ahumada et al., 1991; Pen˜a et al., 1994; Quick and Crawford, 1983). To summarize, it has been reported that the baking performance of durum wheat improves as gluten becomes stronger, but loaf volumes of the best performing durum wheat cultivars were substantially lower than for bread wheat. Some of the aforementioned studies have acknowledged the inferior baking potential of durum wheat, and focused on improving baking performance by blending durum wheat with common wheat. Very strong gluten durum wheat has tenacious gluten, which imparts inextensible dough and associated dough handling problems, and lower loaf volume due to reduced oven response (Ammar et al., 2000; Edwards et al., 2001; Quaglia, 1988; Rao et al., 2001). Ammar et al. (2000) reported that durum wheat genotypes expressing high-molecular weight (HMW) glutenin subunit 20 exhibit weak dough properties and inferior baking quality. Genetically, durum wheats are tetraploids (AABB), and lack the D genome found in hexaploid common wheats (AABBDD). Removal of the D genome from common wheat greatly reduces its baking potential (Kerber and Tipples, 1969) and is considered at least partly responsible for the relatively poor baking quality of durum wheat. Redaelli et al. (1997) working with near-isogenic lines of common wheat, demonstrated that chromosome 1D strongly influenced both dough elasticity and extensibility. Incorporation of proteins encoded by the D-genome is being pursued to improve durum wheat baking quality (Ceoloni et al., 1996; Joppa et al., 1998; Lafiandra et al., 2000; Pogna et al., 1996). Durum wheat bread often is made from reground semolina (Quaglia, 1988). Because of the extreme hardness of durum wheat, care must be taken while reducing semolina particle size to avoid excessive starch damage, which can adversely affect baking performance (Dexter et al., 1994). For Canadian durum wheat of relatively weak gluten strength, Dexter et al. (1994) reported that baking quality was favored when fermentation time was short, but to our knowledge there has been no study on the fermentation tolerance of durum wheats with a range of gluten strength. This study used semolina reduction as a tool to investigate the influences of semolina particle size, starch damage and fermentation time on the baking performance of durum wheat genotypes from North America and Italy, with a gluten strength range from relatively weak to strong. The impacts of protein composition on physical dough properties and bread-making potential were also examined. 2. Experimental 2.1. Materials Eleven durum wheat genotypes, grown under identical environmental conditions in Regina, Saskatchewan, were

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kindly provided by Dr. John Clarke, Agriculture and AgriFood Canada, Semi-Arid Prairie Research Centre, Swift Current, Saskatchewan. Five genotypes were from Canada (registered varieties AC Melita, AC Morse and Kyle, and breeding lines DT 674 and DT 369), one from the USA (variety Durex), and five from Italy (the varieties Arcangelo, Creso, Grazia, Ofanto and Simeto). These genotypes were chosen for their diverse genetics and gluten strength. All samples were very sound, meeting the Canadian Grain Commission physical standards for the No. 1 Canada Western Amber Durum wheat grade. 2.2. Milling Samples were tempered to 16% moisture overnight at room temperature and milled into straight grade semolina on an Allis-Chalmers Laboratory Mill in conjunction with a laboratory purifier as described by Dexter et al. (1990). One-third of the semolina generated was blended with onethird of the flour, produced as a by-product of semolina milling, to give a straight-run product, referred to hereafter as ‘coarse granulars’. The remaining semolina was divided into two portions, and each was reduced gently either twice or six times, on corrugated rolls to reduce particle size and to increase starch damage, thereby increasing gassing power, before combining with flour by-product to produce granulars of medium and fine particle size of extraction rate and refinement equivalent to coarse granulars. Particle size of granulars was determined on a Ro-Tap sieve shaker (W.S. Tyler, Mentor, OH) using US standard sieves #40 (420 mm ), #60 (250 mm), #80 (180 mm) and #100 (150 mm). 2.3. Analytical tests Wheat moisture content was determined with a HalRoss dielectric moisture meter (Model No. 919, Labtronics, Canadian Aviation Electronics Ltd., Winnipeg, MB) by American Association of Cereal Chemists (2000) Approved Method 44-11, and moisture content of granulars was determined with a Brabender (South Hackensack, NJ) oven by AACC (2000) Approved Method 44-15A. Ash content and starch damage were determined by AACC (2000) Approved Methods 08-01 and 76-31, respectively. Protein content (%N  5.7) was determined by combustion nitrogen analysis with an LECO (Model FP-428 CNA Analyser, St. Joseph, MI) calibrated against EDTA. Gassing power of a slurry of granulars in 10 ml of a 3% suspension of compressed yeast containing 3% sugar was measured according to AACC Approved Method 22-11. The equipment used was a GasSmart computerized pressuremeter system (National Manufacturing Division, Lincoln, NE) using GasSmart software version 3.31. The amount of carbon dioxide produced was measured as gas pressure at 300 min.

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2.4. Protein characterization of granulars Gliadins were separated by acid-PAGE according to Tkachuk and Mellish (1980). HMW glutenin subunits were separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) (Laemmli, 1974) and classified by the nomenclature of Payne and Lawrence (1983). Protein was fractionated by sequential extractions with 50% 1-propanol and 50% 1-propanol containing 0.1% dithiothreitol followed by centrifugation according to Sapirstein and Johnson (2000) to yield monomeric protein (MP) (mainly gliadins), insoluble glutenin (IG) and residue protein (RP). MP and IG were directly quantified in supernatants by UV spectrophotometry (214 nm) as described (Sapirstein and Johnson, 2000). RP was calculated by subtracting the sum of MP and IG content from semolina protein content. 2.5. Physical dough tests International Association for Cereal Science and Technology (1980) Standard No. 121 was followed to obtain alveograph curves (Model MA82, Chopin SA, Villeneuvela-Garenne, France), and parameters were generated by a factory-installed computer program. Farinograph curves (C.W. Brabender, South Hackensack, NJ) were obtained in a 50-g bowl by AACC (2000) Approved Method 54-21. Mixograph curves (National Manufacturing Division, TMCO, Lincoln, NE) were obtained with a 2-g computerized direct drive mixograph equipped with a water-jacketed bowl maintained at 25 1C and 88 rpm. Fixed water absorption of 50% (14% mb) was chosen based on previous experience with durum wheat semolina (Edwards et al., 1999). Data were analyzed using Mixsmart software supplied with the instrument. Mixograph parameters were calculated essentially as described by Khatkar et al. (1996). Parameters recorded were mixing time (MT) to peak development, peak dough resistance (PDR), work input to peak (WIP) dough resistance, and breakdown resistance (BR) calculated as the percentage reduction in dough resistance, 2 min after MT. 2.6. Breadmaking Pup loaves (100 g granulars) were prepared by the remixto-peak process using equipment described by Kilborn and Tipples (1981). In the standard procedure, a lean (no fat) formula dough, containing (granulars weight basis) 3% compressed yeast, 1% salt, 2.5% sucrose, 15 ppm potassium bromate and 0.1% malt syrup (60 l) undergoes a 165 min initial fermentation, following which the dough is remixed in a recording dough mixer to 10% past peak consistency, rested for 20 min prior to sheeting and molding, and given a final proof of 60 min and baked. In additional experiments, fermentation time prior to remixing was shortened to 90 and 15 min.

Baking absorption was determined from dough handling properties at panning. Dough sheet length was measured after the final sheeting pass before molding. Loaf volume was determined by rapeseed displacement. 2.7. Experimental design and statistics All experiments were performed in a completely randomized design. Data are the means of at least duplicate determinations, with the exception of milling, wheat moisture content, farinograph and alveograph, which were determined singly. Statistical analyses were performed using SAS software (Version 8.2, SAS Institute, Cary, NC). 3. Results and discussion 3.1. Properties of granulars Extraction rate and properties of granulars showed considerable variation as would be expected from a diverse collection of genotypes from Canada, Italy and the USA (Table 1). Extraction rate of granulars (semolina and flour combined) averaged 75.0%, ranging from 73.3% for AC Morse to 76.2% for DT 674. Protein content of granulars averaged 12.0%, ranging from 11.1% for Arcangelo to 12.7% for AC Melita and AC Morse. The mean value for ash content of granulars was 0.69%, Kyle having the lowest ash content, 0.66%, and Ofanto the highest, 0.76%. 3.2. Protein characterization All of the durum wheat genotypes in this study were ggliadin-45 types according to lactic acid PAGE. The presence of g-gliadin-42 and the absence of g-gliadin-45 in durum wheat genotypes are associated with weak gluten and poor pasta texture, whereas the absence of g-gliadin-42 and the presence of g-gliadin-45 are associated with moderate to very strong gluten (Damidaux et al., 1978; Zillman and Bushuk, 1979) and superior pasta texture Table 1 Yield and properties of granulars (semolina and flour combined)a Genotype

Country of origin

Milling yield (%)

Protein content (%)

Ash content (%)

Durex Kyle AC Melita AC Morse DT 369 DT 674 Arcangelo Creso Grazia Ofanto Simeto

USA Canada Canada Canada Canada Canada Italy Italy Italy Italy Italy

75.8 75.3 74.0 73.3 74.5 76.2 74.8 75.1 75.8 74.7 75.7

11.9 12.4 12.7 12.7 11.6 11.9 11.1 11.4 12.0 12.5 12.0

0.69 0.66 0.71 0.64 0.69 0.68 0.69 0.75 0.66 0.76 0.67

a

Granulars yield is expressed as proportion of wheat on constant moisture basis. Analytical data expressed on 14% mb.

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(Kosmolak et al., 1980). Payne et al. (1984) were the first to show that two types of low-molecular weight glutenin subunits (LMW-GS), designated LMW-1 (associated with g-42 gliadin) and LMW-2 (associated with g-45 gliadin) are related, respectively, to poor and good durum wheat gluten elasticity and inferior and superior pasta cooking quality. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) revealed three high-molecular-weight (HMW) GS patterns, 6+8, 7+8 and 20 (Table 2). The effect of HMW-GS patterns on durum wheat gluten strength have not been studied extensively (Oak and Dexter, 2006). Ammar et al. (2000) reported that durum wheat genotypes carrying HMW-GS 20 exhibited generally weaker dough properties and inferior baking quality to those expressing HMW-GS 6+8 and 7+8. Shewry et al. (2003) confirmed an association of HMW-GS 20 with inferior durum wheat dough strength using molecular and transformational studies. Sissons et al. (2005) similarly concluded that HMW-GS 20 was associated with weak gluten strength, whereas the presence of HMW-GS 7+8 or 6+8 would improve gluten strength. The durum wheat genotypes exhibited significant differences ðPo0:01Þ in the proportion of protein solubility fractions (Table 2). The propanol-soluble MP fraction was strongly correlated to protein content (r ¼ 0.90), which was expected, because MP is predominately gliadins (Sapirstein and Fu, 1998), the major storage protein of wheat. IG, the protein fraction insoluble in propanol, and soluble in propanol-dithiothreitol, is strongly associated with gluten strength of common wheat (Sapirstein and Fu, 1998). The HMW-GS 20 genotypes, Arcangelo, Grazia and Creso exhibited among the lowest IG contents. As shown below, the technological properties of the durum genotypes that relate to gluten strength (alveograph W, dough sheet Table 2 High-molecular-weight glutenin subunit patterns and proportion of granulars protein in solubility fractions for eleven durum wheat genotypesa Genotype

HMW-GSb

MP (%)c

IG (%)d

RP (%)e

Durex Kyle AC Melita AC Morse DT 369 DT 674 Arcangelo Creso Grazia Ofanto Simeto

6+8 6+8 6+8 6+8 6+8 6+8 20 6+8 20 20 7+8

56.6fg 61.1ab 58.1def 57.6ef 54.5h 59.4bcd 59.2cde 56.6fg 60.8ab 59.9bc 53.7h

22.8a 17.5ef 22.3ab 19.8cd 23.6a 18.4def 17.0f 20.8bc 18.8de 18.2def 21.0bc

20.7c 21.5bc 19.6c 22.6abc 21.9bc 22.2abc 23.8ab 22.9abc 20.4c 21.9bc 25.3a

a Means within a column followed by the same letter are not significantly different ðPo0:05Þ. All values expressed on 14% mb. b HMW-GS, high-molecular-weight glutenin subunits. c MP, monomeric protein (mainly gliadins) soluble in 50% 1-propanol. d IG ¼ insoluble glutenin; residue of MP extracted in 50% 1-propanol and 0.1% dithiothreitol. e RP, residual non-extractable protein.

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length, mixograph development time and work input, Farinograph development time, remix time and loaf volume) were all very well predicted by direct spectrophotometric measurement of IG content, confirming the value of IG as an excellent predictor of durum wheat dough strength. Sapirstein and Fu (1998) found no evidence of LMW-GS in the RP fraction in common wheat flour, but found trace amounts of HMW-GS encoded by Glu-D1 loci. That conclusion was reached based on SDS-PAGE of RP fractions. As durum wheat lacks the D-genome, it can be assumed that RP of durum wheat is predominantly, if not exclusively, composed of non-gluten protein. 3.3. Alveograph properties The alveograph has become widely accepted internationally as a durum wheat gluten strength indicator (D’Egidio et al., 1990). Alveograph parameters for coarse granulars indicated a wide range of dough strength among the durum wheat genotypes (Table 3). Alveograph W value in particular and tenacity (P, an indicator of dough elasticity) were strongly correlated ðPo0:01Þ to IG content (r ¼ 0:90 and 0.76, respectively, Fig. 1). Two of the HMWGS 20 genotypes, Arcangelo and Ofanto, gave among the weakest alveograph curves. The other, Grazia, was anomalous, having a W value in excess of 200 despite its relatively low IG content of 17.0% (Table 2). 3.4. Impact of coarse granulars reduction on the properties of granulars There was a need to address the possibility that coarse granulars would not have sufficient starch damage to assure adequate gassing power throughout the long fermentation associated with the remix-to-peak procedure. The hard texture of durum wheat semolina can result in very high starch damage under harsh grinding conditions. Accordingly, portions of coarse granulars were gradually reduced with corrugated rolls to avoid inducing excessive starch damage that could be detrimental to baking quality

Table 3 Alveograph properties of coarse granulars for eleven durum wheat genotypes Genotype

P (1.1  height) (mm)

Length (mm)

P=L

W (J  104)

Durex Kyle AC Melita AC Morse DT 369 DT 674 Arcangelo Creso Grazia Ofanto Simeto

63 34 78 50 76 40 40 82 65 52 89

96 102 97 106 93 109 75 76 113 90 62

0.66 0.33 0.80 0.47 0.82 0.37 0.53 1.08 0.58 0.58 1.44

220 99 266 165 252 120 77 208 213 129 204

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154

100

300

R2 = 0.58

255 210 165 120 North American

75

Alveograph P (mm)

Alveograph W (J x 10 -4)

R2 = 0.81

80

60

40

North American Italian

Italian

20

30 15

17

19 21 23 Insoluble glutenin (% of granulars protein)

15

25

17

19 21 23 Insoluble glutenin (% of granulars protein)

25

Fig. 1. Alveograph W and P values as function of insoluble glutenin content for North American and Italian durum wheat granulars.

70

70

64 G

2R

G

6R

50

45

40

36

19

15

15

29

28

27

30

Fraction (%)

Fraction (%)

50

43 36

40

29

30 20

18

27

27 18

16

12

12

7

10

7

10 1

1 0

0 > 250 µm

(A)

2R

60

60

20

65

6R

180-250 µm

150-180 µm

<150 µm

> 250 µm (B)

180-250 µm

150-180 µm

<150 µm

Fig. 2. Particle size distribution of durum wheat granulars (G), twice reduced (2R) and six times reduced (6R) granulars from milling of North American (A) and Italian (B) wheat genotypes.

(Dexter et al., 1994). As seen in Fig. 2, the particle size of granulars was dramatically altered by reduction. For example, whereas greater than 64% of granulars’ particle size exceeded 250 mm, that size fraction was reduced to 16% and 1%, respectively, for the twice-reduced (2R) and six-times reduced (6R) semolina product. Starch damage and gassing power also increased progressively from coarse to fine (6R) granulars (Fig. 3). Averaged over all genotypes, the starch damage of fine granulars attained a level (6.9%) typical of that found in Canadian hard common wheat flour (Edwards et al., 2004). As expected there was a very close relationship between starch damage and gassing power ðr ¼ 0:94Þ. Interestingly, granulars of Italian genotypes within each grinding treatment had significantly higher starch damage and gassing power compared to corresponding North American wheats, suggesting that the Italian durum wheats had harder kernels. This higher starch damage explains the higher alveograph P (tenacity) values obtained for the Italian granulars (Fig. 1) which is an outcome of their higher water

absorption (Fig. 4) and increased dough stiffness resulting in higher alveograph curves (Dexter et al., 1994). 3.5. Farinograph and mixograph properties of coarse, medium and fine granulars The effects of gradual reduction of granulars on farinograph parameters were similar to those reported previously by Dexter et al. (1994). Higher starch damage associated with reduction induced an increase in farinograph water absorption of about 4% and 6% over coarse granulars for medium and fine granulars, respectively (Fig. 4). Dough development time decreased progressively as granulars became finer, attributable to greater surface area of finer particles, more rapid absorption to the core of finer particles, and more uptake of water as damaged starch increased. As granulars became finer, stability decreased progressively possibly reflecting the inability of damaged starch to hold all of the water absorbed initially. Mixing tolerance similarly decreased as shown by mixing

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16 North American

North American 15

Italian Gassing Power (PSI)

Starch Damage (%)

8

7

6

5

Italian

14

13

12

4

11

3

(A)

155

10 G

2R

6R

(B)

G

2R

6R

Fig. 3. Starch damage (A) and gassing power (B) of durum wheat granulars (G), twice reduced (2R) and six times reduced (6R) granulars from milling of North American and Italian genotypes.

6 North American durum Italian durum

5

DDT (min)

Absorption (%)

70

65

60

4

55

3 G

(A)

2R

6R

(B)

G

2R

6R

G

2R

6R

48

18

MTI (BU)

Stability (min)

39 12

30

6 21

0 (C)

12 G

2R

6R

(D)

Fig. 4. Farinograph parameters for durum wheat granulars (G), twice reduced (2R) and six times reduced (6R) granulars from milling of North American and Italian genotypes: (A) absorption; (B) dough development time; (C) dough stability, and (D) mixing tolerance index.

tolerance index but for North American durum genotypes, that decrease was evident only for the initial reduction of granulars to medium particle size (Fig. 4). On average, North American genotypes possessed stronger farinograph properties for all granulars products compared to Italian counterparts. This difference in dough strength most likely derives from the higher average IG protein content of the North American genotypes which possessed a more favorable HMW-GS composition, as none contained HMW-GS 20. A very strong relationship existed between

farinograph development time and IG content (r ¼ 0:91, Fig. 5). Reduction of granulars also had significant impact on 2 g micro-mixograph parameters (Fig. 6). Mean MT declined as granulars became finer, particularly when coarse granulars were reduced to medium particle size. Mixograph curves were obtained at constant 50% water absorption because increasing water absorption imparted excessive dough stickiness for the weaker genotypes. Therefore, higher starch damage and resulting higher water

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absorption capacity, associated with reduction of granulars, induced higher PDR. Mean WIP was slightly, but significantly, less ðPo0:01Þ for the medium and fine granulars compared to the coarse granulars. The relatively moderate drop in mean work input, despite a pronounced reduction in mean MT, is attributable to more rapid work input into stiffer dough of finer granulars during mixing. Similar to farinograph mixing tolerance index, mixogram BR increased progressively and significantly, i.e. mixing tolerance decreased, as granulars particle size was reduced (Fig. 6). 7 R2 = 0.83 DT369

Development time (min)

6

3.6. Remix-to-peak baking performance of coarse and fine granulars

AC Melita Simeto

5 DT674

Durex

AC Morse Creso

Kyle

4

Grazia Ofanto North American

3

Arcangelo Italian

2 15

17

19

21

23

25

Insoluble Glutenin (% of granulars protein) Fig. 5. Relationship between farinograph dough development time and insoluble glutenin content of North American and Italian durum wheat granulars.

6

The remix-to-peak baking process was chosen to evaluate durum wheat baking quality because its lean (no fat) formula and relatively long fermentation time are consistent with traditional Italian durum wheat bread processes (Quaglia, 1988). Coarse and fine granulars were baked to determine if granulars particle size had an impact on remix-to-peak baking results (Fig. 7). Baking absorption was not significantly affected by granulars particle size (average of coarse and fine granulars, 60.4% and 60.7%, respectively) despite the higher starch damage and resulting higher farinograph water absorption of fine granulars. This can be explained by higher fermentation loss as starch damage increases (Tipples, 1969). For higher starch damage flours, unless baking absorption is reduced to 44

North American durum PDR (% Torque)

Italian durum

5 MT (min)

Dough strength rankings according to farinograph and mixograph methods, whether performed on coarse granulars or fine granulars, were in general agreement with previously discussed alveograph strength rankings obtained on coarse granulars (Table 3). Alveographs were recorded only on coarse granulars because internationally recognized alveograph methods (AACC International, ICC and ISO) are performed at constant water absorption. Pronounced effects on alveograph curves due to higher starch damage and higher water absorption induced by reducing granulars do not relate to the properties of dough when water absorption is optimized for baking (Dexter et al., 1994).

4 3 2 2R

6R

2R

6R

2R

6R

8 7

130

BR (% Torque)

WIP (% Torque * min)

G

(B)

140

120 110 100

(C)

36

32 G

(A)

40

6 5 4 3 2

G

2R

6R

(D)

G

Fig. 6. Mixograph parameters for durum wheat granulars (G), twice reduced (2R) and six times reduced (6R) granulars from milling of North American and Italian genotypes: (A) peak dough mixing time (MT); (B) peak dough resistance (PDR); (C) work input to peak dough development (WIP); and (D) breakdown resistance (BR).

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157

10 65

G G

6R

8 Remix time (min)

Baking absorption (%)

63

6R

61 59 57 55

6 4 2

53 m et o G ra zi a C re so O fa Ar nto ca ng el o

Si

M AC

D

el

et o G ra zi a C re so O fa Ar nto ca ng el o

m Si

el ita T3 69 D ur AC ex M or se Ky le D T6 74

M

D

AC

(B)

(A) 65 Dough sheet length (mm)

ita T3 69 D u AC rex M or se Ky le D T6 74

0

51

850 G

G

6R

Loaf volume (cc)

60 55 50 45 40

6R

750 650 550

35 o el ng

ca Ar

O

fa

nt

o

so

a zi ra

C

G

re

o et m Si

74

le

T6 D

se

Ky

or M

AC

69

D

T3

ur

ita el M AC

D

o

o

el

nt

ng

fa O

ca Ar

a

so

zi

C

ra

G

re

o et m Si

74

le

T6 D

se or

Ky

ex M AC

69

ur

D

T3

el

ita D

M AC

(C)

ex

450

30

(D)

Fig. 7. Bread making parameters for durum wheat granulars (G), and six times reduced (6R) granulars from milling of North American and Italian durum wheat genotypes. Results for all parameters are ranked by decreasing loaf volume of granulars within groups of North American and Italian genotypes: (A) baking absorption; (B) dough remix time; (C) dough sheet length prior to panning; and (D) loaf volume.

accommodate fermentation loss, dough becomes too sticky to handle at make-up. Remix-to-peak time (Fig. 7) was consistently and significantly longer for fine granulars (average of coarse and fine granulars, 3.0 and 3.4 min, respectively), in contrast to the shorter farinograph development times (Fig. 4) and mixograph MTs (Fig. 6) observed for finer granulars. At the remix stage, dough is fully hydrated, eliminating the effects of particle size on rate of water uptake during mixing. The longer remix-to-peak times for the fine granulars may be due to differences in dough stiffness despite optimization of water absorption to accommodate sheeting and molding. Genotype rankings for remix-to-peak time were essentially the same for fine and coarse granulars (Fig. 7). The HMW-GS 20 genotypes, Arcangelo, Grazia and Ofanto, had among the shortest remix-to-peak times, consistent with their short farinograph dough development and mixograph MT rankings. Reduction in particle size of granulars resulted in minor effects on baking results (Fig. 7). North American genotypes such as AC Melita, DT369, Durex and AC Morse exhibited slightly higher bread loaf volumes when granulars were reduced, whereas others exhibited no effect or slightly lower results. Mean loaf volumes for coarse

(656 cm3) and fine granulars (653 cm3) did not differ significantly. It was concluded that reducing particle size of granulars did not offer any advantages to the quality of bread prepared by the remix-to-peak method. Accordingly, subsequent experiments to evaluate fermentation tolerance were conducted on coarse granulars. Loaf volumes generally ranked according to previously discussed gluten strength indicators.

3.7. Effect of fermentation time on remix-to-peak baking performance Fermentation time is a critical baking process parameter. During fermentation, the combined effects of development of acidity, and enzymatic and oxidation–reduction processes, result in physical changes to dough properties referred to as ‘mellowing’ (Kulp, 1988). Little information has been published on the effect of fermentation time on durum wheat baking performance. Baking absorption was not significantly affected when fermentation time was increased from 15 to 90 min (Fig. 8). However, baking absorption declined significantly by an average of 5% when fermentation time was increased to the

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158

Fermentation time (min) 15

90

14

165

Remix time (min)

65

60

90

165

10 8 6 4 2

zi a O fa nt o C re s Si o m Ar eto ca ng el o

G ra

AC

D

M AC elita M or s D e T3 69 D ur ex

zi a O fa nt o C re so Si m Ar eto ca ng el o

G ra

M AC elita M or se D T3 69 D ur ex Ky le D T6 74

AC

(A)

le T6 74

0

55

(B) 60

15

90

850

165

15

90

165

55 Loaf volume (cc)

50 45 40

750 650 550

35

(C)

el

o

o et

ng

Ar

ca

m Si

nt

re C

fa

so

o

a zi O

AC

ra

M AC elita M or s D e T3 69 D ur ex Ky le D T6 74

o el

o et

ng

ca Ar

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m

so

o

re

nt

C

fa O

G

ra

zi

74

le

T6

Ky

a

450 D

AC

M AC elita M or s D e T3 69 D ur ex

30

G

Dough sheet length (cm)

15

12

Ky

Baking absorption (%)

70

(D)

Fig. 8. Bread making parameters as a function of dough fermentation time (min) for durum wheat granulars from milling of North American and Italian durum genotypes. Results for all parameters are ranked by decreasing loaf volume within separated groups of individual North American and Italian genotypes: (A) baking absorption; (B) dough remix time; (C) dough sheet length prior to panning; and (D) loaf volume.

conventional 165 min, indicating lack of fermentation tolerance. The mellowing effect of fermentation on dough strength was evident from the general tendency of a progressive decrease in remix-to-peak times as fermentation time was extended (Fig. 8). The weaker genotypes (under 4 min remix time at 15 min fermentation), exhibited relatively modest declines in remix time as fermentation time increased. Remix-to-peak times for the stronger genotypes, Durex, DT 369 and Creso declined by over 50%. Interestingly, for four of the strongest genotypes (DT369, Durex, Creso and Simeto), remix times with shorter fermentation were distinctly higher than those for other genotypes, and not in step with corresponding loaf volumes (Fig. 8). The relatively low correlations between remix time and loaf volumes at 15, 90 and 165 min fermentation (r ¼ 0:43, 0.36 and 0.54, respectively) confirm this observation (Table 4). Remix time variation for the semolina granulars, as with other gluten strength parameters, was strongly related to gluten protein compositional factors (Table 4), particularly for results at the shorter fermentation times of 15 and 90 min. Remix time at 15 min fermentation for example, was highly negatively correlated

to MP content (essentially gliadins) ðr ¼ 0:88Þ and highly positively correlated with IG content ðr ¼ 0:96Þ. Likewise the ratio of IG to MP was strongly associated with remix times at 15 and 90 fermentation (r ¼ 0:96 and 0.93, respectively). This result clearly highlights the complementary functionality of gliadins and HMW polymeric glutenin which are the main constituents of the MP and IG fractions, respectively. Fermentation time did not affect dough sheet length significantly. This can be explained by redevelopment of the dough during remixing, and the adjustment of dough water content to facilitate sheeting. As with essentially all technological quality properties of the granulars, dough sheet lengths were significantly different among genotypes (Fig. 8), with variation strongly negatively related to IG content (r ¼ 0:88 to 0.90) and the ratio of IG to MP (r ¼ 0:84 to 0.87). Additionally, dough sheet length exhibited strong inverse relationships to remix-to-peak time at each fermentation time (r ¼ 0:63 to 0.81), as well as to loaf volumes (r ¼ 0:65 to 0.87). Dough sheet length is not a traditional measure of gluten strength of durum doughs, and this appears to be the first time that this test has been reported with tetraploid wheats.

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Table 4 Simple Pearson correlation (r) between protein compositional factors and breadmaking properties of Semolina granulars at different fermentation timesa

SP MP/SP IG/SP RP/SP IG/MP LV15 LV90 LV165

RT15

RT90

RT165

DSL15

DSL90

DSL165

LV15

LV90

LV165

0.24 0.88 0.96 0.04 0.96 0.43

0.15 0.94 0.93 0.22 0.93

0.04 0.78 0.73 0.26 0.73

0.09 0.55 0.90 0.42 0.84 0.77

0.18 0.64 0.90 0.28 0.87

0.25 0.64 0.88 0.26 0.85

0.65 0.16 0.63 0.63 0.52

0.51 0.17 0.64 0.63 0.53

0.49 0.40 0.81 0.52 0.73

0.36

0.65 0.54

0.87

a SP, semolina protein; MP/SP, monomeric proteins per unit SP; IG/SP, insoluble glutenin per unit SPC; RP/PC, residue protein per unit SP; IG/MP, ratio of insoluble glutenin to monomeric protein; RT15, RT90 and RT165, dough remix time based on 15, 90 and 165 min fermentation; DSL15, DSL90 and DSL165, dough sheet length based on 15, 90 and 165 min fermentation; LV15, LV90 and LV165, loaf volume based on 15, 90 and 165 min fermentation.

Edwards and Preston (2005) found little variation (41 cm on average) in dough sheet length for hard red spring wheat genotypes, that otherwise varied significantly in dough strength and breadmaking quality. In contrast, durum dough sheet length ranged widely from 35 to 55 cm in this study, and was independent of the large variation in baking absorptions necessitated by the range of fermentation times used (Fig. 8). Accordingly, the plasticizing influence of water did not affect dough sheet length. While dough sheet length might be interpreted as a measure of dough extensibility, that would be an incorrect conclusion. There was no correlation between dough sheet length of semolina granulars at different fermentation times and alveograph L (r ¼ 0:16 to 0:06). In contrast, the corresponding correlations between dough sheet length and alveograph W were very high (r ¼ 0:90 to 0:92). Accordingly, dough sheet length appears to be measuring the elasticity of semolina dough very effectively. Alveograph P (tenacity), which also measures dough elasticity was also well correlated with dough sheet length (r ¼ 0:67 to 0.78) at different fermentation times, although the association between tenacity values and loaf volumes (r ¼ 0:36 to 0.59) were much lower than corresponding correlations for dough sheet length (Table 4). Loaf volume progressively declined as fermentation time was extended for all genotypes (Fig. 8). The genotypes essentially ranked in the same order at each fermentation time. Dexter et al. (1994) previously reported for commercial composites of Canadian durum wheat, that baking quality was better when fermentation time was short. At that time, the variety Kyle was the predominant Canadian durum wheat. Kyle was one of the genotypes in this study, and is among the weakest. The current study would indicate that short fermentation is also preferable to achieve maximum loaf volume potential for stronger gluten durum wheat genotypes. Loaf volume was less strongly related to IG compared to other measures of gluten strength at different fermentation times (r ¼ 0:63 to 0.81) (Table 4). Interestingly, loaf volume was inversely related to RP content (r ¼ 0:63 to 0.52). As previously noted, this fraction is expected to be

devoid of gluten proteins and its functionality for breadmaking should be negative as was previously observed (Sapirstein and Fu, 1998). Preston et al. (1984) have reported that remix loaf volume for strong bread wheat flour remains relatively constant over a fermentation time range of 45–195 min. The relatively poor fermentation tolerance of many of the durum wheat genotypes in this study is probably due in large part to the absence of D-genome encoded HMW glutenin subunits and the lower average molecular weight distribution of polymeric glutenin that would likely result (Southan and MacRitchie, 1999). The higher proportion of non-gluten RP in durum granulars in the current study (22.1% on average, Table 2) compared to 15.7% determined previously for a set of common wheats (Sapirstein and Fu, 1998) may also be a contributing factor for the lower fermentation tolerance. Nevertheless, genotypes with relatively high levels of insoluble polymeric glutenin are well known to be associated with higher levels of dough elasticity and strength, and would mitigate the dough weakening effect of fermentation. That the strongest and most elastic doughs in this study were associated with the highest loaf volumes and the highest IG contents provides a clear indication that high volume durum bread can be readily achieved by maximizing the content of IG protein. 4. Conclusions The dough strength and breadmaking quality of durum wheat genotypes were strongly related to the proportion of IG which provides a measure of HMW polymeric glutenin. Three genotypes with HMW-GS 20 exhibited weak dough properties, corroborating recent reports that the presence of that subunit in durum wheat is associated with weak gluten (Ammar et al., 2000; Shewry et al., 2003). Dough MT became shorter as particle size of the granulars was reduced by gradual reduction with corrugated rolls. Higher starch damage of finer granulars resulted in higher farinograph water absorption. However, remix-to-peak baking absorption declined as fermentation time was extended, and was comparable for coarse and fine

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granulars at the standard 165 min fermentation time, due to greater fermentation loss associated with greater starch damage of the fine granulars. Loaf volume was unaffected by the particle size of the granulars, indicating, assuming there is sufficient gassing power to sustain gas production throughout fermentation, that there is no apparent advantage to regrinding semolina for baking. The extreme hardness of durum wheat presents the risk of excessive starch damage during regrinding which can adversely affect bread quality (Dexter et al., 1994). When fermentation time was increased from 15 to 165 min, bread volume decreased progressively for all genotypes, confirming that short fermentation time is advantageous for durum wheat bread quality regardless of strength. A factor associated with this lack of fermentation tolerance is the absence of HMW-GS encoded by GluD1 loci which is lacking in durum wheat. The high content of the non-gluten containing RP fraction may also be a contributing factor. Dough elasticity, as measured by alveograph P, and dough sheet length in particular, increased as the gluten strength and IG content of the genotypes increased. Spectrophotometrically determined IG content proved to be an excellent predictor of these properties. In this study, some of the stronger genotypes exhibited loaf volume potential equivalent to that expected of good-quality bread wheats, particularly when fermentation time was short. Durum wheat breeding programs traditionally have concentrated on selecting for pasta quality because of its overriding commercial importance, and have not selected for baking quality. The results of this study indicate that there is potential to identify conventional durum wheat genotypes with improved baking potential by screening for high content of IG. Acknowledgments We gratefully acknowledge the financial support of the Natural Sciences and Engineering Research Council of Canada. We thank Wayne Johnson of the University of Manitoba Food Science Department and Craig Taplin and David Turnock of the Canadian Grain Commission for their expert technical assistance. References AACC International, 2000. Approved Methods of the AACC, 10th ed. Method 08-01, ash-basic method; Method 22-11, measurement of gassing power by the pressure meter method; Method 44-11; moisturedielectric meter method; Method 44-15A, moisture–air oven methods; Method 54-21, Farinograph method for flour; Method 76-31, determination of damaged starch, spectrophotometric method. AACC International, St. Paul, MN. Ammar, K., Kronstad, W.E., Morris, C.F., 2000. Breadmaking quality of selected durum wheat genotypes and its relationship with high molecular weight glutenin subunits allelic variation and gluten protein polymeric composition. Cereal Chemistry 77, 230–236. Boggini, G., Pogna, N.E., 1989. The breadmaking quality and storage protein composition of durum wheat. Journal of Cereal Science 9, 131–138.

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