Influence of Flour Quality and Baking Process on Hearth Bread Characteristics Made Using Gentle Mixing

Influence of Flour Quality and Baking Process on Hearth Bread Characteristics Made Using Gentle Mixing

Journal of Cereal Science 30 (1999) 61–70 Article No. jcrs.1998.0245, available online at http://www.idealibrary.com on Influence of Flour Quality an...

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Journal of Cereal Science 30 (1999) 61–70 Article No. jcrs.1998.0245, available online at http://www.idealibrary.com on

Influence of Flour Quality and Baking Process on Hearth Bread Characteristics Made Using Gentle Mixing E. M. Færgestad, E. M. Magnus, S. Sahlstro¨m and T. Næs MATFORSK—Norwegian Food Research Institute, Osloveien 1, N-1430 A˚s, Norway Received 9 March 1998

ABSTRACT Hearth bread was made from 12 blends of four flours, which varied in protein content (10·2–14·3%) and protein quality, by a straight dough baking procedure. Doughs were mixed using a Farinograph operated at 63 rpm for variable mixing times (5–25 min), and proof times were also varied (35–60 min). Loaf volume was strongly positively related to protein content (r=0·95), Farinograph dough development time (FDT) (r=0·88) and Farinograph dough stability (FDS) (r=−0·97), but not to Zeleny sedimentation volume, SDS sedimentation volume or Mixograph peak time (MPT). Similar observations were found for the form ratio of loaves. The positive relationships between protein content on the one hand and loaf volume and form ratio on the other were only observed at medium (15 min) and long (25 min) mixing times, but not after a short mixing time (5 min). Furthermore, loaf characteristics were strongly affected by the process parameters, giving independent effects on loaf volume vs. form ratio.  1999 Academic Press

Keywords: protein content, protein quality, Farinograph, hearth bread quality.

INTRODUCTION Both protein content and protein quality have major effects on the baking potential of wheat flours1,2. Their effects on the end product quality depend on the baking procedure used, however.

 : SDS=sodium dodecyl sulphate; HRS=Hard Red Spring; HRW=Hard Red Winter; ISO=International Association for Standardisation; AACC=American Association for Cereal Chemistry; SAS=statistical analysis system; PCA=principal component analysis; PC=principal component; FDT= Farinograph dough development time; FDS=Farinograph dough stability; BU=Brabender units; ICC= International Association for Cereal Science and Technology. Corresponding author: E. M. Færgestad. 0733–5210/99/040061+10 $30.00/0

Even the ranking of various flour qualities might change with different baking procedure3,4. This makes evaluation of wheat flour quality a challenge. Most research relating flour quality to bread quality has focused on pan bread. In many European countries, however, hearth bread types are commonly made, which do not involue the use of a pan. The present paper is part of a series of investigations dealing with the influence of flour quality and baking process parameters on hearth bread characteristics. The Farinograph was used as the mixing machine in the present study as the Farinograph ISO method (5530–1) is frequently used for quality evaluation of wheat flour; the Farinograph was operated at 63 rpm for the baking test. The purpose of the present study was to describe how flour quality, with variable protein content and protein quality, baking process and interactions  1999 Academic Press

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among these factors affect the characteristics of hearth bread. MATERIAL AND METHODS Material The material consisted of blends of Folke, a Norwegian winter wheat variety, Tjalve, a Norwegian spring wheat variety, and the U.S. wheat classes Hard Red Winter wheat (HRW) and Hard Red Spring wheat (HRS) obtained by the former Norwegian Grain Corporation (Oslo, Norway). These wheat qualities were selected as they are commonly used in commercial flour blends in Norway. The Norwegian winter wheat selected had a lower protein content than would be used in practice to ensure large variation in protein content of the flour blends. The wheats (30 tons per sample) were milled on a commercial mill (Simon mill with Miag rollers, England) by Regal Mølle A.S. (Moss, Norway). The grain was conditioned for 16 h to 16·0–16·5% moisture prior to milling by adding moisture in two steps. The extraction rates obtained were 75·7% for Tjalve, 77·5% for Folke, 77·1% for HRW and 77·7% for HRS. Ascorbic acid was added to the flours (30 ppm) immediately after milling. Each of the four flours (600 kg per sample) were blended thoroughly at Norgesmøllene DA (Vaksdal, Norway) using a Forberg mixer (Halvor Forberg AS, Larvik, Norway), which has a fluidised zone for mixing. Thereafter, 24 flour blends were made using the Forberg mixer. The material used in the present report was a selection of 11 flour blends (including flour of pure Tjalve) giving a total of 12 flours (flour nos. 1, 2, 4, 7, 10, 11, 12, 14, 17, 18, 20 and 21) [Fig. 1(a)]. As an illustration, the line from Folke to Tjalve in Figure 1(a) represents 0, 25, 50, 75 and 100% proportions of Tjalve. An additional flour, flour 21, was prepared, which corresponded to the commercial flour used traditionally in Norway (25% HRS, 42% Tjalve, 16·5% Folke and 16·5% HRW). Grain and flour analyses Protein contents were analysed as Kjeldahl N (ICC Standard no. 105, N∗5·7, presented on dry weight basis); duplicate measurements were made on each of two replicate samples of each flour and flour blend. Farinograph mixing characteristics (ISO

method 5530–1) and Zeleny sedimentation volumes (ISO method 5529-1978) were measured using two replicates carried out sequentially. Mixograph mixing characteristics5 and ash contents (AACC Approved Method 08–01) were measured once per flour. SDS sedimentation volumes were measured on wholemeal of the four wheats (AACC approved method 56–70, AACC). For SDS sedimentation volumes, duplicate measurements were made on two replicated samples on each flour. Baking experiment The experimental baking procedure was a smallscale straight-dough baking test using a 300 g Farinograph bowl operated at 63 rpm (Brabender, Duisburg, Germany) for mixing of doughs. The water aditition levels used in the baking tests for the individual flours were determined according to the 500 BU line attained in the Fariongraph test (ISO method 5530–1). Based on total dough weight, 2% fat (partially hydrogenated fish oil, AS Pals, Oslo, Norway), 0·75% NaCl and 0·6% dry yeast (Red Saf-Instant, S.I.L. Lesaffres, France, rehydrated in 8·4 mL water before use) were added. Distilled water (30 °C) was added during the first 30 s of mixing, and the final dough temperature was 27 °C. The dough was fermented in a fermentation cabinet (Lillnord A/S, Odder, Denmark) at 27 °C and RH 70% for 10 min. Thereafter, each dough was divided into three 150 g pieces, rounded into its final form on the rounding table of an Extensograph and proofed at 35 °C and 70 % RH in a proofing cabinet (Lillnord A/S, Odder, Denmark). The loaves were baked for 20 min in a rotating hearth oven equipped with a fan (Bago-line Type BEX 1.0, Fjellebroen A/S, Faaborg, Denmark). Live steam was injected during the first 35 s of baking (1·5 L water), and temperature was deliberately reduced from 250 to 220 °C immediately after the loaves were put into the oven. Experimental design The study was conducted as a combination of a set of blends6 for the flours, a full factorial design7 in the process variables and no replicates. Ten of the flour blends were combinations of the three pure flours Folke, Tjalve and HRS [Fig. 1(a)]. These 10 samples were designed according to a so-called simplex lattice design plan6. Two extra

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Figure 1 (a) Flours and blends used in the study. Those marked with circles were included in the baking test. (b) Protein contents of the flours. (c) Zeleny sedimentation volumes of all flours (marked with squares) and SDS sedimentation volumes of whole grain flours of the four base flours (marked with circles). Standard deviations of the replicates were 0·5 mL for the Zeleny sedimentation test and 0·92 mL for the SDS sedimentation test. (d) Mixograph peak times.

flour blends (flour nos. 10 and 21) were added for inclusion of the fourth flour dimension (HRW), and were not designed according to an established design strategy. The process variables were mixing time (three levels: 5, 15 and 25 min) and proofing time (three levels: 35, 47·5 and 60 min). All 12 flours were cross-classified with both process variables, giving a full factorial design. The study consisted in total of 108 baking experiments (12 flours×3 mixing times×3 proof times=108), and all 108 bakes were randomised.

Analyses of loaf characteristics After cooling to room temperature for 1 h, each of the three loaves per dough was weighed, and volume was measured three times per loaf (giving nine measurements per sample) by the rapeseed displacement method8. Loaf height and width (as an average of two directions with an angle of 90 °) were measured using a PAV-caliper (ABC Maskin AS, Skien, Norway), and the form ratio (the height/width relation) was calculated. Subjective evaluation of the products was made by skilled bakers for the characters: overall outer

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appearance, crust cracking, form ratio of the loaves and blisters under the crust. For these subjective properties, a scale from one to four was used, where four corresponds to the highest quality and one to the lowest. Loaf grain was scored according to Dallmann’s pore table9. Statistical analyses Analysis of variance of flour measurements and loaf properties were performed by the general linear model procedure in SAS version 6.02 (SAS Institute, NC 1989). Average values for the three loaves from each dough were used in statistical calculations. Flour type, mixing time and proofing time were regarded as systematic effects, and the three factor interactions were used for estimation of error. Although the mixture design of flour samples was conducted in a similar way to a ‘split plot’ design7, with each flour blend being used for several bakings, the data were regarded as independent mixtures taken from the same batches of flour. The reason why this can be done, lies in very thorough blending of the flours and the flour blends, which is described more in detail by Næs and Færgestad10. Tukey’s test for pairwise comparison was used to identify which flour types or levels of the processes differed from each other. Simple correlations between variables were performed by SYSTAT version 7.01 (for Windows SPSS Inc., IL, U.S.A.). An overview of the results was obtained by the multivariate method, principal component analysis (PCA)11. The computation was conducted using the program Unscrambler (CAMO A/S, Trondheim, Norway). In PCA, the information in the data is projected down to a small number of new variables called principal components (PCs), which are linear combinations of the original data. The different PCs are orthogonal to each other, and estimated to give, in decreasing order, the best description of the variability in the data. All variables were centred and scaled to unit variance prior to the analyses, and full cross-validation12 was used for evaluation of the model. RESULTS AND DISCUSSION Flour analysis The ash contents of Tjalve, Folke, HRW and HRS flours were 0·62%, 0·58%, 0·64% and 0·67%, respectively, and protein content varied from 9·2–

14·9% for the four basic flours, and 10·2–14·3% for the flour blends used in the baking test [Fig. 1(b)]. Water absorption, as determined by the Farinograph (500 BU), did not differ significantly among the flours (average value of all flours 61%), whereas large differences were observed in the shapes of the Farinographs. Farinograph dough development time (FDT) of Folke was 1·6 min, Tjalve 2·0 min, HRW 2·3 min and HRS 5·0 min, and average Farinograph dough stabilities (FDSs) were 90 BU, 55 BU, 45 BU and 15 BU, respectively. The standard deviations of the two replicated Farinographs were 0·2 min for FDT and 3·7 BU for FDS. The Farinograph mixing characteristics were significantly related to variation in protein content (r=0·89 for FDT and r= −0·94 for FDS), but not to the sedimentation tests or Mixograph peak time (MPT). When viewing Figure 1, it can be seen that in the line of flour blends from Tjalve to HRS, protein content increases, whereas sedimentation volumes and Mixograph peak times decrease. The close relation between Farinograph mixing characteristics and protein content shows that the Farinographs mainly reflect variation in protein content. Previous reasearch13 has also found FDT to be strongly related to protein content, but not to protein quality measurements, whereas the opposite was found for MDT. Loaf characteristics Flour quality, the process parameters and interactions among these factors had significant effects on most loaf properties (Table I).

Effects of flour quality and interactions between flour and process Loaf volume of the various flours, calculated as an average of the nine baking processes, corresponded strongly to protein content and Farinograph mixing characteristics. The correlation coefficient between loaf volume and protein content was r= 0·95 [Fig. 2(a)], that with FDT, r=0·88, and that with FDS, r=−0·97. Loaf volume was, however, not significantly related to Zeleny sedimentation volume, as illustrated in Figure 2(b), SDS sedimentation volume or MPT. The relation between flour quality and loaf volume appears to agree with an earlier report14 showing that differences in protein quality do not influence loaf volume when loaves of the various

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Table I Results of ANOVA. (a) Significant level for p>0·05, F=flour, M=mixing time, P=proofing time. (b) Average values of flours (presented only for the four corners of the design), mixing time (5, 15 and 25 min) and proofing time (35, 47·5 and 60 min). Subjective evaluations Weight Volume Height (a) F M P F×M F×P M×P

Width

Form ratio Overall outer (H/W) appearance

0·000 0·010 0·000

0·000 0·000 0·000 0·021

Blisters

Crust crack

0·000

0·002 0·000

Grain score

Form ratio

0·000 0·000

0·000 0·000

0·025 0·001 0·000

0·000 0·000 0·000 0·000

0·000 0·000 0·000 0·000

0·004

0·038

0·004

(b) 1(=Tjalve) 7(=75%Folke) 10(=75% HRW) 20(=75% HRS)

123·8a 123·0ab 123·0ab 121·8b

485·1c 442·7d 497·6bc 543·3a

6·8cd 6·5e 7·1ab 7·3a

11·5bc 11·3c 11·5abc 11·9a

0·60ab 0·58b 0·62a 0·62a

3·2ab 2·9b 3·5a 3·0ab

3·9a 4·0a 3·9a 3·3b

2·9bc 2·8c 3·3ab 3·2abc

7·2a 7·2a 7·4a 7·5a

3·2a 3·0a 3·4a 2·9a

5 min mix 15 min mix 25 min mix

123·6a 122·7b 122·7b

462·3c 518·4a 507·2b

6·4b 7·2a 7·2a

11·6ab 11·6a 11·5b

0·55b 0·62a 0·63a

2·8b 3·5a 3·3a

3·9a 3·7a 3·8a

2·6b 3·4a 3·4a

7·6a 7·3b 7·2b

2·7b 3·5a 3·4a

35 min proof 47·5 min proof 60 min proof

124·5a 123·0b 121·5c

435·1c 503·0b 549·7a

7·0a 6·9b 6·8c

11·0c 11·7b 12·1a

0·64a 0·59b 0·56c

3·3a 3·3a 3·0b

3·6b 3·8a 3·9a

3·2a 3·1a 3·1a

7·7a 7·3b 7·1c

3·4a 3·2a 3·0b

0·000 0·000

0·000

0·000

0·000

Small letters (a–e) indicate flours or processes that are significantly different from each other (by Tukey’s test) when comparing within flour, mixing time and proofing time, respectively.

flours are baked under the same mixing conditions and absorption levels. In the present study, all flours were mixed at the same set of mixing times, and Farinograph water absorption was not significantly different among the flours. Finney et al.15 and Roels et al.14 concluded that variation in glutenin quality is responsible for differences in the mixing requirement, and that effects of glutenin quality on loaf volume is achieved by optimising the mixing of the dough. Several studies support this conclusion. In two studies16,17 no relation was observed between protein content and mixing requirement, but strong correlations were observed between protein content and loaf volume when baked in an optimised baking test. In another study13 there was no relation between protein quality and loaf volume in a long fermentation test using fixed mixing time, but a strong correlation was observed between protein quality and loaf volume in a rapid optimised baking test. In the present investigation, however, the differences in response to increased mixing time

also corresponded to the variation in flour protein content, FDT and FDS, but not to variation in sedimentation volume or MPT as seen by plots of protein content vs. loaf volume for each of the nine processes (Fig. 3). The lack of relation between response to increased mixing time and variation in MPT may be due to the low mixing intensity obtained in a Farinograph bowl operated at 63 rpm. The Farinograph involves very gentle mixing18, when operated at 63 rpm, compared with pin mixers used in the above mentioned raports13–17. A mixing speed of 180 rpm in a Farinograph was found19to correspond to a standard Mixograph and to test bakery pin mixers, whereas a mixing speed of 63 rpm showed no correlation to those mixers. When viewing results of the various process variables (Fig. 3) and the significant interaction between flour and mixing time (Table I), it is seen that the positive effect of protein content on loaf volume was only observed at medium and long mixing times. Similar interactions were found for

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Figure 2 Loaf volume of the flours calculated as an average of the processes, presented as a function of (a) protein content and (b) Zeleny sedimentation volume.

loaf height and form ratio (Table I). Loaves at the shortest process time (5 min mixing and 35 min proofing) had a subjective evaluation of the overall outer appearance of 3·2 calculated as an average of the flours, which means acceptable products although not high volumes (Fig. 3). It may also be worth noting that the use of one flour component with very low protein content (9·2%) in the flour blends did not harm the baking performance. It is reasonable to conclude that it is the protein content of the final flour blend that matters most. The form ratio of loaves was also significantly related to protein content (r=0·78) and FDT (r= 0·84), but not to MPT. This observation contrasts to results of another study at our laboratory20 where the form ratio of hearth loaves was influenced mainly by protein quality. This discrepancy will be investigated in subsequent papers, and may be related to differences in mixing performance or the material investigated.

Effects of the baking process From the results of PCA [Fig. 4 (a)] it can be seen that the process parameters were more important than flour quality in describing the variability of hearth loaf characteristics for the present study. The processes span most of the variability in the two first, and most important, PCs. The two first PCs accounted for 31 and 28%, respectively, of the total variability. Mixing and proofing times affected loaf volume and form ratio of loaves strongly, but in different ways. Loaf volume was positively affected by both process parameters, whereas the form ratio was positively affected by mixing time and negatively affected by proofing time. This is seen from analysis of variance (Table I), by comparing scores and loadings of the two first PCs in Figure 4 and by photographs of loaves of one flour in Figure 5. The measured value of form ratio and bakers’ judgement of the form ratio were the most important factors in determining the subjective evaluation of overall outer appearance, whereas loaf volume showed no relation to the overall outer appearance (Figs. 4 and 6). This illustrates the complexity of evaluating hearth loaves. For hearth loaves, loaf volume and form ratio are two important characteristics that may vary independently. Most research on baking performances, however, is concerned with pan bread, and focuses mainly on loaf volume. As mixing time and proofing time increased, the loaf weight was reduced and the crumb structure became more open (lower value of grain score on Dallmann’s pore table) (Table I, Figs. 4 and 6). Increasing the mixing time also enhanced the crust cracking, which was regarded as a positive property by the bakers. For flour no. 20, which had the highest protein content, there were large blisters under the crust at medium and long mixing time when proofing time was short, but not at long proofing time (Fig. 5). The phenomenon of blisters below the crust for this flour spanned out the third PC in the PCA, accounting for 19% of the total variability (not shown). Seventy-eight per cent of the total variability of loaf characteristics is thereby accounted for by the three first PCs. The need for long proofing time for flour 20 when mixing time was short, illustrates the importance of a balance between mixing time and proofing time for hearth loaves. The need for such balance is also verified by all the significant interactions between mixing time and proofing time in Table I.

Flour quality and hearth bread

Figure 3 Loaf volume of flours at each of the nine processes presented as a function of protein content. Flour blends at the corner of the experimental design are marked: flour no. 7 (Β), flour no. 10 (Κ), flour no. 1 (Φ) and flour no. 20 (Α). 67

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Figure 4 Results of PCA. (a) Score plot of PC1 and PC2. Samples are indicated by mixing times (5, 15 and 25 min) and proofing times (S=short=35 min, M=medium=47·5 min and L=long=60 min), and processes located close are marked by circles. (b) Loading plot of PC1 and PC2.

A final comment to be made with respect to the baking test is that we have not observed so-called ‘unmixing effects’21 as postulated22 to be a potential problem when using a short resting period between mixing and rounding of the dough. CONCLUSIONS Loaf volume, and its response to increasing mixing time were strongly positively related to flour pro-

tein content and Farinograph mixing characteristics, but not to Zeleny sedimentation volume, SDS sedimentation volume or Mixograph mixing time. This may be related to the slow mixing performed as the doughs were mixed in a Farinograph bowl operated at 63 rpm, which is similar to the mixing performed by the Farinograph ISO method (5530–1). The present study has also shown that for hearth bread, the form ratio of loaves is of major import-

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Figure 5 Photographs of loaves at the lowest and highest levels of the two processes (mixing time and proofing time) for flour no. 20. The grain score was 8·0 at 5 min mixing time and 35 min proofing time, 7·7 at 25 min mixing time and 35 min proofing time, 7·2 at 5 min mixing time and 60 min proofing time and 7·2 at 25 min mixing time and 60 min proofing time.

ance, and form ratio and loaf volume may vary independently as effected by the baking process. Further research is necessary to investigate effects of flour quality on form ratio of hearth loaves.

the manuscript. We would also like to thank the former Norwegian Grain Corporation for providing wheat, Regal Mølle A.S. for milling the grain and Norgesmøllene DA for successful blending and mixing of the flours.

Acknowledgements

REFERENCES

We would like to thank the bakers A.O. Nielsen and L.A. Fardal for skilful performance of the baking experiment, and the reviewers for valuable comments to

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17. Figure 6 Plots of selected variables. (a) Subjective evaluation of outer appearance (S-Overall) vs. subjective evaluation of form ratio (S-Form ratio). (b) Subjective evaluation of form ratio (S-Form ratio) vs. measured value of form ratio (Form ratio=height/width). (c) Loaf volume vs. subjective evaluation of overall outer appearance (S-Overall).

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