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JFS S: Sensory and Food Quality

A Novel Bread Making Process UsingSalt-Stressed Baker’s YeastLIEN-TE YEH, ALBERT LINTON CHARLES, CHI-TANG HO, AND TZOU-CHI HUANG

ABSTRACT: By adjusting the mixing order of ingredients in traditional formula, an innovative bread making pro-cess was developed. The effect of salt-stressed Baker’s yeast on bread dough of different sugar levels was investigated.Baker’s yeast was stressed in 7% salt solution then mixed into dough, which was then evaluated for fermentationtime, dough fermentation producing gas, dough expansion, bread specific volumes, and sensory and physical prop-erties. The results of this study indicated that salt-stressed Baker’s yeast shortened fermentation time in 16% and24% sugar dough. Forty minutes of salt stress produced significant amount of gas and increased bread specific vol-umes. The bread was softer and significantly improved sensory properties for aroma, taste, and overall acceptabilitywere obtained.

Keywords: Baker’s yeast, bread dough, salt stress, texture profile analysis

Introduction

Traditionally, bread making uses various techniques includingstraight dough, sponge dough, water brews, and sour dough

(Doerry 1995). It is known that high concentration of salt inhibitsyeast fermentation as a result of the physicochemical effects byhigh osmotic pressures (Pyler 1988). However, no report was foundin the literature on the use of soaking Baker’s yeast in a salt so-lution prior to mixing with other ingredients for bread making.The response of Saccharomyces cerevisiae, the major microorgan-ism of Baker’s yeast, to osmotic stress has been widely characterized(Tamas and Hohmann 2003) and S. cerevisiae cells adapt to envi-ronmental osmolarity variations by adjusting water content, ionfluxes, and their glycerol levels in their membranes, thus control-ling their internal osmolarity (Francisca and others 1999). In S. cere-visiae, glycerol was recognized as a compatible solute with doughingredients, based on the observation that an increase in glycerolproduction and intracellular accumulation also correlated with adecrease in water activity of the medium (Brown 1978). It is alsoknown that an exposure of cells to a salt shock solution induces thesynthesis of stress protein and the accumulation of glycerol (Lewisand others 1995). Moreover, glycerol is a low-molecular-weight os-molyte that is osmotically active. Significant amount of glycerol ac-cumulated in cells of S. cerevisiae, Zygosaccharomyces rouxii, andDebaryomyces hansenii in their exponential growth phase (Reedand others 1987). Glycerol accumulation is also controlled at thelevel of membrane permeability through a specific channel protein,glycerol exporter (Fps1p) (Luyten and others 1995). Under hyperos-motic stress, the Fps1p channel closes rapidly, allowing an increasein intracellular glycerol, which is synthesized by the reduction ofdihydroxyacetone phosphate to glycerol 3-phosphate by glycerol3-phosphate dehydrogenase, followed by a dephosphorylation ofglycerol 3-phosphate (Tamas and Hohmann 2003).

MS 20090100 Submitted 2/3/2009, Accepted 8/3/2009. Authors Yeh andHuang are with Dept. of Food Science and Technology, Natl. Ping-tung Univ. of Science and Technology, 912, Pingtung, Taiwan. AuthorCharles is with Dept. of Tropical Agriculture and Intl. Cooperation, Natl.Pingtung Univ. of Science and Technology, 912, Pingtung, Taiwan. Au-thor Ho is with Dept. of Food Science, Rutgers Univ., 65 Dudley Rd.,New Brunswick, NJ 08901-8520, U.S.A. Direct inquiries to author Huang(E-mail: tchuang@mail.npust.edu.tw).

Baker’s yeast cells incubated in 0.2 M glycerol are reported tohave high leavening ability in dough containing a high concentra-tion of sucrose (sweet dough). A hyperosmotic medium containing0.5% yeast extract, 0.5% peptone, and 20% sucrose was developedto increase the fermentation ability of Baker’s yeast (Hirasawa andYokoigawa 2001). These researchers found a high correlation be-tween intracellular glycerol accumulation and fermentation abilityof the tested yeast.

The purpose of this study was to evaluate the effects of soakedBaker’s yeast in salt solution before mixing with traditional ingredi-ents in bread making. The fermentation time, dough producing gas,dough expansion, bread specific volumes, TPA, and sensory analy-sis were evaluated.

Materials and Methods

MaterialsCommercial grade wheat bread flour was used in this study. The

flour has proximate composition of 13.6% protein (moisture con-tent of 14%) and 0.52% ash. In addition, 65.2% water absorption,20.9 min stability time, and 13.7 min dough development time ofthe sample flour were recorded using a Farinograph parameter ana-lyzer (Brabender, OHgG, Duisburg, Germany). Instant Baker’s yeastpowder, specifically produced for bread making, was purchasedfrom Yung Cheng Industry Ltd., Taipei, Taiwan.

MethodsMoisture, ash, and protein contents, respectively, were deter-

mined following the approved AACC (1983a) methods 44-15A,08-01, and 46-30. The water absorption of wheat flour and the re-sistance of wheat dough to mixing process were determined using aFarinograph (C.W. Brabender Instruments Inc., South Hackensack,N.J., U.S.A.), according to the approved AACC (1983b) method 54-21.

Glycerol determinationsGlycerol in yeast solution was determined using Boehringer

Mannheim method and kit (Cat. nr 148 270- glycerol kinase linkedto NADH oxidation via the pyruvate kinase/lactate dehydrogenasedetection of the ADP formed) (Myers and others 1998).

C© 2009 Institute of Food Technologists R© Vol. 74, Nr. 9, 2009—JOURNAL OF FOOD SCIENCE S399doi: 10.1111/j.1750-3841.2009.01337.xFurther reproduction without permission is prohibited

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A novel bread making process . . .

Bread making processTraditional straight dough process. A straight dough process

was carried out for preparing the bread samples. Dough recipeswith different sugar levels are shown in Table 1. The ingredientswere mixed in an experiment grade mixer (Hobart Inc., Troy, Ohio,U.S.A.). All ingredients were placed in the mixing bowl and mixed1 min at low speed (nr 1) and 15 min at middle speed (nr 2). Thedough was mixed to optimum based on a skilled baker experi-ence. The target dough temperature was set at 26 ± 0.2 ◦C. Eachbatch had a total dough weight of 2550 g. The dough then fer-mented in a controlled fermentation cabinet at 28 ◦C, 75% RH.Fermentation time was defined as the time needed for the doughvolume to reach 2.5 folds more than the original volume. At thistime, the dough was divided into four 540 ± 1 g pieces, molded,paned (4.5 × 10.5 × 3 inch) and proofed at 38 ◦C, 85% RH in afermentation cabinet. Bread dough loaves were then baked for 40min at 200 ◦C. Baked loaves were cooled at room temperature for60 min, and stored at 25 ◦C, 75% to 85% RH for 24 h. Four repli-cates of bread loaves from each of the 3 different baking sets wereevaluated.

Effect of salt-stressed Baker’s yeast on straight dough pro-cess. The total amount of ingredients was the same as traditionaldough contents shown in Table 1. However, this modified mixingprocess was carried out in 3 steps, with the ingredients separatedinto 3 blocks as shown in Table 1. First, Baker’s yeast, water, sugar,flour, and milk were mixed and stirred for 5 min to activate theyeast. Second, salt water (25 ± 2 ◦C) was mixed into the activatedyeast suspension and the mixture was allowed to soak for 20 and40 min, respectively. Finally, the yeast–salt solution was mixed withother ingredients as in traditional bread making formula as sum-marized in the 3rd block of ingredients in Table 1.

Dough expansionDough prepared for bread making was divided and weighed

into 50 ± 0.1 g samples for the dough expansion test (Sangnarkand Noomhorm 2004). Dough samples were rounded, sheeted, andmolded as in the baking test to make a cylindrical shape and in-serted into a 250-mL glass cylinder. Each piece of dough was com-pressed to 70-mL before testing, and then the dough was fermentedin a fermentor at 28 ◦C and 75% RH. Dough volume was recordedevery 10 min for a total duration of 180 min.

Table 1 --- Formula (in baker’s percent) of 3 different sugarcontents in traditional straight dough and salt-stressedBaker’s yeast.

Traditional Salt-stressed Baker’s% sugar yeast % sugar

Ingredients 8 16 24 8 16 24

Yeast 1 1 1Water 2.275 2.275 2.275Sugar 0.2 0.2 0.2Bread flour 0.2 0.2 0.2Milk powder 0.15 0.15 0.15Water 17.1 17.1 17.1Salt 1.5 1.5 1.5Bread flour 100 100 100 99.8 99.8 99.8Yeast 1 1 1 --- --- ---Milk powder 4 4 4 3.85 3.85 3.85Sugar 8 16 24 7.8 15.8 23.8Salt 1.5 1.5 1.5 --- --- ---Water 63 63 63 43.625 43.625 43.625Butter 4 4 4 4 4 4Total 181.5 189.5 197.5 181.5 189.5 197.5

Gas producing by dough fermentationDough pieces were trimmed to 100 ± 0.1 g and placed into glass

chambers that were immersed in 30 ◦C water bath. Tubes fromglass chambers were connected to a Risograph (R-Design, Pullman,Wash., U.S.A.), which collected data as volume of gas produced dur-ing 120 min fermentation. All dough was tested in triplicate (Myersand others 1998).

Loaf volumeOne hour after removal of baked loaves from the oven, their mass

and volume were measured (Sangnark and Noomhorm 2004). Loafvolume was determined by the sesame seed displacement method.Specific volume index was obtained from divided volume with loafmass (Sangnark and Noomhorm 2004).

Bread textureBread firmness was determined according to the approved AACC

(1996) method 74-09, using the texture analyzer (TA-XT-Plus, StableMicro Systems, Ltd., Godalming, U.K.). After storing for 1 d, breadsamples were cut into 1.25 cm slices. The first 2 slices of bread fromeither end were excluded from the testing. Two slices of bread werestacked together and the compression force to reduce their heightby 25% was measured by using a 36-mm dia cylindrical probe withpretest speed of 5 mm/s and test speed of 5 mm/s. Four measure-ments per loaf for each replication were recorded, the maximumpeak force value was recorded, and the average was calculated inforce unit (Sangnark and Noomhorm 2004).

Sensory evaluationA panel of 18 students at the Baking Technology and Manage-

ment Dept. (Kaohsiung City, Taiwan Republic of China) and 2 pro-fessional bakers was trained to become familiar with the sensoryattributes of bread samples following the method of Sangnark andNoomhorm (2004). Bread samples were evaluated on the basis ofacceptability of their aroma, taste, and the overall quality (volume,texture, color, and flavor) by a hedonic 9-point scale, where 9 ismost liked and 1 is the least liked. Immediately before sensory test-ing, loaves were sliced into 2.5-cm thick slices. The end slices werediscarded and 4 × 4 cm squared pieces were prepared from eachslice and immediately placed in plastic boxes. Each box was givena 3-digit code number before testing. Three different sugar con-tent loaves, either control or salt-stressed bread from triplicate runswere tested. Six samples were presented in each test and 360 sam-ples were evaluated in each test.

Statistical analysisOne-way analysis of variance (ANOVA) was conducted using a

statistical software package (version 8.01, SAS 1999). A significantlevel of 5% was adopted for all comparisons. Duncan’s multiplerange test was used to determine significant differences betweenvarious treatments.

Results and Discussion

Effect of salt-stress Baker’s yeast on glycerol contentTable 3 summarizes the amount of glycerol with different stress

times of Baker’s yeast at 7% NaCl solution. Glycerol content inBaker’s yeast was found to be in a 2.8-fold increase compared tothe control. These results agree with findings reported in Lewis andothers’ (1995) study, in that, an increase in glycerol production cor-responded to an increase in NaCl concentration of the medium.Glycerol is an example of solutes produced by S. cerevisiae under

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stress conditions, such as salt and heat shock. Similar results ob-served by Carvalheiro and others (1999) indicated that increasingNaCl concentration from 0.25 to 0.75 M in cultures of S. cerevisiaeresulted in significant accumulation of glycerol. The productionand increase in intercellular accumulation of glycerol in cells werefound when S. cerevisiae cells were subjected to osmotic stress (Larsand others 1991).

Effect of salt stress on dough rheological propertiesAfter salt stress, fermentation time was shortened significantly

for the 16% and 24% sugar dough (Table 4). Significant amountof gas was produced when Baker’s yeast was stressed for 40 min

Table 2 --- Tabulated scores of sensory evaluation of breadbased on control compared with salt-stressed Baker’syeast 40 min.a

Aroma Taste Overall quality

8% sugar control 6.2a ± 1.2 5.7a ± 2.1 6.0a ± 1.98% sugar stressed 7.5b ± 0.9 6.9b ± 1.3 7.3b ± 1.416% sugar control 6.5a ± 1.5 5.3a ± 1.8 5.8a ± 1.716% sugar stressed 7.6b ± 1.0 6.5b ± 1.0 7.2b ± 1.524% sugar control 6.6a ± 1.7 5.1a ± 1.5 5.3a ± 2.124% sugar stressed 7.7b ± 1.2 6.3b ± 1.6 7.0b ± 1.1aValues are mean ± SD. Means within a group with different letters are signifi-cantly different at P < 0.05.

Table 3 --- Effect of 7% salt-stressed Baker’s yeast at dif-ferent times on glycerol content.a

Solution Glycerol (mg/mL)

Control 2.05 ± 0.15aSalt stress 20 min 5.75 ± 0.29bSalt stress 40 min 6.02 ± 0.32baValues are mean ± SD for triple separate experiments. Means within a columnwith different alphabets are significantly different at P < 0.05.

Table 4 --- Influence of stress time on fermentation time(min) at different levels of dough sugar.a

Stress time (min) 8% Sugar 16% Sugar 24% Sugar

Control 89 ± 6.8a 120 ± 8.3a 142 ± 5.9a20 88 ± 7.1a 96 ± 2.8b 118 ± 4.2b40 77 ± 3.5a 92 ± 2.1b 105 ± 4.2caValues are mean ± SD for triple separate experiments. Means within a columnwith different letters are significantly different at P < 0.05.

(Table 5). From the curves shown in Figure 1, the dough volumeexpansion for salt-stressed Baker’s yeast was faster than the con-trol. The results obtained agree with previous findings of Myers andothers (1998) that glycerol-added yeast exhibited greater fermen-tation activity when inoculated into sweet bread dough. Franciscaand others (1999) also predicted that newly designed biotechno-logical process for glycerol accumulation, and to obtain improvedbaker’s yeast strains were useful for the production of sweet dough.

Effect of salt-stressed Baker’syeast on fresh bread quality

The effect of salt-stressed Baker’s yeast on specific volume indexis shown in Table 6. The effect of salt-stressed Baker’s yeast com-pared to control was significantly higher at 40 min. The specificvolume index of bread was also significantly improved. The resultsagree with previous findings of Lombard and others (2000), in that,when glycerol was added to the control recipe, loaf volume was in-creased. A possible reason for this could be due to glycerol acting asa lubricant for the gas bubbles, allowing greater expansion. Cauvainand Cyster (1996) also found that glycerol increased the volume ofchocolate cake. Alternatively, the glycerol could increase the viscos-ity of the lamella between the bubbles, reducing the rate of collapseof the dough during formation.

Table 5 --- Influence of stress time on dough produced gas(mL) at different levels of dough sugar.a

Stress time (min) 8% Sugar 16% Sugar 24% Sugar

Control 348 ± 22.5b 263 ± 31.8b 156 ± 13.4c20 383 ± 10.6ab 325 ± 35.4ab 230 ± 7.1b40 440 ± 35.4a 354 ± 8.5a 266 ± 8.5aaValues are mean ± SD for triple separate experiments. Means within a columnwith different letters are significantly different at P < 0.05.

Table 6 --- Influence of stress period on specific volumesindex at different levels of sweet bread dough sugar.a

Stress time(min) 8% Sugar 16% Sugar 24% Sugar

Control 4.985 ± 0.078b 5.001 ± 0.137b 5.013 ± 0.116b20 5.149 ± 0.169ab 5.164 ± 0.185ab 5.046 ± 0.166b40 5.194 ± 0.069a 5.252 ± 0.049a 5.367 ± 0.042aaValues are mean ± SD for triple separate experiments. Means within a columnwith different letters are significantly different at P < 0.05.

Figure 1 --- Dough expansion of 24%sugar in different stressed times.

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Table 7 --- Influence of stress time on bread firmness (g)after 1 d post-bake at different levels of dough sugar.a

Stress time (min) 8% Sugar 16% Sugar 24% Sugar

Control 317 ± 28a 336 ± 31a 329 ± 25a20 248 ± 27b 266 ± 23b 246 ± 28b40 231 ± 13b 245 ± 15b 244 ± 11baValues are mean ± SD for triple separate experiments. Means with differentletters are significantly different at P < 0.05.

Influence of salt-stressed Baker’s yeaston the characteristics of stored bread

During storage, the most profound changes to bread are relatedto crumb firmness. Table 7 summarizes the effect of salt-stressedBaker’s yeast on firmness of bread crumb. Bread samples were no-ticeably softer in crumb structure, similar to the report of Barrettand others (2000) who found that glycerol reduced bread firmnessafter storage. Lombard and others (2000) also observed that theforce required to compress the steamed bread decreased with theaddition of glycerol. Working with cake, Cauvain and Cyster (1996)also found that the addition of glycerol resulted in a softer crumbstructure. The effects of glycerol on bread quality characteristics,particularly staling, were studied. Glycerol at 0.5% improved breadquality and had a large effect in reduction of crumb firmness at 1and 5 d storage (Galal and Johnson 1976). According to Pyler (1988),glycerol functions as a humectant resulting in a softer crumb struc-ture. As stated, specific volume increased with increasing levels ofglycerol. Therefore, the larger loaf would have a less dense glutennetwork giving less resistance to compression. Overall, better sen-sory properties for aroma, taste, and overall acceptability (Table 2)were obtained for samples made with salt-stressed Baker’s yeast for40 min compared to control samples.

Conclusions

The effect of salt-stressed Baker’s yeast in bread making processwas investigated. Not only shorter fermentation time but also

softer bread, and significant sensory properties for aroma, taste,

and overall acceptability were obtained. It was concluded that salt-stressed Baker’s yeast had significantly improved bread quality.

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