The optimization of a laboratory processing procedure for southern-style Chinese steamed bread

*Correspondent: Fax: 161 2 9888 5821.e-mail: kquail@ wheatcrc.csiro.au

The optimization of a laboratory processing procedurefor southern-style Chinese steamed bread

S. Huang, K. Quail* & R. Moss

BRI Australia Limited, PO Box 7, North Ryde, NSW 2113, Australia

Summary A response surface methodology (RSM) design was used to optimize the laboratory pro-cessing procedure for southern-style Chinese steamed bread (SSCSB). A screening testwas applied to weak, medium and strong flours to establish critical variables. Consumerpreference testing on the eating quality of southern-style steamed bread (SSSB) estab-lished a scoring system for quality assessment of this product. For further RSM opti-mization testing, only the strong and medium flours were used. The following settingswere established as optimal laboratory processing procedures for this style of steamedbread: farinograph mixer (300-g bowl; speed 60 rpm); compressed yeast (1.5%); wateraddition [80% of farinograph water absorption (FWA)]; mixing time (50% of farinographdough development time (FDDT); fermentation time (150 min); remixing time (180%FDDT); fermentation temperature (328C); relative humidity (RH; 85%); sheeting time (20passes); proving time (35 min); steaming rate (155 g of steam m23 min21); and steam time(20 min). The adequacy of the predictive models generated using the RSM procedure andreproducibility of the method for this style steamed bread were verified.

Keywords Optimization test, processing variable, response surface methodology, steamed bread quality.

Introduction

China is the world’s largest wheat producer andconsumer, with a total wheat production of103 million tonnes in 1994–95 (Rees & Cockinos,1995) and an average per capita consumption of86 kg as wheat-based food products (Anon,1994). Major changes have taken place in Chinesefood habits in recent years as living standardshave been improved. However, steamed bread isstill the staple food in the wheat-growing areas ofnorthern China and is also popular in the south.There are three major styles of steamed bread inChina and South-East Asian countries: northernstyle (chiang mian mantou), southern style (xiaomian mantou) and Guangdong style (Huanget al., 1991; Huang & Quail, 1995). Northernstyle is preferred in northern China, and southernstyle, which used to be preferred only in southern

China, is now popular throughout China.However steamed bread and steamed buns pro-duced in Guangdong, Hainan, Fujaing provinces,Hong Kong and Taiwan and other East andSouth-East Asian countries have distinct charac-teristics and are referred to as ‘Guangdong orCantonese style’.

Recent surveys showed that almost all of thesteamed bread consumed in cities was manufac-tured in small factories and that there wasincreasing production and consumption of SSSBin the cities of northern China. There was also atrend towards high-quality steamed bread pro-duction for which consumers paid a premiumprice. A standard for steamed bread flour waspublished in China in 1993 (Anon, 1993). Flourquality criteria for different styles of steamedbread from some modern Chinese mills have beenestablished. Wheat breeding programmes toimprove grain quality have also been initiated.

The production of steamed bread in small fac-tories largely depends on manual labour, and the

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process relies heavily on the worker’s skills. Thequality of steamed bread from these small facto-ries varies with processing conditions and thequality of flour used. There is still some confusionabout flour quality requirements for differentstyles of steamed bread. More research is neededin order to prepare detailed specifications of flourquality for different styles of steamed bread.

An investigation of flour quality requirementsfor northern-style steamed bread (NSSB) hasbeen completed (Huang et al., 1996). The opti-mization of a test scale processing procedure forSSSB is required as a tool to define the process-ing and flour quality requirements for this style ofsteamed bread.

Materials and methods

Flour samples

Three flours of different strengths (A, B and C)were used in preliminary trials to establish opti-mal mixing intensity. Three additional flours (D,E and F) were used for response surface method-ology (RSM) screening tests, and two of theseflours were used for the optimization tests (E andF). Another set of flours (F, G, H, I and J) wasused for a consumer test.

Flour moisture, protein content and maltosefigures were determined by use of the AmericanAssociation of Cereal Chemists (AACC) methods(1983). Colour grade and dough properties(farinograph and extensograph) were measuredusing procedures produced by the RoyalAustralian Chemical Institute (RACI) (1988).

Determination of optimal mixing intensity

A preliminary experiment established an appro-priate mixing intensity for SSSB. A formula con-sisting of flour (50 g), compressed yeast (0.75 g)and water [308C; 80% farinograph water absorp-tion (FWA)] were mixed in a Do-corder E330(50-g bowl) at speeds of 10, 30, 45, 60, 90, 120and 240 rounds per minute (rpm) for half of thetotal mixing time [total mixing time was definedas farinograph dough development time(FDDT) 3 60/corresponding mixing speed]. Thedough was then fermented for 90 min [308C; 85%relative humidity (RH)], remixed for the remain-

ing time and sheeted five times by passingthrough a pair of rollers (diameter 11 cm; gap7.2 mm and 11 rev min21). After each pass, thedough was folded end-to-end and resheeted in aunidirectional manner. After dividing, eachdough piece (100 g) was placed into an extenso-graph rounder (smooth surface facing up), round-ed (20 times), proved (25 min; 308C; 85% RH)and steamed (20 min) over gently boiling water.

Steamed bread preparation for RSM tests

Unless otherwise stated, all values for the pro-cessing variables were chosen according to theRSM designs. The method for steamed breadpreparation was as described by Huang et al.(1993), except that the amount of flour used formixing was 240 g and the additional flour forremixing was 60 g.

Loaf scoring procedure

SSSB was scored according to the protocol out-lined in Table 1. The maximum marks allocatedfor each quality parameter were assigned toreflect consumer preference in China. Thedescriptive categories were allocated as follows:outstanding (higher than 90), excellent (85–90),very good (80–85), good (75–80), unsatisfactory(65–70), poor (60–65) and unacceptable (below60).

The colour and texture of steamed breads wereassessed objectively using a scoring system(Table 2) based on the objective assessment meth-ods for NSSB (Huang et al., 1995) and guided bythe consumer test results (see Results and discus-sion). The volume, width and height of eachbread were measured as described previously(Huang et al., 1993). Breads were scored subjec-tively by the researcher for surface smoothness,shininess and internal crumb structure.

RSM experimental design

Screening experimentsA fractional factorial design (Joglekar & May,1991) was chosen to determine which of eightindependent variables were most critical to thequality of SSSB prepared from flours of differentstrengths (D, E and F; Table 3). The design per-

Optimized method for southern style steamed bread S. Huang et al.


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mitted the estimation of all main effects, but two-way interactions were confounded with oneanother. The eight independent variables (wateraddition, mixing and remixing time, fermentationtemperature, fermentation time, sheeting time,proving time and steam generation rate) wereselected from preliminary trials. The ranges ofvariables were selected to represent the extremesof commercial production. They were as follows:water addition, 75–85% of FWA; mixing andremixing time, 0.25–1.75 FDDT; fermentationtemperature, 30–38 8C; fermentation time,60–180 min; sheeting time, 0–20 passes; provingtime, 10–30 min; steam generation rate,86.7–293 g of steam m23 min21. For each flour,baking trials were conducted in a randomizedorder over 7 days. Nine dependent variables orresponses were measured for each treatment: spe-cific volume (sv), spread ratio (sr), colour (both of

skin and crumb), exterior smoothness, shininess,structure, softness and cohesiveness, elasticity andtotal score as described in Table 1.

Optimization experimentsA central composite design (Joglekar & May,1991) was used to optimize the levels of the criti-cal independent variables identified in the screen-ing studies. The design consisted of threevariables at five levels and required 20 trials. Thethree variables for medium flour (E) were remix-ing time (0.25, 0.66, 1.25, 1.84, 2.25 FDDT), fer-mentation time (60, 96.5, 150, 204, 240 min) andproving time (10, 16, 25, 34, 40 min); for strongflour (F) they were proving time (10, 16, 25, 34,40 min), fermentation time (60, 84, 120, 156,180 min) and sheeting (0, 6, 15, 24, 30 passes).For both experiments, the ranges of the indepen-dent variables were expanded to produce a more



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Quality parameter Full Criterion

score

Specific volume (sv) 025 score 5 25 – (3.2 – sv)/0.08(volume/weight, ml g21)

Spread ratio (sr) 010 sr score(weight/height) 1.40–1.44 10

1.45–1.49 091.50–1.54 081.55–1.59 071.60–1.64 061.65–1.69 051.70–1.74 041.75–1.79 031.80–1.84 021.85–1.89 01.1.90 00

Exterior appearanceWhiteness

Skin 005 High score given to very white skin and crumb(objective)

Crumb 005Brightness 005 High score given to shiny skin (subjective)Smoothness 010 High score given to very smooth skin, free of

wrinkles, dimples, blisters or gelatinized spots(subjective)

Structure 010 High score given to evenly open crumb (subjective)Softness and cohesiveness 010 High score given to soft and cohesive crumb

(objective)Elasticity 010 High score given to elastic crumb (objective)Stickiness 010 High score given to crumb that does not stick to

teeth when chewing (objective)

Total score 100

Table 1 Quality evaluationsystem for southern-style steamedbread

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pronounced effect on the measured responses.The nine responses were the same as for thescreening test. Treatments were prepared in a ran-domized order over 7 days for both medium andstrong flours.

Consumer test

Steamed breads representing a range of qualitytypes were prepared using five flours of differentstrengths (Table 3; flour F, G, H, I and J). Anoptimized combination of variables was chosen toproduce steamed bread based on the results of theRSM screening tests. The values were for flour J(weak), water addition (85% FWA), mixing time(1.8 FDDT), remix time (1.8 FDDT), sheeting (20passes) and steam generation rate (293 g ofsteam m23 min21); for flour H and I (medium),water addition (85% FWA), mixing time(0.5 FDDT), remixing time (1.8 FDDT), sheeting(20 passes) and steam generation rate(86.7 g m23 min21); for flours F and G (strong),water addition (75% FWA), mixing time (0.5FDDT), remixing time (1.8 FDDT), sheeting (25passes), steam generation rate (86.7 g m23 min21).The remaining variables were the same for all fiveflours: yeast (1.5 %), fermentation time (120 min),

proving time (30 min), fermentation temperature(32 8C), steam time (20 min).

Forty-one people of Chinese origin either livingin or visiting Australia were chosen to assess theeating quality of SSSB using a seven-point hedo-nic test (Meilgaard et al., 1987). The average of apanellist’s stay in Australia was 2.6 years, and for61% it was less than 2 years. Almost all panellistsconsumed steamed bread frequently when theywere in China. SSSB was preferred by 83%,whereas 12.2% preferred northern style, and onlyone person had a preference for Guangdong stylebefore the experiment. Sixty-three per cent ofpanellists were originally from southern Chinaand 36.6% were from northern China. More thanhalf (58.5%) were men, and the group had anaverage age of 40 years (range 21–68 years). Thetest was conducted in sensory test booths at theBRI Australia Ltd over 2 days. Panellists wereasked to rate their liking of each steamed breadand to identify which steamed bread they likedthe most. Scores were attributed to each steamedbread according to the extent of liking, (1 5 dis-like very much; 7 5 like very much). Averagescores for each sample were calculated from thehedonic score of the 41 panellists. In addition,panellists were also asked to select the sample



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Table 2 Scoring system for the assessment of textural properties of southern-style steamed bread

Quality Full Quality Full Quality Full

parameter score Criterion parameter score Criterion parameter score Criterion

p1a(N) Score A2/A1b(%) Score A3/A1c(%) Score

Softness 10 ,5.00 06 Elasticity 10 .79.0 10 Non- 10 ,1.50 10and co- 5.01–6.50 07 78.9–78.0 09 stickiness 1.51–2.00 09hesiveness 6.51–8.00 08 77.9–77.0 08 2.01–2.50 08

8.01–9.50 09 76.9–76.0 07 2.51–3.00 079.51–11.00 10 75.9–75.0 06 3.01–3.50 04

11.01–12.50 09 74.9–74.0 05 3.51–4.00 0212.51–14.00 08 73.9–73.0 04 .4.00 0014.01–15.50 07 72.9–72.0 0315.51–17.00 06 71.9–71.0 0217.01–18.50 05 , 71.0 0118.51–20.00 0420.01–21.50 03.21.51 02

ap1 5 the peak force during the first compression cycle.bA2/A1 5 the ratio of the peak force area during the second compression cycle to the peak force area during the first

compression cycle.cA3/A1 5 the ratio of the negative force area during the first compression cycle to the peak force area during the first

compression cycle.

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they liked the most, thus the value was expressedas a percentage of the total number of panellistand is referred to as overall preference.

Instron compression tests on each of thesteamed breads used for consumer testing were asdescribed previously (Huang et al., 1995). Themaximum compression force (p1) and ratio ofA2:A1 were recorded and calculated.

Statistics

Two software programs, ‘Discovery’ and‘Optimisation’ (Joglekar & May, 1991) were usedto analyse the screening and optimization experi-ments respectively.

Results and discussion

Preliminary experiments

Flour analytical data are presented in Table 3.

Determination of optimal mixing intensity

Mixing intensity had similar effects on specificvolume and surface smoothness of steamed bread.Specific volume increased up to 60 rpm for allflours and tended to decrease at speeds greaterthan 60 rpm (Fig. 1). The strong and mediumflours showed a greater response to mixing inten-sity than weak flour. The sensitivity of stronger

flour to mixing intensity may help explain thereported processing difficulties experienced withsteamed bread made from stronger flour(Rubenthaler et al., 1992). Based on these results,60 rpm was selected as the optimal mixing inten-sity for strong, medium and weak flours

Eating quality preference of SSSB

The consumer panel identified significant differ-ences between the steamed breads made from thefive flours (Table 4). The steamed bread madefrom strong flour (G) had the highest averagescore (6.2 out of 7) and overall preference(46.3%). The steamed bread made from weakflour (J) had the lowest average score (4.9 out of7) and preference (2.4%), whereas steamed breadmade from flours F (medium to strong strength),H and I (medium strength) have intermediatescores and preferences. The physical tests indicatethat the preferred bread type had the softest andmost elastic texture of the five samples. A scoringsystem for eating quality assessment was estab-lished by comparing the consumer test score withthe results from Instron compression test(Table 4).

Screening experiments

The effects of the eight processing variables ontotal scores of steamed breads made from the



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Table 3 Flour sample dataa

Flour Moisture Proteinb Maltose Colourc Farinograph Extensograph

(%) (%) (%)

Water Development Extensibility Maximum

absorption time (cm) resistance

(%) (min) (BU)

A 13 07.6 1.4 20.45 53 01.4 16.6 155B 13.9 11.4 1.2 20.93 59 07.3 17.8 750C 13.5 14.6 1.6 20.03 61 09 17.7 820D 15.1 07.6 1.4 20 54 01.5 17.1 220E 13.8 09.6 2.6 20.2 64.7 03.4 17.4 300F 13.2 12.6 2 20.1 64.4 07.9 18.6 600G 13.5 21.3 64.9 13.1 23.7 470H 09.2 57.4 03.5 17.1 355I 08.9 56.4 04.9 15.1 370J 07.9 53.5 01.5 13.7 285

aResults are expressed on 14% mb. All determinations were made at least in duplicate.bProtein was calculated as N 3 5.7%.cColour determined by Simon colour grader series IV.

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weak, medium and strong flours are outlined inTable 5. The magnitude of the effect indicates thesensitivity of the response to the processing vari-able and is calculated as the difference in themean response as the independent variable ischanged from a low to high level. Total score wasused as an overall measure of steamed breadquality (Table 1).

For the strong flour, proving time was the mostcritical variable, increasing this had a strong pos-itive effect on total score of steamed bread, suchthat extending proving time from 10 to 30 min,increased the total score by 20.6%. Fermentationtime and water addition were also critical vari-

ables, but they had negative effects on the totalscore. Sheeting time was the next most criticalvariable, which had a positive effect on totalscore.

Considering the opposite effects of water addi-tion on weak, medium and strong flours, a mid-dle setting of water addition (80% of FWA) waschosen for all flours. Proving time, fermentationtime and sheeting time were selected as the vari-ables to be investigated further in the optimiza-tion trials for the strong flour.

When considering the medium flour, fermenta-tion time and remixing time were the two criticalvariables that had strong positive effects on total



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Figure 1 Effect of mixing speed on the specific volume of steamed bread. Error bars represent 61 standard deviation.

Floura F G H I J

Average score 05.5c 06.2b 05.2cd 05.5c 04.9d

Preference (%) 19.5 46.3 19.5 12.3 02.4p1

e(N) 12 10 12 11 12A2/A1f(%) 75 76 75 73 74

aFlour letter, see Table 3.b,c,dFigures followed by different letters are significantly different (P , 0.05).eSoftness (p1) 5 maximum compression force using the Instron compression test.fElasticity (A2/A1) 5 ratio of the positive force area during the second cycle compression

to the positive force area during the first cycle compression test.

Table 4 The results of consumertest on eating quality ofsouthern-style Chinese steamedbread

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scores of steamed bread. Increasing the fermenta-tion time from 60 min to 180 min and remixingtime from 0.25 to 1.75 FDDT increased totalscores by 22.4% and 17.2% respectively. Therewas a set of confounded significant interactions(four two-factor interactions). Change of settingsof the corresponding variables from low to highgave a 24.8% increase in total score. Additionaltrials were used to distinguish between the fourtwo-factor interactions (data not shown). Theinteraction between fermentation time and prov-ing time was recognized to have significance(P , 0.001). Therefore, fermentation time, remix-ing time and proving time were selected for fur-ther investigation in the optimization trials for themedium flour.

For the weak flour, remixing time, wateraddition and steam rate were identified as thecritical variables affecting the total score ofsteamed bread. However, changing the settings of processing variables did not have a strongeffects on the total score, as was noted for the steamed breads made from the medium andstrong flours. The poor score and lack ofresponse to processing variables confirmed thepoor suitability of this flour for the production of SSSB.

Although the average score for the mediumflour was similar to the weak flour, it showed astronger response to variables and under somecombinations produced high scores, showinggood bread-making potential.

The levels of those processing variables thatwere not further investigated in the subsequentoptimization experiments were set at values thatthe screening tests indicated would produce breadof satisfactory quality. Water addition was dis-cussed above. Steam rate had a negative effect(23.0) on the total score of steamed bread madefrom strong flour but had a positive effect (4.3)on the total score of steamed bread made fromweak flour and had little effect (1.8) on the totalscore of steamed bread made from the mediumflour (Table 5). Consequently, an intermediaterate of 155 g of steam m23 min21 was selected.Fermentation temperature had a negative effect(23.7, 21.3 and 20.6 respectively) on the totalscores of steamed bread made from the weak,medium and strong flours and thus 32 8C wasadopted. Mixing time had effects (1.5, 1.9 and 1.4respectively) on the total scores of steamed breadmade from the weak, medium and strong flours,and 0.5 FDDT was chosen for the mixing timesetting.

Sheeting had a small negative effect on thetotal score of steamed bread made from the medi-um flour, and 5 passes were selected for the opti-mization trial for the medium flour. Remixingtime had little effect on the total score of steamedbread made from the strong flour, and thereforethe optimization setting of the remixing time formedium flour was also considered suitable for thestrong flour. An FDDT of 1.8 was selected foroptimization trials for the strong flour.



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Table 5 The effects of eightprocessing variables on totalscore of steamed bread madefrom the weak, medium andstrong flours

Independent Weak flour (D) Medium flour (E) Strong flour (F)

variables

Effecta Effect as Effecta Effect as Effecta Effect as

per cent per cent per cent

of meanb of meanb of meanb

Total score (mean) /55.82 /59 /71.28Remixing time 24.76 8.5 /10.17 17.2 20.63 00.9Water addition 24.51 8.1 21.63 02.8 24.73 06.6Steam rate 24.26 7.6 21.78 03 23.03 04.3Fermentation

temperature 23.66 6.6 21.28 02.2 20.64 00.9Proof time 22.99 5.4 21.02 01.7 /14.66 20.6Mixing time 21.51 2.7 21.92 03.3 21.37 01.9Fermentation time 20.84 1.5 /13.23 22.4 25.04 07.1Sheeting time 20.29 0.5 22.57 04.4 23.46 04.8

aEffect 5 difference in the response as the setting of the independent variable ischanged from low to high level.

bEffect as % of mean 5 difference/mean 3 100%.

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Optimization experiments

Medium flourThe results from the regression analyses for themedium flour are outlined in Table 6.Fermentation time had a strong positive effect onspecific volume, softness and cohesiveness, andtotal score. However, it had a negative effect onspread ratio of steamed bread. Proving time hadstrong positive effects on specific volume, spreadratio, softness and cohesiveness but had no sig-nificant effect on the total score of steamed bread,whereas remixing time had less of an effect on thespecific volume and the total score of steamedbread than fermentation time. Specific volume,spread ratio, structure, softness and cohesivenessand the total score were also influenced by signif-icant quadratic and interaction effects. In partic-ular, there was a strong interaction betweenfermentation time and proving time for specificvolume, spread ratio and the total score.

The sufficiency of the models to predict theresponses to changes in the processing variablesare indicated by the magnitudes of both the coef-ficient of determination (r2) and the coefficient ofvariation (CV), as well as the overall model sig-nificance. Models for specific volume, spreadratio, softness and cohesiveness and the totalscore were adequate for such predictions.

Contour plots were generated from the regres-sion equation for the total score. As the experi-mental design permits only two variables to bechanged at one time, fermentation time and prov-ing time, we chose the variables that had thelargest effects on most of the responses and hada strong interaction. Remixing time was held con-stant at its low (1.25 FDDT), medium (1.5 FDDTand 1.8 FDDT) and high level (2.25 FDDT) inorder to evaluate its effect on the total score ofsteamed bread. It was obvious that the remixingtime at its top setting of 2.25 FDDT produced thelargest area with a high total score (. 75.0).However, considering the difficulties in handlingdough that became sticky at a higher mixing time,the strong flour produced quite a large area withhigh total score at 1.8 FDDT remixing time; thiswas selected as the optimized setting for theremixing time (Fig. 2). Poor total scores wereproduced by the combination of inadequate fer-mentation time and either very short or too long

proving time. An increase in fermentation timeimproved steamed bread quality. Within themedium range of proving time, however, increas-ing the fermentation time had a very limitedeffect on total scores. The effect of fermentationtime on total scores was dependent upon thelength of proving time, which indicated the inter-action between fermentation time and provingtime.

To identify the common region of acceptabilityfor the combinations of fermentation time andproving time (remixing time 5 1.8 FDDT), con-tour plots for specific volume, spread ratio, soft-ness and cohesiveness were superimposed over thetotal score contour plot (Fig. 2, shaded). For eachresponse, low and high acceptability limits wereset as follows: specific volume (2.4–3.2), spreadratio score (2–10), softness and cohesiveness score(8.5–10.0), total score (70–100). The upper limitsrepresent the top value for the response, whereasthe lower limits were based on the limits of con-sumer acceptance. The shaded region indicatesthe range for both fermentation time and provingtime that simultaneously optimize these quality



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Figure 2 Contour plot of total score (out of 100) ofsteamed bread made from a medium flour as a functionof fermentation time and proving time at a remixing timeof 1.8 FDDT where the contour value was 0 5 60.0,1 5 62.5, 2 5 65.0, 3 5 67.5, 4 5 70.0, 5 5 72.5,6 5 75.0. The acceptability region (shaded) was obtainedby superimposing contour plots of four responses: svscore, sr score, softness and cohesiveness, and total scoreat their low and high limits, 15–25, 2–10, 8.5–10 and70–100 respectively. Symbols show low-limit margin of svscore (– – –) and softness and cohesiveness (• • •).

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Table 6 Regression equation coefficients, r2 and coefficients of variation (CV) associate with selected best-fitting modelsa from the optimization test for the medium andstrong flours

Effects of Medium flour (E) Strong flour (F)

independent

variables Specific Spread Exterior Structure Softness and Elasticity Total Specific Spread Exterior Structure Softness and Elasticity Total

volume ratio smoothness cohesiveness score volume ratio smoothness cohesiveness score

Linearb

b1 20.10*** 20.02 NS NS 20.61** NS 23.21*** 20.06*** NS NS NS NS NS 21.82**b2 NS NS 20.87*** 20.72** NS NS NSb3 20.11*** 20.12*** NS NS 20.47** 21.30** NS 20.22*** 20.04*** NS NS 21.35*** 01.3*** 25.73***b4 20.02* NS NS NS NS NS 21.33*

Quadraticb1

2 20.05*** 20.02 NS 20.33* 20.71*** NS 21.80** NS NS NS NS NS NS NSb2

2 NS NS NS 20.51* NS NS NSb3

2 20.11*** NS 20.63* 20.56** 20.71*** 20.91* 24.79*** NS 20.01** NS NS 20.48* NS 21.44*b4

2 NS 20.02 NS NS NS NS NS

Interactionb1b3 20.10*** 20.04** NS NS NS NS 22.16** NS NS NS NS 20.50* NS NSb1b4 NS NS NS NS NS NS NS NS NS NS NS NS NS NSb3b4 20.07*** NS NS NS NS NS NS NS NS NS NS NS NS NSr2 20.96 20.94 20.42 20.64 20.79 20.43 20.86 20.90 20.78 20.67 20.36 20.67 00.43 20.84CV(%) 21.31 21.40 29.36 25.52 25.07 /17.25 22.39 22.05 20.93 24.87 29.67 27.21 10.56 22.33Modelsignificance 20.00 20.00 20.13 20.02 20.00 20.11 20.00 20.00 20.00 20.01 20.14 20.01 00.11 20.00

aIf any independent variable appeared in a cross-product term or square term that is significant at P , 0.05, the main effect was kept in a response surface equation, although it isnot significant.

bb1 5 fermentation time, b2 5 sheeting time, b3 5 proving time and b4 5 remixing time.c***P , 0.001, **P , 0.01, *P , 0.05, NS 5 not significant.

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parameters and are predicted to produce steamedbread of high quality. The lower limits, whichwere set for total score (70), specific volume (2.4),and softness and cohesiveness score (8.5), definedthe acceptability region, whereas the set forspread ratio score (2) did not affect the region.That is, if total score, specific volume and soft-ness and cohesiveness score were not superim-posed, the acceptability region would be muchlarger. From this plot, a range of 132–240 min forfermentation time and 20–35 min for provingtime was identified as being the most suitablecombination for steamed bread made from themedium flour.

Strong flourResults from the regression analyses for thestrong flour are also outlined in Table 6. Provingtime was clearly the most important processingvariable, significantly influencing most responsesexcept exterior smoothness and crumb structure.Fermentation time had significant negative effectson specific volume and the total score of steamedbread. Sheeting time had a positive effect on exte-rior smoothness but a negative effect on crumbstructure. There were some quadratic effects butnot much interaction. Models for all responsesexcept structure and elasticity were adequate forpredicting the responses to changes in provingtime, fermentation time and sheeting time.Contour plots were generated from the regressionequation for total score. Proving time and fer-mentation time, the most critical variables, werechosen for the axes. Sheeting time was held con-stant at its low, medium and high level in orderto evaluate the effect on the total score ofsteamed bread. It was found that 5 sheeting pass-es produced a slightly larger area with a higherscore (. 85) than the greater number of passesdid. However, more sheeting improved exteriorsmoothness, a very important quality parameterfor consumers and 20 sheeting passes was thusselected. Contour plots for all responses exceptstructure and elasticity (models were inadequate)were superimposed over the total score contourplot to identify a common region of acceptability(Fig. 3, shaded). The acceptability limits were thesame as for medium flour, except for exteriorsmoothness (8.5–10.0). Softness and cohesivenessand exterior smoothness defined the acceptability

region for strong flour. From this plot, a range ofproving time from 28 to 40 min and fermentationtime from 60 to 168 min was judged the mostsuitable combination for steamed bread madefrom the strong flour.

To form a single test method for SSSB, theresults from the two optimization trials were com-bined. As the acceptability region for the mediumflour (Fig. 2) did not perfectly match the accept-ability region for the strong flour (Fig. 3), somecompromises had to be made in order to form asingle test method. From the results of consumertesting, it was apparent that Chinese people pre-ferred the eating characteristics of SSSB madefrom the stronger flour. On this basis compro-mises were made in favour of the optimum vari-ables for the strong flour. An optimized setting ofproving time (35 min) and fermentation time(150 min) was finally chosen for the single testmethod. For the strong flour, this optimized set-ting was in the middle of the acceptability regionbut just on the edge of the optimized region forthe medium flour (Fig. 2).



354


Figure 3 Contour plot of total score (out of 100) ofsteamed bread made from a strong flour as a function offermentation time and proving time when sheeting timeswere 20. The contour value was 0 5 60.0, 1 5 62.5,2 5 65.0, 3 5 67.5, 4 5 70.0, 5 5 72.5, 6 5 75.0,7 5 77.5, 8 5 80.0, 9 5 82.5. The acceptability region(shaded) was obtained by superimposing contour plots offive responses: sv score, sr core, exterior smoothness,softness and cohesiveness and total score at their low tohigh limits. The low and high limits and symbols are thesame as for the medium flour except exterior smoothness(8.5–10) ––––.

345-357 IJFST166 16/12/98 1:57 pm Page 354

Although in the screening test, sheeting hada minor negative effect on total score of steamedbread made from the medium flour, sheeting hada positive effect on the total score and exteriorsmoothness of steamed bread made from themedium flour under optimized settings for othervariables (Table 7). Therefore, the final setting of20 passes for the single test method would beexpected to result in steamed bread with a totalscore in the middle of the acceptability region forthe medium flour.

Verification

The optimized settings for the single test methodwere used for verifying the adequacy of the pre-dictive regression models (except for sheetingtime, because the predictive models for the medi-um flour were based on five passes of sheetingtime, both five and 20 passes of sheeting wereincluded).

These conditions were as follows: water addi-tion, 80% FWA; mixing time, 0.5 FDDT; fer-mentation time, 150 min; fermentationtemperature, 32 8C; remixing time, 1.8 FDDT;sheeting time, 20 passes; proving time, 35 min;steam rate, 155 g of steam m23 min21.

Steamed bread was produced from both thestrong and the medium flours according to thedefined procedure. Five replications were com-pleted for each flour, and the results are present-ed in Table 7. The differences between predictedand actual values for all responses were small,except the spread ratio score for the mediumflour. This indicated that most of the predictivemodels were adequate except that for the spreadratio. The low coefficients of variation associatedwith each response indicated the good repro-ducibility of the method.

Some optimized settings for the procedure forSSSB such as fermentation temperature, sheetingtime, steam rate and time were the same as thosefor NSSB. However, other optimized settingswere quite different between the two procedures,particularly water addition, remix time, fermenta-tion time and proving time. The water additionincreased from 70% FWA to 80% FWA, remix-ing time increased from 0.25 FDDT to 1.8FDDT, fermentation time increased from 60 minto 150 min and proving time increased from



355


Tab

le 7

Pre

dict

ed a

nd o

bser

ved

valu

es o

f qu

ality

para

met

ers

of s

outh

ern-

styl

e st

eam

ed b

read

mad

e fr

om t

he m

ediu

m a

nd s

tron

g flo

urs

Qu

ality

Med

ium

flo

ur

Str

on

g fl

ou

r

para

mete

r

Ob

serv

ed

Ob

se

rve

d

Avera

ge

SD

CV

(%)

Av

era

ge

SD

CV

(%)

Pre

dic

ted

Dif

fere

nce

cP

red

icte

dD

iffe

ren

ce

c

(five

(five

(20

(five

(20

(five

(20

(five

(20

(2

0

(20

(2

0

passes)a

passes)a

passes)

passes)a

passes)

passes)a

passes)

passes)a

pa

sse

s)

pa

sse

s)b

pa

sse

s)b

pa

sse

s)b

sv s

core

17.1

14.2

15.6

0.45

0.76

03.0

94.

882

2.91

18.2

18.9

0.67

3.53

20.

7sr

sco

re03

06.8

070.

450

06.5

80

23.

809

090.

717.

862

0S

oft

nes

s an

dco

hes

iven

ess

09.4

07.8

090.

840

10.7

30

21.

609

.609

.80.

454.

562

0.2

Tota

l sco

re69

.767

.875

.72.

951.

8804

.35

2.48

22

83.5

86.7

1.26

1.45

23.

2

a Fiv

e p

asse

s 5

shee

tin

g t

ime

was

five

pas

ses.

b20

pas

ses

5sh

eeti

ng

tim

e w

as 2

0 p

asse

s.c D

iffe

ren

ce 5

pre

dic

ted

val

ue

2o

bse

rved

val

ue.

345-357 IJFST166 16/12/98 1:57 pm Page 355

20 min to 35 min (northern style and southernstyle respectively). The increased mixing, fermen-tation and proving appear to result in higher vol-umes and a softer, more open crumb texture.

NSSB bread has a dense and more cohesivecrumb than southern style. It seems that thecrumb quality characteristics of SSSB are moreclosely aligned to those of Western-style panbread than those for northern style.

For pan bread, in the sponge and doughprocess, the sponge mixing is normally of relativebrief duration, whereas the more crucial phase ofdough development is reserved for the more exten-sive mixing of the final dough. This is consistentwith the findings for SSSB, in which sponge fer-mentation times may vary from 2.5 to 6 h. Ford(1968) pointed out that sponge times held within3.5–4.5 h yield bread with better keeping qualities,grain and texture than is the case when fermenta-tion is either greatly reduced or extended. Theincreasing of the fermentation time to 150 min forSSSB is also consistent with the pan bread experi-ence as it improves softness and elasticity for eat-ing quality. The longer proving time (35 min) isalso necessary to allow the dough to relax after theextensive remixing and cell expansion and thusachieve appropriate crumb structure.

Conclusions

Mixing intensity affects the quality of steamedbread, particularly when made from flours ofmedium-to-strong dough strength. A medium mix-ing intensity was found to be suitable for the pro-duction of steamed bread.

Results from RSM screening and optimizationtrials indicated that proving time had a significantpositive effect on the quality of steamed breadmade from strong flour, whereas fermentationtime had a positive effect on that made from medi-um flour. There was a strong interaction betweenfermentation time and proving time, positivelyaffecting the total score of steamed bread madefrom medium flour. Sheeting had positive effectson the total score and the exterior smoothnessscore for both types of flour.

The optimized laboratory method is suitable forflour assessment for SSSB. The method is signifi-cantly different from that for northern style andwarrants separate testing until more is understood

about the flour quality requirements for southernstyle.

Acknowledgements

This project was funded by the Grains Researchand Development Corporation and the BRIAustralia Limited. (project BRI 35M). Theauthors would like to thank Mrs Annesley Watson(Arnotts Research Centre) for helpful advice anddiscussion.

References

AACC (1983). Approved Methods of the AmericanAssociation of Cereal Chemists, Vols. 1 and 2. St Paul,Minnesota: American Association of Cereal Chemists.

Anon (1993). Wheat Flour for Steamed Bread, StandardNo SB/T 10139–93. In: Professional Standards of thePeople’s Republic of China (in Chinese). Pp. 15–19.Beijing, China: Ministry of Commerce.

Anon, (1994). China’s consumption trends. World Grain.12, 10–11.

Ford, K. W. (1968). The conditions of bread doughthrough fermentation. In. Proceedings of the 47thAnnual Meeting of the American Society of BakeryEngineers, Chicago, Illinois. Pp.87–91.

Huang, S. & Quail, K. (1995). Wheat based foods. CerealsInternational. Autumn, 6–9.

Huang, S. D., Miskelly, D. M. & Moss, R. (1991). Recentadvances in research on Chinese steamed bread. In.Proceedings of Cereals International Conference (editedby D. J. Martin, & Wrigley, C. W.). Pp. 428–435.Parkvill: The Cereal Chemistry Division, RoyalAustralian Chemical Institute.

Huang, S., Betker, S., Quail, K. & Moss, R. (1993). Anoptimised processing procedure by response surfacemethodology (RSM) for northern style Chinese steamedbread. Journal of Cereal Science, 18, 89–102.

Huang, S., Quail, K., Moss, R. & Best, J. (1995).Objective methods for the quality assessment ofnorthern style Chinese steamed bread. Journal of CerealScience, 21, 49–55.

Huang, S., Quail, K. & Moss, R. (1996). Establishment offlour quality guidelines for northern style chinesesteamed bread. Journal of Cereal Science, 24, 179–185.

Joglekar, A. M. & May, A. T. (1991). Discovery andOptimisation Software Packages, International Qual-Tech. Ltd., 2820 Fountain Lane North, Minneapolis,Minnesota 55447.

Meilgaard, M., Civille, G. V. & Carr, B. T. (1987).Sensory Evaluation Techniques. Pp.143–162. Florida:CRC Press.

RACI (1988). Official Testing Methods of the CerealChemistry Division. Melbourne: Royal AustralianChemical Institute,

Rees, R. O. & Cockinos, A. (1995). Outlook for wheat.



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In: Outlook 95 – Proceedings of the National Agriculturaland Resources Outlook Conference, ABARE. Pp.157–165.

Rubenthaler, G. L., Pomeranz, Y. & Huang, M. L.(1992). Steamed bread. IV. Negative steamer-spring ofstrong flours. Cereal Chemistry, 69, 334–337.



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Received ?? ???? 1997, Revised and accepted ?? ???? 1997

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Documents

The optimization of a laboratory processing procedure for southern-style Chinese steamed bread