research article technological properties of wheat

Research ArticleTechnological Properties of Wheat/Trifoliate Yam(Dioscorea dumetorum) Hardened Tubers Composite Flours

Véronique Josette Essa’a, Roger M. Mbanga Baleba, and Gabriel Nama Medoua

Centre for Food and Nutrition Research, IMPM, P.O. Box 6163, Yaounde, Cameroon

Correspondence should be addressed to Gabriel Nama Medoua; [email protected]

Received 6 August 2015; Revised 11 December 2015; Accepted 15 December 2015

Academic Editor: Ma Murcia

Copyright © 2015 Veronique Josette Essa’a et al.This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in anymedium, provided the originalwork is properly cited.

The ability of trifoliate hardened-yam flours to partially substitute wheat flour in food formulations was assessed.Three varieties ofhardened-yam flour were incorporated in wheat flour in proportions of 0, 10, 20, 30, 40, and 50% (w/w). Samples were evaluatedfor protein content, Zeleny sedimentation index, Hagberg falling number, functional properties (WAC, WSI, and OAC), and somerheological properties including dough rupture pressure (𝑃), extensibility (𝐿), stability (𝑃/𝐿), and deformation energy (𝑊). Resultsshowed that trifoliate hardened-yam flours do not have acceptable baking properties as pictured by the low Zeleny sedimentationindex and the low Hagberg falling number. Protein quality (Zeleny index, 31) of wheat flour helped to compensate gluten deficitof yam flours, but the amylasic activity determined by the Hagberg falling number could not be adjusted, which resulted in aloss of extensibility (𝐿) of the paste at 10% substitution. Multivariate analysis of experimental data regrouped wheat flour and allwheat/hardened-yam treated with kanwa composite flours in one homogeneous cluster. Although wheat/hardened-yam treatedwith kanwa composite flours had physicochemical and functional properties similar to wheat, the inadequate diastasic activitymakes them inappropriate for bread making, marking the strongest influence of that parameter.

1. Introduction

Trifoliate yam (Dioscorea dumetorum) tubers are good sourceof nutrients and energy [1]. Their storage under tropicalambient conditions makes them susceptible to a hardeningphenomenon characterised by loss of the ability to softenduring cooking [2, 3]. In an attempt to add more value toD. dumetorum as an important source of food and energy,Medoua et al. [4, 5] developed schemes for processing of itshardened tubers into flours and suggested that these flourscan be used in bakery.

Composite flour can be defined as a mixture of flours,starches, and other ingredients intended to replace wheatflour totally or partially in bakery and pastry products[6]. Composite flour has several advantages for developingcountries including the reduction of wheat flour importationand promotion of high-yielding, native plant species [7].In this regard, several developing countries have initiatedprogrammes to evaluate the feasibility of alternative locallyavailable flours as a substitute for wheat flour [8] and severalauthors successfully developed composite flours where wheat

flour is partially replaced by cassava [9], taro [10], banana [11],yam [12], sorghum [8], soybean [13], cocoyam [14], chickpea[15], lupin [16], sweet potato [17], or maize [18].

To the best of our knowledge, no study has been per-formed so far to assess the aptitude of trifoliate hardened-yam to partially substitute wheat flour in food formulation.The present study was therefore designed to evaluate theaptitude to develop trifoliate hardened-yam-wheat compositeflours. Generally, composite flours are developed to be usedin bakery and in pastry-making and are suitable to producebread, biscuits, noodles, and various cakes. Evaluating tech-nological value of composite flour can be done either bydirect appreciation, corresponding to the implementation ofa production test at a reduced scale, or by indirect apprecia-tion, corresponding to chemical, functional, and rheologicalanalysis. This last alternative was chosen in the present study.

2. Materials and Methods

2.1. Materials. Trifoliate yam, D. dumetorum cv., yellowtubers were harvested at maturity in a farm at Esse in

Hindawi Publishing CorporationJournal of Food ProcessingVolume 2015, Article ID 425121, 8 pageshttp://dx.doi.org/10.1155/2015/425121

2 Journal of Food Processing

the Centre Region of Cameroon. They were immediatelytransported to the laboratory in Yaounde and stored underprevailing tropical ambient conditions (19–28∘C, 60–85%RH) for 14 days. Hardening of stored tubers was characterisedby a rough and fluffy surface of peeled tubers as opposed tothe smooth andmoist surface of freshly harvested ones. Afterstorage, the samples of hardened tubers were thoroughlywashed with water, peeled, chopped into chips of 1 cmthickness, and divided in three lots. Samples of the first lotwere not pretreated, samples of the second lot were pretreatedby fermenting the yam slices during 7 days in a closed systemas described by Medoua et al. [5], and samples of the thirdlot were pretreated by soaking yam slices in a solution of 1%kanwa alkaline salt for 16 h as described by Medoua et al. [4].The samples of each lot were, respectively, dried at 40∘C in aventilated oven for 24 h and the dried samples were groundinto flour to pass through a 400 𝜇m sieve.

Commercial wheat flour without additive was used toproduce composite flours by incorporating hardened-yamflours into wheat flour at the levels of 0, 10, 20, 30, 40, and50%. The resulting flours were coded as follows:

(i) W: 100% wheat flour,(ii) H10: 90% wheat/10% hardened-yam composite flour,(iii) H20: 80%wheat/20% hardened-yam composite flour,(iv) H30: 70% wheat/30% hardened-yam composite flour,(v) H40: 60%wheat/40%hardened-yam composite flour,(vi) H50: 50%wheat/50% hardened-yam composite flour,(vii) F10: 90% wheat/10% fermented hardened-yam com-

posite flour,(viii) F20: 80% wheat/20% fermented hardened-yam com-

posite flour,(ix) F30: 70% wheat/30% fermented hardened-yam com-

posite flour,(x) F40: 60% wheat/40% fermented hardened-yam com-

posite flour,(xi) F50: 50% wheat/50% fermented hardened-yam com-

posite flour,(xii) K10: 90% wheat/10% hardened-yam treated with

kanwa composite flour,(xiii) K20: 80% wheat/20% hardened-yam treated with

kanwa composite flour,(xiv) K30: 70% wheat/30% hardened-yam treated with

kanwa composite flour,(xv) K40: 60% wheat/40% hardened-yam treated with

kanwa composite flour,(xvi) K50: 50% wheat/50% hardened-yam treated with

kanwa composite flour.

2.2. Technological Characteristics of Flours. Protein content(𝑁 × 5.7 for wheat flour and 𝑁 × 6.25 for compositeflours) was determined by the AACC International ApprovedMethod 46-12.01 [19]. The moisture and ash contents were,

respectively, determined according to the AOAC OfficialMethods 925.10 and 920.87 [20]. Zeleny sedimentation indexand Hagberg falling number were, respectively, determinedaccording to the AACC International Approved Methods56-60.01 [21] and 56-81.03 [22].

2.2.1. Functional Properties. Water absorption capacity andwater solubility index were determined as described by Belloet al. [23] and Anderson et al. [24]. Oil absorption capacitywas estimated by centrifuging a known quantity of floursaturated with oil as described by Sosulski [25]. The leastgelatinisation concentration was estimated according to themethod of Coffman and Garcia [26]. The bulk density ofthe paste obtained after mixing 100 g of flour with a givenquantity of water to obtain a water content of 60% wasdetermined according to themethoddescribed byOkezie andBello [27]. Emulsion activity and stability were determinedaccording to the method described by Neto et al. [28]. Floursample (1 g) was mixed with 3mL of distilled water and3mL of cotton oil in a graduated tube. Then, the mixturewas shaken for 10min in a KS10 agitator and centrifugedat 2500 rpm for 5min. Emulsion activity was calculated bydividing the volume of the emulsified layer by the volumeof total content in the tube. The emulsion stability wasdetermined by heating the emulsion for 30 at 80∘C and thencooled and centrifuged again at 2500 rpm for 5min. Theemulsion stability was expressed as the % of emulsifyingactivity remaining after heating.

2.2.2. Colour Measurement. Colour was measured using acolorimeter (Lovibond RT Colour Measurement Kit V2.28)with an observation window of 10∘ and D65 light source. Thecolorimeter was calibratedwith a white standard (𝐿∗ = 93.87,𝑎∗

= 0.18, and 𝑏∗ = 2.71) andCIE 𝐿∗𝑎∗𝑏∗ parameters of eachsample were determined on the basis of triplicate measure-ments.

The colour derivative functions of 𝐶∗ [chroma = (𝑎∗2 +𝑏∗2

)1/2] and𝐻∗ [hue angle = tan−1(𝑏∗/𝑎∗)] were also calcu-

lated.

2.2.3. Rheological Properties. Alveograph characteristics(tenacity 𝑃, extensibility 𝐿, stability 𝑃/𝐿, and deformationenergy 𝑊) were determined under conditions of constantdough water content (40%) and mixing time (28min),according to the AACC International Approved Method54-30.02 [29] using the Alveo-Consistograph (Chopin,Villeneuve-La-Garenne, France) with a built-in diaphragmpump to supply air for inflating the tested dough piece.

2.3. Statistical Analysis. All measurements were carried outin triplicate. Statistical analyses of data were performed usingSPSS 10.1 (SPSS Inc., Chicago, Illinois, USA) and STATIS-TICA 6 (Data Analysis Software System, StatSoft, Inc., USA).Analysis of variance (ANOVA), Duncan multiple range test,principal component analysis (PCA), and hierarchical clusteranalysis (HCA) were performed. Statistical significance wasdefined at 𝑃 ≤ 0.05.

Journal of Food Processing 3

Table 1: Some physicochemical properties of experimental flours.

Flour type

Hardened-yam Fermentedhardened-yam

Hardened-yam treated withkanwa Wheat

Proteins (% DM) 9.6 ± 0.1 9.9 ± 0.1 8.4 ± 0.1 11.17 ± 0.02Hagberg falling number (s) 104 ± 2 62 ± 1 287 ± 14 321 ± 1Zeleny index (mL) 7 ± 0.4 8 ± 0.2 4 ± 0.4 31 ± 0.6Least gelatinisation concentration 10.5 ± 0.7 13.0 ± 0.0 7.5 ± 0.7 5.5 ± 0.7Mean ± SD, 𝑛 = 3.

3. Results and Discussion

Table 1 displays some physicochemical properties of wheatand yam flours. It was noted that protein content of yamflours (9.9–8.4 g/100 g) is relatively low compared to wheatflour. Zeleny sedimentation index which defines the capacityof proteins to form aggregate in acid medium (related toits content in glutelin) was low for various yam flours; inall the cases, it was below the minimum acceptable valueset at 15mL (Norm ISO 5529), marking the absence ofglutelin in yam flours. The diastasic activity of yam flourwas very strong as illustrated by the small values of Hagbergindex. This strong diastasic activity led to a maximum starchliquefaction (specially for hardened-yamflour and fermentedhardened-yam flour) and a low water retention capacity,which explained why, compare with wheat flour, hardened-yam flours presented a lower viscosity during cooking aspictured by the higher values of least gelatinisation concen-tration. In general, these results showed that hardened-yamflours do not have acceptable baking properties.

The protein content and the gluten quality (Zeleny index,31) of wheat flour used in this study could help compensatingprotein deficit of different yam flours, but the amylasicactivity determined by the Hagberg falling number was justat the standard level and could hardly adjust the enzymaticlevel in composite flours.

Table 2 displays some physico-chemical properties ofwheat/hardened-yam composite flours. After incorporationof wheat flour, the baking properties were significantlyimproved. Zeleny index remained in acceptable level untila substitution rate of 50% for hardened-yam and fermentedhardened-yam flours, and 30% for hardened-yam treatedwith kanwa flour.

In general, water absorption capacity (WAC), oil absorp-tion capacity (OAC), water solubility index (WSI), and theleast gelification concentration (LGC) increased with thesubstitution level. This evolution was similar to the onenoted by Njintang et al. [30] during substitution of wheatflour by taro flour. Increasing of WAC with substitutionof hardened-yam flours suggested that wheat/hardened-yamcomposite flours could be used in food systems such as breadmaking that require lots of water to improve mechanicalcharacteristics of the dough. Since variation of OAC wasassociated with presence of nonpolar chains, results of thepresent study suggested that substitution of wheat flourby hardened-yam flours significantly increased oil fixation

sites in the composites flours. Thus, wheat/hardened-yamcomposite flours could be potentially useful in the structuralinteraction of food, especially for flavour retention and thetaste improvement of products.

Emulsion activity (EA) and emulsion stability (ES) ofwheat/hardened-yam composite flours significantly decrea-sed with the increase of hardened-yam flour substitution.This result agreed with the study reported by Yatsumatsu etal. [31] who correlated the decrease of EA with the increase offibre content, as it was reported thatD. dumetorum hardenedtubers are rich in fibres [32].

In this study, a decrease of bulk density was notedwith the increase of substitution rate of various hardened-yam flours. This is valuable if one considers the worksreported by Nelson-Quartey et al. [33] and Akubor andBadifu [34] which, respectively, showed that a decrease ofbulk density promotes proper formulation of infant foods,and that decrease of the density during incorporation ofTreculia africana flour in wheat flour is good for productionof cookies.

To have a better understanding of relations existingbetween basic parameters of flours based on their physic-ochemical and functional properties, experimental resultswere analysed using HCA and PCA method.

Original data introduced for analysis, [𝑋 = (16, 10)],comprised 10 variables measured in 16 samples, where eachentry matrix was the mean value of three replicates. The datawere autoevaluated before analysis.

Figure 1 displays results ofHCA. In this dendogram, thereare fourmain groups for the similarity 0.6 (similarity index =100 −(𝐷link/𝐷max)∗100). Wheat flour forms a similar groupwith wheat/hardened-yam treated with kanwa compositeflours (K10, K20, K30, K40, and K50). This suggested that,until 50% substitution, wheat/hardened-yam treated withkanwa composite flours preserves the physicochemical andfunctional properties of wheat flour. Wheat/hardened-yamcomposite flours (H) and wheat/fermented hardened-yamcomposite flours (F) are spatially away from the group formedby wheat and form a single group at the index of similarityof 0.4 characterized by a small Hagberg falling number(Table 2).

Analysis of varimax-rotated principal components gavesimilar trends and characteristics to those observed in HCA,but with the advantage that correlations between variablesand samples become clearer. Varimax-rotated loading fac-tors representing correlations between principal components


Table2:Ph

ysicochemicalandfunctio

nalpropertieso

fwheat/hardened-yam

compo

sites

flours.

Yam

Proteins

(%)

Hagberg

falling

number(s)

Zeleny

index

(mL)

WSI

(%)

WAC

(%)

OAC

(%)

EA(%

)ES

(%)

Density(g/m

L)LG

C(%

)

Hardened

0%11.17±0.02

f321±

1e31±0.6e

11.6±0.1a

106.0±0.5a

173.1±

0.9a

46.6±0.6d

61.7±0.4e

0.66±0.01

d5.5±0.7a

10%

11.01±0.02

e204±7d

25±0.5d

18.4±0.6b

118.2±0.4b

176.1±

0.2a

b46

.2±0.7d

46.0±1.4

d0.66±0.01

d6.5±0.7a

b

20%

10.86±0.02

d171±

1c23±0.5c

19.2±0.2b

130.0±1.0

c181.2±0.0b

c44

.9±0.4d

42.8±1.1

d0.63±0.00

c7.5±0.7b

c

30%

10.71±

0.01

c151±

2b21±0.3c

20.2±0.1c

149.3±2.0d

186.2±1.1

cd41.2±0.7c

38.9±2.0c

0.59±0.00

b8.5±0.7c

d

40%

10.56±0.01

b137±7a

19±0.8b

20.8±0.8c

d166.3±7.1

e188.6±0.3c

d38.7±1.1

b35.0±2.4b

0.56±0.00

a9.5±0.7d

e

50%

10.40±0.01

a135±8a

17±0.5a

21.8±0.2d

193.7±4.7f

190.7±7.5

d35.1±0.3a

31.0±1.4

a0.55±0.01

a10.5±0.7e

Hardened-tre

ated

with

kanw

a0%

11.17±0.02

f321±

1a31±0.6d

11.6±0.1a

106.0±0.5a

173.1±

0.9a

46.6±0.6e

61.7±0.4b

0.66±0.01

d5.5±0.7a

10%

10.90±0.02

e307±4b

21±0.5c

17.7±0.3b

123.2±3.5b

174.2±3.5a

42.6±1.0

d55.2±1.7

a0.67±0.00

d8.0±0.0b

20%

10.63±0.02

d303±3b

18±1.1

b18.3±0.0b

c135.1±

2.6c

176.2±3.8a

b38.9±1.6

c53.9±2.7a

0.64±0.01

c6.5±0.7a

b

30%

10.36±0.01

c301±

4b16±1.6

b18.8±0.3c

d155.0±6.2d

180.7±0.9b

c34.7±1.7

b55.1±1.6

a0.63±0.01

bc5.5±0.7a

40%

10.10±0.01

b302±0b

14±0.5a

19.3±0.5e

178.9±7.0

e183.3±0.6c

d31.3±1.9

ab55.2±0.7a

0.61±0.01

b5.5±0.7a

50%

9.83±0.01

a308±13

b13±0.5a

20.1±0.4f

211.0±0.0f

188.3±1.7

d28.4±1.3

a54.8±0.2a

0.59±0.00

a5.5±0.7a

Hardened-ferm

ented

0%11.17±0.02

f321±

1d31±0.6e

11.6±0.1a

106.0±0.5a

173.1±

0.9a

46.6±0.6c

61.7±0.4d

0.66±0.01

d5.5±0.7a

10%

11.05±0.02

e129±0c

26±0.5d

20.0±0.2b

120.2±0.2b

176.5±11.0

a46

.5±0.5c

49.0±1.3

c0.67±0.01

d7.5±0.7b

20%

10.93±0.02

d74±2b

24±0.5c

21.2±0.2c

136.9±0.7c

183.1±

1.7ab

45.4±0.6c

47.0±1.5

c0.64±0.01

c9.5±0.7c

30%

10.81±

0.01

c64±1a

22±0.3c

22.1±0.1d

165.5±1.5

d192.5±0.3b

c42.4±1.5

b45.8±1.1

bc0.61±0.00

b11.5±0.7d

40%

10.69±0.01

b62±0a

20±0.8b

23.3±0.6e

211.6±4.9e

200.3±0.1cd

40.2±0.2a

b42.8±0.2a

b0.61±0.01

b12.0±0.0d

e

50%

10.57±0.01

a62±1a

18±0.5a

23.9±0.4e

249.6±1.8

f207.5±0.5d

38.5±1.3

a41.6±2.2a

0.53±0.00

a13.5±0.7e

Mean±SD

,𝑛=3.

Means

ofthes

amec

olum

nfore

achtre

atmenth

avingdifferent

superscriptsares

ignificantly

different

at𝑃≤0.05accordingto

Dun

cantest.


20 30 40 50 60 70 80 90 10010

F50F40F30F20F10D50D40D30D20D10K50K40K30K20K10

W

(Dlink/Dmax) ∗ 100

Figure 1: HCA on wheat flour and 15 wheat/hardened-yam com-posite flours.

Table 3: Loadings for the first four varimax rotated principalcomponents.

Variables PC1 PC2 PC3 PC4Proteins 0.58∗ −0.80∗ −0.07 −0.06WSI −0.88∗ −0.25 0.00 0.41WAC −0.93∗ 0.19 −0.27 −0.10OAC −0.93∗ −0.19 −0.27 −0.12EA 0.56 −0.82∗ −0.03 0.01ES 0.65∗ 0.50 −0.56 0.04Density 0.90∗ −0.05 −0.18 0.36Zeleny index 0.66∗ −0.70∗ −0.09 −0.19LGC −0.70∗ −0.64∗ −0.19 −0.04Hagberg falling number 0.55 0.80∗ 0.01 −0.14Eigen value 5.62 3.25 0.54 0.38% total variance 56.20 32.45 5.35 3.84Cumulated Eigen value 5.62 8.87 9.40 9.78Cumulated variance (%) 56.20 88.65 94.01 97.84∗Loadings with absolute values higher than 0.56 represent a significantcontribution.WAC: water absorption capacity.OAC: oil absorption capacity.WSI: water solubility index.EA: emulsion activity.ES: emulsion stability.LGC: least gelatinisation concentration.

(PC) and original data are presented in Table 3 with theirvariances and Eigen values. PC1 included 56.2% of thevariance in the introduced data and loadings, suggesting thatit has a significant contribution to the functional properties.PC2 describes 32.45% of the total variance and has asmain contributor physicochemical properties and emulsionactivity. PC3 and PC4 only describe 5.35 and 3.84% of thetotal variance, respectively. Thus, PC1 and PC2 representing88.65% total variance in the data can be enough to restitutethe maximum of information contained in the original data.

Results of HCA for variables are presented in Figure 2.In the dendogram obtained, three groups were observed for

0 20 40 60 80 100

Hagberg

OAC

WAC

ES

EA

Zeleny

WSI

Bulk density

LGC

Proteins

(Dlink/Dmax) ∗ 100

Figure 2: Dendogram (HCA) for the physicochemical and func-tional properties of flours.

a similarity index of 0.6.The diastasic activity of flours repre-sented by the Hagberg falling number is spatially separatedfrom the main group formed by proteins, density, Zelenyindex, LGC, WSI, EA, and ES and forms a single group ata similarity index of about 0.1 with WAC and OAC. Thissuggested that technological properties of wheat/hardened-yam composite flours at substitution levels used in this studyaremainly influenced by the diastasic activity and correlationthat may exist between diastasic activity, WAC, and OAC.

Figure 3 presents the scores and the varimax-rotatedloadings of the first two principal components. In thisfigure, it is remarkable to note that wheat (W) and thevarious wheat/hardened-yam treated with kanwa compositeflours (K10, K20, K30, K40, and K50) form a group that isdistinguished by a high Hagberg falling number, a low OAC,and a lowWSI.The second group formedbywheat/hardened-yam composite flours (H10, H20, H30, H40, and H50) andwheat/fermented hardened-yam composite flours (F10, F20,F30, F40, and F50) is mainly characterised by a low Hagbergfalling number, a high OAC, and a high WSI. At this level ofanalysis, it could be suggested that the technological prop-erties of wheat/hardened-yam treated with kanwa compositeflours are similar to those of wheat. However, a more detailedobservation of this group can allow subdividing it into threesubgroups consisting, respectively, of W, K10-K20-K30, andK40-K50, which are differentiated by variation in WAC,protein content, Zeleny index, and EA.

Rheological properties of composite flours assessed byalveograph analysis are presented in Table 4. The effect ofa partial substitution of wheat flour by various hardened-yam flours induced changes in the alveograph characteristics.For all composite flours, a drastic decrease of all parametersmeasured was noted at 10% substitution rate, followed bya progressive increase with increasing substitution rate. Thealveograph characteristics in all cases were below the min-imum threshold for the use of flour in bakery. This trendis different from the one noted by Yatsumatsu et al. [31]for wheat/taro composite flours and by Balla et al. [35] for


Scores

WD10D20D30D40

D50K10

K20

K30K40

K50

F10F20F30F40F50

−3

−2

−1

0

1

2

3

4

5

CP2:

32.

45%

−6 −4 −2 2 4 60CP1: 56.20%(a)

Proteins

WSI

WAC

EA

ES

Bulk density

ZelenyLGC

Hagberg

Loadings

−1.0

−0.5

0.0

0.5

1.0

CP2:

32.

45%

0.5 1.00.0 −0.5−1.0

CP1: 56.20%

OAC

(b)

Figure 3: Scores and varimax-rotated loadings for the first two principal components.

Table 4: Rheologic characteristics of various wheat/hardened-yamcomposite flours.

Rheologiccharacteristics 0% 10% 20% 30% 40%

Incorporation level of hardened-yam flour𝑃 (mm) 69 9 22 31 42𝐿 (mm) 58 9 11 10 10𝑃/𝐿 1.19 1.06 2.01 3.11 4.11𝑊 (10−4 J) 148 4 10 16 22

Incorporation level of the flour of hardened-yam treated with kanwa

𝑃 (mm) 69 18 32 50 65𝐿 (mm) 58 9 11 9 9𝑃/𝐿 1.19 1.63 2.78 5.66 7.39W (10−4 J) 148 10 17 23 30

Incorporation level of fermented hardened-yam flour

𝑃 (mm) 69 6 21 26 38𝐿 (mm) 58 8 10 8 9𝑃/𝐿 1.19 0.84 2.19 3.16 4.38𝑊 (10−4 J) 148 2 10 11 17𝑃 = tenacity; 𝐿 = extensibility;𝑊 = deformation energy.

wheat/sorghum composite flours describing a linear increaseof alveograph parameters with increasing substitution rate.Results of this study suggested that wheat/hardened-yamcomposite flours are not suitable for bread making at allsubstitution levels and treatments type used in the study.

Considering the fact that the Zeleny index, indicating thecapacity of proteins to form a viscoelastic mass, is in mostcases at an acceptable level (Zeleny index ≥ 15, Table 2), andthat extensibility (𝐿) of the paste ismainly due to this capacityof gluten, it was surprising to note a loss of extensibilityat 10% of substitution even after using a hard wheat witha protein content of 16 g/100 g DM. It was suggested thatthe phenomenon was due to the strong diastasic activity of

composite flours (Table 2), which could make the paste softand sticking. Hence, an inactivation of enzymes in hardened-yam flours before the mixture with wheat flour could helpimproving the alveograph characteristics of wheat/hardened-yam composite flours andmake these floursmore suitable forbread production.

The colour of flours can be an important parameterthat can directly influence the acceptability of a product.CIE 𝐿∗𝑎∗𝑏∗ parameters of wheat/hardened-yam flours arepresented in Table 5. In general, substitution level changes theCIE 𝐿∗𝑎∗𝑏∗ parameters of composite flours. 𝐿∗ parameter(luminance) increases with substitution of hardened-yamflour and is not significantly affected by the increase of sub-stitution of hardened-yam treated with kanwa and hardened-yam fermented flours. 𝑎∗ parameter (red) decreases with theincrease of the substitution level of various hardened-yamflours, while an increase was noted for 𝑏∗ parameter (yellow).In general, a partial substitution of wheat flour by differenthardened-yam flours in study led to a significant increaseof 𝐶∗ parameter (chroma) that measures colour saturation,and hue angle (𝐻∗), which shows the brightness and yellowcolour of composite flours obtained.

4. Conclusion

Under standard condition of breadmaking, floursmade fromD. dumetorum hardened tubers did not present any bakingproperty. A partial substitution of wheat flour by hardened-yam flours straightened the baking properties of the flours(except for the Hagberg falling number which remained low)and significantly influenced the functional properties of theflours. Multivariate analysis (HCA and PCA) of experimentaldata brought together the different flours studied in twogroups defined in two principal components: the first groupwas composed by wheat and various wheat/hardened-yamtreated with kanwa composite flours (K10, K20, K30, K40,and K50) and was characterised by a high Hagberg fallingnumber and a low WAC and WSI, while the second groupwas composed of wheat/hardened-yam composite flours


Table 5: CIE 𝐿∗𝑎∗𝑏∗ colour parameters of wheat/hardened-yam composite flours.

CIE colour parameters 0% 10% 20% 30% 40% 50%Incorporation level of hardened-yam flour

𝐿∗ 93.47 ± 0.75a 96.34 ± 0.75bc 96.38 ± 0.75bc 94.62 ± 0.75ab 96.97 ± 0.75c 95.86 ± 0.75bc

𝑎∗ 0.10 ± 0.01d −0.46 ± 0.07c −1.00 ± 0.14b −1.19 ± 0.14b −1.52 ± 0.14a −1.60 ± 0.14a

𝑏∗ 10.41 ± 0.02a 13.10 ± 0.02b 15.38 ± 0.02c 16.21 ± 0.02d 16.80 ± 0.02e 18.00 ± 0.02f

𝐶∗ 10.41 ± 0.02a 13.11 ± 0.02b 15.42 ± 0.02c 16.26 ± 0.02d 16.88 ± 0.02e 18.08 ± 0.02f

𝐻∗ 88.98 ± 0.62a 91.81 ± 0.62b 93.67 ± 0.62c 94.12 ± 0.62c 95.06 ± 0.62c 94.96 ± 0.62c

Incorporation level of the flour of hardened-yam treated with kanwa𝐿∗ 93.47 ± 0.75a 94.11 ± 0.75a 92.99 ± 0.75a 94.61 ± 0.75a 94.11 ± 0.75a 93.90 ± 0.75a

𝑎∗ 0.10 ± 0.01c −0.43 ± 0.14b −0.89 ± 0.14a −0.91 ± 0.14a −1.09 ± 0.14a −1.04 ± 0.14a

𝑏∗ 10.41 ± 0.02a 13.05 ± 0.02b 13.25 ± 0.02c 14.23 ± 0.02d 13.99 ± 0.02e 14.90 ± 0.02f

𝐶∗ 10.41 ± 0.02a 13.06 ± 0.02b 13.29 ± 0.02c 14.27 ± 0.02d 14.05 ± 0.02e 14.94 ± 0.02f

𝐻∗ 88.98 ± 0.62a 91.88 ± 0.62b 93.82 ± 0.62c 93.61 ± 0.62c 94.44 ± 0.62c 93.95 ± 0.62c

Incorporation level of the flour of fermented hardened-yam𝐿∗ 93.47 ± 0.75a 92.88 ± 0.75a 92.28 ± 0.75a 92.09 ± 0.75a 93.75 ± 0.75a 93.04 ± 0.75a

𝑎∗ 0.10 ± 0.01a 0.07 ± 0.14a −0.08 ± 0.14a −0.05 ± 0.14a −0.12 ± 0.14a −0.12 ± 0.14a

𝑏∗ 10.41 ± 0.02a 12.19 ± 0.02b 13.03 ± 0.02c 13.60 ± 0.02e 13.44 ± 0.02d 13.58 ± 0.02e

𝐶∗ 10.41 ± 0.02a 12.19 ± 0.02b 13.03 ± 0.02c 13.60 ± 0.02e 13.44 ± 0.02d 13.58 ± 0.02e

𝐻∗ 88.98 ± 0.62a 89.69 ± 0.62a 90.37 ± 0.62a 90.18 ± 0.62a 90.52 ± 0.62a 90.52 ± 0.62a

Mean ± SD, 𝑛 = 3.Means of the same line for each treatment having different superscripts are significantly different at 𝑃 ≤ 0.05 according to Duncan test.

(H10, H20, H30, H40, and H50) and wheat/fermentedhardened-yam composite flours (F10, F20, F30, F40, andF50) and was characterized by a low Hagberg falling numberand a high WAC and WSI. In all the cases the inadequatediastasic activity was the limiting factor preventing thewheat/hardened-yam composite flours to be appropriate forbread making.

Conflict of Interests

The authors declare no conflict of interests.

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