functional properties of non-wheat flour substitutes in composite flours. ii. amylolytic...

9
Functional Properties of Non-Wheat Flour Substitutes in Composite Flours. II. Amylolytic Susceptibility of Non-Wheat Starches Introduction A partial replacement of wheat flour with flour of non-cereal origin may significantly affect the "diastatic activity" of the composite blend and hence its breadmaking quality. If the "diastatic activity" of a flour, or a flour mixture, is determined at tempera- tures below the gelatinization temperature of the starch present in the tested material, the results 166 Starches from tubers of some species of the genus Dioscorea (D. rotundata Poir.), D. alta. L., D. cayenensis Lam., D. esculenta (Lour.) Birk., roots of cassava (Manihot utilissima Poh!.), cormels of cocoyam (Xanthosoma sagittifolium Schott.), fruits of plantain (Musa paradisiaca L.) together with starches from sorghum (Sorgho ROF) and millet (SOUNA II) were tested for suscep- tibility of the ungelatinized granules to the action of bacterial alpha-amylase, fungal glucoamylase and malt diastase. Though all starches were found more resistant to enzymatic degradation when compared with starch extraded from the Canadian hard red spring wheat, considerable differences were observed between individual starches. Among non-cereal starches, cassava starch was found the most susceptible one, whereas large granule yam and plantain starches did not show any significant degree of digestion even after 48 hours treatment with the enzymes. Scanning electron microscopy revealed that the mode of the enzymatic attack on the granules of cassava and cocoyam starch- both being composed starches, differed from that on cereal starch granules. The reduction of the diastatic activity of composite flours, in which wheat flour was replaced by less susceptible starches, reflected in a lower CO2 production in sucrose-free doughs during fermentation. Des recherches ont ete effectuees pour demontrer I'activite amylolytique de l' a-amylase d'origine bacterienne, de la gluco- amylase produite par certaines moisissures et de la diastase du malt sur des granules non-gelifees d'amidons provenant de tubercules de certaines espeoes de genre Dioscorea (D. rotunda, Poir., D. alata L., D. cayenensis Lam., D. esculenta (Lour.) Birk., de tubercules de manioc (Manihot utilissima Poh.), de tubercules de taro Xanthosoma sagittifolium Schott.), des fruits de plantain (Musa paradisiaca L.), ainsi que des amidons de sorgho (Sorgho ROF) et de millet (Souna II). Bien que tous les amidons furent trouves plus resistants it une degradation enzymatique par rapport it l' amidon de ble canadien de type dur-rouge printemps, de tres grandes differences furent observees ootre les amidons con- sideres. Parmi les amidons ne provenant pas de cereales, I'amidon de manioc fut Ie plus facilement attaque, tandis ques les amidons de taro et de plantain ne presenterent aucun signes de degradation, meme apres 48 h de traitement enzymatique. La technique de la microscopie electronique it balayage montra que Ie mode d'attaque enzymatique sur les granules d'amidons de taro et de manioc - les deux etant des amidons composes - differait de celui sur les granules d'amidons de cereales. La reduction de I'activite diastatique sur des farines composees, dans lesquelles la farine de ble etait remplacee par des amidons mains sensibles, se refleta pendant la fermentation par une production plus basse en CO 2 dans des pates sans sucre. Abstract Resume V. Rasper, G. Perry, and C. L. Duitschaever Department of Food Science University of Guelph Guelph, Ontariu reflect not only the actual enzymatic activity of the sample, but also the amylolytic susceptibility of un· gelatinized starch granules. This susceptibility is determined primarily by the inherent resistance of the starch granules, but is further influenced by various chemical and mechanical factors. Amongst them, the physical damage of the granules as it occurs during the process of milling or grinding has to be considered as the predominant one. Many research workers have reported differences in the amylolytic susceptibility of starches of different origin and attempted to find some exploration for their specific behavior (Sandstedt, 1954, Badenhuizen, 1955, 1965 and 1971; Schoch and Leach, 1961; Evers and McDermott, 1970; Evers et al., 1971; Gallant et al., 1973). Though it is obvious that the differences in the primary resistance of the intact granules depend on the genetically inherited degree of molecular asso- ciation within the granule, there is still more know- ledge required to ellucidate the relation between the strength and type of this molecular association and various properties of the granules including their resistance to enzymatic attack. Cereal starches in ungelatinized form are known for their lesser resistance to the enzymatic degrada- tion compared with starches of other origin. However, if wheat Hour in a composite blend is partially re- placed by a root or tuber starch, it has to be expected that the total amylolytic susceptibility of the mixture will be reduced not only due to a lower inherited primary susceptibility of non-cereal starches, but also due to a lower degree of physical damage of their granules. Tuber or root starches are usually prepared simply by the water extraction of grated pulp without being subject to any heavy shearing or any other force due to milling. Though severe damage of starch granules changes the baking quality of the flour very unfavorably, a certain degree of damage may even be desirable to obtain the required "diastatic activity" for the optimum baking performance (Farrand, 1964; Tipples, 1969; Lorens and Johnson, 1970; Dodds, 1971). In the present study, several starches of West African origin were tested for their amylolytic suscep- tibility both in vitro using pure starch suspensions and in mixtures of a typical bread flour and the respective starch. Functional properties of these starches, including their effect on the baking quality of the wheat flour/starch mixtures, were reported in Part I of this paper. J. Inst. Ca.n. SCI. Techno!. Aliment. Vo!. 7, No.3, 1974

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Functional Properties of Non-Wheat Flour Substitutes inComposite Flours. II. Amylolytic Susceptibility of Non-Wheat

Starches

IntroductionA partial replacement of wheat flour with flour

of non-cereal origin may significantly affect the"diastatic activity" of the composite blend and henceits breadmaking quality. If the "diastatic activity" ofa flour, or a flour mixture, is determined at tempera­tures below the gelatinization temperature of thestarch present in the tested material, the results

166

Starches from tubers of some species of the genus Dioscorea(D. rotundata Poir.), D. alta. L., D. cayenensis Lam., D. esculenta(Lour.) Birk., roots of cassava (Manihot utilissima Poh!.), cormelsof cocoyam (Xanthosoma sagittifolium Schott.), fruits of plantain(Musa paradisiaca L.) together with starches from sorghum(Sorgho ROF) and millet (SOUNA II) were tested for suscep­tibility of the ungelatinized granules to the action of bacterialalpha-amylase, fungal glucoamylase and malt diastase. Thoughall starches were found more resistant to enzymatic degradationwhen compared with starch extraded from the Canadian hard redspring wheat, considerable differences were observed betweenindividual starches. Among non-cereal starches, cassava starch wasfound the most susceptible one, whereas large granule yam andplantain starches did not show any significant degree of digestioneven after 48 hours treatment with the enzymes.

Scanning electron microscopy revealed that the mode of theenzymatic attack on the granules of cassava and cocoyam starch­both being composed starches, differed from that on cereal starchgranules. The reduction of the diastatic activity of compositeflours, in which wheat flour was replaced by less susceptiblestarches, reflected in a lower CO2 production in sucrose-freedoughs during fermentation.

Des recherches ont ete effectuees pour demontrer I'activiteamylolytique de l'a-amylase d'origine bacterienne, de la gluco­amylase produite par certaines moisissures et de la diastase dumalt sur des granules non-gelifees d'amidons provenant detubercules de certaines espeoes de genre Dioscorea (D. rotunda,Poir., D. alata L., D. cayenensis Lam., D. esculenta (Lour.) Birk.,de tubercules de manioc (Manihot utilissima Poh.), de tuberculesde taro Xanthosoma sagittifolium Schott.), des fruits de plantain(Musa paradisiaca L.), ainsi que des amidons de sorgho (SorghoROF) et de millet (Souna II). Bien que tous les amidons furenttrouves plus resistants it une degradation enzymatique par rapportit l'amidon de ble canadien de type dur-rouge printemps, detres grandes differences furent observees ootre les amidons con­sideres. Parmi les amidons ne provenant pas de cereales, I'amidonde manioc fut Ie plus facilement attaque, tandis ques les amidonsde taro et de plantain ne presenterent aucun signes de degradation,meme apres 48 h de traitement enzymatique. La technique de lamicroscopie electronique it balayage montra que Ie mode d'attaqueenzymatique sur les granules d'amidons de taro et de manioc ­les deux etant des amidons composes - differait de celui sur lesgranules d'amidons de cereales. La reduction de I'activitediastatique sur des farines composees, dans lesquelles la farinede ble etait remplacee par des amidons mains sensibles, se refletapendant la fermentation par une production plus basse en CO2dans des pates sans sucre.

Abstract

Resume

V. Rasper, G. Perry, and C. L. DuitschaeverDepartment of Food Science

University of GuelphGuelph, Ontariu

reflect not only the actual enzymatic activity of thesample, but also the amylolytic susceptibility of un·gelatinized starch granules. This susceptibility isdetermined primarily by the inherent resistance of thestarch granules, but is further influenced by variouschemical and mechanical factors. Amongst them, thephysical damage of the granules as it occurs duringthe process of milling or grinding has to be consideredas the predominant one.

Many research workers have reported differencesin the amylolytic susceptibility of starches of differentorigin and attempted to find some exploration fortheir specific behavior (Sandstedt, 1954, Badenhuizen,1955, 1965 and 1971; Schoch and Leach, 1961; Eversand McDermott, 1970; Evers et al., 1971; Gallant etal., 1973). Though it is obvious that the differences inthe primary resistance of the intact granules dependon the genetically inherited degree of molecular asso­ciation within the granule, there is still more know-ledge required to ellucidate the relation between thestrength and type of this molecular association andvarious properties of the granules including theirresistance to enzymatic attack.

Cereal starches in ungelatinized form are knownfor their lesser resistance to the enzymatic degrada­tion compared with starches of other origin. However,if wheat Hour in a composite blend is partially re­placed by a root or tuber starch, it has to be expectedthat the total amylolytic susceptibility of the mixturewill be reduced not only due to a lower inheritedprimary susceptibility of non-cereal starches, but alsodue to a lower degree of physical damage of theirgranules. Tuber or root starches are usually preparedsimply by the water extraction of grated pulp withoutbeing subject to any heavy shearing or any other forcedue to milling. Though severe damage of starchgranules changes the baking quality of the flour veryunfavorably, a certain degree of damage may even bedesirable to obtain the required "diastatic activity" forthe optimum baking performance (Farrand, 1964;Tipples, 1969; Lorens and Johnson, 1970; Dodds,1971).

In the present study, several starches of WestAfrican origin were tested for their amylolytic suscep­tibility both in vitro using pure starch suspensionsand in mixtures of a typical bread flour and therespective starch. Functional properties of thesestarches, including their effect on the baking qualityof the wheat flour/starch mixtures, were reported inPart I of this paper.

J. Inst. Ca.n. SCI. Techno!. Aliment. Vo!. 7, No.3, 1974

Materials and MethodsThe origin of all starches used in this study and

their preparation was described in Part I of this paper.Cereal starches apart from those prepared from flours,were also prepared directly from debranned grainsafter a proteolytic treatment (Evers et al.) 1971),making it possible to obtain starch granules free fromdamage. The grains were mechanically debranned withthe Palyi dehulling unit (deMan, 1973). All starches,vere tested for physical damage using a c'Olorimetricmethod according to Williams and Feg-ol (1969).

To estimate enzyme susceptibility of starchgranules in vitro a procedure similar to that of Leachand Schoch (1961) was used. Starch suspensions wereprepared by suspending 0.5 g of pure starch (drysolids) in 10 ml of the appropriate buffer solution and5 ml of the enzyme solution. To prevent micro­organism contamination and growth during the diges­tion period, three drops of toluene were added. Thestarches were allowed to digest at 30°C for 24 and 48hours with constant shaking. At the end of the diges­tion period, 1 ml of 10% H 2S04 and 1 ml of 10%sodium tungstate solution were added and the volumeof the suspension was made up to 100 ml with distilledwater. After centrifugation, reducing sugars in theclear supernate were determined colorimetrically bythe Folin-Wu method (AOAC, 1970) and their concen­tration expressed in terms of maltose equivalent (%maltose on starch dry solid basis).

The following enzyme preparations were used:Bacterial alpha-amylase (BDH Chemicals Limited,approx. 10 EU per mg, M/15 phosphate buffer, pH6.24) ; fungal amy}oglucosidase (Sigma Chemical Com­pany, U.S.A., Grade II, acetate buffer, pH 5.0) ; maltdiastase (BDH Chemicals Limited, approximately 0.8to 1.0 EU per mg, acetate buffer, pH 4.8).

The activities of all these enzymes were tested ona soluble starch solution under the conditions identicalto those of the actual tests on ungelatinized granules.Since the preparations differed in their activities, theconcentrations of the individual enzymatic solutionsapplied to the starch suspensi'ons were adjusted so thatall suspensions were exposed to the same enzymaticactivity. The activity of the alpha-amylase solution(1% enzyme dosage on starch solid basis) was taken asstandard.

All starches and enzymes were tested for reducingsugars and necessary corrections were made in thecalculation of the maltose equivalents.

The susceptibility of tested starches to wheatdiastatic system was studied on mixtures of wheatflour (commercial bread flour milled from CanadianHard Red Spring wheats and kindly supplied byMaple Leaf Mills Limited, Port Oolborne, Ontario)and respective starches. In these mixtures, 15% flourdry solids was replaced by an equivalent quantity ofstarch dry solids. Reducing sugars produced after 1hour digestion at 30°C and pH 4.8 were determinedUsing AACC 20-15 Method (AACC, 1965) and expres­sed as "maltose figure" (mg maltose/10 g flour).

The CO2 production during the fermentation of

Can. Inst. Food ScI. Technol. J. Vol. 7, No.3, 1974

doughs prepared from composite blends containing20% added starch was tested volumetrically using amethod described by Kent-Jones and Amos (1967). Thedoughs were prepared with constant moisture absorp­tion (64%, 14% m.b.) using straight dough formula(AACC, 1965) without adding any sucrose.

Starches separated from the liquid phase by cen­trifuging at the end of the in vitro digesti'On experi­ments were thoroughly washed with water thensuction-filtered and serially dehydrated in ethanol toprevent agglomeration of the granules (Yamazaki andWilson, 1964). After final drying at temperatures notexceeding 40°C, the particles were prepared for scan­ning electron microscopy by mounting on specimenstubs, the surface of which was made sticky by apply­ing a very thin layer of a solution obtained by soakingScotch tape in chloroform. The specimens were thencoated with a thin layer of carbon (20 to 50 A)followed by approximately 200 to 300 A of gold. Theywere examined in ETEC Autoscan at acceleratingvoltages of 10 to 20 kV and a tilt of 45°.

Results and DiscussionThe results 'of the tests on pure starches treated

with three different enzymes are graphically presentedin Figures 1 and 2. These diagrams sho)v clearly thelower resistance of cereal starches to enzymatic de­gradation as compared to the resistance of the starchesextracted from roots, tubers or fruits. As expected,wheat starch had the lowest resistance. In agreementwith results reported by Leach and Schoch (1961) andRasper (1969), a relatively high susceptibility to alphaamylase as well as glucoamylase was observed withcassava starch. The maltose equivalents obtained forthis starch after treatment with enzymes were notonly much higher than those for any other non-cerealstarch, but after a two-day digestion period, they evenexceeded those obtained for sorghum and millet starch.However, this relatively high degree of enzymaticdigestion of cassava starch was not observed whenmalt diastase was used. In this case, cassava starchgranules still exhibited a slightly lower resistance tothe enzymatic attack than any non-cereal starch, butthe degree of the degradation did not exceed that ofsorghum or millet starch.

Amongst the other non-cereal starches tested, thelarge granule yam (Dioscorea) starches from tubersof D. rotundata Poir., D. alata L., D. cayenensis Lam.,as well as from fruits of plantain (Musa paradisiacaL.) having the median SED (Stoke's equivalent diam­eter) in the range of 27 to 35 microns, were found themost resistant ones. Small granule yam starch fromthe granules of D. esculenta (Lour.) Birk. (medianSED 7.6 microns) yielded a markedly higher quantityof reducing sugars during the digestion period, givingthus evidence of a higher rate of enzymatic digestion.It has been pointed out by several workers (Schwim­mer, 1945; Leach and Schoch, 1961) that there is norelation between the enzymatic susceptibility and theexternal surface area of the granules. However, resultsobtained in an earlier study (Rasper, 1969) indicatedthat the small granule yam starches were less resistant

167

Fig. 1. Degradation of pure starches in vitro with differentenzymes after 24 hours at 30 o e.

to the enzymatic attack than yam starches character­ized by larger granules. The present results supportthe earlier findings.

Apart from the above mentioned higher relativeresistance of cassava starch to the malt diastaseaction, the diagrams did not show any significantpreferential susceptibility of any tested starch to anyenzyme used. The only exception was D. esoulentastarch, which was found distinctly less resistant tofungal glucoamylase than to bacterial alpha-amylase.With all other starches, the degree of degradation bybacterial alpha - amylase and fungal gluC'oamylaseunder the given test conditions was of the samemagnitude. As expected, treatment of the starches withmalt diastase gave overall lower maltose equivalentsthan treatment with the other two enzymes.

Cereal starches used in the above discussed testswere all extracted from flours. To find out how theresults of these tests might have been affected by thepossible damage of the starch granules due to milling,starches extracted from flours were tested for damageand compared with those prepared from proteolyticallytreated grains. Using a colorimetric method for starchdamage determination, higher values of absorbanceindicating a higher degree of damage were obtainedwith flour starches (Table 1). In accordance with this,flour starches also showed higher values of maltoseequivalents. However, the differences were not of thatmagnitude to change the pattern of relative suscep­tibilities of individual starches as shown in Figures1 and 2.

In the starch damage tests on the non-cerealstarches, the absorbances for all samples were sig­nificantly lower than those for cereal flour starches;the lesser degree of granule damage was quite evident(Table 2).

Scanning electron microscopy revealed not onlythe differences in the resistance to the enzymaticattack between the individual starches but als'o thedifferences in the mode of attack on the granules ofdifferent origin. However, with the highly resistantstarches, SEM appeared somewhat less sensitive thanthe chemical method based on the determination ofreducing sugars in the supernatant. Though the lattergave positive results even with starches from D. rotun­data, D. alata and D. oayenensis, with SEM it wasvery difficult to find any granules of these starcheswhich would show a detectable degree of surfaceerosion due to the enzymatic attack (Figure 3). Eventhe pictures of D. esculenta starch which was foundthe most susceptible among the tested yam starchesdid not show anJ distinct signs of any surface changesdue to the enzymatic attack. On the other hand, coco­yam and cassava starch - both of them being composedstarches, changed their appearance during the diges­tion period quite considerably (Figure 4). The differ­ence between the mode of enzymatic attack on thegranules of these starches and on those of cereal originwas quite obvious. While the erosions on cerealgranules appeared as discrete and more or less circularholes penetrating through several layers of the granule

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168 J. Inst. Can. ScI. Te<:hnol. Aliment. Vol. 7, No.3, 1974

Table 1. Comparison of starches extracted from flours and en zyme treated grains.

Source of

Starch Absorbance

at 555 /.till

Starch extracted from flour Starch extracted from enzyme treated grains---

Maltose equivalent 2-days Absorbance Maltose equivalent 2-days

a-amylase glucoamy- malt diastase at 555 /.tm a-amylase glucoamy- malt dia-lase lase stase

Wheat(HRS)

Sorghum(Sorgho-ROF)Millet(Souna-II)

0.250

1.IlO

0.860

9.44

3.04

3.72

10.16

2.95

3.02

2.80

1.18

1.00

0.010

0.035

0.027

5.20

2.58

3.09

6.69

2.6i

2.85

1.62

Table 2. Granule damflge of non-cereal starches as determinedcolorimetrically.

0.0180.0100.0200.0100.1430.026

Absorbance at 555 mSource of starch

Cassava-Mllnihot utilissima Pobl.Yam-Dioscorea rotundata Poir

Dioscorea alata L.Discorea cayenensis Lam.

Cocoyam-Xanthosoma sagittifolium Schott.Plantain-Musa paradisiaca L.

starch as shown in Figure 6.The enzymatic activity in all these in vitro experi­

ments was evidently much higher than what can beexpected in flours milled from sound materials. Forexample, the applied concentration of a-amylase wasequivalent to approximately 100 units per 1 g of starchdry solids. An enzymatic activity of this magnitude isonly characteristic of wheat which has undergone aconsiderable degree of sprouting (Kneen and Hads,

into its interior (Figure 5), no erosions of this type 1945; Fleming et al.} 1960; Dronzek et al.) 1972). Thewere found on either cassava or cocoyam starch determination of "maltose figures" of composite mix-granules. The enzymatic action changed the whole tures, in which 15% ,of wheat flour was replaced by thesurface of the attacked granules. By corroding the particular starch, gave a better picture of the condi-surface, the enzymes gave them a sponge-like appear- tions in the actual composite flour .system (Figure 7).ance, but the micrographs did not give any clear These results indicated to what extent the susceptibili-evidence of the enzymatic penetration deeply into the ties of different starches might affect the diastaticgranules. Though Evers and cIO-workers (1971) have activity of a composite blend at the given replacementshown that glucoamylase action on wheat starch level. Any partial replacement of wheat flour by andiffers from that of a-amylase, the electron micro- unmodified starch must inevitably result in a lowergraphs in Figure 4 suggest that the action of these "maltose figure" as determined by the method usedtwo enzymes on cassava starch follows a similar simply because of the reduction of the wheat diastasepattern. No difference was found in the action of these concentration. Though this reduction was the sameenzymes on cocoyam starch either. The selective action with all tested mixtures, their "maltose figures" dif-of the enzymes was also quite evident. While some fered quite markedly reflecting thus the differencesgranules were ver! severely attacked by the enzymes, between the individual starches with respect to theirsome others remamed unchanged even after 48 hours susceptibility to wheat diastase. The results were in aof incubation. This was most obvious with wheat good agreement with those from in vitro experiments.

Table 3. The effect of various starches in composite flours (20% wheat flour replacement) on the CO. production during doughfermentation.

Time Wheat Origin of starch in composite flour(min) flour Yam

only Wheat HRS Sorghum Millet Cassava (D. rotundata) Plantain Cocoyam

ml L:,ml ml L:,ml ml L:,ml ml L:,ml ml L:,ml ml L:,ml ml L:,ml ml L:,ml

0 0 0 0 0 0 0 0 033 35 35 33 33 28 29 33

30 33 35 35 33 33 28 29 3340 30 32 33 30 33 32 31

60 73 65 67 66 63 61 61 6434 27 28 28 24 26 25 23

90 107 92 95 94 87 87 86 8752 48 52 42 51 45 48 51

120 159 140 147 136 138 132 134 13865 60 61 58 59 59 58 58

150 224 200 208 194 197 191 192 19667 72 72 67 73 70 70 72

180 291 272 280 261 270 261 262 26884 88 78 71 75 73 74 75

210 375 350 358 332 345 334 336 34375 79 75 74 79 81 77 78

240 450 429 433 406 424 415 413 421

Can. rnst. Food ScI. Techno!. J. Vo!. 7. No.3. 1974 169

3 (a)

3 (b)

Fig. 3. Scanning electron micrographs of Dioscorea starches.a) D. rotundata Poir, a-amylase, 48 hoursb) D. alata, L., a-amylase, 48 hours

170

3 (c)

3 (d)

c) D. cayenensis Lam., a-amylase, 48 hoursd) D. esculenta (Lour). Birk., glucoamylase, 48 hours.

J. Inst. Can. Sci. Technol. AIlment. Vol. 7, No.3. 1974

4 (a)

4 (b)

4 (c)

Fig. 4. Scanning electron micrographs of some non-cerealstarches.a) Cassava (Manihot utilissima Pohl.) starch,

a-amylase, 48 hoursb) Cassava (Manihot utilissima Pohl.) starch,

amylase, 48 hours

Can. lnst. Food Sci. Techno!. J. Vo!. 7, No.3, 1974

c)

d)

4 (d)

Co.~oyam (Xanthosoma sagittifolium Schott.) starch,a-amylase, 48 hoursCocoyam (Xanthosoma sagittifolium Schott.) starch,a-amylase, 48 hours

171

5 (a) 5 (c)

Fig. 5.

172

5 (b)

Scanning electron micrographs of some cereal starches.a) Sorghum (Sorgho ROF) starch, malt diastase,

48 hoursb) Sorghum (Sorgho ROF) starch, a-amylase, 48 hours

c)d)

5 (d)

Millet (Souna II) starch, no treatmentMillet (Souna II) starch, a-amylase, 48 hours.

J. Inst. Can. Sci. Techno!. Aliment. Vol. 7, No.3. 1974

starch.Fig. 7. "Maltose figures" of mixtures containing 15% added

COMPOSITE BLENDSW. flOUR + 15% PURE STARCH

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To get a better picture about the effect of thetested starches on the process of dough fermentation,CO2 production tests were run on doughs from mix­tures in which 20% of wheat flour was substituted bypure starch. All doughs showed first a rapid initialrise for the first 30 to 45 minutes which was obviouslydue to the digestion of the damaged starch. Whendata in Table 3 were compared with those in Tables1 and 2, it became obvious that this initial rise wassteeper with doughs containing more damaged starch.After the noticeable slowdown in the following 30 to45 minutes, the volumes started to increase again ata rate depending upon the type of starch used aswheat flour substitute (Table 3). More marked dif­ferences were noted after punching which followed thefour-hour fermentation (Table 4).

ConclusionsReplacement of wheat flour by a non-wheat starch

in bread dough system, especially by one of non-cerealorigin, may considerably affect the diastatic activityof the mixture at replacement levels of 15 to 20%which are obviously the most common replacementin which wheat flour was replaced by starches fromnon-cereal sources were found to have a reduced dias­concentrations in composite flours. All tested mixturestatic activity due to both a higher primary resistanceof the starch granules and a lower degre€ of theirphysical damage. Sorghum and millet starches ex­tracted from flours were found less susceptible toenzymatic action than wheat flour starch, in spite of arelatively high degree of the granule damage. This in­dicated a considerable difference in the inherited sus­ceptibilities of these cereal starches. Among the non­cereal starches, cassava starch was found the leastresistant when treated with bacterial alpha-amylaseor fungal glucoamylase in vitro. However, its higherresistance to wheat diastase, similar to that of othernon-cereal starches, was obviolls from the results of theexperiments on actual composite flours.

6 (a)

6 (b)

Fig. 6. Scanning electron micrographs of wheat (hard redspring) starch.a) a-amylase, 48 hoursb) gIucoamylase, 48 hours.

Can. Inst. Food ScI. Techno!. J. Vo!. 7. No.3, 1974 173

Table 4. The effect of various starches in composite flours (20% wheat flour replacement) on the CO2 production after the firstpunch following the four hours fermentation.

Time Wheat Origin of starch in composite flour

(mins) flour Yamonly Wheat HRS Sorghum Millet Cassava (D. rotundata) Plantain Cocoyam

ml .0,ml ml L,ml ml L,ml ml L,ml ml L,ml ml L,ml ml .0,ml ml L,ml

0 0 0 0 0 0 0 0 049 38 36 36 22 21 22 24

30 49 38 36 36 22 21 22 2423 19 20 21 17 15 16 17

60 72 57 56 57 39 36 38 4120 14 19 19 12 11 12 12

90 92 71 75 76 51 47 50 5318 17 12 12 12 13 14 11

120 110 88 87 88 63 GO 64 6415 16 10 12 10 12 11 11

150 125 104 97 100 73 72 75 7512 13 8 12 9 6 8 8

180 137 117 105 112 82 78 83 82

AcknowledgementsThe authors are indebted to Mrs. J. Rasper for

laboratory assistance and to Mr. G. L. Mabey, Depart­ment of Nutrition and Food Science, University ofGhana, for providing the plant material for starchextraction. The financial support from the NationalResearch Council of Canada (Operating Grant No.A6453) is greatly appreciated.

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Received October 9, 1973

J. Inst. Can. Sci. Techno!. Aliment. Vol. 7, No.3, 1974