Maria Janete Angeloni Marcona

Diego Jacob Kurtza

Josiane Callegaro Raguzzonib

Ivonne Delgadillob

Marcelo Maraschinc

Valdir Soldid

Valéria Reginattoa

Edna Regina Amantea

a Department of Food Scienceand Technology,Federal University ofSanta Catarina, Florianópolis,Santa Catarina, Brazil

b Department of Chemistry,Aveiro University,Aveiro, Portugal

c Plant Morphogenesisand Biochemistry Laboratory,Federal University ofSanta Catarina, Florianópolis,Santa Catarina, Brazil

d Department of Chemistry,Federal University ofSanta Catarina, Florianópolis,Santa Catarina, Brazil

Expansion Properties of Sour Cassava Starch(Polvilho Azedo): Variables Related to its PracticalApplication in Bakery

Sour cassava starch (polvilho azedo) is a chemically and enzymatically modified starchwith the specific property of expansion in bakery products without the use of anychemical or biological leavening agents. In this work, the cumulative knowledge aboutsour cassava starch is presented in relation to its physicochemical characteristics, withthe purpose of establishing a relation between the application properties and somestructural and chemical characteristics in order to design a model of the modifiedstructure of starch and the most important technical variables. Such approach will helpto provide some quality standards for future adequate valorization of sour cassavastarch, especially with respect to potential use in gluten-free products. This workshowed that a good sour cassava starch is significantly different from low expansioncassava starches with respect to pH, acid factor, swelling power, specific volume, andpolymerization degree (intrinsic viscosity). These variables could be related to themaximization of sour cassava starch expansion for a future predictive decision analysisabout a high quality sour cassava starch to the baking use.

Keywords: Cassava; Expansion; Fermentation; Polvilho

716 Starch/Stärke 61 (2009) 716–726

1 Introduction

Cheese bread and sour cassava starch roscas are twotypical Brazilian products from “polvilho azedo”. This glu-ten-free raw material is produced from cassava starch bychemical and enzymatic modification through a predomi-nantly natural fermentative process [1]. The rheologicalproperties of this natural polymer, such as expansion—the leavening of a dough to two or more times its initialvolume without any addition of yeast—is attributed to itsmain ingredient: sour cassava starch. The substitution ofpolvilho azedo with native cassava starch results in adough with significantly lower expansion [1].

The expansion of sour cassava starch has been exhaus-tively studied [2-10]. Results from these investigationsshowed that the method of drying had a strong influenceon the degree of expansion. Mechanical drying resulted ina significantly lower expansion than sun-drying. It wasproven that the ultraviolet radiation contributed to granulechanges in the fermented cassava starch. On the otherhand, only exposure to sunlight without fermentation or

lactic acid addition was not sufficient to achieve thedesirable expansion properties of the product [10].

Organic acids produced during the fermentative processof cassava starch, predominantly lactic acid, influencedthe sensory properties of the product and contributed tosignificant pH reduction. The starch polymers underwentextensive changes during fermentation [11]. Granulesbecame perforated [1] and the natural amylose/amylo-pectin ratio changed. Besides, the polymerization degreeof the remaining amylose and amylopectin was reducedin the granules [7, 8, 11, 12].

However, current knowledge on sour cassava starchproperties is not sufficient to reliably predict its behavior inbakery products from its chemical characteristics. This isattributed to the lack of definitions on granule character-istics and their effects on dough formulated with sourcassava starch. The objective of this work was to developa chemical scenario of the sour cassava starch expan-sion, which can help to explain the properties expectedby the bakers. It was also attempted to establish anyrelation between physicochemical variables and expan-sion property by a structural model of the sour cassavastarch expansion mechanism, contributing to a futuredecision model to maximize expansion.

Correspondence: Edna Regina Amante, Federal University ofSanta Catarina - Food Science and Technology, Rod Admar Gon-zaga, 1346, Itacorubi Florianópolis Santa Catarina 88034001,Brazil. Phone: 155-48-37215371, Fax: 155 48 37219943, E-mail: eamante@cca.ufsc.br.

© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.starch-journal.com

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DOI 10.1002/star.200900132

Starch/Stärke 61 (2009) 716–726 Effect of Physical-chemical Parameters on Sour Cassava Starch 717

2 Materials and Methods

2.1 Materials

Two samples of native cassava starch from two com-mercial trade marks (samples FMK and FMY) purchasedfrom the local market were mixed, homogenized, andweighed in triplicate. Sour cassava starch samples wereproduced through fermentation in laboratory, simulatingthe industrial process, modified reducing the fermenta-tion time to achieve low expansion performance. Thenative cassava starch samples were distributed intoplastic containers, a volume of water equivalent to two-fold of the mass of the cassava starch was added as wellas 0.5% (w/v) glucose syrup over the volume of water[13]. Anaerobic fermentation occurred at ambient tem-perature, similar to the process in industry, in threerepetitions by each fermentation vat, in randomizedplace of the laboratory. After fermentation, the fermentedstarch of each container was divided into two parts: thefirst one was sun-dried (PASSOL sample) in triplicate thesecond dried in a forced-air oven (PASE sample) (Fabbe)at 457C, also in triplicate. All the dried samples werepacked in low density polyethylene bags and stored atroom temperature until required for the analysis. Allreagents used were of analytical grade. A mix of threeindustrial sour cassava starches, preferred by bakers asthe best products, was used as reference. This samplewas named “polvilho azedo” (PAM). Industrial “Polvilhoazedo” mix and “sour cassava starch sun-dried” fer-mented in laboratory were both sunlight dried samples.

2.2 Physicochemical characterization of thegranules

Moisture and total ash content were analyzed accordingto AOAC method, 921.10 and 923.03, respectively [14].pH values were measured by using a pH meter (modelQ400A, Quimis, Diadema, São Paulo, Brazil). Acid factorwas determined with 25 g samples, with addition of up to50 mL of distilled water. The suspension was titrated witha standard 0.1 M aqueous HCl to pH 3.0 under agitation.The acid factor corresponds to the volume of acid con-sumed [15].

2.3 Absolute density

Absolute density of starch granules was determined byxylene displacement method in a pycnometer at 307C,according to Schoch and Leach [16].

2.4 Baking expansion capacity

The determination of baking expansion capacity followedthe procedures proposed by the CERAT – Tropical RootCentre [17]. Biscuits were formulated with 50 g of samplewith 40 mL boiling water for the production of dough. Thedough was divided into five balls of approximately 10 gand baked at 2007C for 25 min in an electrical oven. Theball diameter was measured with a pachymeter beforeand after baking. Baking expansion capacity was calcu-lated by using the relation between the initial medial di-ameter of the balls before baking and the final medial di-ameter after baking (evaluated at several places of thecooked ball irregular form) [18]. All the measurementswere performed in triplicate.

2.5 Specific volume

Specific volume of the biscuits was determined by therape seed displacement method [19] and calculated asdisplacement/weight (cm3/g).

2.6 Solubility and swelling power

These properties were evaluated at 907C, as described byLeach et al. [20] with modifications. The analysis wascarried out in 50 mL leak proof centrifuge tubes, by takinga suspension of starch in deionized water (0.4 g starchand 36 g deionized water) in water bath under agitation atthe selected temperature. After 30 min for cooling, thevolume was completed until obtaining 40 g and cen-trifuged (3,000 rpm/20 min), collecting the supernatantthat was dried for soluble fraction quantification. The pel-lets containing the swollen starch granules were weighedand the ratio between the final mass and the initial drymatter was considered as the swelling power. The solu-bility was expressed in weight percentage and the swel-ling power in weight increase.

2.7 X-ray diffractometry

The X-ray diffraction patterns of the starch samples weremeasured through the powder method using a PhilipsX’Pert diffractometer (Philips, Eindhoven, Netherlands)under the following conditions: Cu Ka radiation, with l0.154056 nm and measurement range 2 to 407. Scanningspeed was 0.057/s.

2.8 Thermal analysis

The thermal properties of the samples of the starches wereexamined by using a differential scanning calorimeter

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718 M. J. A. Marcon et al. Starch/Stärke 61 (2009) 716–726

(DSC) DSC-50 (Shimadzu, Kyoto, Japan). A starch sample(3.4 mg) was weighed in an aluminum DSC pan and deio-nized water was added to obtain a 30% starch suspen-sion. The lid was carefully put on and hermetically sealedusing sealing tools. To check for water leakage due toimproper sealing, the weights of the sealed pans wererecorded before and after determination. The pans werekept overnight before determination. The sample pan wasplaced carefully in the DSC and was heated at 107C/min,from 20-2207C. An empty pan was used as reference andthe instrument was calibrated using indium. Endothermalcurves showing gelatinization onset, peak, and end tem-peratures (7C) and transition enthalpy (J/g sample weight)of the starch sample were recorded.

2.9 Intrinsic viscosity

The intrinsic viscosity of the cassava starch samples wasdetermined according to the Leach method [21], meas-ured with a thermostatized viscosimeter Schott, AVS 350,CT 52 (Mainz, Germany), at constant temperature (307C),capillary diameter 0.63 mm, capillary constant (K) of0.01511 mm2/s. Solutions of the samples with con-centrations of 0.002, 0.003, 0.004, 0.005, 0.006 and 0.007g/mL were prepared in 0.1 M aqueous KOH. To determinethe flow time of the solvent (0.1 M aq. KOH) and of thestarch solutions, exact 10 mL of solutions were trans-ferred to the 100 mL tube viscosimeter. Specific viscositywas calculated by Equation (1).

Zsp = (Z/Zo-1) = (t/to-1) (1)

Where: Zsp= specific viscosity; Z = viscosity of starch so-lution; Zo= viscosity of solvent (0.1 M aq. KOH); t = flowtime of starch solution; to= flow time of solvent.

The intrinsic viscosity was determined from the extra-polated intersection of the specific viscosity curve withthe y axis.

2.10 Design of chemical model of the sourcassava starch expansion mechanism

Starch granule was studied from the most recently pub-lished models of native granule structure [22, 23], withadaptations according to the changes that occurred dur-ing the fermentation and the sun-drying of sour cassavastarch and industrial samples of polvilho azedo, whichresult in the expansion property of the product.

Based on the data reviewed and collected in this work, amodel to predict the performance of the dough can beproposed, according to its physicochemical parameterssignificantly related to its expansion property. To make

easier future intents of determining the best sour cassavastarches, according to physicochemical properties, somevariables were proposed as negatively or positively re-lated to the maximization of the sour cassava starchexpansion in bakery.

2.11 Attenuated total reflectance-Fourier-transform infrared spectroscopy (ATR-FTIR) and chemometrics

FTIR spectra of cassava starch samples were acquiredusing a golden gate single reflection diamond attenuatedtotal reflectance (ATR) accessory in an IFS-55 spectrom-eter (Bruker, Rheinfelden, Germany). A backgroundspectrum of the clean crystal was acquired and sampleswere spread and measured directly after pressing themon the crystal. The spectra were recorded at the absorb-ance mode from 4000 to 600 cm-1 at the resolution of 4cm-1. Ten replicate spectra (128 co-added scans beforeFourier transform) were collected for each sample, in atotal of 55 spectra. The measured spectra were normal-ized, baseline corrected, and transferred via a JCAMP.DXformat (OPUS v. 5.0, Bruker Biospin) into the data analy-sis software for PCA (The Unscramble v. 9.1). Previouslyto PCA analysis each spectrum within the 3000-600 cm-1

region was standard normal deviates corrected [24].

2.12 Statistical analysis

Physicochemical parameters were determined in tripli-cate for each sample and assay. The results wereexpressed in mean 6 SD. Averages were compared byvariance analysis and when the difference was significant,means were analyzed by Tukey test (p, 0.05%). All starchsamples were analyzed in triplicate (n = 3).

3 Results and Discussion

3.1 Physicochemical characterization of thestarch granules

Sour cassava starch expansion mainly results from theperforations in the fermented granules, formed by theaction of amylolytic enzymes, which firstly attack theamorphous zones of the granules. Part of the amylosediffuses out of the starch granules during wet processing,which occurs with the excess water used in the produc-tion of sour cassava starch [1, 6, 8]. Amylose diffusionduring the fermentation process makes new regionsavailable for enzymatic attack inside the granules. Thegranules of native cassava starch are unaltered and the

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Starch/Stärke 61 (2009) 716–726 Effect of Physical-chemical Parameters on Sour Cassava Starch 719

native starch does not show any expansion property.Therefore, there is a relation between these changes inthe granules and the expansion property.

Sour cassava starch granules also have a lower granuledensity than native cassava starch and there is an inverserelation between granule density and expansion capacity.Tab. 1 shows physicochemical parameters of native cas-sava starch, industrial polvilho azedo, as well oven-driedand sun-dried sour cassava starch.

Cassava starches are sufficiently different to show thatfrom cassava root can be produced starch granules withdiverse characteristics. Native cassava starch sampleswere analyzed separately (samples 1 and 2) due to thenatural variability of starch granule diameter, around 0.5up to 20 mm [25]. This difference can be important instarch properties and it is an example of what can occurin the industrialization of starch, where several starchgranule sizes and structural compaction can influence onits use.

Physicochemical parameters are important to show thedifference between fermented and non-fermented star-ches. At the same time, native cassava starch 2 showsseveral parameters that were statistically similar to thoseof the polvilho azedo, sun, and oven-dried sour cassavastarches. Solubility, intrinsic viscosity, swelling power,absolute density, specific volume, and expansion werestatistically different between natives and sour cassavastarches. The effect of the sun drying was meaningful onspecific volume and expansion, which shows that theseparameters are important for the properties of sour cas-sava starch in bakery.

Granule density, shown in Tab. 1, generally decreasedafter fermentation. This effect could be due to part of theamylose molecules diffusing into the fermentation mediaand depolymerization. This is evidenced by the relationbetween granule density and solubility. Amylose andamylopectin are hydrolyzed to smaller molecules in starchfermentation. Native starch granules have a lower solu-bility than industrial fermented starch (polvilho azedo),due to presence of non-hydrolyzed amylose in the crys-talline region of the granules, while with the fermentedstarch amylose was partially released. The release ofamylose from starch granules decreases the solubilityand density, in oven- and sun-dried sour cassava starchsamples produced in the laboratory. Solubility of polvilhoazedo was higher than that to the fermented starches.Although amylose release during the starch gelatinizationprocess in excess water and heat supply is only cited inliterature, some studies have shown that amylose contentdecreases during sour cassava starch processing atambient temperature [6, 8]. Part of the dextrin moleculesare formed by amylose hydrolysis.

According to Tab. 1, expansion tends to increase withdecrease of pH. Soluble amyloses and other productsformed by starch fermentation contribute as carbonsource for the fermentation process producing lactic,butyric, propionic, and other acids responsible for low-ering of pH [26]. The reduction in pH establishes achemically modified environment in sour cassava starchgranules. While hydroxyl groups are predominant on thesurface of native starch granules [25], sour cassava starchalso contains carboxyl groups. These changes favoredboth the progress of hydrolysis during the sun-drying

Tab. 1. Physicochemical characteristics of cassava starch, industrial (polvilho azedo – PAM), oven-dried (PASE), and sun-dried (PASSOL) sour cassava starches.

Parameters Samples

Cassavastarch(FMK)

Cassavastarch(FMY)

Oven-dried sourcassava starch(PASE)

Sun-dried sourcassava starch(PASSOL)

Polvilho azedo(PAM)

Moisture [g/100 g] 12.5660.12c 11.7260.14b 9.4960.44a 12.5160.27c 14.1960.19dAsh [g/100 g] 0.1260.01b 0.1260.01b 0.0760.01a 0.0860.01ab 0.1960.02cpH 6.1060.02e 4.9760.02cd 4.7660.47bc 4.3660.04b 3.7360.02aAcid factor [mL HCl] 1.7060.02a 2.0660.02b 1.5760.19a 1.5560.01a 2.8360.03dIntrinsic viscosity [mL/g] 196.22614.68c 176.9568.06bc 166.46616.31b 185.1761.10bc 93.4862.75aSwelling power [g/100 g] 34.9260.38c 31.3060.85bc 26.8961.07ab 30.4862.47abc 25,9961.09aSolubility [g/100 g] 27.8460.28b 32.1660.21b 21.8561.23a 22.0861.85a 36.1661.19cAbsolute density [g/cm3] 1.5660.04bc 1.6660.03c 1.4060.04a 1.4160.03a 1.5460.01bcSpecific volume [cm3/g] 2.4160.20a 2.3560.15a 2.5260.43a 5.5960.07b 10.0760.22cBaking expansion capacity 1.1360.01a 1.2360.01a 1.4660.02b 1.7460.14c 1.9960.07d

Mean values in the same line followed by different superscript letters are significantly different (P � 0.05).

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720 M. J. A. Marcon et al. Starch/Stärke 61 (2009) 716–726

process in an acid medium, increasing the granules’ fra-gility when compared to the native starches, as well aspossible secondary reactions involving new polymericunits [1].

Intrinsic viscosity that depends on the starch polymersmolecular weight [25], in this work, was statistically lowerin fermented cassava starches (Tab. 1). This result is indi-cative of the polymerization degree decreasing. Acidifica-tion and sun radiation (UV) contribute to the same freeradicals and similar extent of depolymerization [27]. Valuesfound for intrinsic viscosity by Bertolini et al. [28, 29] fornative cassava starch (169 mL/g) are similar to the resultsof the present work, where the samples PASE and PAS-SOL of sour cassava starch do not present characteristicof fermented starch, when analyzed by the changing in theintrinsic viscosity. Those samples are not significantly dif-ferent from the native cassava starch, but different from thesour cassava starch commercial sample (PAM). PAM is agood sourcassava starch and presented intrinsic viscosityvalues similar to those found in [29] (85.3 mL/g) for sourcassava starch and [28], where irradiated and acidifiedsamples were investigated (99 mL/g). Inherent character-istics of the starch granule can be a significantly factor todefine the depolymerization in fermentation and sun-dry-ing process of cassava starch. Native cassava starch hashigher intrinsic viscosity than sour cassava starch and isunsuitable to achieve expansion properties in bakery [28].

The results of moisture and ash determination are usefulto control the condition of drying and the presence of soilresidues from the starch processing; and the valuesobtained are in accordance with the quality of commercialcassava starch [15].

In order to gain more insights into to the effect of thetreatments on the structural changes of the cassava star-ches, infrared (IR) spectroscopy was used. In the past IRspectroscopy has been applied to study structural char-acteristics of amylose, amylopectin, and starch, forinstance, providing information on chain folding and theratio of ordered to amorphous fractions, e.g. [30-32]. TheFTIR spectra showed the presence of starch (1200-800cm-1), lipids (2924, 2854, and 1740 cm-1), and proteins(1650 to 1500 cm-1) in all the samples, while minor differ-ences, quantitative or structural, were difficult to detect.To extract useful information from the whole very complexspectra, multivariated data analysis was applied, partic-ularly the determination of the principal components(PCA) [33], was applied to the FTIR dataset of native cas-sava starch, polvilho azedo, sun- and oven-dried sourcassava starches. Such an analytical approach couldallow the characterization of the sample relationships(scores plans or axis) and the recovery of their sub-spectral profiles (loadings). PCA has been used effec-

tively in many studies as a data reduction technique, as itpreserves the total variance while minimizing the meansquare approximate errors, and is also used as a meansto identify dominant modes of data [34, 35]. The principalcomponents (PCs), describe the main sources of varia-bility of a dataset and in cases where the data containsmultiple sources of variation the PCs will point to theaverage directions that describe the overall variation.

Fig. 1 shows a PCA scores scatter plot using the wholeFTIR spectral window dataset (3000-600 cm-1) of samplesof native starches (FMK; FMY), polvilho azedo (PAM),oven-dried (PASE), and sun-dried (PASSOL) sour cassavastarches. The classification of the samples resulting fromthe PCA analysis of the IR dataset for the cassava starchrevealed that PC1 vs. PC2 contains 99% of the datasetvariability. Besides, a clear segregation of the commercialstandards of starch is noticed as two groups were detec-ted along PC1 axis. The loadings indicated that the prot-eins (1557, 1540, and 1506 cm-1) can be associated to thediscrimination of the cassava starches observed.

The results show that ATR-FTIR and PCA helped to iden-tify chemical structural changes in the cassava starches,leading to a better characterization of the differencesamong the samples and corroborating to predict, in anyextension, the behavior of the dough containing these rawmaterials. In other words, differences in expansion areexpected to occur when comparing native starches, pol-vilho azedo, oven-dried, and sun-dried sour cassavastarches as revealed by FTIR and PC analyses.

It is evident that sun-drying contributed to the positivechanges on the fermented starch granules, where reduc-tion of the polymerization degree occurs proportionally tothe magnitude of ultraviolet radiation. The use of varieddoses of radiation in this range of wavelength revealed areduction of the fermented granule amylose and a short-ening of amylopectin molecules [10, 27, 28, 36-38].

3.2 Differential scanning calorimetry

The cohesion in the structure of the cassava starch gran-ules was examined by differential scanning calorimetry(DSC). The results of DSC for the cassava starch aqueoussuspensions are shown in Tab. 2 and are in the range ofvalues reported by other authors. The values obtained byHuang et al. [39], Paes et al. [40], Peroni et al. [41] andSilva et al. [42] for the onset temperature of gelatinizationof samples of native cassava starch were: 61.6, 62.7,63.2, 64.5, 57.97C; Tpeak 66.68, 70.6, 66.57C and Tend

72.94, 78.7, 69.97C. For enthalpy changes the valueswere 10.4 J/g [41] and 11.5 J/g [40], other works reportedvalues from 8.5 to 6.5 J/g [43] for native cassava starchheating rates from 2.5 to 57C/min, respectively. Values

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Starch/Stärke 61 (2009) 716–726 Effect of Physical-chemical Parameters on Sour Cassava Starch 721

Fig. 1. PCA scores scatter plot of the FTIR dataset of cassava starch (FMK, FMY), polvilho azedo(PAM), oven-dried (PASE), and sun-dried (PASSOL) sour cassava starches. PC1 x PC2 axes crosseach other at the origin.

Tab. 2. Thermal analysis (DSC) of cassava starch (FMK, FMY), industrial (polvilho azedo PAM), oven-dried (PASE), andsun-dried (PASSOL) sour cassava starches.

Samples Gelatinization temperature [7C] Gelatinization enthalpy [J/g]

Onset Peak Endset

Cassava starch (FMK) 60.37 77.22 94.58 5.97Cassava starch (FMY) 61.91 77.20 108.10 7.46Cassava sour starch sun-dried (PASSOL) 63.65 75.44 90.46 2.75Cassava sour starch oven-dried (PASE) 64.06 76.18 96.59 3.85Polvilho azedo (PAM) 61.23 71.26 88.25 2.55

obtained to sour cassava starch are: Tonset 61.77C, Tpeak

69.47C, Tend 71.97C and DH 3.3 J/g [44].

In comparison to the gelatinization enthalpy values for thenative starches 1 and 2 (5.97 and 7.46 J/g, respectively),the drying process structurally modified the starch gran-ules, both in an oven and in the sunlight.

Despite their compacted nature, the native starchesshowed more pronounced differences in gelatinizationtemperature (range ,50 to 1207C) than the fermentedstarches. This behavior is evidenced by numerous works,showing differences in form, length, and X-ray diffractionpattern. Significant effects of cultivation region, weather,plant age, harvesting season, and several other parame-ters are typical for cassava starches [13, 22, 41, 45].

Gelatinization end temperature was another parameterthat differed among the starches, where the sample ofsun-dried sour cassava starch was more easily gelati-nized than the other samples (low gelatinization energy).

These results are indicative that the sour cassava star-ches show expansion property during baking due to thepartial degradation of the polymeric structure. In con-sequence of this depolymerization a structure is formedthat allows water to diffuse in during cooking, formingan alveolar structure. This behavior is not observed inthe native cassava starch probably because the gelati-nized starch retains water in a polymeric matrix that,along with the water in the dough formulation, formsstarch hydroxyl hydrogen bonds. In contrast, in the sourcassava starch, the hydrolyzed molecules derived fromamylose and amylopectin are predominant. Thesestarch hydroxyl-water bonds and organic acids alsosuffer changes during sun-drying.

3.3 X-Ray diffraction

Tab. 3 shows the main peaks found in X-ray diffracto-grams of cassava natives starch, polvilho azedo, and

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722 M. J. A. Marcon et al. Starch/Stärke 61 (2009) 716–726

Tab. 3. Cassava starches (FMK, FMY), industrial (polvilho azedo), oven-dried (PASE), and sun-dried (PASSOL) sour cas-sava starches, intensity of X-ray diffractograms principal peak intensities.

2 y Intensity

Cassava starchFMK

Cassava starchFMY

Oven-dried sourcassava starch(PASE)

Sun-dried sourcassava starch(PASSOL)

Polvilho azedo(PAM)

157 (14.987 – 15.037) 151 - 129 233 - 222 197 - 217 180 - 188 252 - 271177 (16.987 – 17.037) 150 - 144 252 - 239 242 - 246 186 - 215 288 - 286187 (17.987 – 18.037) 150 - 162 215 - 224 221 - 208 217 - 200 279 - 269237 (22.987 – 23.037) 140 - 115 187 - 169 182 - 168 169 - 154 170 - 210

oven- and sun-dried sour cassava starches. These resultsshow differences in angles and in peak intensity.

According to Atichokudomachai et al. [11], water has asignificant effect on the molecular properties of starch.Presence or absence of residual water can lead to for-mation of linear helicoidal chains and increase crystal-linity, giving changes in X-ray diffraction pattern. Starchgranules of cereals such as wheat, corn, and rice show anA-type diffraction pattern; tubers, such as potato, pos-sess a B-type pattern; and beans, pears, and cassavaexhibit a C-type pattern [46]. Biliaderis [47] reported thattubers, such as cassava and potato, and fruit, waxymaize, and retrograded starches show a B-type diffrac-tion pattern.

The starch studied in this work was classified accordingto the crystallographic pattern proposed by Mestres [48],in which starch granules show the following character-istics: type A – shows higher diffraction intensity peaks: 2y at 15, 17, 18, and 237; type B – at 5.6, 15, 17, 18, and 237

and type C is a mixture of types A and B.

The X-ray diffraction patterns of the starches studied areshown in Fig. 2. The same A-type pattern can beobserved for all samples. However, some alterations on2y angle can indicate crystallographic differences be-tween the samples, which are expected between thenative starches and are more accentuated in sour cas-sava starches. This characterizes these fermented gran-ules. However, uniformity in X-ray patterns among thecultivars of cassava starch, as cited in literature, was notobserved.

Bertolini et al. [28], Huang et al. [39] Franco and Ciacco[49], Hoover and Gunaratne [50], Lacerda [51] and Vieira[52] describe the X-ray diffraction pattern of cassavastarch as A-type, while Paes et al. [40] reported a CA-typepattern. Gomes et al. [44] found A-type pattern, but citedseveral other authors that had found different patterntypes such as: A, B, C, CA and CB. Fig. 2 shows the dif-ferences in the diffractograms of the investigated star-

ches. Native cassava starches showed peaks at the samepoints in spite of their intensities being different, the sameoccurred with the samples of sour cassava starch.

Oven-dried sour cassava starch samples exhibited higherpeak intensities than the sun-dried sour cassava starch.This decrease in peak intensity in the sun-dried sour cas-sava starch can suggest decrease of crystalline areas andincrease of amorphous granule zones. According to Vieira[52], increase of the peak intensity suggests increase ofgranule crystallinity. The diffractogram of polvilho azedoshows higher peak intensities, what could be explainedby new hydrogen bounds formed between smaller mole-cules in an acidic environment.

In general, the peak intensity of the starches studied inthis work was different, but the diffraction pattern was thesame.

3.4 Design of chemical model of the sourcassava starch expansion mechanism

Sour cassava starch expansion is mainly a result of thedifference between native and fermented cassava starchgranules. The main difference is that the fermented gran-ules show perforations formed by the action of amylolyticenzymes, which firstly attack the amorphous zones of thegranules [1, 6, 8]. Sour cassava starch expansion mainlyresults from the perforations in the fermented granules,

Due to its predominantly linear structure, amylose is re-lated with the crystalline regions of granules; the diffusionof this polysaccharide can result in new available regionsfor enzyme action inside the granules. Native cassavastarch does neither undergo these changes nor showexpansion property. Therefore, it is assumed that a rela-tion exists between these changes in the granules andexpansion property.

These modified starches, used in the production of doughfor cheese bread and roscas, have different behavior aftercooking. The expanded structure might not be main-

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Starch/Stärke 61 (2009) 716–726 Effect of Physical-chemical Parameters on Sour Cassava Starch 723

Fig. 2. X-Ray diffraction profile of polvilho azedo (PAM),cassava starches (FMK, FMY), oven-dried (PASE), andsun-dried (PASSOL) sour cassava starch.

tained after cooking. Some sour cassava starches alsoresult in products that might not support the alveolarstructure desirable for the dough. Sour cassava starchcheese bread and roscas can be found on the markethaving firm, alveolar and dry mass, or having soft, non-alveolar, and gummy mass. On the other hand, there areconsumers that prefer the gummy type. In food science,there are no parameters for quality control of sour cas-sava starch that allow a prediction of the behavior of thedifferent kinds of dough made with sour cassava starch.

The results of this work and of others reveal that theevaluation of some parameters does not show correla-tions with the expansion property [2-9, 18], while otherscan still be used as a means of prediction, aiming at thestandardization of sour cassava starch according to theexpectations of several bakers.

Taking together, the results herein found suggests thatthe granule structure is modified in fermented starch.What kind of modifications is related to the expansionproperty is the main question. Our interpretation is basedon a representation of the starch granule internal struc-ture [22], to present a proposal with the intent of showingthe mechanism of granule modification in the sour cas-sava starch during sun-drying, and the main variablesdirectly responsible for maximizing its expansion prop-erty (Fig. 3).

Due to the presence of amylose and amylopectin, nativegranules have superficial negative charge because ofthe numerous hydroxyl groups which are predominanton the surface of starch granules; dilatancy property is aconsequence of this [25]. After fermentation, sour cas-sava starch granules besides hydroxyl groups of amy-lose and amylopectin, also dextrins and carbonylgroups are present. This was also reported by otherauthors [7, 8, 28].

Maximizing the expansion can depend on the degree ofsour starch polymerization, the number of carboxyl andhydroxyl groups, pH, granule density, and other parame-ters that show significant correlation, whether positive ornegative, with the expansion of the dough and its char-acteristics after cooking and also with its storage aftercooking.

4 Conclusions

Parameters of sour cassava starch such as pH, acid fac-tor, solubility, specific volume, and polymerization degree(intrinsic viscosity) can be easily determined and offer adirect relation to the expansion property that can be usedas parameter for quality control of sour cassava starch.

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724 M. J. A. Marcon et al. Starch/Stärke 61 (2009) 716–726

Fig. 3. Schematic of the sourcassava starch chemicalmechanism of modification.

ATR-FTIR and chemometrics (PCA) are useful tools for thecharacterization and classification of cassava starches,helping to predict the behavior of doughs containing theseraw materials.

DSC analysis shows that the sour cassava starch wassufficiently changed during fermentation and sun-drying,with a significantly enthalpy decrease compared to nativecassava starch, and this decrease is proportional to thestarch expansion behavior.

The X-ray pattern was similar for the fermented and nativecassava starches, with some differences in the peakintensities, which means structural modifications of thesour cassava starch.

In the future, a model of the mechanism shall beestablished considering the importance of specificvolume, acid factor, polymerization degree, pH, andnumber of carboxyl and hydroxyl groups for theexpansion property. Consequently, these parameterscan serve as indicators of quality of sour cassavastarch in bakery.

Physicochemical parameters seem to be insufficientwithout a good correlation with the bakers’ expectations.The formulation of a future mathematical model, to max-imize expansion, could allow the establishment of signifi-cant control standards that will depend on a relation be-tween the bakers’ practices and physicochemical pa-rameters related to the favorable behavior of sourcassava starch products.

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Starch/Stärke 61 (2009) 716–726 Effect of Physical-chemical Parameters on Sour Cassava Starch 725

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(Received: January 10, 2009)(Revised: April 20/July 23, 2009)(Accepted: August 10, 2009)

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