(phaseolus lunatus) starch - Wiley Online Library

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EFFECT OF OCTENYLSUCCINYLATION ON FUNCTIONAL PROPERTIES OF LIMA BEAN (PHASEOLUS LUNATUS) STARCH MAIRA SEGURA-CAMPOS, LUIS CHEL-GUERRERO and DAVID BETANCUR-ANCONA1 Facultad de Ingeniería Química Universidad Autónoma de Yucatán Av. Juárez No. 421, Cd. Industrial. C.P. 1288, Apdo. Postal 26, Suc. Las Fuentes, Mérida, Yucatan, Mexico Accepted for Publication April 16, 2008

ABSTRACT The functional properties of lima bean (Phaseolus lunatus) starch modified with octenyl succinic anhydride (OSA) were evaluated and compared with native starch. The OSA starch was produced from a starch aqueous suspension at 40% (w/w) with 3% OSA at pH 7 for 30 min. The modified starch had 0.51% succinyl groups and a 0.008 degree of substitution. Succinylation increased emulsifying capacity from 0.47 mL oil/mL sample in the native starch to 0.53 mL oil/mL sample in the OSA starch. Starch gel clarity (transmittance percentage) increased from 23.8 to 37.3%. Viscosity increased from 700 to 1,000 BU. Gel firmness decreased from 0.3401 kgf for gel rupture in the native starch to 0.0314 kgf for rupture in the OSA starch. Gelatinization temperature decreased from 75.3 to 64.6C and gel enthalpy decreased from 10.7 to 9.7 J/g. Succinylation caused not significant changes in solubility, swelling power and water absorption capacity. OSA starch stability was lower under refrigeration conditions.

PRACTICAL APPLICATIONS The incorporation of octenylsuccinate groups into lima bean starch produce a derivative with more versatility as a food additive providing new and improved functional properties. The octenylsuccinylation allows the use of the lima bean starch in products such as beverages, salad dressings and soups where the use of this starch is limited because lack of diversity in their functional properties necessaries in the alimentary industry. Therefore, the improved properties of the Phaseolus lunatus octenyl succinic anhydride starch make it 1

Corresponding author. TEL: 52999-9460989; FAX: 52999-9460994; EMAIL: [email protected]

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Journal of Food Process Engineering 33 (2010) 712–727. All Rights Reserved. Journal Compilation © 2009 Wiley Periodicals, Inc. No claim to original US government works DOI: 10.1111/j.1745-4530.2008.00299.x

OCTENYLSUCCINYLATION OF LIMA BEAN STARCH

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potentially useful in processes requiring a thickening agent that must gel at lower temperatures; it can also serve to reduce energy consumption during cooking processes or like thickening or emulsifying agent or make it potentially useful as an additive in jellies and candies to provide brightness. However, the election of this derived as additive in food, should take into account the functional properties that it presents, the ingredients and the process conditions.

INTRODUCTION Phaseolus lunatus, or lima bean, is a nonconventional starch source distributed throughout Latin America, the southern United States, Canada and many other regions worldwide. It is widely cultivated in southeast Mexico, where it is known as ib. It is a rich source of carbohydrates (56–60%) with starch yields of 288.4 g/kg when extracted in an alkaline medium at a 1:6 (w/v) flour: water ratio, pH 11 and a 1 h extraction time (Betancur-Ancona et al. 2002; Akinmutimi and Ezea 2006). However, use of this starch in the food industry is limited because of its high gelatinization temperature (75–87C), which requires use of temperatures higher than applied with other common starches for complete gelatinization and thickening during thermal processes. Limitations of this kind diminish the potential uses of starches as thickening and stabilizing agents in food systems (Betancur-Ancona et al. 2001). Native starches contain free hydroxyl groups in the 2, 3 and 6 carbons of the glucose molecule, making them highly reactive. This allows them to be modified by different chemical treatments and thus regulate their properties (Bao et al. 2003). An example of this kind of modification is the succinylation reactions, which are stabilization reactions. These are characterized by diminishing molecule reassociation, and consequent increasing starch stability, through the reaction of hydroxyl groups with monofunctional agents that introduce substitute groups for esterification (Van Hung and Morita 2005). As in all chemical reactions, succinylation depends on factors such as reagent concentration, pH and reaction time. Successful starch modification depends on control of reaction conditions to favor the substitution reaction and minimize the effect of the anhydride and derivative hydrolysis that can occur parallel to the main reaction (Betancur-Ancona et al. 2002). Succinylation can be done using octenyl succinic anhydride (OSA) as a substitution agent. This makes it possible to introduce a chemical group with a long hydrophobic chain into the starch molecule. The derivative acquires the ability to stabilize oil/water emulsions by combining the hydrophobicity of the octenyl group with the carboxyl or sodium carboxylate groups. The amphiphilic nature of these derivatives broadens their potential uses in the food industry (Shogren et al. 2000). Another advantage of this modification is that derivative pasting and gelatinization properties are

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M. SEGURA-CAMPOS, L. CHEL-GUERRERO and D. BETANCUR-ANCONA

more stable because the OSA groups interrupt the linearity of the amylose and the ramified portion of the amylopectin, which is reflected in increased paste viscosity and decreased gelatinization temperature (Trubiano 1986). The incorporation of octenylsuccinate groups into lima bean starch would produce a derivative with more versatility as a food additive by providing new and improved functional properties (Wurzburg 1995). As part of an effort to broaden the use of P. lunatus, the objective of the present study was to evaluate the effect of octenylsuccinylation on the functional properties of P. lunatus starch. MATERIALS AND METHODS Seeds and Chemicals P. lunatus seeds were obtained from the February 2005 harvest in the state of Yucatan, Mexico. The seeds were milled to produce flour from which the native starch was extracted. All chemicals were reagent grade and purchased from J.T. Baker (Phillipsburg, NJ). Starch Isolation A single extraction was done with 6 kg of P. lunatus seeds. Impurities and damaged seeds were removed and the sound seeds milled in a Mykros impact mill (Maquinaria Técnica Industrial, México, D.F.). The resulting flour was sifted through a 20-mesh screen and then processed using the wet fractionation method reported by Betancur-Ancona et al. (2004). Briefly, whole flour (20 mesh) was suspended in distilled water at a 1:6 (w/v) ratio. The pH was then adjusted to 11 with 1 M NaOH, and the dispersion stirred for 1 h at 400 rpm with a mechanical agitator (Caframo Rz-1, Heidolph Schwabach, Germany). The suspension was wet-milled with a Kitchen-Aid mill (St. Joseph, MI) and the fiber solids separated from the starch and protein mix by straining through 80- and 150-mesh sieves. The residue was washed five times with distilled water. The protein–starch suspension was allowed to sediment for 30 min at room temperature to recover the starch fraction, after which the solubilized protein was removed. The starch fraction was then washed three times by resuspension in distilled water and centrifuged at 4,250 ¥ g for 10 min. The product was dried at 50C for 12 h in an air convection oven (Imperial 5, Lab-line instruments, IL), weighed and then milled in a Cyclotec mill (Tecator, Hoganas, Sweden) until it passed through a 20-mesh screen. Preparation of OSA Starch The OSA starch was obtained when the native P. lunatus starch was reacted with OSA according to the procedure described by Báez (1996).


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Briefly, 100 g of a starch suspension (40%, w/w) in water was prepared in a flask placed in a thermostatic bath (Grant model JB-3, Cambridge, UK) at 30C. A uniform slurry was prepared using a mechanical stirrer (Caframo RZI, Wiarton, Ontario, Canada), with stainless steel propeller, operated at 800 rpm. The pH was then measured with a Cole-Parmer Digi-Sense potentiometer (Niles, IL) and adjusted to 7 by simultaneous drop wise addition of a 3% NaOH solution, later on the OSA solution was added too (1.8 mL). This was performed carefully to maintain pH within the value established. After the reaction time had elapsed, pH was adjusted to 6.5 with 0.5 N aqueous HCl and the slurry vacuum-filtered through a piece of sailcloth. The modified starch was recovered and washed with 150 mL distilled water, and the slurry filtered again to remove water. Washing was repeated and the recovered modified starch dried at 50C in a Lab-Line oven (Melrose Park, IL) with mechanical convection. When dried, the product was milled in a Cyclotec mill and sifted through a 20-mesh screen. The percentage of succinyl groups was determined according to the method proposed by Báez (1996). Briefly, 5 g of starch was weighed in an analytical balance model Mettler H20 (Columbus, OH), transferred to a 250-mL beaker; and 50 mL of distilled water and three drops of phenolphthalein were added. The suspension was titrated with 0.1 M NaOH until a pink color remained for 2 min. Then, 25 mL of 0.45 M NaOH was added to the OSA starch suspension and it was shaken vigorously with a magnetic agitator (Lindberg blue model, Corning, NY) for 30 min. Excess alkali was titrated with 0.2 M HCl until the color disappeared. A blank was simultaneously titrated with native starch. Percentage of succinyl groups and degree of substitution (DS) were determined according to Wurzburg (1964) and calculated as follows:

% of succinylation = ([ B − M ] mL × N acid × 0.045 sample weight [ g ]) × 100

(1)

(1) B = mL HCl 0.2 M for blank; (2) M = mL HCl 0.2 M for sample.

DS = 162 × % succinylation 10,000 − ( 99 × % succinylation )

(2)

(1) 162 = Molecular weight of glucose unit; (2) 10,000 = 100 ¥ molecular weight of succinyl group; (3) 99 = Molecular weight of succinyl group - 1. Functional Properties Differential Scanning Calorimetry (DSC). Native and OSA starch gelatinization was determined with a DSC-7 (Perkin-Elmer Corp., Norwalk,

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CT) using the technique described by Ruales and Nair (1994). The DSC was calibrated with indium and the data analyzed using the Pyris software program. Two mL dry basis (d.b.) of starch was placed in an aluminium pan and the moisture level adjusted to 70% by adding deionized water. The pan was then hermetically sealed and left to equilibrate for 1 h at room temperature. It was then placed in the calorimeter and heated from 20 to 120C at a rate of 10C/min, using an empty pan as reference. Gelatinization temperature was determined by automatically computing onset temperature (To), peak temperature (Tp), final temperature (Tf) and gelatinization enthalpy (DH) from the resulting thermogram. Pasting Properties. These properties were evaluated in a Viscoamylograph (Brabender PT-100, Duisburg, Germany) according to Wiesenborn et al. (1994). Briefly, 400 mL of 6% (d.b.) starch suspension was heated to 95C at a rate of 1.5C/min, held at this temperature for 15 min, then cooled to 50C at the same rate and held at this second temperature for another 15 min. Maximum viscosity, consistency, breakdown and setback were calculated in Brabender units (BU) from the resulting amylograms. Emulsifying Capacity (EC). This property was determined following Jiménez-Colmenero and García-Matamoros (1981). Briefly, 300 mg of starch was weighed (d.b.) in an analytical balance model Mettler H20, transferred to a beaker, and then 100 mL distilled water added. The starch suspension was heated to 85C for 20 min and cooled to room temperature. The pH was adjusted to 5.5 with 0.1 N NaOH, and the starch suspension homogenized using a mixer at low speed for 45 s (two electrodes were fixed in the glass of the mixer; these can be connected or disconnected externally to a multimeter). Mixer speed was then switched to high and corn oil added at a constant rate through a hole in the mixer top. Emulsion collapse was detected by an abrupt increase in electrical resistance. No oil was added after this point, the multimeter was disconnected and the amount of oil added was recorded. EC was expressed in mL of oil per mL of sample. Solubility, Swelling Power (SP) and Water Absorption Capacity (WAC). Solubility, water absorption and SP patterns at 60, 70, 80 and 90C were determined using a modified version of Sathe et al. (1981) method. Briefly, 40 mL of a 1% starch suspension (w/v) was prepared in a previously tared, 50-mL centrifuge tube. A magnetic agitator was placed in the tube, and it was kept at a constant temperature (60, 70, 80 or 90C) in a water bath for 30 min. The suspension was then centrifuged at 2,120 g for 15 min, the supernatant decanted and the swollen granules weighed. From the supernatant,


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10 mL was dried in an air convection oven (Imperial V) at 120C for 4 h in a crucible to constant weight. Percentage solubility and SP were calculated using the following formula:

% Solubility = dry weight at 120 C × 400 sample weight

(3)

%Swelling power = weight of swollen granules × 100 sample weight × (100 − % solubiliy )

(4)

WAC was measured using the same conditions as above, but was expressed as weight of the gel formed per sample, divided by treated sample weight. Starch Clarity. Starch clarity was measured using the method of BelloPérez et al. (1999), determining transmittance of a 1% starch paste at 650 nm using a spectrophotometer (Beckman DU-650, Fullerton, CA). Starch suspensions (1%) in tubes with threaded caps were placed in a water bath at 100C for 30 min, agitated by vortexing every 5 min, and left to cool at room temperature. Percentage of transmittance (%T) was determined from these suspensions. Refrigeration and Freezing Stability. Stability under refrigeration and freezing conditions was evaluated using a modified version of Eliasson and Ryang’s (1992) method. Pastes were prepared in a Brabender viscoamylograph. Briefly, 400 mL of 6% (d.b.) starch suspension was heated to 95C at a rate of 1.5C/min, held at this temperature for 15 min, then cooled to 50C at the same rate and held at this second temperature for another 15 min. Portions of 50 mL were placed in centrifuge tubes, cooled to room temperature and stored at 4C and -10C, and then centrifuged at 8,000 ¥ g for 10 min in a J2-HS centrifuge (Beckman Instruments). The water separated from the starch gels during 1, 2, 3, 4 and 5 days was measured. Gel Firmness. Gel firmness was evaluated according to a Hoover and Senanayake’s (1995) modified method, using an Instron Universal Machine (London, U.K.). Briefly, 400 mL of 8% (d.b.) starch suspension was heated to 95C at a rate of 1.5C/min in the Brabender viscoamylograph (Brabender PT-100, Duisburg, Germany), held at this temperature for 10 min and the paste transferred in 40-mL portions into 50-mL Erlenmeyer flasks. These were allowed to cool to room temperature, covered with parafilm and stored at 4C for 24 h. The gels were then removed from the flasks, cut at a height of 3 cm and gel penetration measured with an Instron model 4411. Each gel was placed perpendicularly in the equipment and compressed at a speed of 1 mm/sec using a 5-mm probe and a 5-kg cell.

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Statistical Analysis All functional properties were done in triplicate. A Student t statistic with a 5% significance level was applied to compare the differences between means of the native and modified P. lunatus starch functional properties using the Statgraphics plus 5.1 computer software (Statistical Graphics Corporation, Warrenton, VA) and according to Montgomery (1991) methods.

RESULTS AND DISCUSSION Modification of Native Starch The percentage of succinyl groups (0.51) in the OSA P. lunatus starch was lower than the 0.86 to 1.58% reported by Betancur-Ancona et al. (2002) for esterification of Canavalia ensiformis starch, but similar to the 0.15 to 0.51% reported by Báez (1996) for esterification of corn starch with succinic anhydride. Higher degrees of substitution than observed in the present study (0.008) have been reported for OSA esterification of rice (0.018) (Song et al. 2006) and corn (0.03–0.11) (Shogren et al. 2000), and with succinic anhydride esterification of cassava starch (0.22) (Jyothi et al. 2005). These differences can be attributed to reagent type, reaction conditions (modifying agent concentration, pH and reaction time), granule shape and even chain size (the substitution reaction incorporates a substituting group with a long hydrophobic chain). Functional Properties Gelatinization. Gelatinization onset (To), peak (Tp) and final (Tf) temperatures were 67.9, 75.3 and 89.3C, respectively, for the P. lunatus native starch granules and 56.7, 64.6 and 72.4C, respectively, for the OSA starch (Table 1). Wurzburg [(1995]) reported that stabilized starches are characterized by a decrease in gelatinization temperature, among other properties. The incorporation of OSA groups to the starch molecule interrupt the lineality of TABLE 1. GELATINIZATION PARAMETERS OF NATIVE AND OCTENYL SUCCINIC ANHYDRIDE (OSA) PHASEOLUS LUNATUS STARCHES Starch

Onset temperature (C)

Peak temperature (C)

Final temperature (C)

Enthalpy (J/g)

Native OSA

67.9 ⫾ 0.34a 56.7 ⫾ 1.62b

75.3 ⫾ 0.26a 64.6 ⫾ 0.18b

89.3 ⫾ 0.98a 72.4 ⫾ 1.11b

10.72 ⫾ 0.22a 9.73 ⫾ 0.09b

a,b

Different letters in the same column indicate statistical difference (P < 0.05).


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the amylose and amylopectin being reflected by a decrease of the gelatinization temperature (Trubiano 1986). This coincides with the present study in which the DSC thermograms showed the modified P. lunatus starch to have a lower gelatinization temperature (64.6C) than the native starch (75.3C). A similar pattern was reported in esterification of C. ensiformis starch with 4% acetic acid (Betancur-Ancona et al. 1997) and with 4% succinic anhydride (Betancur-Ancona et al. 2002) at pH 8–8.5 for 1 h. Esterification lowered the To and Tf of the OSA starch in comparison with those of the native starch. Gel enthalpy DH (J/g) for the OSA starch was 9.73 J/g, whereas for the native starch it was 10.72 J/g, meaning that the former required less energy to gelatinize than the latter. This does not coincide with Czuchajowska et al. (1998), who reported that lower gelatinization enthalpy values are linked to higher amylose levels. In the P. lunatus native starch studied here the amylose proportion was higher (32.4%) than in the OSA starch (23.6%), but the native starch enthalpy value was higher than that of the modified starch (SeguraCampos et al. 2007). This suggests that these phenomena may be governed more by crystal structure and organization than by amylose content. Pasting Properties. Succination increased viscosity from 700 BU in the native starch to 1,000 BU in the OSA starch (Table 2). Viscosity decreased notably during the heating stages and then increased during cooling, indicating that the OSA starch is unstable in heating–cooling processes. This must be considered when incorporating this starch into products since upon cooling its paste viscosity will increase, which will be reflected in a higher thickening TABLE 2. PASTING PROPERTIES OF NATIVE AND OCTENYL SUCCINIC ANHYDRIDE (OSA) PHASEOLUS LUNATUS STARCHES Parameter

Native starch

OSA starch

Initial gelatinization temperature (C) Maximum viscosity (BU) Viscosity at 95C (BU) Viscosity at 95C for 15 min (BU) Viscosity at 50C (BU) Viscosity at 50C for 15 min Breakdown* Consistency† Setback‡

72 700 630 580 750 880 120 170 50

79.5 1,000 830 710 880 1,280 290 170 -120

* Breakdown: peak viscosity (BU) – viscosity at 95C ¥ 15 min (BU). † Consistency: viscosity at 50C (BU) – peak viscosity (BU). ‡ Setback: viscosity at 50C (BU) – viscosity at 95C ¥ 15 min (BU).

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capacity. One of the reported improvements in succinated starches is increased viscosity (Wurzburg 1986; Báez 1996). The present results support this, as do those of Báez (1996) for succinated corn starch, Betancur-Ancona et al. (2002) for succinated C. ensiformis starch and Jyothi et al. (2005) for succinated cassava starch. The OSA starch in the present study had higher fragility than the native starch, indicating that its viscosity decreased during heating because of the swelling of its starch molecules, consequently making them more fragile (Table 2). Consistency of the modified starch was the same as in the native starch, although it had lower settling values. This indicates that the OSA starch was less stable in heating-cooling processes, although it would have higher thickening capacity upon cooling in foods to which it was added. EC. The OSA starch had a higher EC (0.53 mL oil/mL sample) than the native starch (0.47 mL oil/mL sample). Succinylation helped to introduce a substituting group with a long hydrophobic chain into the starch molecule, producing a derivative with low surface activity properties that would make it useful in emulsion preparation (Wurzburg 1986; Wurzburg 1995). Solubility, SP and WAC. Solubility (Fig. 1), SP (Fig. 2) and WAC (Fig. 3) were directly correlated to increases in temperature. The native and OSA P. lunatus starch water absorption and SP patterns showed that in the 70 to 90C range the granules swelled gradually as temperature increased due to rupture of the intermolecular hydrogen bridges in the amorphous areas, which allowed progressive water absorption. Gujska et al. (1994) found the same result for pinto bean and navy bean starches: a clear increase in swelling starting at 70C.

FIG. 1. SOLUBILITY OF THE NATIVE AND OCTENYL SUCCINIC ANHYDRIDE (OSA) PHASEOLUS LUNATUS STARCH


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FIG. 2. SWELLING POWER OF THE NATIVE AND OCTENYL SUCCINIC ANHYDRIDE (OSA) PHASEOLUS LUNATUS STARCH

FIG. 3. WATER ABSORPTION CAPACITY OF THE NATIVE AND OCTENYL SUCCINIC ANHYDRIDE (OSA) PHASEOLUS LUNATUS STARCH

The solubility, SP and WAC levels observed here for the OSA starch were statistically similar to those for the native starch, probably because of the low substitution level in the modification reaction. This differed from Jyothi et al. (2005), who reported an increase in the SP of succinated cassava starch from 29 to 45 mL/g (DS = 0.022), although they reported no significant changes in solubility at 90C (16.7 to 24.3%) when compared with the native starch (21.6%). Also, Betancur-Ancona et al. (2002) and Betancur-Ancona et al. (1997) reported increased solubility and SP in succinated (DS = 0.014) and acetylated (DS = 0.091) C. ensiformis starches, respectively. This was caused by higher substitution levels, and introduction of hydrophilic substitute groups, which, because of their ability to form hydrogen bridges, allowed a greater reception of water molecules, guaranteeing that the water that penetrated the granule was retained to a higher degree, and therefore increased

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swelling. Van Hung and Morita (2005), and Singh et al. (2004) reported the same behavior in acetylated wheat (DS = 0.043), potato (DS = 0.154) and corn (DS = 0.104) starches. The present results can be attributed to the low substitution levels attained, granule structure type (which reduced interaction with water) and the presence or introduction of octenylsuccinic groups into the starch molecule. These groups have a high nonpolar proportion which reduces water absorption during heating as well as water retention inside the starch molecules. Starch Gel Clarity. The native and OSA P. lunatus starch transmittance (%T) values were 23.8 and 37.3%, respectively. As was expected, the modified starch was more translucent than the native starch because introduction of the substitute chemical groups generates functional properties such as increased paste clarity (Wurzburg 1995). Craig et al. (1989) stated that starch clarity is a result of high reflection as the characteristic arrangement of gel molecular chains reduces the intensity of the light transmitted through them. The present results are similar to those reported by Jyothi et al. (2005) succinylated cassava starch. They reported improvements in gel clarity from 21.4% in the native starch to 21.8–28.9% in the derivative starches. Bhandari and Singhal (2002) also reported increased paste clarity in succinated yucca and amaranth starches, with a positive correlation between percentage of transmitted light and degree of substitution. Song et al. (2006) observed the same pattern in rice OSA starches (DS = 0.0188), with increases from 12.2% in the native starch to 35.2 % in the succinated starch. Clarity is a key parameter in starch paste quality because it provides shine and opacity to product color. The OSA P. lunatus starch’s excellent clarity makes it potentially useful in products such as fruit pie fillings and candies. Refrigeration and Freezing Stability. Compared with the native starch, the P. lunatus OSA starch had high syneresis, and therefore low stability in refrigeration and freezing cycles (Figs. 4 and 5). This low stability in refrigeration processes is a disadvantage in the food industry because it means the OSA starch behaves like a sponge, initially absorbing water and then releasing it when centrifuged (8,000 ¥ g during 15 min). Its high syneresis can probably be attributed to the reorganization of the molecules (amylose and amylopectin) of the OSA starch gel, which leads to the gel releasing water (Ferrero et al. 1993; Yuan et al. 1993). The OSA starch behavior could be caused by the nonpolar character of octenil chains and the decrease of the OSA starch capacity of the forming hydrogen bond, as well as by the longitude of the amylose chains, as short chains facilitate its lixiviation toward the aqueous means, and by hydrolysis reactions that could take place in a simultaneous way during the esterification reaction.


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FIG. 4. STABILITY OF THE NATIVE AND OCTENYL SUCCINIC ANHYDRIDE (OSA) PHASEOLUS LUNATUS PASTES TO REFRIGERATION TEMPERATURE

FIG. 5. STABILITY OF THE NATIVE AND OCTENYL SUCCINIC ANHYDRIDE (OSA) PHASEOLUS LUNATUS PASTES TO FREEZING TEMPERATURE

Successive freezing and thawing of starches can also affect their structure since formation and melting of ice crystals can lead to starch paste redistribution and dilution (Soni et al. 1990). This is probably what occurred in the P. lunatus OSA starch. The retained water would have been released from inter- and intramolecular associations, resulting in two separate phases: one polymer-rich (gel); and another polymer-poor (liquid). This coincides with the low freezing–thawing stability reported for Zea mays and Amaranthus hypochondriacus starch gels (Baker and Rayas-Duarte 1998) and banana acetylated starches (Bello-Pérez et al. 2002). Under refrigeration processes the P. lunatus OSA starch was less stable than its native, but under freezing processes they behaved similarly. Formation of rigid structures because of the association of amylose and amylopectin molecules during the esterification reaction gives this starch high syneresis (starts on day 1 of storage). This is vital to consider when using the studied OSA starch as a food additive, since it requires storage at low temperatures.

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TABLE 3. GEL FIRMNESS OF PHASEOLUS LUNATUS NATIVE AND OCTENYL SUCCINIC ANHYDRIDE STARCHES Starch

Max. load (kgf)

Deformation (mm)

Native Octenylsuccinate

0.3401 ⫾ 0.02 0.0314 ⫾ 0.01b

7.27 ⫾ 0.03a 14.9 ⫾ 0.18b

a,b

a

Different letters in the same column indicate statistical difference (P < 0.05).

Gel Firmness. The native and OSA P. lunatus starch gels had statistically different (P < 0.05) gel firmness values (Table 3). The native P. lunatus starch gel was firmer, requiring 0.3401 kgf of force for rupture, while the OSA starch required only 0.0314 kgf for rupture. Bao et al. (2003) reported similar results for OSA-modified rice, wheat and potato starches, with modified gel hardness increasing as degree of substitution decreased. Czuchajowska et al. (1998) observed a positive correlation between gel firmness and amylose content in chick pea (var. Latah) and pea (var. SS Alaska) starch gels. Wang and White (1994) stated that amylose determines gel firmness to a high degree because its molecules bond to one other, forming hydrogen bridges that create a rigid three-dimensional network. Apparent amylose content in the studied OSA P. lunatus starch (23.6%) was lower than in the native starch (32.4%), probably accounting for the former’s lower firmness (Segura-Campos 2007). The results also indicate, however, that the OSA starch gel was more elastic than the native starch (14.90 vs. 7.27 mm). This difference in gel elasticity may be because of the lower apparent amylose content of the OSA starch, which is associated with development of less rigid gels (Czuchajowska et al. 1998).

CONCLUSIONS Octenylsuccinylation of lima bean P. lunatus starch increased its EC from 0.47 to 0.53 mL oil/mL sample; increased viscosity from 700 BU to 1,000 BU; increased starch gel clarity from 23.8 to 37.3%T; decreased gel firmness from 0.3401 kgf for gel rupture in the native starch to 0.0314 kgf in the OSA starch; decreased gelatinization temperature from 75.3 to 64.6C; and decreased gel enthalpy from 10.72 to 9.73 J/g. However, the modification reaction caused no significant changes in solubility, SP and WAC. The OSA starch was less stable than the native starch in refrigeration processes, but had similar stability in freezing processes. The functional properties of the studied OSA P. lunatus


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starch make it potentially useful in processes requiring a thickening agent that must gel at lower temperatures. It can also serve to reduce energy consumption during cooking processes or like thickening or emulsifying agent in soups, sauces, purees, salad dressings or meat products. Their high transmittances make it potentially useful as an additive in jellies and candies to provide brightness. However, its low firmness and syneresis (i.e., low stability) under refrigeration and freezing conditions make it inadequate for use as a thickener, stabilizer or gelling agent in refrigerated or frozen foods.

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