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Determination of some physicochemical and rheological characteristics of starch obtained from Brosimum alicastrum swartz seeds
Food Hydrocolloids 45 (2015) 48e54
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Determination of some physicochemical and rheological characteristics of starch obtained from Brosimum alicastrum swartz seeds n a, C.R. Ríos-Soberanis b, V.M. Moo-Huchin a, M.J. Cabrera-Sierra b, R.J. Estrada-Leo c c ndez a, I.A. Estrada-Mota a, D. Betancur-Ancona , L. Chel-Guerrero , A. Ortiz-Ferna a , * rez-Pacheco E. Pe gico Superior de Calkiní en el Estado de Campeche, Av. Ah Canul SN por Carretera Federal, C.P. 24900 Calkiní, Campeche, Mexico Instituto Tecnolo n, Unidad de Materiales, Calle 43, No. 130, Colonia Chuburna de Hidalgo, C.P. 97200 M n, Mexico n Científica de Yucata Centro de Investigacio erida, Yucata c n, Perif de Hidalgo Inn, noma de Yucata Facultad de Ingeniería Química, Universidad Auto erico Norte Km 33.5, tablaje Catastral 13615, Colonia Chuburna C.P. 97203, Mexico a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 July 2014 Accepted 10 November 2014 Available online 18 November 2014
Starch sources with different physicochemical properties are demanded by new applications that require specific properties. Ramon starch was characterized by X-ray diffraction, thermogravimetric analysis, fourier transform infrared spectroscopy (FTIR) analysis and rheology, and compared to corn starch. Ramon starch exhibited a C-type X-ray diffraction pattern. According to thermogravimetric analysis, degradation of corn and Ramon starches occurred in the temperature range between 292 and 369 C, which coincides with the degradation of other starches studied. Pasting properties varied among the corn and Ramon starches. Ramon and corn starches were characterized as viscoelastic systems with G0 > G00 , during the stages of heating-cooling kinetics. These results support the potential use of Ramon starch as a thickening and gelling agent in food, an excipient in pharmaceutical solid forms, and as biodegradable polymers for food packaging. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Brosimum alicastrum swartz Starch Physicochemical characterization Rheology
1. Introduction Biopolymers, based on renewable and/or biodegradable resources are becoming increasingly attractive not only to the plastics industry but also to the general public. They are classified according to their source; polymers based on renewable resources (starch and cellulose), biodegradable polymers based on bio-derived monomers (vegetable oils and lactic acid) and polymers synthesized by microorganisms (polyhydroxyalkanoates) (Valero-Valdivieso, n, & Uscategui, 2013). Ortego The preparation of different materials based on starch has significant advantages due to the fact that it derives from a renewable source, abundant in nature, which is also biodegradable and economically viable. These are just a few reasons why so much investigation has been carried out on this particular polysaccharide.
* Corresponding author. Av. Ah-Canul S/N por Carretera Federal Campecherida, Mexico. Tel.: þ529968134870x1002; fax: þ529968134870x2000. Me rez-Pacheco). E-mail address: [email protected] (E. Pe http://dx.doi.org/10.1016/j.foodhyd.2014.11.009 0268-005X/© 2014 Elsevier Ltd. All rights reserved.
Starch is an important component in a large number of agricultural products such as cereals, legumes, tubercles and some fruits at a physiologically immature stage (Bertolini, 2010). It is employed as a raw material in many applications, ranging from the formation of food texture and consistency to the manufacture of paper, adhesives and biodegradable packaging (Zhao & Whistler, 1994). It is also used as a functional ingredient (thickener, stabilizer and gelifier) in the food industry. Currently, the main sources of starch are corn, potato, yucca, etc. (Nafchi Abdorreza, Cheng, & Karim, 2011; Siracusa, Rocculi, Romani, & Rosa, 2008; Zamudio-Flores, Bellorez, Vargas-Torres, Herna ndez-Uribe, & Romero-Bastida, 2007). Pe However, in many developing countries, these agricultural products are used to feed the population; thus, any shortage could lead to an increase in global hunger. In order to address this problem, scientists are focusing their attention on the extraction of this polysaccharide from non-conventional sources such as the Enternez-Herna ndez et al., 2011). In this sense olobium cyclocarpum (Jime therefore, it is important to find new natural sources for the extraction of starch, which can be used as raw material in industrial processes without competing with human nutrition. New starch
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sources with different physicochemical properties are demanded by new applications that require specific properties, such as high viscosity and transparent gels. For example, a starch that develops high viscosity values has potential applications as a thickener. rez-Pacheco et al. (2014) isolated 92.5% of starch from Ramon Pe seeds (Brosimum alicastrum swartz) and reported the proximate composition, morphology and functional properties. Ramon starch granules were ovalespherical and rounded with sizes between 6.5 and 15 mm with amylose content of 25.36%. They also reported gelatinization temperature of 83.05 C and transition enthalpy of 21.4 J/g. At 90 C, solubility was 20.42%, swelling power 17.64 g water/g starch and water absorption capacity was 13 g water/g starch. Nevertheless, the performance of a given starch in any application is governed by its physicochemical properties. Therefore, it is necessary to study other important properties of the Ramon starch such as X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy (FTIR) analysis and rheology to provide it a broad range of potential industrial uses. The aim of this study, therefore, was to determine some physicochemical and rheological properties of starch extracted from the seeds of the Ramon fruit. The results were compared with those of corn starch. This investigation supports the potential of this starch for industrial applications.
Samples were analyzed with a Siemens D-5000 powder diffractometer equipped with a crystalline graphite monochromator under the following operating conditions: Cu Ka radiation; voltage, 40 kV; chart speed, 10 mm; running rate, 2q/min. The base line of the diffractogram was corrected in the scanning interval and the n 7.0, (Orivector was normalized using the software Origin versio ginLab Corporation, USA). The crystallinity was determined acneTesta, Me ndezeMontealvo, Ottenhof, Farhat, and cording to Milla rez (2005). BelloePe
2. Materials and methods
The thermal properties of starch powders were measured with a TGA Perkin Elmer 7/DX thermal analyzer. A 6 mg sample was placed in a platinum pan and heated from 50 C to 500 C a 10 C/min to monitor the temperature at which decomposition occurred. During the entire process, nitrogen at 3.7 bar was delivered through the system containing the sample at 20 ml/min.
2.1. Materials Fruits of the Ramon tree were obtained in September, 2013 from the northern region of the State of Campeche, located in the Peninsula of Yucatan, in the southeast of Mexico. Corn starch (SigmaeAldrich) was used as reference; which is used extensively in the manufacture of food and other applications due to their structural and physicochemical characteristics. 2.2. Isolation of starch Ramon seed flour and starch extraction technique were acrez-Pacheco et al. (2014). Five hundred grams of cording to Pe Ramon seed flour was mixed with 5 L of sodium bisulfite (0.1%, w/v) and left to sit for 12 h; pH was adjusted to 10 with NaOH 1 N and the mixture was left to sit for a further 30 min at room temperature. The suspension was then filtered through plastic cloth (100-mesh) strainers to separate the residue (fiber) from the liquid substance (proteins and starch); the residue was subjected to the extraction process once again in order to obtain the maximum amount of starch. The suspension (protein and starch) was sifted once again through a 200-mesh screen and the liquid fraction was left to precipitate for 30 min after which the supernatant was removed with a siphon. The remaining liquid was washed three times by resuspension in distilled water and the starch recovered after the final wash by centrifuging at 2500 rpm for 10 min in an Eppendorf centrifuge (model 5702-R). After isolation the starch was dried in a convection oven at 60 C for 24 h, ground in an IKA MF-10 grinder with a sieve size of 0.5 mm and sifted through a 100-mesh screen. Finally, the starch was stored in hermetically sealed glass containers until subsequent analysis. 2.3. X-ray powder diffraction (XRD) Briefly, 20 mg (dry basis, d.b) of starch was weighed out and its moisture content adjusted to 20% by adding distilled water. The samples were allowed to equilibrate at room temperature for 2 h, and applied as a thin film to an aluminum sample container.
2.4. Fourier transform infrared spectroscopy (FTIR) analysis The FTIR spectroscopy analyses were performed on corn and Ramon starch samples in order to characterize qualitatively the organic compounds of the solids by using the transmission technique. The specimens were prepared by grinding the solid powder starch with 200 mg potassium bromide (KBr) powder and then pressing the mixture into a tablet. The FTIR spectrum of the powder complexes was measured at room temperature with a ThermoNicolet (Nexus 670-FTIR) spectrometer in a spectral range of 4000e400 cm1. 2.5. Thermogravimetric analysis (TGA)
2.6. Pasting properties of starches Pasting properties were evaluated following the method of Wiesenborn, Orr, Casper, and Tacke (1994), using a viscoamylograph (Brabender PT-100, Germany). Briefly, 400 ml of 6% (d.b.) starch suspension were heated to 95 C at a rate of 1.5 C/min, held at this temperature for 15 min, then cooled to 50 C at the same rate and held at this second temperature for another 15 min and finally cooled to 30 C at the same rate. Maximum viscosity, consistency, breakdown and setback were calculated in Brabender Units (BU) from the resulting amylograms. 2.7. Rheological profile According to previous experiences, starch dispersions with 10% (w/v) total solids showed some precipitation of solids during the resting period, while those with less than 5% (w/v) total solids did not produce proper homogenous gels by heating, thus, samples with 5% (w/v) total solids were less difficult to handle. To determine the viscoelastic properties of starch dispersions with the latter concentration, oscillatory tests were run in triplicate in an AR 2000 rheometer (TA Instruments, New Castle, DE). A cone and plate geometry was used with 60 mm diameter, angle a ¼ 4 and a waterfilled solvent trap. Before measurement, samples were stirred at 30/ s for 2 min at room temperature to homogenize the solution and prevent sedimentation. Samples were left to rest for 50 s to stabilize. A vapor trap was attached to the geometry to reduce water evaporation to a minimum, and a thin layer of silicone paste was applied to the edge of the geometry to seal the trap. Initial sample temperature was set at 25 C, and the starches pasted or gelled in situ by applying either heating or cooling at a constant rate of 2.5 C/min. The linear viscoelastic region (LVR) was determined by running strain amplitude sweeps (1 Hz) from 0.1 to 10% at 95 C and then at 25 C for heating-cooling kinetics (i.e., initial stage I,
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25e95 C; final stage F, 95 Ce25 C). Once the LVR was determined, the rheometer was programmed for frequency sweeps (0.1e20 Hz) at the same temperatures mentioned above for all starch dispersions, but with a constant strain of 4% for corn and Ramon starch. Gel homogeneity was assessed visually at the end of each test. Storage or elastic modulus (G0 ), loss or viscous modulus (G00 ) and loss tangent (Tan d ¼ G00 /G0 ) were evaluated for each test, and all tests were run in triplicate. From the amplitude sweep tests, data of the dynamic viscosity versus strain were examined using the software of the equipment. Data were reported in logarithmic scale.
3. Results and discussion 3.1. X-ray powder diffraction (XRD) The X-ray diffraction patterns of starch allow a characterization of the crystal packing in the native granules. Starch granules present a semi-crystalline structure corresponding to different polymorphic forms, which are classified into three types, namely A, B and C, based on their characteristics and distinct X-ray diffraction on, Colonna, Planchot, & Ball, 1998; Zobel, 1988a). patterns (Bule The crystallinity is exclusively associated with the packing of amylopectin double helices, while the amorphous regions mainly represent amylose (Zobel, 1988a). The packing of amylose and amylopectin within the granules has been reported to vary among the starches, with A-type polymorphs being found mainly in cereal starches, B-type found in tubers, root, high amylose cereal starches, and retrograded starches and with pulse starches presenting a Ctype, this last type corresponding to the coexistence of A and B-type polymorphs (Liu, 2005). The X-ray diffraction patterns of the corn and Ramon starches are given in Fig. 1. In Ramon starch, the highest intensity XRD peaks for the 2q angles were 15 , 17, 18 , 20 , 23 and 26 , slightly different from the 15 , 17, 18 and 23 of the corn starch. The Ramon starch exhibited C-type crystal as classified (Zobel, 1988b), while the corn starch exhibited A-type crystal. It has been proposed that these differences in the diffraction patterns of different starch sources are due to the radial arrangement of the amylopectin chains. This arrangement consists of a region with ramification points and another containing ordered double helices, on et al., 1998). composed of short chains of amylopectin (Bule The highest (percentage of) crystallinity obtained was for Ramon starch (30.56 ± 0.98) and the lowest values for corn starch
(26.68 ± 0.78). The differences in relative crystallinity between Ramon starch and corn starch could be attributed to differences in crystallite size, amount of crystalline regions, orientation of the double helices within the crystalline domains, or the extent of interaction between double helices (Hoover & Ratnayake, 2002). According to the results, the percentage of crystallinity obtained for the Ramon starch are similar to those reported for pulse starches such as pinto bean, pigeon pea, pea, lentil, black bean and grasspea (Hoover, Hughes, Chung, & Liu, 2010). rez-Pacheco et al. (2014), the Ramon starch According to Pe showed enthalpy values (DHgel) higher than those of corn starch. This result could be explained by the difference in crystallinity of the starches analyzed in this work (Ramon ¼ 30.56% and ~ on, Corn ¼ 26.68%) (Fig. 1). Some reports (Iturriaga, Lopez, & An 2004) indicated that the presence of crystalline zones increases the amount of thermal energy required to initiate the melting of starch while the amorphous zones reduce the amount of energy. Therefore, Ramon starch requires a higher temperature to gelatinize, indicating that it presents more thermally and structurally stable crystalline regions, in comparison with corn starch. 3.2. Fourier Transform Infrared Spectroscopy (FTIR) analysis The information obtained with this technique is related to the short-range ordering in the starch molecule (Sevenou, Hill, Farhat, & Mitchell, 2002). Fig. 2 shows the FTIR spectra corresponding to the Ramon and corn starches. Absorption at 3389e3420 cm1 was observed in both starches, corresponding to the stretching vibrations of the hydroxyl groups (eOH) and contributing in the interand intra-molecular interactions of OHe; which is a particular characteristic of starch structure (Fang, Fowler, Tomkinson, & Hill, 2002). The band observed at 2930 cm1 corresponds to the stretching vibration of the hydrogen with respect to the bonds (CeH) associated with the glucopyranose ring (Mano, Koniarova, & Reis, 2003). The water absorbed by the starch appears in the spectrum with a characteristic medium band between 1640 and 1650 cm1 (Kacurakova & Wilson, 2001). Other bands were observed between 1421 and 1300 cm1, corresponding to CeH bonds. In the region known as “fingerprint”, characteristic peaks of starch can be observed at 1155, 1087 and 1019 cm1, corresponding to the vibrations of glucose CeOeC bonds, and at 928, 862, 764, 709, 605 and 573 cm1, attributed to the pyranose ring (Chi et al., 2007). In starch there is an amorphous region and a crystalline region; the quantity of each is important in predicting the response of this polysaccharide when it is processed or that of the products that contain starch when they are stored. The absorbance ratio (bands) of 1022:1047 cm1 was used to represent the order in the starches. The wave length band of 1047 cm1 is related to the ordered region, and the band at 1022 cm1 to the amorphous component (Van Soest, Tournois, Wit, & Vliegenthart, 1995). The values obtained for this ratio were 1.04 and 1.14 for corn starch and Ramon starch, respectively. The Ramon starch had greater ordering (more crystalline areas) than corn starch, coinciding with the crystallinity values obtained by X-ray diffraction, although the latter technique measures long-range ordering in the sample. 3.3. Thermogravimetric analysis (TGA)
Fig. 1. X-ray diffraction patterns of Ramon and corn starches.
The thermal behavior of the Ramon starch was investigated with TGA. Fig. 3a and b shows the thermogram (TG) and its derivative (DTG), as a function of the temperature, for Ramon and corn starches, respectively. For the samples, the thermal decomposition process was developed in three steps. The first step, corresponding
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Fig. 2. FTIR spectra of Ramon and corn starches.
Fig. 3. TGA results of the thermal decomposition and its derivative (DTG); a) Ramon starch; b) corn starch.
to a reduction in mass at temperatures below 150 C, can be associated to the loss of water of the samples (Liu et al., 2010), this value is approximately 10% of the weight for Ramon starch, while in corn starch sample, it reaches up to 8% (Fig. 3). In the second stage (250 ± 10 C T 360 ± 10 C), mass loss is due to the main decomposition processes of starch macromolecules (Liu et al., 2010). Both Ramon and corn starches showed high temperature decomposition (333.7 C and 338.4 C, respectively), which is consistent with the degradation of starch studied by Mano et al. (2003). This result indicates that Ramon starch shows greater similarity with corn starch, this finding is consistent with the rez-Pacheco et al. (2014). amylose determination reported by Pe In the second stage, the mass of the Ramon starch was diminished by 67%, while the mass of the corn starch was diminished by 72%. In the third stage (T > 400 C), inert carbonaceous residues were formed; mass loss became stabilized. Fig. 3 also shows the first derivative DTG curves of the main stage corresponding to the degradation of the starches studied. The well-defined peak in these curves permits to identify the beginning
and end if the event corresponding to thermal degradation. This stage begins with a rapid dehydration and decomposition of hydroxyl groups in glucose rings to form water molecules. According to Liu et al. (2010) during this stage the main chain breaking occurs when CeCeH, CeO, and CeC bounds break. The gaseous decomposition products consist primarily of H2O, CO, and CO2. As can be seen in Fig. 3, the DTG curves exhibited only one peak, indicating the possibility of a simple mechanism of reaction involving degradation of the starch polymers (amylose and amylopectin) (Liu et al., 2010). However, the DTG of the corn starch presented a peak at 311 C; this peak in the DTG has been reported in literature and is attributed to the degradation of protein (Porter, Vollrath, Tian, Chen, & Shao, 2009). 3.4. Pasting properties A paste is defined as a viscous mass consisting of a continuous phase of solubilized amylose and/or amylopectin and a discontinuous phase of granule ghosts and fragments. Pasting refers specifically to changes in the starch upon further heating after
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gelatinization has occurred, including further swelling and leaching of polysaccharides from the starch granule, and increased viscosity which occurs with the application of shear forces (Atwell, Hood, Lineback, Varriano-Marston, & Zobel, 1988). The pasting properties of starches are reported to be influenced by size, rigidity, amylose/amylopectin ratio and swelling power of the granules (Singh, Kaur, Ezekiel, & Guraya, 2005). Table 1 summarizes the pasting properties of Ramon starch and corn starch measured in the Brabender Viscoamilograph. The pasting properties of Ramon starch differed from those of corn starch. As shown in Table 1, during the heating stage, the viscosity increases gradually until a maximum value is obtained (267 UB at 92 C for Ramon starch and 252 UB at 92 C for corn starch). This is due to the fact that, when the granules of starch are heated in excess of water, the phenomenon of heat and moisture transfer occurs, causing swelling of the granules; on reaching the cooking stage of the paste (95 C for 15 min), Ramon starch presented a slight increase in viscosity that was higher in the cooling step, while corn starch showed a slight decrease in viscosity values that increased in the cooling step, these values, however, were still higher than those of Ramon starch. The increment observed in the viscosity values during the cooling step is due to a molecular re-association, i.e. the liberated amylose forms three-dimensional networks (entanglements) since it interacts with the molecules of water by means of hydrogen bonds (Thomas & Atwell, 1999). Breakdown and setback viscosities were observed to be highest in corn starch but lowest in Ramon starch. The higher breakdown for corn starch in comparison with that of Ramon starch suggested that corn starch was less resistant to heat and mechanical shear and hence more prone to loss of viscosity upon holding and shearing. The setback is the viscosity increase resulting from the rearrangement of amylose molecules that have leached from swollen starch granules during cooling, and is generally used as a measure of the gelling ability or retrogradation tendency of starch (Karim, Norziah, & Seow, 2000). The consistency of Ramon starch in heating and cooling processes, measured with continuous shearing force, makes it potentially useful in products requiring sterilization, such as sauces and baby food. Its pasting properties indicate that it remains stable in cooking processes; however, its viscosity increases when cooled, indicating that it is not stable in cooling processes. These are vital aspects to consider when incorporating this starch into a food production process.
3.5. Rheological profile The ideal starch for many food products is one which, at low concentrations, produces a smooth texture with a heavy-bodied paste that remains soft and flexible at low temperature and Table 1 Paste properties of Ramon and corn starches. Parameter
Ramon starch
Corn starch
Initial gelatinization temperature ( C) Maximum viscosity (BU) Viscosity at 95 C Maximum viscosity temperature ( C) Viscosity at 95 C for 15 min (BU) Viscosity at 50 C (BU) Viscosidad a 50 C por 15 min (BU) Breakdown (BU)a Consistency (BU)b Setback (BU)c
82 267 202 92 265 386 441 2 119 121
72 252 241 92 236 539 520 16 287 303
a b c
Breakdown, maximum viscosity (BU) d viscosity at 95 C for 15 min (BU). Consistency, viscosity at 50 C (BU) d maximum viscosity (BU). Setback, viscosity at 50 C (BU) d Viscosity at 95 C for 15 min (BU).
retains its thickening power at high temperatures and high shear. In this respect, the study of rheological properties is of major importance. The strain amplitude sweep, used to define the linear viscoelastic region (LVR) applied to the starch dispersions with 5% (w/v) total solids, during the initial stage at 95 C, shown in Fig. 4a, was usually linear, beginning at values greater than approximately 1% strain or deformation. Each plot is essentially flat, with the storage modulus (G0 ) dominating the measured amplitude strain range. Both starches exhibited viscoelastic gel-like behavior, with overall Tan d values (G00 /G0 ) ranging from 0.08 to 0.34, which are consistent with those of amorphous polymers (Ferry, 1980), a structure presented by starches when they are heated at temperatures higher than their gelatinization temperatures (83 C for Ramon starch and 71 C for corn starch), destroying their crystallinity, but maintaining the amorphous material. During initial heating from 25 C (ambient temperature) to 95 C, gelation probably occurred due to the formation of a network of physical bonds between molecules as a result of phase change from solid to gel (Chel-Guerrero, Cruz-Cervera, Betancur-Ancona, & SolorzaFeria, 2011). Local helical structure, microcrystallites and nodular domains have been proposed as the interactions that give rise to such a physical gelation (Ferry, 1980). No evidence was observed of sudden changes in the moduli, which would indicate a breakdown in starch structure. Similar amplitude profiles were observed after cooling to 25 C in the final stage (Fig. 4b). The LVR was well defined within the tested strain range with the flat plots indicating that the moduli had no real amplitude dependence in all samples. The G0 values were higher than the G00 values, and Tan d values ranged from about 0.05 to 0.6; this is typical of “weak” viscoelastic gels exhibiting high elasticity within the studied amplitude interval. Linear viscoelastic behavior was observed in the frequency sweep profiles for the starch dispersions with 5% (w/v) total solids at 95 C (heating stage) and 25 C (cooling stage) (Fig. 4). In the starches, the G0 > G00 relationship remained unchanged across the applied frequency range, at both 95 and 25 C. The elasticity (G0 ) was significantly higher, approximately twice as high, from corn starch, in comparison with the G0 obtained from Ramon starch. In all starch gels, the elastic (G0 ) modulus was more affected by the cooling process, when going from the heating to the cooling stage (G0 25 C > G0 95 C) (Fig. 4c and d). This may have occurred due to gel structure reinforcement during cooling caused by enhanced interactions between amylose/amylopectin molecules producing double-helix aggregation (Chel-Guerrero et al., 2011). Firstly, when starches are heated, their amylose molecules dissolve inside the starch granules forming a colloidal solution. As the temperature increases, in this case from 25 C (initial stage) to 95 C (heating stage), modulus values (G0 and G00 ) also increase due to granule swelling and increased intermolecular interactions, giving place to starch gelatinization. Gelatinized starch systems have been described as suspensions of swollen starch granules in a continuous phase. During heating, and before G0 and G00 reached maximum values, the starch granules acted as rigid fillers within the continuous phase. The initial increase in G0 and G00 was due to a progressive swelling of the starch granules so that they finally become close-packed (Zobel, 1988b). Although the loss modulus followed the same trend the G00 25 C > G00 95 C ratio was observed in the starch gels, the increase in G00 values was less than that of G0 values (Fig. 4c and d), suggesting that the viscous modulus behavior could be a function of starch source due to the different physical characteristics and changes of the starches during heating. Starch granule size can determine differences in moduli and any modifications in starch characterisndeztics may affect modulus values (Gonz alez-Reyes, Me rez, 2003). Montealvo, Solorza-Feria, Toro-Vazquez, & Bello-Pe
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Fig. 4. Strain amplitude sweep (a and b) and frequency sweep (c and d) of starch dispersions with 5% (w/v) of total solids for Ramon and corn starches at 25 C and 95 C.
The increase in modulus values (G0 , G00 ) caused by cooling from 95 C (initial) to 25 C (final stage), was probably the result of the formation of a packing system with higher rigidity through an increase in cross-links between neighboring molecules, which would have increased the degree of physical intertwining. This behavior during starch cooling is evidence of gel formation (Ferry, 1980). The corn and Ramon starches transitioned from being weak viscoelastic gels (Fig. 4) to gels with enhanced molecular interactions that conserved some properties of weak systems (overall Tan d values <0.6) without adopting a rigid structure. These results corroborate that Ramon starch has potential applications as a thickening and stabilizing agent that could be used to control consistency in food systems such as gravies, soups, puddings, etc., taking into account the data of its thermal properties previously mentioned.
4. Conclusions Physicochemical characterization methods such as X-ray diffraction, FTIR, paste properties and rheology reveal differences between the starches studied herein. According to paste properties, the Ramon starch exhibited higher resistance to heat and heat stability than corn starch, therefore it can be widely used as main component in products that need to be exposed to high temperatures. Due to the rheological properties and paste formation, Ramon starch can also be employed as a pharmaceutical excipient in tablet and capsule formulation, and has a potential use as thickening and gelling agent
in food. Ramon starch viscosity characteristics would allow its application in an actual field of interest such as the elaboration of adhesives and biodegradable polymers for food packaging. On the other hand, the detailed characterization of Ramon starch properties also provides a valuable contribution to a better understanding of its textural properties. Acknowledgments The authors would like to express their gratitude to the Professional Development Program (PRODEP), for the financial support to the project and to the Mexican Council for Science and Technology (CONACYT) for the provision of Grant 60204/CM0042. References Atwell, W. A., Hood, L. F., Lineback, D. R., Varriano-Marston, E., & Zobel, H. F. (1988). The terminology and methodology associated with basic starch phenomena. Cereal Foods World, 33, 306e311. Bertolini, A. C. (2010). Starches. Characterization, properties, and applications. Boca Raton, Florida: CRC Press. on, A., Colonna, P., Planchot, V., & Ball, S. (1998). Starch granules: structure and Bule biosynthesis. International Journal of Biological Macromolecules, 23, 85e112. Chel-Guerrero, L., Cruz-Cervera, G., Betancur-Ancona, D., & Solorza-Feria, J. (2011). Chemical composition, thermal and viscoelastic characterization of tuber starches growing in the Yucatan Peninsula of Mexico. Journal of Food Process Engineering, 34, 363e382. Chi, H., Xu, K., Xuc, D., Song, C., Zhang, W., & Wang, P. (2007). Synthesis of dodecenyl succinic anhydride (DDSA) corn starch. Food Research International, 40, 232e238. Fang, J. M., Fowler, P. A., Tomkinson, J., & Hill, C. A. (2002). The preparation and characterization of a series of chemically modified potato starches. Carbohydrate Polymers, 47, 245e252.
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Ferry, J. D. (1980). Viscoelastic properties of polymers (3rd ed.). New York, NY: Wiley. lez-Reyes, E., Me ndez-Montealvo, G., Solorza-Feria, J., Toro-Vazquez, J., & Gonza rez, L. (2003). Rheological and thermal characterization of Okenia Bello-Pe hypogaea (Schlech. & Cham.) starch. Carbohydrate Polymers, 52(3), 297e310. Hoover, R., & Ratnayake, W. S. (2002). Starch characteristics of black bean, chick pea, lentil, navy bean and pinto bean cultivars grown in Canada. Food chemistry, 78, 489e498. Hoover, R., Hughes, T., Chung, H., & Liu, Q. (2010). Composition, molecular structure, properties, and modification of pulse starches: a review. Food Research International, 43, 399e413. ~ on, M. (2004). Thermal and physicochemical characIturriaga, L., Lopez, B., & An terization of seven argentine rice flours and starches. Food Research International, 37, 439e447. nez-Herna ndez, J., Meneses-Esparza, F., Rosendo-Escobar, J., Vivar-Vera, M. A., Jime rez, L. A., & García-Sua rez, F. J. (2011). Extraccio n y caracterizacio n del Bello-Pe n de las semillas de Enterolobium cyclocarpum Extraction and characalmido terization of starch from Enterolobium cyclocarpum seeds. CyTA e Journal of Food, 9(2), 89e95. Kacurakova, M., & Wilson, R. (2001). Developments in mid-infrared FT-IR spectroscopy of selected carbohydrates. Carbohydrate Polymers, 44, 291e303. Karim, A. A., Norziah, M. H., & Seow, C. C. (2000). Methods for the study of starch retrogradation. Food Chemistry, 71, 9e36. Liu, Q. (2005). Understanding starches and their Role in foods. In S. W. Cui (Ed.), Food Carbohydrates: Chemistry, physical properties, and applications (1st ed.). (pp. 309e356). Boca Raton, FL: Taylor & Francis Group, LLC. Liu, X., Yu, L., Xie, F., Li, M., Chen, L., & Li, X. (2010). Kinetics and mechanism of thermal decomposition of corn starches with different amylose/amylopectin €rke, 62, 139e146. ratios. Starch/Sta Mano, J. F., Koniarova, D., & Reis, R. L. (2003). Thermal properties of thermoplastic starch/synthetic polymer blends with potential biomedical applicability. Journal of Materials Science, 14, 127e135. ndezeMontealvo, M. G., Ottenhof, M. A., Farhat, I. A., & Mill aneTesta, C. E., Me rez, L. A. (2005). Determination of the molecular and structural charBelloePe acteristics of okenia, mango and banana starches. Journal of Agricultural and Food Chemistry, 53, 495e501. Nafchi Abdorreza, M., Cheng, L. H., & Karim, A. A. (2011). Effects of plasticizers on thermal properties and heat sealability of sago starch films. Food Hydrocolloids, 25, 56e60.
rez-Pacheco, E., Moo-Huchin, V. M., Estrada-Leo n, R. J., Ortiz-Ferna ndez, A., MayPe Hern andez, L. H., Ríos-Soberanis, C. R., et al. (2014). Isolation and characterization of starch obtained from Brosimum alicastrum Swarts Seeds. Carbohydrate Polymers, 101, 920e927. Porter, D., Vollrath, F., Tian, K., Chen, X., & Shao, Z. (2009). A kinetic model for thermal degradation in polymers with specific application to proteins. Polymer, 50, 1814e1818. Sevenou, O., Hill, S. E., Farhat, I. A., & Mitchell, J. R. (2002). Organization of the external region of the starch granule as determined by infrared spectroscopy. International Journal of Biological Macromolecules, 3, 79e85. Singh, N., Kaur, L., Ezekiel, R., & Guraya, H. S. (2005). Microstructural cooking and textural characteristics of potato (Solanumtuberosum L.) tubers in relation to physicochemical and functional properties of their flours. Journal of the Science of Food and Agriculture, 85, 1275e1284. Siracusa, V., Rocculi, P., Romani, S., & Rosa, M. D. (2008). Biodegradable polymers for food packaging: a review. Trends in Food Science & Technology, 19, 634e643. Thomas, D. J., & Atwell, W. A. (1999). Starches. USA: American Association of Cereal Chemists. n, Y., & Uscategui, Y. (2013). Biopolymers: progress Valero-Valdivieso, M. F., Ortego and prospects. Dyna, 80(181), 171e180. Van Soest, J. J., Tournois, H., Wit, D., & Vliegenthart, J. F. (1995). Short-range structure in (partially) crystalline potato starch determined with attenuated total reflectance Fourier-transform IR spectroscopy. Carbohydrate Research, 279, 201e214. Wiesenborn, D., Orr, P., Casper, H., & Tacke, B. (1994). Potato starch paste behavior as related to some physical/chemical properties. Journal of Food Science, 59(3), 644e648. rez, L. A., Vargas-Torres, A., Herna ndez-Uribe, J. P., & Zamudio-Flores, P. B., Bello-Pe n parcial de películas preparadas Romero-Bastida, C. A. (2007). Caracterizacio n oxidado de pla tano. Agrociencia, 41, 837e844. con almido Zhao, J., & Whistler, R. L. (1994). Spherical aggregates of starch granules as flavor carriers. Food Technology, 48(7), 104e105. Zobel, H. F. (1988a). Molecules to granules: a comprehensive starch review. Starch/ €rke, 40, 41e50. Sta Zobel, H. F. (1988b). Starch crystal transformations and their industrial importance. €rke, 40, 1e7. Starch/Sta
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Determination of some physicochemical and rheological characteristics of starch obtained from Brosimum alicastrum swartz seeds n a, C.R. Ríos-Soberanis b, V.M. Moo-Huchin a, M.J. Cabrera-Sierra b, R.J. Estrada-Leo c c ndez a, I.A. Estrada-Mota a, D. Betancur-Ancona , L. Chel-Guerrero , A. Ortiz-Ferna a , * rez-Pacheco E. Pe gico Superior de Calkiní en el Estado de Campeche, Av. Ah Canul SN por Carretera Federal, C.P. 24900 Calkiní, Campeche, Mexico Instituto Tecnolo n, Unidad de Materiales, Calle 43, No. 130, Colonia Chuburna de Hidalgo, C.P. 97200 M n, Mexico n Científica de Yucata Centro de Investigacio erida, Yucata c n, Perif de Hidalgo Inn, noma de Yucata Facultad de Ingeniería Química, Universidad Auto erico Norte Km 33.5, tablaje Catastral 13615, Colonia Chuburna C.P. 97203, Mexico a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 July 2014 Accepted 10 November 2014 Available online 18 November 2014
Starch sources with different physicochemical properties are demanded by new applications that require specific properties. Ramon starch was characterized by X-ray diffraction, thermogravimetric analysis, fourier transform infrared spectroscopy (FTIR) analysis and rheology, and compared to corn starch. Ramon starch exhibited a C-type X-ray diffraction pattern. According to thermogravimetric analysis, degradation of corn and Ramon starches occurred in the temperature range between 292 and 369 C, which coincides with the degradation of other starches studied. Pasting properties varied among the corn and Ramon starches. Ramon and corn starches were characterized as viscoelastic systems with G0 > G00 , during the stages of heating-cooling kinetics. These results support the potential use of Ramon starch as a thickening and gelling agent in food, an excipient in pharmaceutical solid forms, and as biodegradable polymers for food packaging. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Brosimum alicastrum swartz Starch Physicochemical characterization Rheology
1. Introduction Biopolymers, based on renewable and/or biodegradable resources are becoming increasingly attractive not only to the plastics industry but also to the general public. They are classified according to their source; polymers based on renewable resources (starch and cellulose), biodegradable polymers based on bio-derived monomers (vegetable oils and lactic acid) and polymers synthesized by microorganisms (polyhydroxyalkanoates) (Valero-Valdivieso, n, & Uscategui, 2013). Ortego The preparation of different materials based on starch has significant advantages due to the fact that it derives from a renewable source, abundant in nature, which is also biodegradable and economically viable. These are just a few reasons why so much investigation has been carried out on this particular polysaccharide.
* Corresponding author. Av. Ah-Canul S/N por Carretera Federal Campecherida, Mexico. Tel.: þ529968134870x1002; fax: þ529968134870x2000. Me rez-Pacheco). E-mail address: [email protected] (E. Pe http://dx.doi.org/10.1016/j.foodhyd.2014.11.009 0268-005X/© 2014 Elsevier Ltd. All rights reserved.
Starch is an important component in a large number of agricultural products such as cereals, legumes, tubercles and some fruits at a physiologically immature stage (Bertolini, 2010). It is employed as a raw material in many applications, ranging from the formation of food texture and consistency to the manufacture of paper, adhesives and biodegradable packaging (Zhao & Whistler, 1994). It is also used as a functional ingredient (thickener, stabilizer and gelifier) in the food industry. Currently, the main sources of starch are corn, potato, yucca, etc. (Nafchi Abdorreza, Cheng, & Karim, 2011; Siracusa, Rocculi, Romani, & Rosa, 2008; Zamudio-Flores, Bellorez, Vargas-Torres, Herna ndez-Uribe, & Romero-Bastida, 2007). Pe However, in many developing countries, these agricultural products are used to feed the population; thus, any shortage could lead to an increase in global hunger. In order to address this problem, scientists are focusing their attention on the extraction of this polysaccharide from non-conventional sources such as the Enternez-Herna ndez et al., 2011). In this sense olobium cyclocarpum (Jime therefore, it is important to find new natural sources for the extraction of starch, which can be used as raw material in industrial processes without competing with human nutrition. New starch
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sources with different physicochemical properties are demanded by new applications that require specific properties, such as high viscosity and transparent gels. For example, a starch that develops high viscosity values has potential applications as a thickener. rez-Pacheco et al. (2014) isolated 92.5% of starch from Ramon Pe seeds (Brosimum alicastrum swartz) and reported the proximate composition, morphology and functional properties. Ramon starch granules were ovalespherical and rounded with sizes between 6.5 and 15 mm with amylose content of 25.36%. They also reported gelatinization temperature of 83.05 C and transition enthalpy of 21.4 J/g. At 90 C, solubility was 20.42%, swelling power 17.64 g water/g starch and water absorption capacity was 13 g water/g starch. Nevertheless, the performance of a given starch in any application is governed by its physicochemical properties. Therefore, it is necessary to study other important properties of the Ramon starch such as X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy (FTIR) analysis and rheology to provide it a broad range of potential industrial uses. The aim of this study, therefore, was to determine some physicochemical and rheological properties of starch extracted from the seeds of the Ramon fruit. The results were compared with those of corn starch. This investigation supports the potential of this starch for industrial applications.
Samples were analyzed with a Siemens D-5000 powder diffractometer equipped with a crystalline graphite monochromator under the following operating conditions: Cu Ka radiation; voltage, 40 kV; chart speed, 10 mm; running rate, 2q/min. The base line of the diffractogram was corrected in the scanning interval and the n 7.0, (Orivector was normalized using the software Origin versio ginLab Corporation, USA). The crystallinity was determined acneTesta, Me ndezeMontealvo, Ottenhof, Farhat, and cording to Milla rez (2005). BelloePe
2. Materials and methods
The thermal properties of starch powders were measured with a TGA Perkin Elmer 7/DX thermal analyzer. A 6 mg sample was placed in a platinum pan and heated from 50 C to 500 C a 10 C/min to monitor the temperature at which decomposition occurred. During the entire process, nitrogen at 3.7 bar was delivered through the system containing the sample at 20 ml/min.
2.1. Materials Fruits of the Ramon tree were obtained in September, 2013 from the northern region of the State of Campeche, located in the Peninsula of Yucatan, in the southeast of Mexico. Corn starch (SigmaeAldrich) was used as reference; which is used extensively in the manufacture of food and other applications due to their structural and physicochemical characteristics. 2.2. Isolation of starch Ramon seed flour and starch extraction technique were acrez-Pacheco et al. (2014). Five hundred grams of cording to Pe Ramon seed flour was mixed with 5 L of sodium bisulfite (0.1%, w/v) and left to sit for 12 h; pH was adjusted to 10 with NaOH 1 N and the mixture was left to sit for a further 30 min at room temperature. The suspension was then filtered through plastic cloth (100-mesh) strainers to separate the residue (fiber) from the liquid substance (proteins and starch); the residue was subjected to the extraction process once again in order to obtain the maximum amount of starch. The suspension (protein and starch) was sifted once again through a 200-mesh screen and the liquid fraction was left to precipitate for 30 min after which the supernatant was removed with a siphon. The remaining liquid was washed three times by resuspension in distilled water and the starch recovered after the final wash by centrifuging at 2500 rpm for 10 min in an Eppendorf centrifuge (model 5702-R). After isolation the starch was dried in a convection oven at 60 C for 24 h, ground in an IKA MF-10 grinder with a sieve size of 0.5 mm and sifted through a 100-mesh screen. Finally, the starch was stored in hermetically sealed glass containers until subsequent analysis. 2.3. X-ray powder diffraction (XRD) Briefly, 20 mg (dry basis, d.b) of starch was weighed out and its moisture content adjusted to 20% by adding distilled water. The samples were allowed to equilibrate at room temperature for 2 h, and applied as a thin film to an aluminum sample container.
2.4. Fourier transform infrared spectroscopy (FTIR) analysis The FTIR spectroscopy analyses were performed on corn and Ramon starch samples in order to characterize qualitatively the organic compounds of the solids by using the transmission technique. The specimens were prepared by grinding the solid powder starch with 200 mg potassium bromide (KBr) powder and then pressing the mixture into a tablet. The FTIR spectrum of the powder complexes was measured at room temperature with a ThermoNicolet (Nexus 670-FTIR) spectrometer in a spectral range of 4000e400 cm1. 2.5. Thermogravimetric analysis (TGA)
2.6. Pasting properties of starches Pasting properties were evaluated following the method of Wiesenborn, Orr, Casper, and Tacke (1994), using a viscoamylograph (Brabender PT-100, Germany). Briefly, 400 ml of 6% (d.b.) starch suspension were heated to 95 C at a rate of 1.5 C/min, held at this temperature for 15 min, then cooled to 50 C at the same rate and held at this second temperature for another 15 min and finally cooled to 30 C at the same rate. Maximum viscosity, consistency, breakdown and setback were calculated in Brabender Units (BU) from the resulting amylograms. 2.7. Rheological profile According to previous experiences, starch dispersions with 10% (w/v) total solids showed some precipitation of solids during the resting period, while those with less than 5% (w/v) total solids did not produce proper homogenous gels by heating, thus, samples with 5% (w/v) total solids were less difficult to handle. To determine the viscoelastic properties of starch dispersions with the latter concentration, oscillatory tests were run in triplicate in an AR 2000 rheometer (TA Instruments, New Castle, DE). A cone and plate geometry was used with 60 mm diameter, angle a ¼ 4 and a waterfilled solvent trap. Before measurement, samples were stirred at 30/ s for 2 min at room temperature to homogenize the solution and prevent sedimentation. Samples were left to rest for 50 s to stabilize. A vapor trap was attached to the geometry to reduce water evaporation to a minimum, and a thin layer of silicone paste was applied to the edge of the geometry to seal the trap. Initial sample temperature was set at 25 C, and the starches pasted or gelled in situ by applying either heating or cooling at a constant rate of 2.5 C/min. The linear viscoelastic region (LVR) was determined by running strain amplitude sweeps (1 Hz) from 0.1 to 10% at 95 C and then at 25 C for heating-cooling kinetics (i.e., initial stage I,
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25e95 C; final stage F, 95 Ce25 C). Once the LVR was determined, the rheometer was programmed for frequency sweeps (0.1e20 Hz) at the same temperatures mentioned above for all starch dispersions, but with a constant strain of 4% for corn and Ramon starch. Gel homogeneity was assessed visually at the end of each test. Storage or elastic modulus (G0 ), loss or viscous modulus (G00 ) and loss tangent (Tan d ¼ G00 /G0 ) were evaluated for each test, and all tests were run in triplicate. From the amplitude sweep tests, data of the dynamic viscosity versus strain were examined using the software of the equipment. Data were reported in logarithmic scale.
3. Results and discussion 3.1. X-ray powder diffraction (XRD) The X-ray diffraction patterns of starch allow a characterization of the crystal packing in the native granules. Starch granules present a semi-crystalline structure corresponding to different polymorphic forms, which are classified into three types, namely A, B and C, based on their characteristics and distinct X-ray diffraction on, Colonna, Planchot, & Ball, 1998; Zobel, 1988a). patterns (Bule The crystallinity is exclusively associated with the packing of amylopectin double helices, while the amorphous regions mainly represent amylose (Zobel, 1988a). The packing of amylose and amylopectin within the granules has been reported to vary among the starches, with A-type polymorphs being found mainly in cereal starches, B-type found in tubers, root, high amylose cereal starches, and retrograded starches and with pulse starches presenting a Ctype, this last type corresponding to the coexistence of A and B-type polymorphs (Liu, 2005). The X-ray diffraction patterns of the corn and Ramon starches are given in Fig. 1. In Ramon starch, the highest intensity XRD peaks for the 2q angles were 15 , 17, 18 , 20 , 23 and 26 , slightly different from the 15 , 17, 18 and 23 of the corn starch. The Ramon starch exhibited C-type crystal as classified (Zobel, 1988b), while the corn starch exhibited A-type crystal. It has been proposed that these differences in the diffraction patterns of different starch sources are due to the radial arrangement of the amylopectin chains. This arrangement consists of a region with ramification points and another containing ordered double helices, on et al., 1998). composed of short chains of amylopectin (Bule The highest (percentage of) crystallinity obtained was for Ramon starch (30.56 ± 0.98) and the lowest values for corn starch
(26.68 ± 0.78). The differences in relative crystallinity between Ramon starch and corn starch could be attributed to differences in crystallite size, amount of crystalline regions, orientation of the double helices within the crystalline domains, or the extent of interaction between double helices (Hoover & Ratnayake, 2002). According to the results, the percentage of crystallinity obtained for the Ramon starch are similar to those reported for pulse starches such as pinto bean, pigeon pea, pea, lentil, black bean and grasspea (Hoover, Hughes, Chung, & Liu, 2010). rez-Pacheco et al. (2014), the Ramon starch According to Pe showed enthalpy values (DHgel) higher than those of corn starch. This result could be explained by the difference in crystallinity of the starches analyzed in this work (Ramon ¼ 30.56% and ~ on, Corn ¼ 26.68%) (Fig. 1). Some reports (Iturriaga, Lopez, & An 2004) indicated that the presence of crystalline zones increases the amount of thermal energy required to initiate the melting of starch while the amorphous zones reduce the amount of energy. Therefore, Ramon starch requires a higher temperature to gelatinize, indicating that it presents more thermally and structurally stable crystalline regions, in comparison with corn starch. 3.2. Fourier Transform Infrared Spectroscopy (FTIR) analysis The information obtained with this technique is related to the short-range ordering in the starch molecule (Sevenou, Hill, Farhat, & Mitchell, 2002). Fig. 2 shows the FTIR spectra corresponding to the Ramon and corn starches. Absorption at 3389e3420 cm1 was observed in both starches, corresponding to the stretching vibrations of the hydroxyl groups (eOH) and contributing in the interand intra-molecular interactions of OHe; which is a particular characteristic of starch structure (Fang, Fowler, Tomkinson, & Hill, 2002). The band observed at 2930 cm1 corresponds to the stretching vibration of the hydrogen with respect to the bonds (CeH) associated with the glucopyranose ring (Mano, Koniarova, & Reis, 2003). The water absorbed by the starch appears in the spectrum with a characteristic medium band between 1640 and 1650 cm1 (Kacurakova & Wilson, 2001). Other bands were observed between 1421 and 1300 cm1, corresponding to CeH bonds. In the region known as “fingerprint”, characteristic peaks of starch can be observed at 1155, 1087 and 1019 cm1, corresponding to the vibrations of glucose CeOeC bonds, and at 928, 862, 764, 709, 605 and 573 cm1, attributed to the pyranose ring (Chi et al., 2007). In starch there is an amorphous region and a crystalline region; the quantity of each is important in predicting the response of this polysaccharide when it is processed or that of the products that contain starch when they are stored. The absorbance ratio (bands) of 1022:1047 cm1 was used to represent the order in the starches. The wave length band of 1047 cm1 is related to the ordered region, and the band at 1022 cm1 to the amorphous component (Van Soest, Tournois, Wit, & Vliegenthart, 1995). The values obtained for this ratio were 1.04 and 1.14 for corn starch and Ramon starch, respectively. The Ramon starch had greater ordering (more crystalline areas) than corn starch, coinciding with the crystallinity values obtained by X-ray diffraction, although the latter technique measures long-range ordering in the sample. 3.3. Thermogravimetric analysis (TGA)
Fig. 1. X-ray diffraction patterns of Ramon and corn starches.
The thermal behavior of the Ramon starch was investigated with TGA. Fig. 3a and b shows the thermogram (TG) and its derivative (DTG), as a function of the temperature, for Ramon and corn starches, respectively. For the samples, the thermal decomposition process was developed in three steps. The first step, corresponding
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Fig. 2. FTIR spectra of Ramon and corn starches.
Fig. 3. TGA results of the thermal decomposition and its derivative (DTG); a) Ramon starch; b) corn starch.
to a reduction in mass at temperatures below 150 C, can be associated to the loss of water of the samples (Liu et al., 2010), this value is approximately 10% of the weight for Ramon starch, while in corn starch sample, it reaches up to 8% (Fig. 3). In the second stage (250 ± 10 C T 360 ± 10 C), mass loss is due to the main decomposition processes of starch macromolecules (Liu et al., 2010). Both Ramon and corn starches showed high temperature decomposition (333.7 C and 338.4 C, respectively), which is consistent with the degradation of starch studied by Mano et al. (2003). This result indicates that Ramon starch shows greater similarity with corn starch, this finding is consistent with the rez-Pacheco et al. (2014). amylose determination reported by Pe In the second stage, the mass of the Ramon starch was diminished by 67%, while the mass of the corn starch was diminished by 72%. In the third stage (T > 400 C), inert carbonaceous residues were formed; mass loss became stabilized. Fig. 3 also shows the first derivative DTG curves of the main stage corresponding to the degradation of the starches studied. The well-defined peak in these curves permits to identify the beginning
and end if the event corresponding to thermal degradation. This stage begins with a rapid dehydration and decomposition of hydroxyl groups in glucose rings to form water molecules. According to Liu et al. (2010) during this stage the main chain breaking occurs when CeCeH, CeO, and CeC bounds break. The gaseous decomposition products consist primarily of H2O, CO, and CO2. As can be seen in Fig. 3, the DTG curves exhibited only one peak, indicating the possibility of a simple mechanism of reaction involving degradation of the starch polymers (amylose and amylopectin) (Liu et al., 2010). However, the DTG of the corn starch presented a peak at 311 C; this peak in the DTG has been reported in literature and is attributed to the degradation of protein (Porter, Vollrath, Tian, Chen, & Shao, 2009). 3.4. Pasting properties A paste is defined as a viscous mass consisting of a continuous phase of solubilized amylose and/or amylopectin and a discontinuous phase of granule ghosts and fragments. Pasting refers specifically to changes in the starch upon further heating after
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gelatinization has occurred, including further swelling and leaching of polysaccharides from the starch granule, and increased viscosity which occurs with the application of shear forces (Atwell, Hood, Lineback, Varriano-Marston, & Zobel, 1988). The pasting properties of starches are reported to be influenced by size, rigidity, amylose/amylopectin ratio and swelling power of the granules (Singh, Kaur, Ezekiel, & Guraya, 2005). Table 1 summarizes the pasting properties of Ramon starch and corn starch measured in the Brabender Viscoamilograph. The pasting properties of Ramon starch differed from those of corn starch. As shown in Table 1, during the heating stage, the viscosity increases gradually until a maximum value is obtained (267 UB at 92 C for Ramon starch and 252 UB at 92 C for corn starch). This is due to the fact that, when the granules of starch are heated in excess of water, the phenomenon of heat and moisture transfer occurs, causing swelling of the granules; on reaching the cooking stage of the paste (95 C for 15 min), Ramon starch presented a slight increase in viscosity that was higher in the cooling step, while corn starch showed a slight decrease in viscosity values that increased in the cooling step, these values, however, were still higher than those of Ramon starch. The increment observed in the viscosity values during the cooling step is due to a molecular re-association, i.e. the liberated amylose forms three-dimensional networks (entanglements) since it interacts with the molecules of water by means of hydrogen bonds (Thomas & Atwell, 1999). Breakdown and setback viscosities were observed to be highest in corn starch but lowest in Ramon starch. The higher breakdown for corn starch in comparison with that of Ramon starch suggested that corn starch was less resistant to heat and mechanical shear and hence more prone to loss of viscosity upon holding and shearing. The setback is the viscosity increase resulting from the rearrangement of amylose molecules that have leached from swollen starch granules during cooling, and is generally used as a measure of the gelling ability or retrogradation tendency of starch (Karim, Norziah, & Seow, 2000). The consistency of Ramon starch in heating and cooling processes, measured with continuous shearing force, makes it potentially useful in products requiring sterilization, such as sauces and baby food. Its pasting properties indicate that it remains stable in cooking processes; however, its viscosity increases when cooled, indicating that it is not stable in cooling processes. These are vital aspects to consider when incorporating this starch into a food production process.
3.5. Rheological profile The ideal starch for many food products is one which, at low concentrations, produces a smooth texture with a heavy-bodied paste that remains soft and flexible at low temperature and Table 1 Paste properties of Ramon and corn starches. Parameter
Ramon starch
Corn starch
Initial gelatinization temperature ( C) Maximum viscosity (BU) Viscosity at 95 C Maximum viscosity temperature ( C) Viscosity at 95 C for 15 min (BU) Viscosity at 50 C (BU) Viscosidad a 50 C por 15 min (BU) Breakdown (BU)a Consistency (BU)b Setback (BU)c
82 267 202 92 265 386 441 2 119 121
72 252 241 92 236 539 520 16 287 303
a b c
Breakdown, maximum viscosity (BU) d viscosity at 95 C for 15 min (BU). Consistency, viscosity at 50 C (BU) d maximum viscosity (BU). Setback, viscosity at 50 C (BU) d Viscosity at 95 C for 15 min (BU).
retains its thickening power at high temperatures and high shear. In this respect, the study of rheological properties is of major importance. The strain amplitude sweep, used to define the linear viscoelastic region (LVR) applied to the starch dispersions with 5% (w/v) total solids, during the initial stage at 95 C, shown in Fig. 4a, was usually linear, beginning at values greater than approximately 1% strain or deformation. Each plot is essentially flat, with the storage modulus (G0 ) dominating the measured amplitude strain range. Both starches exhibited viscoelastic gel-like behavior, with overall Tan d values (G00 /G0 ) ranging from 0.08 to 0.34, which are consistent with those of amorphous polymers (Ferry, 1980), a structure presented by starches when they are heated at temperatures higher than their gelatinization temperatures (83 C for Ramon starch and 71 C for corn starch), destroying their crystallinity, but maintaining the amorphous material. During initial heating from 25 C (ambient temperature) to 95 C, gelation probably occurred due to the formation of a network of physical bonds between molecules as a result of phase change from solid to gel (Chel-Guerrero, Cruz-Cervera, Betancur-Ancona, & SolorzaFeria, 2011). Local helical structure, microcrystallites and nodular domains have been proposed as the interactions that give rise to such a physical gelation (Ferry, 1980). No evidence was observed of sudden changes in the moduli, which would indicate a breakdown in starch structure. Similar amplitude profiles were observed after cooling to 25 C in the final stage (Fig. 4b). The LVR was well defined within the tested strain range with the flat plots indicating that the moduli had no real amplitude dependence in all samples. The G0 values were higher than the G00 values, and Tan d values ranged from about 0.05 to 0.6; this is typical of “weak” viscoelastic gels exhibiting high elasticity within the studied amplitude interval. Linear viscoelastic behavior was observed in the frequency sweep profiles for the starch dispersions with 5% (w/v) total solids at 95 C (heating stage) and 25 C (cooling stage) (Fig. 4). In the starches, the G0 > G00 relationship remained unchanged across the applied frequency range, at both 95 and 25 C. The elasticity (G0 ) was significantly higher, approximately twice as high, from corn starch, in comparison with the G0 obtained from Ramon starch. In all starch gels, the elastic (G0 ) modulus was more affected by the cooling process, when going from the heating to the cooling stage (G0 25 C > G0 95 C) (Fig. 4c and d). This may have occurred due to gel structure reinforcement during cooling caused by enhanced interactions between amylose/amylopectin molecules producing double-helix aggregation (Chel-Guerrero et al., 2011). Firstly, when starches are heated, their amylose molecules dissolve inside the starch granules forming a colloidal solution. As the temperature increases, in this case from 25 C (initial stage) to 95 C (heating stage), modulus values (G0 and G00 ) also increase due to granule swelling and increased intermolecular interactions, giving place to starch gelatinization. Gelatinized starch systems have been described as suspensions of swollen starch granules in a continuous phase. During heating, and before G0 and G00 reached maximum values, the starch granules acted as rigid fillers within the continuous phase. The initial increase in G0 and G00 was due to a progressive swelling of the starch granules so that they finally become close-packed (Zobel, 1988b). Although the loss modulus followed the same trend the G00 25 C > G00 95 C ratio was observed in the starch gels, the increase in G00 values was less than that of G0 values (Fig. 4c and d), suggesting that the viscous modulus behavior could be a function of starch source due to the different physical characteristics and changes of the starches during heating. Starch granule size can determine differences in moduli and any modifications in starch characterisndeztics may affect modulus values (Gonz alez-Reyes, Me rez, 2003). Montealvo, Solorza-Feria, Toro-Vazquez, & Bello-Pe
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Fig. 4. Strain amplitude sweep (a and b) and frequency sweep (c and d) of starch dispersions with 5% (w/v) of total solids for Ramon and corn starches at 25 C and 95 C.
The increase in modulus values (G0 , G00 ) caused by cooling from 95 C (initial) to 25 C (final stage), was probably the result of the formation of a packing system with higher rigidity through an increase in cross-links between neighboring molecules, which would have increased the degree of physical intertwining. This behavior during starch cooling is evidence of gel formation (Ferry, 1980). The corn and Ramon starches transitioned from being weak viscoelastic gels (Fig. 4) to gels with enhanced molecular interactions that conserved some properties of weak systems (overall Tan d values <0.6) without adopting a rigid structure. These results corroborate that Ramon starch has potential applications as a thickening and stabilizing agent that could be used to control consistency in food systems such as gravies, soups, puddings, etc., taking into account the data of its thermal properties previously mentioned.
4. Conclusions Physicochemical characterization methods such as X-ray diffraction, FTIR, paste properties and rheology reveal differences between the starches studied herein. According to paste properties, the Ramon starch exhibited higher resistance to heat and heat stability than corn starch, therefore it can be widely used as main component in products that need to be exposed to high temperatures. Due to the rheological properties and paste formation, Ramon starch can also be employed as a pharmaceutical excipient in tablet and capsule formulation, and has a potential use as thickening and gelling agent
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