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Pasting and gel characteristics of normal and waxy maize starch in glucose syrup solutions
Journal of Cereal Science 79 (2018) 253e258
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Pasting and gel characteristics of normal and waxy maize starch in glucose syrup solutions Wiktor Berski*, Rafał Ziobro w, Poland Department of Carbohydrate Technology, University of Agriculture in Krako
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 June 2017 Received in revised form 10 November 2017 Accepted 10 November 2017 Available online 11 November 2017
Sugars are among the constituents which significantly affect the process of starch gelatinization and settle properties of the resulting gels. The information about the influence of sugar mixture like glucose syrup (GS) on starch pasting, as well as on properties and stability of the resulting gel is important for wide range of food applications. In order to determine role of amylose in observed phenomena the study involved normal (MS) and waxy maize (WS) starches. Starch suspensions were pasted in GS solutions, and the texture of resulting gels was also evaluated. In the presence of glucose syrups pastes and gels of MS and WS change their rheological properties. This involves an increase in pasting temperature and viscosity of the pastes, and modification of texture properties of stored gels. In the case of MS application of GS led to incremental decrease of gel hardness, while an opposite effect could be seen for weak WS gels. All these effects were highly dependent on starch type, and concentration of GS. It is assumed that the main factor for observed differences was amylose content. This difference clearly shows that amylose containing starch granules require more water for full gelatinization than their amylopectin counterparts. © 2017 Published by Elsevier Ltd.
Keywords: Avrami equation Glucose syrup Pasting Retrogradation Texture
1. Introduction Physico-chemical properties and interactions with other components of food systems are crucial for application of starches in food technology. Sugars, or more precisely soluble mono-, di- and oligosaccharides, are among the constituents which significantly influence the process of starch gelatinization and settle properties of the resulting gels (Torley and van der Molen, 2005). Their impact on starch gelatinization was excessively studied (Bean et al., 1978; Beleia et al., 1996; Berski et al., 2016; Sopade et al., 2004; Spies and Hoseney, 1982) using various techniques, but mostly focusing on rheological methods. The comparison between individual sugars was often an aim of such studies, but much less attention was paid to possible synergistic or antagonistic effects appearing in
List of abbreviation: MS, normal maize starch; WS, waxy maize starch; GS, glucose syrup; HPS, hot paste stability; HPSI, hot paste stability index; PT, pasting temperature; PVT, temperature at maximum viscosity; TPV, time needed to reach maximum viscosity; PV, maximum viscosity; MV, minimum viscosity; TV, through viscosity; BD, breakdown (BD ¼ PVeMV); SB, setback (SB ¼ TVeMV), BD% ¼ BD PV , SB . SB% ¼ TV * Corresponding author. Department of Carbohydrate Technology, University of w, 30-149 Krako w, Balicka 122, Poland. Agriculture in Krako E-mail address: [email protected] (W. Berski). https://doi.org/10.1016/j.jcs.2017.11.008 0733-5210/© 2017 Published by Elsevier Ltd.
mixtures of various saccharides, such as honey or starch syrups (Torley and van der Molen, 2005). The initial view, that sugars influence starch gelatinization mostly by binding water (D'Appolonia, 1972; Derby et al., 1975; Hoseney et al., 1977), thus apparently increasing starch concentration (Kohyama and Nishinari, 1991) and shifting its transition temperatures towards higher values seems to be still predominating. There are some other mechanisms which could be involved in the observed increase of gelatinization temperature, not necessarily mutually contradictive. According to Spies and Hoseney (1982) sugar molecules decrease water activity in the system and stabilize amorphous regions of starch granule, which requires more energy [higher temperature] for a disruption. According to Evans and Haisman (1982) decreasing water activity is accompanied by a reduction in the volume of water inside starch granules. Chungcharoen and Lund (1987) and Slade and Levine (1987) suggest that the water-saccharide system works as anti-plasticiser in comparison to water, thus requiring stronger forces (higher energy) to disrupt the granules. Kohyama and Nishinari (1991) suggest that sugar stabilizes crystalline regions of starch granule and immobilizes part of water which results in the observed shift of gelatinization temperature. The influence of various sugars is not the same however, and there is no general rule for predicting their behavior
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in food systems. The size of the molecules doesn't seem to be especially important, e.g. maltotriose (trisaccharide) inhibits pasting more than maltose, but less than succrose (which are both disaccharides). The number and conformation of hydroxyl groups seems to be more significant, as it was proposed by Kohyama and Nishinari (1991). Even a type of glycosidic bonds between identical sugar molecules could make a difference, as in the case of maltose and gentiobiose (Spies and Hoseney, 1982). Summarizing it seems that saccharides retard gelatinization by two main mechanisms e decrease of water activity and stabilization of certain parts of starch granules via hydrogen bonds. The use of starch syrups in food industry is still growing due to economical and technological reasons (Blanchard and Katz, 2006). However in most cases such syrups consist of a range of different sugars in various proportions. The information about the influence of such mixture on starch pasting, as well as on the properties and stability of the resulting gel seems to be important. Especially if we consider the effects on corn starch, which is produced in the greatest amount. In order to better understand the role of amylose level for observed phenomena the study involved also waxy maize starch. 2. Materials and methods 2.1. Material Samples of starches investigated in this research were as follow: normal maize starch (MS) and waxy maize starch (WS) were produced by National Starch. Amylose content in starches was measured according to Morrison and Laignelet (1983). Briefly starch was dissolved in ureaddimethylsulphoxide (UDMSO) and aliquots of the solution were used to determine amylose content. This method is based on formation of blue color complex that amylose forms with iodine. Starch samples were characterized by the following content of amylose 20.89 ± 0.09 (MS) and 0.11 ± 0.01% (WS). Glucose syrup G36 was produced by Cargill (Ka˛ ty Wrocławskie, Poland). Weight average molar mass of sugar syrup was 4214 g/ mol, and the degree of polymerization distribution was published elsewhere. The share of sugars with a different DP contained in the investigated glucose syrup determined by HPLC was: DP 1 (8.5% ± 0.2), DP 2 (16.1% ± 0.1), DP 3 (13.6% ± 0.3), DP 4 (48.9% ± 0.2) DP > 5 (12.8% ± 0.1), so about 75.3% were sugars with DP 3 (Berski et al., 2016). 2.2. Methods
temperature profile: initial temperature 45 C, heating to 96 C, holding for 10 min, cooling to 25 C and holding for 5 min. Heating and cooling rate was 4.5 C/min, and the measuring cylinder was rotating at 150 rpm. (Berski et al., 2014). To determine the stability of hot paste viscosity (HPS) the peak viscosity temperature was determined and time maintained above 80% of peak viscosity (Kiribuchi-Otobe et al., 2001). Another attempt is based on hot paste stability index (HPSI ¼ AAPc ), where Ac is a area under a pasting curve measured between peak viscosity and end of heating period, whereas AP is an area of hypothetical rectangle, with height of peak viscosity, and other side is a distance between peak viscosity and end of heating period (the same value as for Ac). 2.2.3. Determination of texture profile analysis (TPA) This analysis was performed on 5% and 10% starch gels. Starch (22.5 g or 45 db) was placed in viscograph Brabender bowl 450 ml (Duisburg, Germany) and then water (0%) or glucose syrup (10, 20, 30, 40 or 50%) was added in order to obtain final 5% (or 10%) suspension. The temperature profile was as follows: initial temperature 25 C, heating to 96 C, holding for 20 min, cooling to 25 C and holding for 10 min. Heating and cooling rate was 1.5 C/min, and the measuring cylinder was rotating at 75 rpm. Paste was transferred into plastic container (40 ml, 37 mm) and allowed to cool down to ambient temperature within 2 h. Then samples were stored at refrigerated conditions up to seven days. TPA analysis was performed using TA-TX2 texture analyzer (stable Microsystems, Surrey, England) using standard TPA protocol and P/20 measuring device (aluminum cylinder 4 20 mm). The tests were performed at 0, 1, 5 and 7 day. Before analysis samples were allowed to equilibrate to room temperature (Berski et al., 2016). Obtained data were used in order to determine the course of starch retrogradation. The changes of hardness during storage were described by Avrami equation:
Q¼
n DH∞ DHt ¼ ekt DH∞ DH0
(1)
where q is the fraction of unrecrystallized sample; DH0 [N], DH∞ [N] and DHt [N] are hardness at zero time, ∞ and t time, respectively, k (h-n) is a rate constant, and n is the Avrami exponent (Ziobro et al., 2013). In order to facilitate the direct comparison among all investigated samples, the equation exponent was considered as equal to 1. After simplifying and transforming the equation takes the form:
2.2.1. Preparations of glucose syrup solutions Glucose syrup solutions (GS) of different concentrations (10%, 20%, 30%, 40% or 50%) were prepared by dissolving a proper amount of glucose syrup (100, 200, 300, 400 or 500 g db) in water, under constant stirring in glass beaker using mechanical stirrer until dissolved, at 30 C, and then refill with water up to 1000 g. Prepared in this manner stock syrup solutions were denoted as 10, 20, 30, 40 or 50 and used for samples preparation (Berski et al., 2016). Water activity (aw) of glucose syrup solutions was measured (LabMaster-aw, Switzerland), and was as follows: 0.987 (10%), 0.983 (20%), 0.979 (30%), 0.973 (40%), 0.963 (50%).
DHt ¼ DH∞ ðDH∞ DH0 Þ$ekt
2.2.2. Rheological examination of the 5% and10% starch pastes Pasting characteristics were performed in water (without syrup - 0%) and water based solutions of glucose syrup (10, 20, 30, 40 or 50%) using Micro Visco Amylo-Graph Brabender, Duisburg, Germany. 5 g (or 10 g) of starch (db) was used to prepare 5% (or 10%) (w/w) dispersions, which were pasted using the following
3.1. Starch pasting characteristics
(2)
All the measurements were done at least in two replications. In order to determine statistically significant differences among the means there were performed One-way analysis of variance (ANOVA) and least significant difference (LSD) at significance level of 0.05 was calculated using the Tukey post hoc test. Calculations were performed using the statistical package Statistica 9.0 (StatSoft Inc., USA). 3. Results and discussion
Pasting characteristics of water 5% and 10% suspensions of normal and waxy starch with a share of 10, 20, 30, 40 and 50% starch syrup were compared with control samples, with no added sugars, denoted as 0 (Table 1, Fig. 1). Lower pasting temperature
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255
Table 1 Selected parameters of pasting profile of 5% and 10% maize and waxy maize starch pastes in presence of glucose syrup. Concentration
5%
Starch
MS
WS
10%
MS
WS
Syrup
PT
[%]
[ C]
0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50
81.6a 82.8ba 83.9bc 84.5bc 85.2c 90.4d 68.8a 69.9ab 71.7ab 72.1ab 72.5b 76.4c 71.8dc 72.5d 72.8d 76.5e 78.0ef 80.2f 66.6a 67.4ab 69.5cb 70.6dc 72.5d 75.8e
PVT
TPV
HPS
[sec.] 90.4a 89.4a 91.7ab 94.4cb 96.0c 96.0c 75.8a 79.0ba 81.7bc 82.2bc 82.4bc 84.7c 83.9cb 88cd 88cd 88.4cd 91.3de 96.0e 73.1a 73.4a 75.2a 80.9b 80.3b 86.1c
617.4a 645.0ab 630.0a 670.2b 715.2c 927.6d 409.8a 454.8b 450.0b 472.8bc 510.0c 575.4d 522.6dbc 589.8de 595.2de 615.05e 645.05e 870.00f 372.6a 354.95a 372.6a 460.2b 472.8bc 540.0dc
PV
MV
TV
BD
SB
[B.U.] 693c 683c 688c 638bc 613b 523a 393c 310bc 268ab 273ab 170a 210ab 213cd 198cbd 253cd 365e 715f 645f 258d 178acb 180acb 113a 123ab 115a
39a 49b 64c 76d 95f 89e 121a 148b 175c 194d 224e 250f 276a 351b 377c 404d 476f 491fg 340b 406d 431e 497g 556h 639i
BD%
SB%
HPSI
57.8bcd 60.2cd 62.2d 55bc 51.8b 45.4a 32.8a 33.2a 35.9ab 37.6abc 39bc 42.3c 55.8efg 47.6ced 62.1g 59.0fg 55.3efg 38.2ab 35.2a 37.8ab 41.8abc 40.7abc 45.2bcd 52.2efd
89.0bc 88.3b 84.8a 92.2cd 95.1de 98.0e 76.4c 72.8b 70.7ab 70.4ab 69.0a 68.4a 69.7bc 65.1ba 71.2bc 80.1cd 93.5de 98.5e 59.4ba 55.6a 63.6ba 61.6ba 61.9ba 62.4ba
[%] 34a 42b 52c 67d 86e 86e 75a 86b 100c 107c 127d 146e 159a 190cb 224de 278f 440h 492i 167ab 190c 204cd 239e 279f 323g
81a 106b 138c 150cd 158d 183e 110a 130a 155b 172b 207c 254d 363bc 366bc 571d 702e 980g 795f 260a 311ba 353bc 406c 514d 701e
5a 7ab 12b 8ab 8ab 3a 46a 62b 75c 87cd 99de 104e 118c 162e 153ed 127cd 38b 2a 172e 216f 226f 258g 277g 309h
47a 64ab 86cd 83cd 95d 72cb 37a 43ab 56bc 65c 81d 108e 203bc 174abc 355ef 414f 543g 304ed 92.0a 118ab 148abc 165abc 233cd 366ef
12.8bc 14.4bc 18.8c 10.6b 7.9ba 3.4a 38.0a 41.6ba 41.6ba 42.9b 44.0b 44.7b 42.6de 46.1fde 40.6d 31.3c 7.9b 0.4a 50.5gf 53.1g 52.4g 52gf 49.8gf 48.4gfe
*MS. normal maize starch; WS. waxy maize starch; PT. pasting temperature; PVT. temperature at maximum viscosity; TPV. time needed to reach maximum viscosity; PV. SB maximum viscosity; MV. minimum viscosity; TV. through viscosity; BD. breakdown (BD ¼ PVeMV); SB. setback (SB ¼ TVeMV); BD% ¼ BD PV ; SB% ¼ TV ; HPS. hot paste stability; HPSI. hot paste stability index. Different letters in column within concentration range imply statistically significant differences at the significance level a ¼ 0.05.
Fig. 1. Pasting profile of 5% and 10% maize (MS_5% and MS_10%) and waxy maize (WS_5% and WS_10%) starch suspensions.
(PT) of waxy starch in comparison to MS is well known, and caused by the lack of amylose, the component of starch granule retarding disintegration of the granules (Hermansson and Svegmark, 1996). An increase of PT with rising share of glucose syrup above 20% (MS) or 40% (WS) could be observed (Table 1, Fig. 1), but the difference between PT of MS and WS remains unchanged. The increase in PT caused by the presence of sugars is known and follows the retardation of granule swelling (Berski et al., 2016). Increased starch concentration (from 5% to 10%) resulted in observed lower PT, due to fact that the same volume was occupied by greater amount of swelling starch granules, and an increase in viscosity was observed earlier.
In the presence of glucose syrup (GS) an increase in peak viscosity (PV) of starch pastes could be observed, which is parallel to the concentration of GS. The values of this parameter are much larger in the case of WS, because it is rich in amylopectin, which nchez et al., 2010; Song could swell much more than amylose (Sa and Jane, 2000; Tester and Morrison, 1990). For 5% starch pastes, in the case of MS, the largest almost 2.3-fold increase in viscosity could be observed after application of 40% syrup, while in the case of WS more than twice increase was measured for sample containing 50% GS. For 10% starch pastes a constant increase was still observed, almost 1.8 for MS, and 1.9 for WS. An increase caused by the presence of GS was also observed in temperatures, at which the maximum viscosity of paste could be measured (PVT). Their values continually rise up to 30% GS concentration in the case of MS, and up to 20% concentration for WS samples when 5% starch pastes are evaluated. For 10% MS pastes this threshold was moved up to 40% GS, whereas for WS remained unchanged, but in fact it occurred at lower temperature than for 5% pastes. This trend could be to some extent explained by slower swelling of the granules, because higher temperatures are obtained after longer times of analysis (TPV). In the case of 5% MS pastes prepared with 40 and 50% of GS, maximum viscosity is obtained after reaching maximum temperature, but the difference in TPV values is still significant (715.2 vs 927.6 min). For 10% pastes TPV values are lower than for respective 5% pastes. Nevertheless the results demonstrate growing resistance of starch granules towards pasting with increasing GS concentration. After reaching maximum viscosity MS pastes tended to stabilize their rheological behavior, and no statistically significant changes in viscosity values during heating were observed as compared to PV, when 10e30% GS preparations were used. In the case of MS, pastes prepared in 40% (only for 5% MS paste) and 50% GS maximum viscosity (PV) was not reached during heating period. For 10% MS lower hot paste stability was observed, that was followed by
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corresponding values of BD% and HPSI, but for pastes prepared in 40 and 50% GS these values were quite similar like for 5% MS. Obtained results allow to draw a conclusion, that higher GS concentrations better stabilize paste viscosity. In contrary to this pattern maximum viscosity of WS pastes was always obtained below 96 C, which was caused by the lack of amylose, responsible for swelling retardation (Blazek and Copeland, 2009). Further heating of WS pastes caused a significant decrease in paste viscosity. Such a behavior is also related to the absence of linear glucans, which could cross-link with amylopectin and thus form a network stabilizing paste rheology. Further decrease of viscosity occurred after holding WS pastes at maximum temperature. Low resistance to shear and temperature of WS gels was finally reflected by the values of BD% and HPSI. Application of GS did not worsen stability of 5% MS pastes at 96 C, and only a slight decrease in viscosity values could be observed after the end of holding period. But for 10% MS pastes prepared with GS within range 0e30% some decrease was observed The values of breakdown (BD) and hot paste stability index (HPSI) varied slightly between individual samples, with no strong trends up to 30% concentration of GS. Above this level, the pastes tended to be stabilized by increasing GS proportion (smaller BD%, larger HPSI). The HPS parameter proposed by Kiribuchi-Otobe et al. (2001) to describe hot paste stability failed in this case, because longer times required for reaching maximum viscosity, resulted in shortening of the period in which viscosity was above 80% of its peak value (which for all 5% MS samples lasted until the end of a holding phase). In the case of WS pastes a decrease observed after reaching maximum value was amplified by growing GS levels. A strong increasing trend could be observed for BD (and BD%) values, which was accompanied with less significant changes in HPSI values. On other hand, for 10% WS pastes an increased stability was observed when GS concentration was over 20%. The lack of amylose seems to enhance the changes in paste viscosity caused by syrup addition. Initial increase observed for a system with fully swollen granules and highly concentrated syrup solution outside of them, is followed by a sharp decrease in viscosity (even to about 50% of the peak value), resulting from elevated shear. Quick disruption of the swollen granules could be seen in a growing slope of the resulting curves. Evidently the dextrins present in starch syrup and dissolved amylopectin molecules could not form a stable network, probably because of too short linear segments (not allowing formation of cross-links between adjacent amylopectin molecules). During the cooling period (to 25 C) an increase in viscosity of starch pastes could be observed, and the final values depended strongly on the concentration of GS, generally increasing with its level. Only in the case of MS pastes with 50% GS final value was lower in comparison to 40% GS ones. This exception could be due to excessive level of sugars, which reduced water activity below the values allowing full pasting of starch granules. The retardation of peak viscosity, discussed above, seems to favor such a view. In the case of WS starch the level of water activity required for full gelatinization is seemingly smaller, because of the lack amylose, so similar phenomenon could not be observed. After holding the pastes at 25 C for 10 min, only small changes in viscosity could be observed, mostly in the case of MS. Higher values of final viscosity determined for 5% WS samples is in nchez et al. (2010) and Song and agreement with the results of Sa Jane (2000) and could be explained by the lack of amylose, responsible for reduced granule swelling (Hermansson and Svegmark, 1996). In contradiction, for 10% systems final viscosity values were higher for MS than for WS pastes due to excessive formation of hydrogen bonds between amylose chains profusely
occurring in the vicinity, and by greater integrity of swollen MS granules. Setback value (SB, Table 1) is sometimes regarded as an indicator of starch retrogradation. A drop in SB% observed with growing concentration of GS in the case of MS may suggest decreasing retrogradation susceptibility, probably caused by limited leaching of amylose out of the granules. Such statement could be supported by lower appropriate values for 10%, when smaller amount of water was available due to higher starch concentration. In the case of WS pastes an increase of SB% could be seen with rising GS levels, which is probably due to better dissolving of amylopectin fragments, which could form stronger networks upon cooling. 3.2. Gelling characteristics Hardness of the gels prepared with MS was higher than of WS samples, with exception for gels prepared in 50% GS, and 10% gel prepared with 40% GS at last day of storage (Table 2). This again reflects the lack of amylose in WS samples, which is especially important for network formation and gel structure (Banerjee and Bhattacharya, 2012). Cross-links between amylopectin molecules are less frequent, because of their branched character, and could be formed only by the external chains. It was observed, that stronger gels could be formed by starch containing high levels of amylose and longer chains of amylopectin (Mua and Jackson, 1997). Retrogradation of waxy starches results in soft gels, which contain amylopectin aggregates but do not form a continuous network (Wang et al., 2015), and therefore could be easily deformed despite of their high adhesiveness. Hardness of 5% MS gels with 10% GS was higher than of those prepared with pure water, but further increase of GS concentration caused a drop in this parameter. In the case of 10% MS gels with 20%
Table 2 Changes in hardness of 5% and 10% gels from maize and waxy maize starches. Syrup [%]
day
Hardness [N] 5%
10%
MS 0
10
20
30
40
50
0 10 20 30 40 50
WS f
MS a
WS abc
1 2 7 1 2 7 1 2 7 1 2 7 1 2 7 1 2 7
1.383 1.659g 2.185hi 2.031h 2.344ij 2.522j 0.636cde 0.736de 0.885e 0.384abc 0.444bc 0.548cd 0.441bc 0.465c 0.473c 0.196a 0.209a 0.274ab
0.136 0.14a 0.146a 0.191bc 0.194bc 0.207bc 0.179b 0.188b 0.193bc 0.199bc 0.219cd 0.248de 0.324f 0.341f 0.426h 0.278e 0.314f 0.382g
6.090 7.175bcd 11.195f 9.395def 11.431fg 14.676h 11.084efg 13.905gh 18.421i 7.961bcd 8.266cde 8.757cdef 6.749abcd 7.488bcd 8.162cde 4.129a 4.961ab 7.367abcde
0.385a 0.588ab 1.039ab 0.432ab 0.797ab 3.362de 0.61abc 1.242abcd 5.161ef 0.937ab 1.682abcd 7.253fg 1.747bcd 3.946e 13.001h 2.513cd 7.99g 29.089i
1 2 7
0.912a 1.053b 1.234c
0.225a 0.233a 0.267b
7.729a 9.333b 11.969c
1.253a 3.311b 11.7c
1.742d 2.299e 0.752c 0.458b 0.460b 0.226a
0.142a 0.197ab 0.192a 0.222ab 0.364c 0.324bc
8.153b 11.265c 14.893d 8.274b 7.566b 5.109a
0.671a 1.53b 2.338bc 2.702c 6.231d 13.197e
*Different letters in column imply statistically significant differences at the significance level a ¼ 0.05.
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GS the samples were also harder than reference (0% GS) It seems that at a certain concentration, sugars prevent formation of compact gels, while their lower amounts may stiffen the amyloseamylopectin network. Similarly in the studies on starch-inulin gels (Krystyjan et al., 2015) a slight increase (in comparison to pure starch gels) could be observed in their firmness when 10% of inulin was used, but further elevation of its level up to 20% caused its decrease, and only the highest applied amounts of inulin (25%) resulted in significant strengthening of the gels. In the case of waxy starch no typical gel could be formed, but hardness of the sample increased during storage, which confirms earlier results (Han et al., 2005). Hardness of WS systems was small, but increased with increasing levels of GS. The effect could to be a consequence of small number of linkages between external branches of AP, which might be increased due to a presence of short chain dextrins, or simply an effect of reduced water activity in such systems. Analyzing the influence of storage time on hardness of MS and WS gels (Table 2) it seems that the effects for both types of starch differ and strongly depend on GS concentration. In the case of MS gels prepared without syrup, prolonged storage leads to their visible strengthening. Addition of 10% GS (and additionally 20% GS for 10% MS gel) amplifies this dependence, but further increase of GS level stabilizes gel properties over time (there are no significant differences between only slightly rising values). Quite a different pattern could be observed for WS gels. 5% gels prepared with water or syrup levels below 20% do not reveal significant changes during 7 days. Above this level hardening is evident. For 10% WS gels a critical GS concentration was lowered. During storage of MS obtained with the use of GS, syneresis could be observed, and gel lost some water, which was especially visible after 7 days of storage. No such phenomenon could be found in the case of WS gels. The observed increase in gel hardness may indicate retrogradation pattern (Wang et al., 2015), which could be described using Avrami equation (Fig. 2). The calculated parameters are shown in Table 3. As it could be observed the introduction of GS to MS system caused an increase in values of individual parameters of Avrami model in comparison to water system (0%). For 10% MS this increase is observed up to 20% GS. Further addition of glucose syrup caused a drop in H∞ indicating final gel strength, demonstrating inhibiting influence of GS onto crystallization of starch molecules. Similar
257
Table 3 Avrami equation parameters. Concentration
Starch
Syrup
H∞ [N]
H0 [N]
K [h1]
R2 [-]
5%
MS
0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50
2.2862 2.5228 0.9002 0.5629 0.4974 0.4662 0.1476 0.2226 0.1930 0.2507 0.5756 0.3944 15,9327 15,1492 18,9759 8,8181 8,8912 8,8269 1.1705 53.6842 83.7168 99.4397 36.0883 66.4178
0.9843 1.1705 0.4751 0.2933 0.3763 0.1794 0.1307 0.1867 0.1558 0.1647 0.2990 0.2255 4,8706 6,3995 6,6921 7,4893 5,6208 3,1187 0.1122 0.1234 0.2530 0.3383 0.6026 3.4774
0.0152 0.0422 0.0198 0.0170 0.0272 0.0023 0.0156 0.0046 0.0408 0.0210 0.0036 0.0154 0,0051 0,0175 0,0184 0,0183 0,0176 0,0081 0.0124 0.0004 0.0004 0.0005 0.0028 0.0037
1.0000 1.0000 1.0000 1.0000 1.0000 0.9989 1.0000 0.9925 1.0000 1.0000 0.9988 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 0.9990 0.9990 0.9994 1.0000 1.0000
WS
10%
MS
WS
dependence (except for the 5% gel containing 40% GS, and 10% gel containing 40% and 50% GS) could be seen in the case of H0, showing decreasing initial hardness of the gel. Because a rise in paste viscosity was accompanying GS addition, this decrease could be due to smaller amounts of leached amylose, available for network formation, and thus creation of a gel structure (Banerjee and Bhattacharya, 2012). The value of K indicates the rate of retrogradation and could be interpreted as rate constant of this process. It could be seen that the introduction of GS leads to an initial increase in K, and afterward a drop in its value for MS gels. The above data suggest that glucose syrup addition results in both retardation and reduction of the extent of starch retrogradation. In the case of WS gels the pattern is different. An introduction of GS resulted in an increase of gel hardness, which was reflected by the Avrami parameters. The value of H∞ grew in parallel to syrup level, reaching maximum value for 40% GS in case for 5% WS gel. For 10% Ws gels with addition of GS the character of changes was not well described by Avrami equation, at least within evaluated period of storage time. H∞ grew, values were reaching remarkable high values, but rather with no physical sense. It demonstrates an increasing extent of retrogradation which could be enhanced by the presence of small dextrins, forming hydrogen bonds with external branches of amylopectin. Also H0 parameter showing initial gel hardness increased with adding syrup, reaching maximum for 40% GS in case of 5% WS gels. For 10% Ws gels H0 values had no physical interpretation. No coherent pattern could be found for the values of K.
4. Conclusions
Fig. 2. Changes in hardness of 5% and 10% maize (MS_5% and MS_10%) and waxy maize (WS_5% and WS_10%) starch gels during storage.
In the presence of glucose syrups pastes and gels of maize starch, both normal and waxy, change their rheological properties. This involves an increase in pasting temperature and viscosity of the pastes, and modification of texture properties of stored gels. In the case of MS gels application of GS led to incremental decrease of hardness, while an opposite effect could be seen for weak WS gels. All these effects were highly dependent on the type of starch, and GS and starch concentration. It is assumed that the main factor for
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observed differences was amylose content. In the case of MS a significant retardation of starch pasting could be seen, as a result of increasing GS. Similar changes in WS were less pronounced. Application of GS had opposite influence on stability of the obtained pastes, which was smaller in the case of waxy starch and slightly improved in the case of MS. At the highest 50% applied level of GS a decrease in MS paste viscosity in comparison to 40% GS sample was measured, which was not detected in the case of WS. This difference clearly shows that amylose containing starch granules require more water for full gelatinization than their amylopectin counterparts. Elevating GS levels had varying effects on texture properties of the gels, which were softened in the case of MS and hardened in the case of WS. References Banerjee, S., Bhattacharya, S., 2012. Food gels: gelling process and new applications. Crit. Rev. Food Sci. Nutr. 52, 334e346. https://doi.org/10.1080/10408398.2010. 500234. Bean, M.M., Yamazaki, W.T., Donelson, D.H., 1978. Wheat starch gelatinization in sugar solutions. II. Fructose, glucose, and sucrose: cake performance. Cereal Chem. 55, 945e951. Beleia, A., Miller, R.A., Hoseney, R.C., 1996. Starch gelatinization in sugar solutions. €rke 48, 259e262. https://doi.org/10.1002/star.19960480705. Starch/Sta Berski, W., Krystyjan, M., Buksa, K., Zie˛ c, G., Gambus, H., 2014. Chemical, physical and rheological properties of oat flour affected by the isolation of beta-glucan preparation. J. Cereal Sci. 60, 533e539. https://doi.org/10.1016/j.jcs.2014.09.001. Berski, W., Krystyjan, M., Zie˛ c, G., Litwinek, D., Gambus, H., 2016. The influence of starch hydrolyzate on physicochemical properties of pastes and gels prepared from oat flour and starch. J. Cereal Sci. 70, 16e22. https://doi.org/10.1016/j.jcs. 2016.05.011. Blanchard, P.H., Katz, F.R., 2006. Starch hydrolysates. In: Food Polysaccharides and Their Applications. Taylor & Francis, Boca Raton, FL, pp. 119e145. Blazek, J., Copeland, L., 2009. Effect of monopalmitin on pasting properties of wheat starches with varying amylose content. Carbohydr. Polym. 78, 131e136. https:// doi.org/10.1016/j.carbpol.2009.03.023. Chungcharoen, A., Lund, B.D., 1987. Influence of solutes and water on rice starch gelatinization. Cereal Chem. 64, 240e243. D'Appolonia, B.L., 1972. Effect of bread ingredients on starch-gelatinization properties as measured by the amylograph. Cereal Chem. 49, 532e543. Derby, R.I., Miller, B.F., Trimbo, H.B., 1975. Visual observation of wheat-starch gelatinization in limited water systems. Cereal Chem. 52, 702e713. Evans, I.D., Haisman, D.R., 1982. The effect of solutes on the gelatinization tem€rke 34, 224e231. https://doi.org/10. perature range of potato starch. Starch/Sta 1002/star.19820340704.
Han, J.-A., Lee, B.-H., Lim, W.J., Lim, S.-T., 2005. Utilization of hydroxypropylated waxy rice and corn starches in Korean waxy rice cake to retard retrogradation. Cereal Chem. 82, 88e92. https://doi.org/10.1094/CC-82-0088. Hermansson, A.-M., Svegmark, K., 1996. Developments in the understanding of starch functionality. Trends Food Sci. Technol. 7, 345e353. https://doi.org/ 10.1016/S0924-2244(96)10036-4. https://doi.org/doi. Hoseney, R.C., Atwell, W.A., Lineback, D.R., 1977. Scanning electron microscopy of starch isolated from baked products. Cereal Foods World 22, 56e60. Kiribuchi-Otobe, C., Yanagisawa, T., Yoshida, H., 2001. Genetic analysis and some properties of starch in waxy mutant wheat tanikei A6599-4. Breed. Sci. 51, 241e245. https://doi.org/10.1270/jsbbs.51.241. Kohyama, K., Nishinari, K., 1991. Effect of soluble sugars on gelatinization and retrogradation of sweet potato starch. J. Agric. Food Chem. 39, 1406e1410. https://doi.org/10.1021/jf00008a010. Krystyjan, M., Ciesielski, W., Khachatryan, G., Sikora, M., Tomasik, P., 2015. Structure, rheological, textural and thermal properties of potato starch e inulin gels. LWT - Food Sci. Technol. 60, 131e136. https://doi.org/10.1016/j.lwt.2014.07.056. Morrison, W.R., Laignelet, B., 1983. An improved colorimetric procedure for determining apparent and total amylose in cereal and other starches. J. Cereal Sci. 1, 9e20. https://doi.org/10.1016/S0733-5210(83)80004-6. Mua, J.P., Jackson, D.S., 1997. Relationships between functional attributes and molecular structures of amylose and amylopectin fractions from corn starch. J. Agric. Food Chem. 45, 3848e3854. https://doi.org/10.1021/jf9608783. nchez, T., Dufour, D., Moreno, I.X., Ceballos, H., 2010. Comparison of pasting and Sa gel stabilities of waxy and normal starches from potato, maize, and rice with those of a novel waxy cassava starch under thermal, chemical, and mechanical stress. J. Agric. Food Chem. 58, 5093e5099. https://doi.org/10.1021/jf1001606. Slade, L., Levine, H., 1987. Recent advances in starch retrogradation. In: Industrial Polysaccharides. Gordon and Breach Science, New York, pp. 387e430. Song, Y., Jane, J., 2000. Characterization of barley starches of waxy, normal, and high amylose varieties. Carbohydr. Polym. 41, 365e377. https://doi.org/10.1016/ S0144-8617(99)00098-3. Sopade, P.A., Halley, P.J., Junming, L.L., 2004. Gelatinisation of starch in mixtures of sugars. II. Application of differential scanning calorimetry. Carbohydr. Polym. 58, 311e321. https://doi.org/10.1016/j.carbpol.2004.07.007. Spies, R.D., Hoseney, R.C., 1982. Effect of sugars on starch gelatinization. Cereal Chem. 59, 128e131. Tester, R., Morrison, W., 1990. Swelling and gelatinization of cereal starches. I. Effects of amylopectin, amylose, and lipids. Cereal Chem. 67, 551e557. Torley, P.J., van der Molen, F., 2005. Gelatinization of starch in mixed sugar systems. LWT - Food Sci. Technol. 38, 762e771. https://doi.org/10.1016/j.lwt.2004.09.001. https://doi.org/doi. Wang, S., Li, C., Copeland, L., Niu, Q., Wang, S., 2015. Starch retrogradation: a comprehensive review. Compr. Rev. Food Sci. Food Saf. 14, 568e585. https://doi. org/10.1111/1541-4337.12143. Ziobro, R., Witczak, T., Juszczak, L., Korus, J., 2013. Supplementation of gluten-free bread with non-gluten proteins. Effect on dough rheological properties and bread characteristic. Food Hydrocoll. 32, 213e220. https://doi.org/10.1016/j. foodhyd.2013.01.006.
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Journal of Cereal Science journal homepage: www.elsevier.com/locate/jcs
Pasting and gel characteristics of normal and waxy maize starch in glucose syrup solutions Wiktor Berski*, Rafał Ziobro w, Poland Department of Carbohydrate Technology, University of Agriculture in Krako
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 June 2017 Received in revised form 10 November 2017 Accepted 10 November 2017 Available online 11 November 2017
Sugars are among the constituents which significantly affect the process of starch gelatinization and settle properties of the resulting gels. The information about the influence of sugar mixture like glucose syrup (GS) on starch pasting, as well as on properties and stability of the resulting gel is important for wide range of food applications. In order to determine role of amylose in observed phenomena the study involved normal (MS) and waxy maize (WS) starches. Starch suspensions were pasted in GS solutions, and the texture of resulting gels was also evaluated. In the presence of glucose syrups pastes and gels of MS and WS change their rheological properties. This involves an increase in pasting temperature and viscosity of the pastes, and modification of texture properties of stored gels. In the case of MS application of GS led to incremental decrease of gel hardness, while an opposite effect could be seen for weak WS gels. All these effects were highly dependent on starch type, and concentration of GS. It is assumed that the main factor for observed differences was amylose content. This difference clearly shows that amylose containing starch granules require more water for full gelatinization than their amylopectin counterparts. © 2017 Published by Elsevier Ltd.
Keywords: Avrami equation Glucose syrup Pasting Retrogradation Texture
1. Introduction Physico-chemical properties and interactions with other components of food systems are crucial for application of starches in food technology. Sugars, or more precisely soluble mono-, di- and oligosaccharides, are among the constituents which significantly influence the process of starch gelatinization and settle properties of the resulting gels (Torley and van der Molen, 2005). Their impact on starch gelatinization was excessively studied (Bean et al., 1978; Beleia et al., 1996; Berski et al., 2016; Sopade et al., 2004; Spies and Hoseney, 1982) using various techniques, but mostly focusing on rheological methods. The comparison between individual sugars was often an aim of such studies, but much less attention was paid to possible synergistic or antagonistic effects appearing in
List of abbreviation: MS, normal maize starch; WS, waxy maize starch; GS, glucose syrup; HPS, hot paste stability; HPSI, hot paste stability index; PT, pasting temperature; PVT, temperature at maximum viscosity; TPV, time needed to reach maximum viscosity; PV, maximum viscosity; MV, minimum viscosity; TV, through viscosity; BD, breakdown (BD ¼ PVeMV); SB, setback (SB ¼ TVeMV), BD% ¼ BD PV , SB . SB% ¼ TV * Corresponding author. Department of Carbohydrate Technology, University of w, 30-149 Krako w, Balicka 122, Poland. Agriculture in Krako E-mail address: [email protected] (W. Berski). https://doi.org/10.1016/j.jcs.2017.11.008 0733-5210/© 2017 Published by Elsevier Ltd.
mixtures of various saccharides, such as honey or starch syrups (Torley and van der Molen, 2005). The initial view, that sugars influence starch gelatinization mostly by binding water (D'Appolonia, 1972; Derby et al., 1975; Hoseney et al., 1977), thus apparently increasing starch concentration (Kohyama and Nishinari, 1991) and shifting its transition temperatures towards higher values seems to be still predominating. There are some other mechanisms which could be involved in the observed increase of gelatinization temperature, not necessarily mutually contradictive. According to Spies and Hoseney (1982) sugar molecules decrease water activity in the system and stabilize amorphous regions of starch granule, which requires more energy [higher temperature] for a disruption. According to Evans and Haisman (1982) decreasing water activity is accompanied by a reduction in the volume of water inside starch granules. Chungcharoen and Lund (1987) and Slade and Levine (1987) suggest that the water-saccharide system works as anti-plasticiser in comparison to water, thus requiring stronger forces (higher energy) to disrupt the granules. Kohyama and Nishinari (1991) suggest that sugar stabilizes crystalline regions of starch granule and immobilizes part of water which results in the observed shift of gelatinization temperature. The influence of various sugars is not the same however, and there is no general rule for predicting their behavior
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in food systems. The size of the molecules doesn't seem to be especially important, e.g. maltotriose (trisaccharide) inhibits pasting more than maltose, but less than succrose (which are both disaccharides). The number and conformation of hydroxyl groups seems to be more significant, as it was proposed by Kohyama and Nishinari (1991). Even a type of glycosidic bonds between identical sugar molecules could make a difference, as in the case of maltose and gentiobiose (Spies and Hoseney, 1982). Summarizing it seems that saccharides retard gelatinization by two main mechanisms e decrease of water activity and stabilization of certain parts of starch granules via hydrogen bonds. The use of starch syrups in food industry is still growing due to economical and technological reasons (Blanchard and Katz, 2006). However in most cases such syrups consist of a range of different sugars in various proportions. The information about the influence of such mixture on starch pasting, as well as on the properties and stability of the resulting gel seems to be important. Especially if we consider the effects on corn starch, which is produced in the greatest amount. In order to better understand the role of amylose level for observed phenomena the study involved also waxy maize starch. 2. Materials and methods 2.1. Material Samples of starches investigated in this research were as follow: normal maize starch (MS) and waxy maize starch (WS) were produced by National Starch. Amylose content in starches was measured according to Morrison and Laignelet (1983). Briefly starch was dissolved in ureaddimethylsulphoxide (UDMSO) and aliquots of the solution were used to determine amylose content. This method is based on formation of blue color complex that amylose forms with iodine. Starch samples were characterized by the following content of amylose 20.89 ± 0.09 (MS) and 0.11 ± 0.01% (WS). Glucose syrup G36 was produced by Cargill (Ka˛ ty Wrocławskie, Poland). Weight average molar mass of sugar syrup was 4214 g/ mol, and the degree of polymerization distribution was published elsewhere. The share of sugars with a different DP contained in the investigated glucose syrup determined by HPLC was: DP 1 (8.5% ± 0.2), DP 2 (16.1% ± 0.1), DP 3 (13.6% ± 0.3), DP 4 (48.9% ± 0.2) DP > 5 (12.8% ± 0.1), so about 75.3% were sugars with DP 3 (Berski et al., 2016). 2.2. Methods
temperature profile: initial temperature 45 C, heating to 96 C, holding for 10 min, cooling to 25 C and holding for 5 min. Heating and cooling rate was 4.5 C/min, and the measuring cylinder was rotating at 150 rpm. (Berski et al., 2014). To determine the stability of hot paste viscosity (HPS) the peak viscosity temperature was determined and time maintained above 80% of peak viscosity (Kiribuchi-Otobe et al., 2001). Another attempt is based on hot paste stability index (HPSI ¼ AAPc ), where Ac is a area under a pasting curve measured between peak viscosity and end of heating period, whereas AP is an area of hypothetical rectangle, with height of peak viscosity, and other side is a distance between peak viscosity and end of heating period (the same value as for Ac). 2.2.3. Determination of texture profile analysis (TPA) This analysis was performed on 5% and 10% starch gels. Starch (22.5 g or 45 db) was placed in viscograph Brabender bowl 450 ml (Duisburg, Germany) and then water (0%) or glucose syrup (10, 20, 30, 40 or 50%) was added in order to obtain final 5% (or 10%) suspension. The temperature profile was as follows: initial temperature 25 C, heating to 96 C, holding for 20 min, cooling to 25 C and holding for 10 min. Heating and cooling rate was 1.5 C/min, and the measuring cylinder was rotating at 75 rpm. Paste was transferred into plastic container (40 ml, 37 mm) and allowed to cool down to ambient temperature within 2 h. Then samples were stored at refrigerated conditions up to seven days. TPA analysis was performed using TA-TX2 texture analyzer (stable Microsystems, Surrey, England) using standard TPA protocol and P/20 measuring device (aluminum cylinder 4 20 mm). The tests were performed at 0, 1, 5 and 7 day. Before analysis samples were allowed to equilibrate to room temperature (Berski et al., 2016). Obtained data were used in order to determine the course of starch retrogradation. The changes of hardness during storage were described by Avrami equation:
Q¼
n DH∞ DHt ¼ ekt DH∞ DH0
(1)
where q is the fraction of unrecrystallized sample; DH0 [N], DH∞ [N] and DHt [N] are hardness at zero time, ∞ and t time, respectively, k (h-n) is a rate constant, and n is the Avrami exponent (Ziobro et al., 2013). In order to facilitate the direct comparison among all investigated samples, the equation exponent was considered as equal to 1. After simplifying and transforming the equation takes the form:
2.2.1. Preparations of glucose syrup solutions Glucose syrup solutions (GS) of different concentrations (10%, 20%, 30%, 40% or 50%) were prepared by dissolving a proper amount of glucose syrup (100, 200, 300, 400 or 500 g db) in water, under constant stirring in glass beaker using mechanical stirrer until dissolved, at 30 C, and then refill with water up to 1000 g. Prepared in this manner stock syrup solutions were denoted as 10, 20, 30, 40 or 50 and used for samples preparation (Berski et al., 2016). Water activity (aw) of glucose syrup solutions was measured (LabMaster-aw, Switzerland), and was as follows: 0.987 (10%), 0.983 (20%), 0.979 (30%), 0.973 (40%), 0.963 (50%).
DHt ¼ DH∞ ðDH∞ DH0 Þ$ekt
2.2.2. Rheological examination of the 5% and10% starch pastes Pasting characteristics were performed in water (without syrup - 0%) and water based solutions of glucose syrup (10, 20, 30, 40 or 50%) using Micro Visco Amylo-Graph Brabender, Duisburg, Germany. 5 g (or 10 g) of starch (db) was used to prepare 5% (or 10%) (w/w) dispersions, which were pasted using the following
3.1. Starch pasting characteristics
(2)
All the measurements were done at least in two replications. In order to determine statistically significant differences among the means there were performed One-way analysis of variance (ANOVA) and least significant difference (LSD) at significance level of 0.05 was calculated using the Tukey post hoc test. Calculations were performed using the statistical package Statistica 9.0 (StatSoft Inc., USA). 3. Results and discussion
Pasting characteristics of water 5% and 10% suspensions of normal and waxy starch with a share of 10, 20, 30, 40 and 50% starch syrup were compared with control samples, with no added sugars, denoted as 0 (Table 1, Fig. 1). Lower pasting temperature
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255
Table 1 Selected parameters of pasting profile of 5% and 10% maize and waxy maize starch pastes in presence of glucose syrup. Concentration
5%
Starch
MS
WS
10%
MS
WS
Syrup
PT
[%]
[ C]
0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50
81.6a 82.8ba 83.9bc 84.5bc 85.2c 90.4d 68.8a 69.9ab 71.7ab 72.1ab 72.5b 76.4c 71.8dc 72.5d 72.8d 76.5e 78.0ef 80.2f 66.6a 67.4ab 69.5cb 70.6dc 72.5d 75.8e
PVT
TPV
HPS
[sec.] 90.4a 89.4a 91.7ab 94.4cb 96.0c 96.0c 75.8a 79.0ba 81.7bc 82.2bc 82.4bc 84.7c 83.9cb 88cd 88cd 88.4cd 91.3de 96.0e 73.1a 73.4a 75.2a 80.9b 80.3b 86.1c
617.4a 645.0ab 630.0a 670.2b 715.2c 927.6d 409.8a 454.8b 450.0b 472.8bc 510.0c 575.4d 522.6dbc 589.8de 595.2de 615.05e 645.05e 870.00f 372.6a 354.95a 372.6a 460.2b 472.8bc 540.0dc
PV
MV
TV
BD
SB
[B.U.] 693c 683c 688c 638bc 613b 523a 393c 310bc 268ab 273ab 170a 210ab 213cd 198cbd 253cd 365e 715f 645f 258d 178acb 180acb 113a 123ab 115a
39a 49b 64c 76d 95f 89e 121a 148b 175c 194d 224e 250f 276a 351b 377c 404d 476f 491fg 340b 406d 431e 497g 556h 639i
BD%
SB%
HPSI
57.8bcd 60.2cd 62.2d 55bc 51.8b 45.4a 32.8a 33.2a 35.9ab 37.6abc 39bc 42.3c 55.8efg 47.6ced 62.1g 59.0fg 55.3efg 38.2ab 35.2a 37.8ab 41.8abc 40.7abc 45.2bcd 52.2efd
89.0bc 88.3b 84.8a 92.2cd 95.1de 98.0e 76.4c 72.8b 70.7ab 70.4ab 69.0a 68.4a 69.7bc 65.1ba 71.2bc 80.1cd 93.5de 98.5e 59.4ba 55.6a 63.6ba 61.6ba 61.9ba 62.4ba
[%] 34a 42b 52c 67d 86e 86e 75a 86b 100c 107c 127d 146e 159a 190cb 224de 278f 440h 492i 167ab 190c 204cd 239e 279f 323g
81a 106b 138c 150cd 158d 183e 110a 130a 155b 172b 207c 254d 363bc 366bc 571d 702e 980g 795f 260a 311ba 353bc 406c 514d 701e
5a 7ab 12b 8ab 8ab 3a 46a 62b 75c 87cd 99de 104e 118c 162e 153ed 127cd 38b 2a 172e 216f 226f 258g 277g 309h
47a 64ab 86cd 83cd 95d 72cb 37a 43ab 56bc 65c 81d 108e 203bc 174abc 355ef 414f 543g 304ed 92.0a 118ab 148abc 165abc 233cd 366ef
12.8bc 14.4bc 18.8c 10.6b 7.9ba 3.4a 38.0a 41.6ba 41.6ba 42.9b 44.0b 44.7b 42.6de 46.1fde 40.6d 31.3c 7.9b 0.4a 50.5gf 53.1g 52.4g 52gf 49.8gf 48.4gfe
*MS. normal maize starch; WS. waxy maize starch; PT. pasting temperature; PVT. temperature at maximum viscosity; TPV. time needed to reach maximum viscosity; PV. SB maximum viscosity; MV. minimum viscosity; TV. through viscosity; BD. breakdown (BD ¼ PVeMV); SB. setback (SB ¼ TVeMV); BD% ¼ BD PV ; SB% ¼ TV ; HPS. hot paste stability; HPSI. hot paste stability index. Different letters in column within concentration range imply statistically significant differences at the significance level a ¼ 0.05.
Fig. 1. Pasting profile of 5% and 10% maize (MS_5% and MS_10%) and waxy maize (WS_5% and WS_10%) starch suspensions.
(PT) of waxy starch in comparison to MS is well known, and caused by the lack of amylose, the component of starch granule retarding disintegration of the granules (Hermansson and Svegmark, 1996). An increase of PT with rising share of glucose syrup above 20% (MS) or 40% (WS) could be observed (Table 1, Fig. 1), but the difference between PT of MS and WS remains unchanged. The increase in PT caused by the presence of sugars is known and follows the retardation of granule swelling (Berski et al., 2016). Increased starch concentration (from 5% to 10%) resulted in observed lower PT, due to fact that the same volume was occupied by greater amount of swelling starch granules, and an increase in viscosity was observed earlier.
In the presence of glucose syrup (GS) an increase in peak viscosity (PV) of starch pastes could be observed, which is parallel to the concentration of GS. The values of this parameter are much larger in the case of WS, because it is rich in amylopectin, which nchez et al., 2010; Song could swell much more than amylose (Sa and Jane, 2000; Tester and Morrison, 1990). For 5% starch pastes, in the case of MS, the largest almost 2.3-fold increase in viscosity could be observed after application of 40% syrup, while in the case of WS more than twice increase was measured for sample containing 50% GS. For 10% starch pastes a constant increase was still observed, almost 1.8 for MS, and 1.9 for WS. An increase caused by the presence of GS was also observed in temperatures, at which the maximum viscosity of paste could be measured (PVT). Their values continually rise up to 30% GS concentration in the case of MS, and up to 20% concentration for WS samples when 5% starch pastes are evaluated. For 10% MS pastes this threshold was moved up to 40% GS, whereas for WS remained unchanged, but in fact it occurred at lower temperature than for 5% pastes. This trend could be to some extent explained by slower swelling of the granules, because higher temperatures are obtained after longer times of analysis (TPV). In the case of 5% MS pastes prepared with 40 and 50% of GS, maximum viscosity is obtained after reaching maximum temperature, but the difference in TPV values is still significant (715.2 vs 927.6 min). For 10% pastes TPV values are lower than for respective 5% pastes. Nevertheless the results demonstrate growing resistance of starch granules towards pasting with increasing GS concentration. After reaching maximum viscosity MS pastes tended to stabilize their rheological behavior, and no statistically significant changes in viscosity values during heating were observed as compared to PV, when 10e30% GS preparations were used. In the case of MS, pastes prepared in 40% (only for 5% MS paste) and 50% GS maximum viscosity (PV) was not reached during heating period. For 10% MS lower hot paste stability was observed, that was followed by
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corresponding values of BD% and HPSI, but for pastes prepared in 40 and 50% GS these values were quite similar like for 5% MS. Obtained results allow to draw a conclusion, that higher GS concentrations better stabilize paste viscosity. In contrary to this pattern maximum viscosity of WS pastes was always obtained below 96 C, which was caused by the lack of amylose, responsible for swelling retardation (Blazek and Copeland, 2009). Further heating of WS pastes caused a significant decrease in paste viscosity. Such a behavior is also related to the absence of linear glucans, which could cross-link with amylopectin and thus form a network stabilizing paste rheology. Further decrease of viscosity occurred after holding WS pastes at maximum temperature. Low resistance to shear and temperature of WS gels was finally reflected by the values of BD% and HPSI. Application of GS did not worsen stability of 5% MS pastes at 96 C, and only a slight decrease in viscosity values could be observed after the end of holding period. But for 10% MS pastes prepared with GS within range 0e30% some decrease was observed The values of breakdown (BD) and hot paste stability index (HPSI) varied slightly between individual samples, with no strong trends up to 30% concentration of GS. Above this level, the pastes tended to be stabilized by increasing GS proportion (smaller BD%, larger HPSI). The HPS parameter proposed by Kiribuchi-Otobe et al. (2001) to describe hot paste stability failed in this case, because longer times required for reaching maximum viscosity, resulted in shortening of the period in which viscosity was above 80% of its peak value (which for all 5% MS samples lasted until the end of a holding phase). In the case of WS pastes a decrease observed after reaching maximum value was amplified by growing GS levels. A strong increasing trend could be observed for BD (and BD%) values, which was accompanied with less significant changes in HPSI values. On other hand, for 10% WS pastes an increased stability was observed when GS concentration was over 20%. The lack of amylose seems to enhance the changes in paste viscosity caused by syrup addition. Initial increase observed for a system with fully swollen granules and highly concentrated syrup solution outside of them, is followed by a sharp decrease in viscosity (even to about 50% of the peak value), resulting from elevated shear. Quick disruption of the swollen granules could be seen in a growing slope of the resulting curves. Evidently the dextrins present in starch syrup and dissolved amylopectin molecules could not form a stable network, probably because of too short linear segments (not allowing formation of cross-links between adjacent amylopectin molecules). During the cooling period (to 25 C) an increase in viscosity of starch pastes could be observed, and the final values depended strongly on the concentration of GS, generally increasing with its level. Only in the case of MS pastes with 50% GS final value was lower in comparison to 40% GS ones. This exception could be due to excessive level of sugars, which reduced water activity below the values allowing full pasting of starch granules. The retardation of peak viscosity, discussed above, seems to favor such a view. In the case of WS starch the level of water activity required for full gelatinization is seemingly smaller, because of the lack amylose, so similar phenomenon could not be observed. After holding the pastes at 25 C for 10 min, only small changes in viscosity could be observed, mostly in the case of MS. Higher values of final viscosity determined for 5% WS samples is in nchez et al. (2010) and Song and agreement with the results of Sa Jane (2000) and could be explained by the lack of amylose, responsible for reduced granule swelling (Hermansson and Svegmark, 1996). In contradiction, for 10% systems final viscosity values were higher for MS than for WS pastes due to excessive formation of hydrogen bonds between amylose chains profusely
occurring in the vicinity, and by greater integrity of swollen MS granules. Setback value (SB, Table 1) is sometimes regarded as an indicator of starch retrogradation. A drop in SB% observed with growing concentration of GS in the case of MS may suggest decreasing retrogradation susceptibility, probably caused by limited leaching of amylose out of the granules. Such statement could be supported by lower appropriate values for 10%, when smaller amount of water was available due to higher starch concentration. In the case of WS pastes an increase of SB% could be seen with rising GS levels, which is probably due to better dissolving of amylopectin fragments, which could form stronger networks upon cooling. 3.2. Gelling characteristics Hardness of the gels prepared with MS was higher than of WS samples, with exception for gels prepared in 50% GS, and 10% gel prepared with 40% GS at last day of storage (Table 2). This again reflects the lack of amylose in WS samples, which is especially important for network formation and gel structure (Banerjee and Bhattacharya, 2012). Cross-links between amylopectin molecules are less frequent, because of their branched character, and could be formed only by the external chains. It was observed, that stronger gels could be formed by starch containing high levels of amylose and longer chains of amylopectin (Mua and Jackson, 1997). Retrogradation of waxy starches results in soft gels, which contain amylopectin aggregates but do not form a continuous network (Wang et al., 2015), and therefore could be easily deformed despite of their high adhesiveness. Hardness of 5% MS gels with 10% GS was higher than of those prepared with pure water, but further increase of GS concentration caused a drop in this parameter. In the case of 10% MS gels with 20%
Table 2 Changes in hardness of 5% and 10% gels from maize and waxy maize starches. Syrup [%]
day
Hardness [N] 5%
10%
MS 0
10
20
30
40
50
0 10 20 30 40 50
WS f
MS a
WS abc
1 2 7 1 2 7 1 2 7 1 2 7 1 2 7 1 2 7
1.383 1.659g 2.185hi 2.031h 2.344ij 2.522j 0.636cde 0.736de 0.885e 0.384abc 0.444bc 0.548cd 0.441bc 0.465c 0.473c 0.196a 0.209a 0.274ab
0.136 0.14a 0.146a 0.191bc 0.194bc 0.207bc 0.179b 0.188b 0.193bc 0.199bc 0.219cd 0.248de 0.324f 0.341f 0.426h 0.278e 0.314f 0.382g
6.090 7.175bcd 11.195f 9.395def 11.431fg 14.676h 11.084efg 13.905gh 18.421i 7.961bcd 8.266cde 8.757cdef 6.749abcd 7.488bcd 8.162cde 4.129a 4.961ab 7.367abcde
0.385a 0.588ab 1.039ab 0.432ab 0.797ab 3.362de 0.61abc 1.242abcd 5.161ef 0.937ab 1.682abcd 7.253fg 1.747bcd 3.946e 13.001h 2.513cd 7.99g 29.089i
1 2 7
0.912a 1.053b 1.234c
0.225a 0.233a 0.267b
7.729a 9.333b 11.969c
1.253a 3.311b 11.7c
1.742d 2.299e 0.752c 0.458b 0.460b 0.226a
0.142a 0.197ab 0.192a 0.222ab 0.364c 0.324bc
8.153b 11.265c 14.893d 8.274b 7.566b 5.109a
0.671a 1.53b 2.338bc 2.702c 6.231d 13.197e
*Different letters in column imply statistically significant differences at the significance level a ¼ 0.05.
W. Berski, R. Ziobro / Journal of Cereal Science 79 (2018) 253e258
GS the samples were also harder than reference (0% GS) It seems that at a certain concentration, sugars prevent formation of compact gels, while their lower amounts may stiffen the amyloseamylopectin network. Similarly in the studies on starch-inulin gels (Krystyjan et al., 2015) a slight increase (in comparison to pure starch gels) could be observed in their firmness when 10% of inulin was used, but further elevation of its level up to 20% caused its decrease, and only the highest applied amounts of inulin (25%) resulted in significant strengthening of the gels. In the case of waxy starch no typical gel could be formed, but hardness of the sample increased during storage, which confirms earlier results (Han et al., 2005). Hardness of WS systems was small, but increased with increasing levels of GS. The effect could to be a consequence of small number of linkages between external branches of AP, which might be increased due to a presence of short chain dextrins, or simply an effect of reduced water activity in such systems. Analyzing the influence of storage time on hardness of MS and WS gels (Table 2) it seems that the effects for both types of starch differ and strongly depend on GS concentration. In the case of MS gels prepared without syrup, prolonged storage leads to their visible strengthening. Addition of 10% GS (and additionally 20% GS for 10% MS gel) amplifies this dependence, but further increase of GS level stabilizes gel properties over time (there are no significant differences between only slightly rising values). Quite a different pattern could be observed for WS gels. 5% gels prepared with water or syrup levels below 20% do not reveal significant changes during 7 days. Above this level hardening is evident. For 10% WS gels a critical GS concentration was lowered. During storage of MS obtained with the use of GS, syneresis could be observed, and gel lost some water, which was especially visible after 7 days of storage. No such phenomenon could be found in the case of WS gels. The observed increase in gel hardness may indicate retrogradation pattern (Wang et al., 2015), which could be described using Avrami equation (Fig. 2). The calculated parameters are shown in Table 3. As it could be observed the introduction of GS to MS system caused an increase in values of individual parameters of Avrami model in comparison to water system (0%). For 10% MS this increase is observed up to 20% GS. Further addition of glucose syrup caused a drop in H∞ indicating final gel strength, demonstrating inhibiting influence of GS onto crystallization of starch molecules. Similar
257
Table 3 Avrami equation parameters. Concentration
Starch
Syrup
H∞ [N]
H0 [N]
K [h1]
R2 [-]
5%
MS
0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50
2.2862 2.5228 0.9002 0.5629 0.4974 0.4662 0.1476 0.2226 0.1930 0.2507 0.5756 0.3944 15,9327 15,1492 18,9759 8,8181 8,8912 8,8269 1.1705 53.6842 83.7168 99.4397 36.0883 66.4178
0.9843 1.1705 0.4751 0.2933 0.3763 0.1794 0.1307 0.1867 0.1558 0.1647 0.2990 0.2255 4,8706 6,3995 6,6921 7,4893 5,6208 3,1187 0.1122 0.1234 0.2530 0.3383 0.6026 3.4774
0.0152 0.0422 0.0198 0.0170 0.0272 0.0023 0.0156 0.0046 0.0408 0.0210 0.0036 0.0154 0,0051 0,0175 0,0184 0,0183 0,0176 0,0081 0.0124 0.0004 0.0004 0.0005 0.0028 0.0037
1.0000 1.0000 1.0000 1.0000 1.0000 0.9989 1.0000 0.9925 1.0000 1.0000 0.9988 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 0.9990 0.9990 0.9994 1.0000 1.0000
WS
10%
MS
WS
dependence (except for the 5% gel containing 40% GS, and 10% gel containing 40% and 50% GS) could be seen in the case of H0, showing decreasing initial hardness of the gel. Because a rise in paste viscosity was accompanying GS addition, this decrease could be due to smaller amounts of leached amylose, available for network formation, and thus creation of a gel structure (Banerjee and Bhattacharya, 2012). The value of K indicates the rate of retrogradation and could be interpreted as rate constant of this process. It could be seen that the introduction of GS leads to an initial increase in K, and afterward a drop in its value for MS gels. The above data suggest that glucose syrup addition results in both retardation and reduction of the extent of starch retrogradation. In the case of WS gels the pattern is different. An introduction of GS resulted in an increase of gel hardness, which was reflected by the Avrami parameters. The value of H∞ grew in parallel to syrup level, reaching maximum value for 40% GS in case for 5% WS gel. For 10% Ws gels with addition of GS the character of changes was not well described by Avrami equation, at least within evaluated period of storage time. H∞ grew, values were reaching remarkable high values, but rather with no physical sense. It demonstrates an increasing extent of retrogradation which could be enhanced by the presence of small dextrins, forming hydrogen bonds with external branches of amylopectin. Also H0 parameter showing initial gel hardness increased with adding syrup, reaching maximum for 40% GS in case of 5% WS gels. For 10% Ws gels H0 values had no physical interpretation. No coherent pattern could be found for the values of K.
4. Conclusions
Fig. 2. Changes in hardness of 5% and 10% maize (MS_5% and MS_10%) and waxy maize (WS_5% and WS_10%) starch gels during storage.
In the presence of glucose syrups pastes and gels of maize starch, both normal and waxy, change their rheological properties. This involves an increase in pasting temperature and viscosity of the pastes, and modification of texture properties of stored gels. In the case of MS gels application of GS led to incremental decrease of hardness, while an opposite effect could be seen for weak WS gels. All these effects were highly dependent on the type of starch, and GS and starch concentration. It is assumed that the main factor for
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observed differences was amylose content. In the case of MS a significant retardation of starch pasting could be seen, as a result of increasing GS. Similar changes in WS were less pronounced. Application of GS had opposite influence on stability of the obtained pastes, which was smaller in the case of waxy starch and slightly improved in the case of MS. At the highest 50% applied level of GS a decrease in MS paste viscosity in comparison to 40% GS sample was measured, which was not detected in the case of WS. This difference clearly shows that amylose containing starch granules require more water for full gelatinization than their amylopectin counterparts. Elevating GS levels had varying effects on texture properties of the gels, which were softened in the case of MS and hardened in the case of WS. References Banerjee, S., Bhattacharya, S., 2012. Food gels: gelling process and new applications. Crit. Rev. Food Sci. Nutr. 52, 334e346. https://doi.org/10.1080/10408398.2010. 500234. Bean, M.M., Yamazaki, W.T., Donelson, D.H., 1978. Wheat starch gelatinization in sugar solutions. II. Fructose, glucose, and sucrose: cake performance. Cereal Chem. 55, 945e951. Beleia, A., Miller, R.A., Hoseney, R.C., 1996. Starch gelatinization in sugar solutions. €rke 48, 259e262. https://doi.org/10.1002/star.19960480705. Starch/Sta Berski, W., Krystyjan, M., Buksa, K., Zie˛ c, G., Gambus, H., 2014. Chemical, physical and rheological properties of oat flour affected by the isolation of beta-glucan preparation. J. Cereal Sci. 60, 533e539. https://doi.org/10.1016/j.jcs.2014.09.001. Berski, W., Krystyjan, M., Zie˛ c, G., Litwinek, D., Gambus, H., 2016. The influence of starch hydrolyzate on physicochemical properties of pastes and gels prepared from oat flour and starch. J. Cereal Sci. 70, 16e22. https://doi.org/10.1016/j.jcs. 2016.05.011. Blanchard, P.H., Katz, F.R., 2006. Starch hydrolysates. In: Food Polysaccharides and Their Applications. Taylor & Francis, Boca Raton, FL, pp. 119e145. Blazek, J., Copeland, L., 2009. Effect of monopalmitin on pasting properties of wheat starches with varying amylose content. Carbohydr. Polym. 78, 131e136. https:// doi.org/10.1016/j.carbpol.2009.03.023. Chungcharoen, A., Lund, B.D., 1987. Influence of solutes and water on rice starch gelatinization. Cereal Chem. 64, 240e243. D'Appolonia, B.L., 1972. Effect of bread ingredients on starch-gelatinization properties as measured by the amylograph. Cereal Chem. 49, 532e543. Derby, R.I., Miller, B.F., Trimbo, H.B., 1975. Visual observation of wheat-starch gelatinization in limited water systems. Cereal Chem. 52, 702e713. Evans, I.D., Haisman, D.R., 1982. The effect of solutes on the gelatinization tem€rke 34, 224e231. https://doi.org/10. perature range of potato starch. Starch/Sta 1002/star.19820340704.
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