Article
Effect of heat-moisture treatment on the structural, physicochemical, and rheological characteristics of arrowroot starch Larissa S Pepe, Jaqueline Moraes, Kivia M Albano, ˆnia RN Telis and Ce ´lia ML Franco Va
Abstract The effect of heat-moisture treatment on structural, physicochemical, and rheological characteristics of arrowroot starch was investigated. Heat-moisture treatment was performed with starch samples conditioned to 28% moisture at 100 C for 2, 4, 8, and 16 h. Structural and physicochemical characterization of native and modified starches, as well as rheological assays with gels of native and 4 h modified starches subjected to acid and sterilization stresses were performed. Arrowroot starch had 23.1% of amylose and a CA-type crystalline pattern that changed over the treatment time to A-type. Modified starches had higher pasting temperature and lower peak viscosity while breakdown viscosity practically disappeared, independently of the treatment time. Gelatinization temperature and crystallinity increased, while enthalpy, swelling power, and solubility decreased with the treatment. Gels from modified starches, independently of the stress conditions, were found to have more stable apparent viscosities and higher G0 and G00 than gels from native starch. Heatmoisture treatment caused a reorganization of starch chains that increased molecular interactions. This increase resulted in higher paste stability and strengthened gels that showed higher resistance to shearing and heat, even after acid or sterilization conditions. A treatment time of 4 h was enough to deeply changing the physicochemical properties of starch.
Keywords Starch, physical properties, rheology, viscosity Date received: 13 March 2015; accepted: 16 June 2015
INTRODUCTION Starch is constituted of two biopolymers, amylose and amylopectin. Amylose is an essentially linear macromolecule constituted of glucose units bounded in a-(1–4), whereas amylopectin is a highly branched macromolecule with a-(1–6) branches in the glucose chains bounded in a-(1–4) (Jacobs and Delcour, 1998; Tester, 1997). These two biopolymers form a semicrystalline structure in the starch granule, which consists of crystalline and amorphous lamellas (Jane et al., 1994).
Tuberous roots are very important food crops. After cereals, tubers and roots are the major source of starch for food and industrial uses, but usually, the major drawback of most of these starches is their instability under conditions of high temperature, shearing, and acidity, which limit many of starch applications in industry (Jyothi et al., 2010). Modification of root and tuber starches can improve their stability and result in the specific characteristics desired for various UNESP – Sa ˜o Paulo State University – Department of Food Engineering and Technology, Sa ˜o Paulo, Brazil
Food Science and Technology International 0(0) 1–10 ! The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1082013215595147 fst.sagepub.com
Corresponding author: ´lia ML Franco, Department of Food Engineering and Ce ´ va Technology, UNESP – Sa ˜o Paulo State University, R. Cristo ˜o ´ do Rio Preto, Colombo, 2265 Jardim Nazareth, Sa ˜o Jose Sa ˜o Paulo 15054-000, Brazil. Email: [email protected]
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Food Science and Technology International 0(0) end uses and market needs. Starch can be modified by chemical, physical, enzymatic, and genetic methods; however, the physical methods present a series of advantages. Physically modified starch is considered safe for use in food products, as it does not involve any chemicals (Kaur et al., 2012; Puncha-arnon and Uttapap, 2013). The regulation of chemically modified starch for food (particularly for baby food) is quite strict, in such a way that the demand for physically modified starches is increasing (Devi et al., 2009). Heat-moisture treatment (HMT) is a physical change in which the starch granules are conditioned to moisture levels below 35% and subjected to temperatures ranging from 84 to 120 C during a certain period of time (Gunaratne and Hoover, 2002; Jacobs and Delcour, 1998; Jyothi et al., 2010). HMT may be an alternative to chemical modification for altering the gelatinization and retrogradation properties of tuber and root starches (Gunaratne and Hoover, 2002). HMT causes the rearrangement of amylose and amylopectin chains in the starch, and therefore may modify its X-ray pattern, crystallinity, swelling power, amylose leaching, pasting, and gelatinization properties, as well as its susceptibility to enzymatic or acidic hydrolysis, which also affect the starch rheological properties (Chung et al., 2009; Jyothi et al., 2010; Zavareze and Dias, 2011). Chen et al. (2015) observed that HMT significantly changed crystal structure of wheat starch and the crystalline patterns transferred from A to AþV with moisture content increase, indicating formation of a starch–lipid complex. According to Sui et al. (2015), the levels of moisture content and length of heating have significant impacts on the structural and physicochemical properties of starches but to different extents. Amylose content and amylopectin chain length are also significant factors that determine the physicochemical properties of the final products (Lawal, 2005). Starches from different botanical sources show different responses to different treatment conditions (Jiranuntakul et al., 2011; Lawal, 2005; Moraes et al., 2014; Singh et al., 2011; Sui et al., 2015; Varatharajan et al., 2010; Yadav et al., 2013). All of these studies revealed that when different starches were modified under different conditions, they became more stable when exposed to heat and shearing due to the strengthening of linkages within the granule. However, these studies have not shown the effect of HMT on starch gels subjected to different stress conditions generally used in food processing. Arrowroot starch, obtained from the rhizomes of the tropical plant Maranta arundinacea L., is known for its medicinal properties in the treatment of gastrointestinal disorders, in addition to being a very digestible starch
(Mason, 2009). This starch presents round and oval granules with a large average size, CA- or A-type X-ray diffraction pattern, high gelatinization temperature, and amylose content that can vary between 16 and 27% (Moorthy, 2002; Peroni et al., 2006; Srichuwong et al., 2005). It can be used in bakery products, as an ice cream stabilizer, in jellies, cakes, and foodstuffs for infants (Jyothi et al., 2010; Mason, 2009). Nevertheless, as in the case of most tuber and root starches, arrowroot starch pastes are unstable under heating, shearing, and acid conditions generally used in the food industry. The goal of the present study was to evaluate the effect of HMT on the structural, physicochemical, and rheological characteristics of arrowroot starch and their pastes submitted to different stress conditions in order to improve its stability for different food applications.
MATERIAL AND METHODS Material Arrowroot (M. arundinacea L.) roots of the common variety were obtained from small producers from Minas Gerais state, Brazil, and were used within 24 h after harvesting. Isolation of starch and chemical composition The starch was isolated as described by Peroni et al. (2006) and analyzed in triplicate to determine ash, protein, and lipid contents according to the methods of the American Association of Cereal Chemists (AACC, 2000). Phosphorous content was determined according to Smith and Caruso (1964). To determine apparent amylose content, the starch was defatted and iodine affinities were then determined in triplicate using a potentiometric autotitrator (716SM Titrino, Brinkmann Instruments, Westbury, NY) according to Kasemsuwan et al. (1995). The apparent amylose content was calculated by dividing the iodine affinity of the starch by 20.0% (Takeda et al., 1987). Amylopectin branch chain length distribution The starch was debranched using isoamylase from Pseudomonas sp. (Megazyme International, Ireland), as described by Wong and Jane (1995). Amylopectin branch chain length distribution was analyzed using high-performance anion exchange chromatography with pulse amperometric detector (HPAEC-PAD) (ICS 3000, Dionex Corporation, Sunnyvale, USA) equipped with an AS40 automatic sampler. Samples were filtered (0.22 mm membrane) and injected into the HPAEC-PAD system (20 ml sample loop). The flow rate was 0.8 ml/min at 40 C. The standard
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Pepe et al. quadruple potential (E) waveform was employed with the following periods and pulse potentials: E1 ¼ 0.10 V (t1 ¼ 0.40 s); E2 ¼ –2.00 V (t2 ¼ 0.02 s); E3 ¼ 0.60 V (t3 ¼ 0.01 s); E4 ¼ –0.10 V (t4 ¼ 0.06 s). All eluents were prepared with ultrapure water (18 mV cm) with N2 sparging. Eluent A was 150 mM NaOH and eluent B was 500 mM sodium acetate and 150 mM NaOH. The branched chains of amylopectin were separated using a Dionex CarboPacTM PA-100 guard column (4 mm 50 mm) and a Dionex CarboPacTM PA-100 column (4 mm 250 mm). The gradient of eluent B was 28% at 0 min, 40% at 15 min, and 72% at 105 min. The data were analyzed using the Chromeleon software, version 6.8 (Dionex Corporation, USA). The analyses were performed in duplicate. HMT HMT was performed in triplicate according to Chung et al. (2009), with modifications. Starch samples were dispersed in enough distilled water to obtain 28% of moisture, mixed in a mechanical stirrer for 1 h, stored in plastic bags, and kept under refrigeration at 4 C for 24 h to achieve moisture balance. After this period, the samples were placed in Petri dishes, which were well sealed with parafilm and incubated in an oven at 100 C for 2, 4, 8, and 16 h. The moisture content of the samples was determined after HMT and the water loss during treatment was not significant. After that, the starches were dried at 40 C. X-ray pattern and relative crystallinity Native and modified starches were stored for 10 days at 25 C in a desiccator where a saturated solution of BaCl2 containing 1% of sodium azide maintained 90% of relative humidity. The X-ray patterns of the samples were determined using a wide angle goniometer unit (RINT 2000, Rigaku, Tokyo, Japan) with copper radiation Ka ( ¼ 1542 A˚). The scanning speed was 1 / min at 50 kV and 100 mA. The relative crystallinity was quantitatively estimated based on the relationship between peak and total areas, as described by Nara and Komiya (1983) using Origin software (version 7.5, Microcal Inc, Northampton, USA).
Norwalk, USA). Starch samples (3 mg, dry basis) were weighed in aluminum pans, mixed with distilled water (9 ml), and sealed. The sealed pans were kept at room temperature for 24 h to achieve balance and were scanned at a rate of 5 C/min over a temperature range of 25–100 C. An empty pan was used as a reference. The analysis was performed in triplicate. Water absorption index, water solubility index, and swelling power The water absorption index and water solubility index of the native and modified starches were determined at 30 C according to Linko et al. (1980). Swelling power and solubility in hot water were determined at 90 C according to Schoch (1964). The analyses were performed in triplicate. Rheological characteristics Rheological characteristics of the native and 4 h modified starch gels in normal and stress conditions were determined in order to evaluate the ability of the structural properties of gels to resist against processing conditions generally found in food industry. Native and 4 h modified starch suspensions (5 g 100 ml–1) were heated in a water bath at 100 C for 30 min and cooled to room temperature (normal condition). In the case of acidity stress, the pH of the suspension was reduced to 3.5 with 1 M ascorbic acid before heating, and in the case of sterilization stress, the gels were autoclaved at 121 C for 1 h (Guerreiro and Meneguelli, 2009). The rheological tests were carried out using an AR 2000EX rheometer (TA Instruments, New Castle, USA), with serrated parallel plate geometry 40 mm in diameter and a fixed gap of 800 mm. The steady shear tests were performed in order to determine two flow curves, up and down, with shear rate varying between 1 and 1000 s–1 at a temperature of 25 C, controlled by a Peltier system on the lower plate. Each measurement in the steady shear tests took around 30 s and each complete rheogram was determined in about 30 min. The Power Law (Ostwald–Waele model) was fitted to the downward curve according to equation (1)
s ¼ K_gn Pasting and thermal properties Pasting properties of the native and modified starches were determined using a rapid visco analyzer (RVA-4, Newport Scientific, Warriewood, Australia). Starch concentrations were 10% with a total mass of 27.5 g. The analysis was performed in triplicate. Thermal properties were determined using a differential scanning calorimeter (DSC - Pyris 1, Perkin Elmer,
ð1Þ
in which: s (Pa): shear stress; K (Pa sn): consistency index; g_ (s–1): shear rate; n: flow behavior index. The apparent viscosity (Zap, in Pa s) was calculated using the parameters obtained for the Power Law model, according to equation (2)
Zap ¼ K_gn1
ð2Þ 3
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Food Science and Technology International 0(0)
tan d ¼ G00 =G0
ð3Þ
0.8 0.6 0.4 0.2 0.0
Statistical analysis The data were statistically analyzed using analysis of variance, and the differences were evaluated using the t-test with Tukey’s adjustment. Statistics for Windows (v. 7.0, Statsoft, Tulsa, USA) was used. The significant differences were tested at p 0.05.
RESULTS AND DISCUSSION General composition The arrowroot starch displayed low contents of ash, protein, and lipid (0.27, 0.21, and 0.08%, respectively) indicating that it was pure enough to be used. This starch had 0.024% of phosphorous. Similar result was found by Peroni et al. (2006) who reported that arrowroot starch has higher phosphorous content than cassava, sweet potato, and ginger starches. The phosphorous in root and tuber starches is manly in phosphate form bounded in C6 of amylopectin (Bule´on et al., 1998). The arrowroot starch had 23.12% of apparent amylose, a finding that agreed with previously published data (Peroni et al., 2006; Srichuwong et al., 2005). This amount is similar to that of other root starches, such as cassava (22.81%) (Moraes et al., 2013), sago (21.90%) (Srichuwong et al., 2005), new cocoyam (22.5%) (Gunaratne and Hoover, 2002; Srichuwong et al., 2005), sweet potato (22.60%) (Peroni et al., 2006), and yam (24.6%) (Gunaratne and Hoover, 2002) starches. Amylopectin branch chain length distribution The normalized chain length distribution of debranched amylopectin of the arrowroot starch determined by HPAEC-PAD is shown in Figure 1. The arrowroot starch displayed bimodal distribution with first and second peaks of chain length at degree of polymerization (DP) 12 and 41, respectively. The starch had a smaller proportion of short chains (DP 6–12, 25.8%), compared to cassava (DP 6–12, 31.6%) and Peruvian carrot (DP 6–12, 33.53%) starches, which were analyzed under the same conditions in a previous
12
1.0
Normalized peak area
In oscillatory tests, storage (G0 ) and dissipation (G00 ) moduli were evaluated by running frequency sweeps from 1 to 100 rad/s with a maximum strain of 0.2, which was found to be inside the linear viscoelasticity region after strain sweeps at fixed frequency. The loss tangent, tan d, was calculated according to equation (3)
41 6
11 16 21 26 31 36 41 46 51 56 61 66 71 DP
Figure 1. Amylopectin branch chain length distribution of native arrowroot starch. DP: degree of polymerization.
study (Moraes et al., 2013). Arrowroot starch does not present the shoulder at DP 17–21 on the amylopectin branch chain length distribution that was observed on the distributions of Peruvian carrot and cassava starches (Moraes et al., 2013), and in that of wheat, barley, du waxy maize, and amaranth starches (Jane et al., 1999). Shoulders on the amylopectin branch chain length distribution indicate imperfections in the crystalline structure of a starch (Genkina et al., 2007; Jane et al., 1999). According to these authors, the chains with DP < 10, which are unable to form double helices, might be located in crystalline areas, which result in imperfections in starch structure. These findings indicate that arrowroot starch with a smaller proportion of short chains has a crystalline structure with less imperfection than those of cassava and Peruvian carrot starches. X-ray diffraction and relative crystallinity The arrowroot starch displayed a CA-type X-ray pattern (Figure 2). Similar result was also found by Jyothi et al. (2010). The C-type pattern is a mixture of A- and B-type patterns and then it contains pure A and B polymorphs in different proportions. There are various kinds of C-type patterns, some resemble the A-type, some the B-type, and some are almost intermediate between the two. These C-types were discriminated as CA, CB, and CC types (Hizukuri, 1961). HMT caused a progressive alteration with treatment time in X-ray pattern, from CA to A-type in arrowroot starch that occurred due to a crystallite transformation from B-type to A-type during the treatment. According to Varatharajan et al. (2010), the differences between A and B polymorphs arise from water content and the way in which the double helix pairs are packed in the crystals. The lattice of the B-type has a large void where 36 water molecules are accommodated. This void is not
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Pepe et al.
Intensity
a
37.4 %
b 51.4 % c
100
200 50 100
53.4 %
d
0
0 0
0
Temperature (°C)
36.8 %
Viscosity (RVU)
300
5
10
15
20
25
5
10
15
20
25
Time (min)
30
Angle 2θ
Figure 2. X-ray diffraction pattern and relative crystallinity of native and HMT-modified arrowroot starches: (a) native, (b) 4 h HMT, (c) 8 h HMT, (d) 16 h HMT.
present in A-type structure that accommodates eight water molecules. The packing of double helices in the B-type starch is less compact and thus, during treatment, they would be more mobile and more prone to disruption than those of A-type starch. In this study, the change in the crystalline pattern of starch during treatment occurred due to dehydration of water molecules, followed by movement of a pair of double helices to the center of the channel of B-type crystallites, which changed from a less thermodynamically stable structure to a more stable A-type model (Moraes et al., 2014; Varatharajan et al., 2010; Zavareze and Dias, 2011). Changes in relative crystallinity after HTM are dependent upon the botanical source of starch and conditions used in the treatment (Zavareze and Dias, 2011). Relative crystallinity increased with treatment time from 36.8% in native starch to 53.4% in 16 h modified starch. Chen et al. (2015) also observed an increase in relative crystallinity of wheat starch modified by HMT at different moisture levels. This increase was expected because HMT leads to rearrangement of the starch molecules that increases interaction between them. However, Sui et al. (2015) observed that X-ray intensities increased but relative crystallinity decreased to a greater extent with increasing moisture content when normal and waxy maize starches were modified by HMT. This treatment also may promote displacement of the double-helical chains within the starch crystals, resulting in a crystalline matrix that is more organized than in native starch (Chen et al., 2015; Zavareze and Dias, 2011). Pasting properties The viscoamylographic profiles of the native and 2, 4, 8, and 16 h modified starches obtained from RVA
Figure 3. Viscosity profiles of native and HMT-modified arrowroot starches: (#) native, («) 2 h HMT, (*) 4 h HMT, () 8 h HMT, () 16 h HMT.
are shown in Figure 3. The native arrowroot starch was found to have a higher pasting temperature and lower pasting viscosities when compared to other root starches, such as Peruvian carrot (Moraes et al., 2013; Vieira and Sarmento, 2008) and cassava (Moraes et al., 2013) starches. High pasting temperatures and low viscosities suggest the presence of strong bonding forces within the granule (Peroni et al., 2006). HMT significantly affected the pasting behavior of the starches, which, independently of the treatment time, revealed a large decrease in peak viscosity; breakdown practically disappeared and pasting temperatures increased, indicating that the starch became more stable when exposed to heat and mechanical shearing. Similar results were found by Moraes et al. (2014), Pinto et al. (2015), Singh et al. (2011), and Yadav et al. (2013) for different starches modified by HMT. This treatment promotes the rearrangement of starch chains, which limits the ability of the granules to swell and reduces the amount of leached amylose, thus decreasing the pasting viscosity (Chen et al., 2015; Lawal, 2005; Pinto et al., 2015). The compaction of granular matter by vapor pressure force, as well as chemical bonding and the interactions that occur during HMT, might also be factors that influence the stability of starches exposed to HMT (Puncha-arnon and Uttapap, 2013). The treatment time mainly affected the pasting properties in the first 4 h. After 8 and 16 h of HMT treatment, there was a slight decrease in final viscosity and setback, and after 16 h of treatment, there was a decrease in peak viscosity. These results indicated that the longer treatments promote more rearrangement in the starch granules. 5
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Food Science and Technology International 0(0) Thermal properties
Endothermic rate flow (mW)
The arrowroot starch had high gelatinization temperatures (to, tp, tc) and H when compared to other root starches. The gelatinization temperature range of this starch varied from 62.4 to 76.2 C, and H was 15.3 J/g. Cassava and Peruvian carrot starches showed lower temperatures, whereas potato and sweet potato starches displayed higher gelatinization temperatures than arrowroot starch, when analyzed at the same conditions in previous studies (Moraes et al., 2013; Rocha et al., 2010). The branch chain length and branching degree of amylopectin, the proportions of amylose and amylopectin, and the architecture of the starch granule are the main factors that affect thermal properties of starch and may explain these differences. HMT caused significant changes in thermal properties of the starch. There was an increase in the gelatinization temperatures and a decrease in H of the
a b c d e
40
50
60
70
80
90
100
Temperature (°C)
Figure 4. DSC curves of native and HMT-modified arrowroot starches: (a) native, (b) 2 h HMT, (c) 4 h HMT, (d) 8 h HMT, (e) 16 h HMT.
modified starches no matter which treatment time was used. There was also an increase in the gelatinization temperature ranges, and after 2 h of treatment, two transition peaks were observed (Figure 4). These results suggested that HMT increased the interaction between starch chains; therefore, higher temperatures were needed for disruption of the crystals. Moreover, the new structure formed had less homogeneous crystals melted at different temperatures, a finding which explains the two peaks observed in many samples. According to Cooke and Gidley (1992), H represents primarily the loss of double helix order rather than loss of crystallinity during gelatinization process. After HMT, the H of arrowroot starch decreased from 15.3 to 11.7 J/g indicating that the treatment may also promote an unwinding of double helices. Water absorption index, water solubility index, and swelling power and solubility at 90 C Native arrowroot starch had low water absorption index and water solubility index values (Table 1). HMT hardly altered these parameters. However, HMT caused a decrease in swelling power and solubility of the starch at 90 C, which suggest that the rearrangement of starch chains caused by HMT allowed for a realignment of bonding forces of the starch chains, thus changing its structure and crystallinity (Chung et al., 2009; Gunaratne and Hoover, 2002; Jacobs and Delcour, 1998). HMT promotes formation of ordered double helices, and in doing so, limits starch swelling and solubility, as suggested by Lawal (2005). According to Gunaratne and Hoover (2002) and Jyothi et al. (2010), HMT promotes additional interactions between amylose–amylose and amylose–amylopectin, which result in a denser granule structure that is partly responsible for the decrease in swelling power. Solubility at 90 C decreased after treatment; however, when the treatment time increased the solubility
Table 1. Water absorption and water solubility indices at 30 C, swelling power and solubility at 90 C of native and HMTmodified arrowroot starches Arrowroot starch
WAI (g/g)
WSI (%)
SP (g/g)
SOL (%)
Native 2 h HMT 4 h HMT 8 h HMT 16 h HMT
1.85 2.03 2.22 2.00 2.07
0.55 0.51 0.40 0.57 0.59
60.43 19.98 26.44 26.64 25.74
25.92 11.80 15.00 16.48 20.77
(0.01)b (0.24)ab (0.01)a (0.03)ab (0.03)ab
(0.09)ab (0.08)ab (0.01)b (0.06)a (0.02)a
(0.7)a (0.44)b (0.14)b (0.54)b (0.29)b
(0.94)a (0.53)d (0.20)c (0.92)c (0.90)b
Average of nine replicates followed by standard deviation. Values followed by the same letter in the same column are not significantly different by Tukey test (P > 0.05). SOL: solubility at 90 C; SP: swelling power; WAI: water absorption index; WAI: water solubility index.
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Pepe et al. also increased; a result that agrees with that obtained by Jyothi et al. (2010). Rheological characteristics Flow curves obtained from steady shearing revealed that all of the gels studied displayed a pseudoplastic behavior, i.e. they are gels in which apparent viscosity decreases as shear rate increases. The pseudoplastic or shear-thinning behavior can be confirmed by the values of the flow behavior index (n)—resulting from fitting Power Law (equation (1)) to the downward flow curves, which were lower than unity in all of the treatments studied (Table 2). HMT caused a decrease in the consistency index (K), which led to lower apparent viscosities (Figure 5). However, the behavior index increased under most of the conditions tested, showing that the flow properties of the starch gels became less dependent upon the imposed shear rate. The lower variation in the
Table 2. Consistency index (K), flow behavior index (n), and determination coefficient (R2) of gels from native and 4 h HMT arrowroot starch Treatment
K (Pa sn)
N
R2
Native Native acidified Native sterilized Treated Treated acidified Treated sterilized
16.18 5.82 7.85 5.69 0.56 2.86
0.38 0.52 0.42 0.51 0.63 0.53
0.984 0.997 0.989 0.995 0.998 0.997
(a)
apparent viscosity as the shear rate increased indicated that HMT decreased the pseudoplasticity of the gels studied. The rheological behavior observed in arrowroot starch gels confirmed the viscoamylograph profiles of the native and 4 h modified starches obtained from RVA (Figure 3), which indicate that, after treatment, the starch became more stable when exposed to mechanical shear. The rheological measurements under oscillatory shearing showed that HMT affected the storage (G0 ) and loss (G00 ) moduli obtained for gels from arrowroot starch (Figure 6). Gels from HMT-treated arrowroot starch, whether subjected to sterilization or acid conditions or not, revealed G0 and G00 levels that were higher than those of native starch gels. In addition, the values of G0 were only slightly dependent on frequency and were higher than G00 . This finding is consistent with the mechanical spectrum that is typical of a gel network. Jyothi et al. (2010) also observed that after HMT the arrowroot starch paste showed a similar behavior. Comparing the curves of the phase angle, tan d (Figure 6(e) and (f)), it is possible to observe that gels made of HTM starches were less frequency dependent, even when subjected to acid or thermal stress. These results suggest that HMT favored the strengthening of arrowroot starch gels and gave them greater resistance, particularly to acidification stress, conditions generally used in food industry.
CONCLUSIONS HMT caused a rearrangement of the amylose and amylopectin molecules in the starch granule, thus changing its physicochemical and rheological properties.
(b) 10
Apparent viscosity (Pa.s)
Apparent viscosity (Pa.s)
10
1
0.1
10
100
Shear rate (1/s)
1000
1
0.1
10
100
1000
Shear rate (1/s)
Figure 5. Apparent viscosity of gels from native and 4 h modified arrowroot starches, some of which were subjected to acidity or sterilization stress: (a) native, (b) 4 h HMT; (#) without stress; (*) acidified; (p) sterilized.
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Food Science and Technology International 0(0)
(a)
(b)
100
G' (Pa)
G' (Pa)
100
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1 10
10
100
Frequency (rad/s)
(d) 100
G'' (Pa)
G'' (Pa)
(c) 100
10
1
10
1 10
100
10
Frequency (rad/s)
(e)
100
Frequency (rad/s)
100
Frequency (rad/s)
(f)
1
tan δ
tan δ
1
0.1
0.1 10
100
10
Frequency (rad/s)
100
Frequency (rad/s)
Figure 6. Storage modulus (G0 ), loss modulus (G00 ), and loss tangent (tan d) of gels from native and 4 h modified arrowroot starches, some of which were subjected to acidity or sterilization stresses: (a), (c), (e): native; (b), (d), (f): 4 h HMT; (#) without stress; () acidified; (m) sterilized.
These changes gave these starches increased stability against shearing and high temperatures, even when subjected to stress conditions of acidity or sterilization. Treatment times higher than 4 h did not increase the stability of starches against high temperatures and shearing, although they did increase their crystallinity. The crystalline structure with less imperfections and strong associative forces present in arrowroot starch contributed to the starch behavior after treatment. Increased stability of gels, high gelatinization temperature, low peak viscosity, and the absence of breakdown are interesting aspects in starch that need to be
considered during the processing of pumped and/or sterilized products. FUNDING The authors thank the Brazilian research development agency CNPq - Conselho Nacional de Desenvolvimento Cientı´ fico e Tecnolo´gico (National Council for Scientific and Technological Development) (grant number 476385/2010-5), for financial support.
DECLARATION OF CONFLICTING INTERESTS The authors declare that there is no conflict of interest.
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Pepe et al. REFERENCES AACC. (2000). Approved Methods of the AACC. 10th edn. St. Paul, MN: American Association of Cereal Chemists. Bule´on A, Colonna P, Planchot V and Ball S. (1998). Starch granules: Structure and biosynthesis. International Journal of Biological Macromolecules 23: 85–112. Chen X, He X, Fu X and Huang Q. (2015). In vitro digestion and physicochemical properties of wheat starch/flour modified by heat-moisture treatment. Journal of Cereal Science 63: 109–115. Chung HJ, Liu Q and Hoover R. (2009). Impact of annealing and heat-moisture treatment on rapidly digestible, slowly digestible and resistant starch levels in native and gelatinized corn, pea and lentil starches. Carbohydrate Polymers 75: 436–447. Cooke D and Gidley MJ. (1992). Loss of crystalline and molecular order during starch gelatinisation: Origin of the enthalpic transition. Carbohydrate Research 227: 103–112. Devi AF, Fibrianto K, Torley PJ and Bhandari B. (2009). Physical properties of cryomilled rice starch. Journal of Cereal Science 49: 278–284. Genkina NK, Wikman J, Bertoft E and Yuryev VP. (2007). Effects of structural imperfection on gelatinization characteristics of amylopectin starches with A- and B-type crystallinity. Biomacromolecules 8: 2329–2335. Guerreiro LMR and Meneguelli FC. (2009). Influeˆncia do tratamento te´rmico e da acidez no comportamento reolo´gico de amidos nativos funcionais de milho cerosos orgaˆnicos comerciais. Food Science and Technology 29: 412–419. Gunaratne A and Hoover R. (2002). Effect of heat–moisture treatment on the structure and physicochemical properties of tuber and root starches. Carbohydrate Polymers 49: 425–437. Hizukuri S. (1961). X-ray diffractometric studies on starches. VI. Crystalline types of amylopectin and effect of temperature and concentration of mother liquor on crystalline type. Agriculture and Biological Chemistry 25: 45–49. Jacobs H and Delcour JA. (1998). Hydrothermal modifications of granular starch, with retention of the granular structure: A review. Journal of Agricultural and Food Chemistry 46: 2895–2905. Jane J, Kasemsuwan T, Leas S, Ia A, Zobel H, Il D, et al. (1994). Anthology of starch granule morphology by scanning electron microscopy. Starch/Sta¨rke 46: 121–129. Jane J, Chen YY, Lee LF, McPherson AE, Wong KS, Radosavljevic M, et al. (1999). Effects of amylopectin branch chain length and amylose content on the gelatinization and pasting properties of starch. Cereal Chemistry 76: 629–637. Jiranuntakul W, Puttanlek C, Rungsardthong V, Punchaarnon S and Uttapap D. (2011). Microstructural and physicochemical properties of heat-moisture treated waxy and normal starches. Journal of Food Engineering 104: 246–258. Jyothi AN, Sajeev MS and Sreekumar JN. (2010). Hydrothermal modifications of tropical tuber starches. 1. Effect of heat-moisture treatment on the physicochemical,
rheological and gelatinization characteristics. Starch– Sta¨rke 62: 28–40. Kasemsuwan T, Jane J, Schnable P, Stinard P and Robertson D. (1995). Characterization of the dominant mutant amylose-extender (Ae1-5180) maize starch. Cereal Chemistry 72: 457–464. Kaur B, Ariffin F, Bhat R and Karim AA. (2012). Progress in starch modification in the last decade. Food Hydrocolloids 26: 398–404. Lawal OS. (2005). Studies on the hydrothermal modifications of new cocoyam (Xanthosoma sagittifolium) starch. International Journal of Biological Macromolecules 37: 268–277. Linko YY, Vuorinen V, Olkku J and Linko P. (1980). The effect of HTST extrusion on retention of cereal amylose activity and on enzymatic hydrolysis of barley starch. In: Linko P and Larinkari Y (eds) Food Process Engineering. London: Applied Science Publishers, pp. 210–223. Mason WR. (2009). Starch use in food. In: BeMiller J and Whistler R (eds) Starch: Chemistry and Technology. West Lafayette: Academic Press, pp. 745–795. Moorthy SN. (2002). Physicochemical and functional properties of tropical tuber starches: A review. Starch–Sta¨rke 54: 559–592. Moraes J, Alves FS and Franco CML. (2013). Effect of ball milling on structural and physicochemical characteristics of cassava and Peruvian carrot starches. Starch–Sta¨rke 65: 200–209. Moraes J, Branzani RS and Franco CML. (2014). Behavior of Peruvian carrot (Arracacia xanthorrhiza) and cassava (Manihot esculenta) starches subjected to heat-moisture treatment. Starch–Sta¨rke 66: 645–654. Nara S and Komiya T. (1983). Studies on the relationship between water-saturated state and crystallinity by the diffraction method for moistened potato starch. Starch– Sta¨rke 35: 407–410. Peroni FHG, Rocha TS and Franco CML. (2006). Some structural and physicochemical characteristics of tuber and root starches. Food Science and Technology International 12: 505–513. Pinto VZ, Vanier NL, Deon VG, Moomand K, Halal SLME, Zavareze ER, et al. (2015). Effects of single and dual physical modifications on pinha˜o starch. Food Chemistry 187: 98–105. Puncha-arnon S and Uttapap D. (2013). Rice starch vs. rice flour: Differences in their properties when modified by heat–moisture treatment. Carbohydrate Polymers 91: 85–91. Rocha TS, Carneiro APA and Franco CML. (2010). Effect of enzymatic hydrolysis on some physicochemical properties of root and tuber granular starches. Food Science and Technology 30: 544–551. Schoch TJ. (1964). Swelling power and solubility of granular starches. In: Whistler RL (ed.) Methods in Carbohydrate Chemistry: Starch. New York: Academic Press, p. 106. Singh H, Chang YH, Lin JH, Singh N and Singh N. (2011). Influence of heat–moisture treatment and annealing on functional properties of sorghum starch. Food Research International 44: 2949–2954.
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Food Science and Technology International 0(0) Smith AR, Caruso TE. (1964). Determination of phosphorous content. In: Whistler RL (ed.) Methods in Carbohydrate Chemistry. New York: Academic Press. pp. 43–47. Srichuwong S, Sunarti TC, Mishima T, Isono N and Hisamatsu M. (2005). Starches from different botanical sources I: Contribution of amylopectin fine structure to thermal properties and enzyme digestibility. Carbohydrate Polymers 60: 529–538. Sui Z, Yao T, Zhao Y, Ye X, Kong X and Ai L. (2015). Effects of heat-moisture treatment reaction conditions on the physicochemical and structural properties of maize starch: Moisture and length of heating. Food Chemistry 173: 1125–1132. Takeda Y, Hizukuri S and Juliano BO. (1987). Structures of rice amylopectins with low and high affinities for iodine. Carbohydrate Research 168: 79–88. Tester RF. (1997). Properties of damaged starch granules: Composition and swelling properties of maize, rice, pea and potato starch fractions in water at various temperatures. Food Hydrocolloids 11: 293–301.
Varatharajan V, Hoover R, Liu Q and Seetharaman K. (2010). The impact of heat-moisture treatment on the molecular structure and physicochemical properties of normal and waxy potato starches. Carbohydrate Polymers 81: 466–475. Vieira FC and Sarmento SBS. (2008). Heat moisture treatment and enzymatic digestibility of Peruvian carrot, sweet potato and ginger starches. Starch/Sta¨rke 60: 223–232. Wong KS and Jane J. (1995). Effects of pushing agents on the separation and detection of debranched amylopectin by high-performance anion-exchange chromatography with pulsed amperometric detection. Journal of Liquid Chromatography 18: 63–80. Yadav BS, Guleria P and Yadav RB. (2013). Hydrothermal modification of Indian water chestnut starch: Influence of heat-moisture treatment and annealing on the physicochemical, gelatinization and pasting characteristics. LWT—Food Science and Technology 53: 211–217. Zavareze ER and Dias ARG. (2011). Impact of heat-moisture treatment and annealing in starches: A review. Carbohydrate Polymers 83: 317–328.
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Effect of heat-moisture treatment on the structural, physicochemical, and rheological characteristics of arrowroot starch Larissa S Pepe, Jaqueline Moraes, Kivia M Albano, ˆnia RN Telis and Ce ´lia ML Franco Va
Abstract The effect of heat-moisture treatment on structural, physicochemical, and rheological characteristics of arrowroot starch was investigated. Heat-moisture treatment was performed with starch samples conditioned to 28% moisture at 100 C for 2, 4, 8, and 16 h. Structural and physicochemical characterization of native and modified starches, as well as rheological assays with gels of native and 4 h modified starches subjected to acid and sterilization stresses were performed. Arrowroot starch had 23.1% of amylose and a CA-type crystalline pattern that changed over the treatment time to A-type. Modified starches had higher pasting temperature and lower peak viscosity while breakdown viscosity practically disappeared, independently of the treatment time. Gelatinization temperature and crystallinity increased, while enthalpy, swelling power, and solubility decreased with the treatment. Gels from modified starches, independently of the stress conditions, were found to have more stable apparent viscosities and higher G0 and G00 than gels from native starch. Heatmoisture treatment caused a reorganization of starch chains that increased molecular interactions. This increase resulted in higher paste stability and strengthened gels that showed higher resistance to shearing and heat, even after acid or sterilization conditions. A treatment time of 4 h was enough to deeply changing the physicochemical properties of starch.
Keywords Starch, physical properties, rheology, viscosity Date received: 13 March 2015; accepted: 16 June 2015
INTRODUCTION Starch is constituted of two biopolymers, amylose and amylopectin. Amylose is an essentially linear macromolecule constituted of glucose units bounded in a-(1–4), whereas amylopectin is a highly branched macromolecule with a-(1–6) branches in the glucose chains bounded in a-(1–4) (Jacobs and Delcour, 1998; Tester, 1997). These two biopolymers form a semicrystalline structure in the starch granule, which consists of crystalline and amorphous lamellas (Jane et al., 1994).
Tuberous roots are very important food crops. After cereals, tubers and roots are the major source of starch for food and industrial uses, but usually, the major drawback of most of these starches is their instability under conditions of high temperature, shearing, and acidity, which limit many of starch applications in industry (Jyothi et al., 2010). Modification of root and tuber starches can improve their stability and result in the specific characteristics desired for various UNESP – Sa ˜o Paulo State University – Department of Food Engineering and Technology, Sa ˜o Paulo, Brazil
Food Science and Technology International 0(0) 1–10 ! The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1082013215595147 fst.sagepub.com
Corresponding author: ´lia ML Franco, Department of Food Engineering and Ce ´ va Technology, UNESP – Sa ˜o Paulo State University, R. Cristo ˜o ´ do Rio Preto, Colombo, 2265 Jardim Nazareth, Sa ˜o Jose Sa ˜o Paulo 15054-000, Brazil. Email: [email protected]
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Food Science and Technology International 0(0) end uses and market needs. Starch can be modified by chemical, physical, enzymatic, and genetic methods; however, the physical methods present a series of advantages. Physically modified starch is considered safe for use in food products, as it does not involve any chemicals (Kaur et al., 2012; Puncha-arnon and Uttapap, 2013). The regulation of chemically modified starch for food (particularly for baby food) is quite strict, in such a way that the demand for physically modified starches is increasing (Devi et al., 2009). Heat-moisture treatment (HMT) is a physical change in which the starch granules are conditioned to moisture levels below 35% and subjected to temperatures ranging from 84 to 120 C during a certain period of time (Gunaratne and Hoover, 2002; Jacobs and Delcour, 1998; Jyothi et al., 2010). HMT may be an alternative to chemical modification for altering the gelatinization and retrogradation properties of tuber and root starches (Gunaratne and Hoover, 2002). HMT causes the rearrangement of amylose and amylopectin chains in the starch, and therefore may modify its X-ray pattern, crystallinity, swelling power, amylose leaching, pasting, and gelatinization properties, as well as its susceptibility to enzymatic or acidic hydrolysis, which also affect the starch rheological properties (Chung et al., 2009; Jyothi et al., 2010; Zavareze and Dias, 2011). Chen et al. (2015) observed that HMT significantly changed crystal structure of wheat starch and the crystalline patterns transferred from A to AþV with moisture content increase, indicating formation of a starch–lipid complex. According to Sui et al. (2015), the levels of moisture content and length of heating have significant impacts on the structural and physicochemical properties of starches but to different extents. Amylose content and amylopectin chain length are also significant factors that determine the physicochemical properties of the final products (Lawal, 2005). Starches from different botanical sources show different responses to different treatment conditions (Jiranuntakul et al., 2011; Lawal, 2005; Moraes et al., 2014; Singh et al., 2011; Sui et al., 2015; Varatharajan et al., 2010; Yadav et al., 2013). All of these studies revealed that when different starches were modified under different conditions, they became more stable when exposed to heat and shearing due to the strengthening of linkages within the granule. However, these studies have not shown the effect of HMT on starch gels subjected to different stress conditions generally used in food processing. Arrowroot starch, obtained from the rhizomes of the tropical plant Maranta arundinacea L., is known for its medicinal properties in the treatment of gastrointestinal disorders, in addition to being a very digestible starch
(Mason, 2009). This starch presents round and oval granules with a large average size, CA- or A-type X-ray diffraction pattern, high gelatinization temperature, and amylose content that can vary between 16 and 27% (Moorthy, 2002; Peroni et al., 2006; Srichuwong et al., 2005). It can be used in bakery products, as an ice cream stabilizer, in jellies, cakes, and foodstuffs for infants (Jyothi et al., 2010; Mason, 2009). Nevertheless, as in the case of most tuber and root starches, arrowroot starch pastes are unstable under heating, shearing, and acid conditions generally used in the food industry. The goal of the present study was to evaluate the effect of HMT on the structural, physicochemical, and rheological characteristics of arrowroot starch and their pastes submitted to different stress conditions in order to improve its stability for different food applications.
MATERIAL AND METHODS Material Arrowroot (M. arundinacea L.) roots of the common variety were obtained from small producers from Minas Gerais state, Brazil, and were used within 24 h after harvesting. Isolation of starch and chemical composition The starch was isolated as described by Peroni et al. (2006) and analyzed in triplicate to determine ash, protein, and lipid contents according to the methods of the American Association of Cereal Chemists (AACC, 2000). Phosphorous content was determined according to Smith and Caruso (1964). To determine apparent amylose content, the starch was defatted and iodine affinities were then determined in triplicate using a potentiometric autotitrator (716SM Titrino, Brinkmann Instruments, Westbury, NY) according to Kasemsuwan et al. (1995). The apparent amylose content was calculated by dividing the iodine affinity of the starch by 20.0% (Takeda et al., 1987). Amylopectin branch chain length distribution The starch was debranched using isoamylase from Pseudomonas sp. (Megazyme International, Ireland), as described by Wong and Jane (1995). Amylopectin branch chain length distribution was analyzed using high-performance anion exchange chromatography with pulse amperometric detector (HPAEC-PAD) (ICS 3000, Dionex Corporation, Sunnyvale, USA) equipped with an AS40 automatic sampler. Samples were filtered (0.22 mm membrane) and injected into the HPAEC-PAD system (20 ml sample loop). The flow rate was 0.8 ml/min at 40 C. The standard
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Pepe et al. quadruple potential (E) waveform was employed with the following periods and pulse potentials: E1 ¼ 0.10 V (t1 ¼ 0.40 s); E2 ¼ –2.00 V (t2 ¼ 0.02 s); E3 ¼ 0.60 V (t3 ¼ 0.01 s); E4 ¼ –0.10 V (t4 ¼ 0.06 s). All eluents were prepared with ultrapure water (18 mV cm) with N2 sparging. Eluent A was 150 mM NaOH and eluent B was 500 mM sodium acetate and 150 mM NaOH. The branched chains of amylopectin were separated using a Dionex CarboPacTM PA-100 guard column (4 mm 50 mm) and a Dionex CarboPacTM PA-100 column (4 mm 250 mm). The gradient of eluent B was 28% at 0 min, 40% at 15 min, and 72% at 105 min. The data were analyzed using the Chromeleon software, version 6.8 (Dionex Corporation, USA). The analyses were performed in duplicate. HMT HMT was performed in triplicate according to Chung et al. (2009), with modifications. Starch samples were dispersed in enough distilled water to obtain 28% of moisture, mixed in a mechanical stirrer for 1 h, stored in plastic bags, and kept under refrigeration at 4 C for 24 h to achieve moisture balance. After this period, the samples were placed in Petri dishes, which were well sealed with parafilm and incubated in an oven at 100 C for 2, 4, 8, and 16 h. The moisture content of the samples was determined after HMT and the water loss during treatment was not significant. After that, the starches were dried at 40 C. X-ray pattern and relative crystallinity Native and modified starches were stored for 10 days at 25 C in a desiccator where a saturated solution of BaCl2 containing 1% of sodium azide maintained 90% of relative humidity. The X-ray patterns of the samples were determined using a wide angle goniometer unit (RINT 2000, Rigaku, Tokyo, Japan) with copper radiation Ka ( ¼ 1542 A˚). The scanning speed was 1 / min at 50 kV and 100 mA. The relative crystallinity was quantitatively estimated based on the relationship between peak and total areas, as described by Nara and Komiya (1983) using Origin software (version 7.5, Microcal Inc, Northampton, USA).
Norwalk, USA). Starch samples (3 mg, dry basis) were weighed in aluminum pans, mixed with distilled water (9 ml), and sealed. The sealed pans were kept at room temperature for 24 h to achieve balance and were scanned at a rate of 5 C/min over a temperature range of 25–100 C. An empty pan was used as a reference. The analysis was performed in triplicate. Water absorption index, water solubility index, and swelling power The water absorption index and water solubility index of the native and modified starches were determined at 30 C according to Linko et al. (1980). Swelling power and solubility in hot water were determined at 90 C according to Schoch (1964). The analyses were performed in triplicate. Rheological characteristics Rheological characteristics of the native and 4 h modified starch gels in normal and stress conditions were determined in order to evaluate the ability of the structural properties of gels to resist against processing conditions generally found in food industry. Native and 4 h modified starch suspensions (5 g 100 ml–1) were heated in a water bath at 100 C for 30 min and cooled to room temperature (normal condition). In the case of acidity stress, the pH of the suspension was reduced to 3.5 with 1 M ascorbic acid before heating, and in the case of sterilization stress, the gels were autoclaved at 121 C for 1 h (Guerreiro and Meneguelli, 2009). The rheological tests were carried out using an AR 2000EX rheometer (TA Instruments, New Castle, USA), with serrated parallel plate geometry 40 mm in diameter and a fixed gap of 800 mm. The steady shear tests were performed in order to determine two flow curves, up and down, with shear rate varying between 1 and 1000 s–1 at a temperature of 25 C, controlled by a Peltier system on the lower plate. Each measurement in the steady shear tests took around 30 s and each complete rheogram was determined in about 30 min. The Power Law (Ostwald–Waele model) was fitted to the downward curve according to equation (1)
s ¼ K_gn Pasting and thermal properties Pasting properties of the native and modified starches were determined using a rapid visco analyzer (RVA-4, Newport Scientific, Warriewood, Australia). Starch concentrations were 10% with a total mass of 27.5 g. The analysis was performed in triplicate. Thermal properties were determined using a differential scanning calorimeter (DSC - Pyris 1, Perkin Elmer,
ð1Þ
in which: s (Pa): shear stress; K (Pa sn): consistency index; g_ (s–1): shear rate; n: flow behavior index. The apparent viscosity (Zap, in Pa s) was calculated using the parameters obtained for the Power Law model, according to equation (2)
Zap ¼ K_gn1
ð2Þ 3
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Food Science and Technology International 0(0)
tan d ¼ G00 =G0
ð3Þ
0.8 0.6 0.4 0.2 0.0
Statistical analysis The data were statistically analyzed using analysis of variance, and the differences were evaluated using the t-test with Tukey’s adjustment. Statistics for Windows (v. 7.0, Statsoft, Tulsa, USA) was used. The significant differences were tested at p 0.05.
RESULTS AND DISCUSSION General composition The arrowroot starch displayed low contents of ash, protein, and lipid (0.27, 0.21, and 0.08%, respectively) indicating that it was pure enough to be used. This starch had 0.024% of phosphorous. Similar result was found by Peroni et al. (2006) who reported that arrowroot starch has higher phosphorous content than cassava, sweet potato, and ginger starches. The phosphorous in root and tuber starches is manly in phosphate form bounded in C6 of amylopectin (Bule´on et al., 1998). The arrowroot starch had 23.12% of apparent amylose, a finding that agreed with previously published data (Peroni et al., 2006; Srichuwong et al., 2005). This amount is similar to that of other root starches, such as cassava (22.81%) (Moraes et al., 2013), sago (21.90%) (Srichuwong et al., 2005), new cocoyam (22.5%) (Gunaratne and Hoover, 2002; Srichuwong et al., 2005), sweet potato (22.60%) (Peroni et al., 2006), and yam (24.6%) (Gunaratne and Hoover, 2002) starches. Amylopectin branch chain length distribution The normalized chain length distribution of debranched amylopectin of the arrowroot starch determined by HPAEC-PAD is shown in Figure 1. The arrowroot starch displayed bimodal distribution with first and second peaks of chain length at degree of polymerization (DP) 12 and 41, respectively. The starch had a smaller proportion of short chains (DP 6–12, 25.8%), compared to cassava (DP 6–12, 31.6%) and Peruvian carrot (DP 6–12, 33.53%) starches, which were analyzed under the same conditions in a previous
12
1.0
Normalized peak area
In oscillatory tests, storage (G0 ) and dissipation (G00 ) moduli were evaluated by running frequency sweeps from 1 to 100 rad/s with a maximum strain of 0.2, which was found to be inside the linear viscoelasticity region after strain sweeps at fixed frequency. The loss tangent, tan d, was calculated according to equation (3)
41 6
11 16 21 26 31 36 41 46 51 56 61 66 71 DP
Figure 1. Amylopectin branch chain length distribution of native arrowroot starch. DP: degree of polymerization.
study (Moraes et al., 2013). Arrowroot starch does not present the shoulder at DP 17–21 on the amylopectin branch chain length distribution that was observed on the distributions of Peruvian carrot and cassava starches (Moraes et al., 2013), and in that of wheat, barley, du waxy maize, and amaranth starches (Jane et al., 1999). Shoulders on the amylopectin branch chain length distribution indicate imperfections in the crystalline structure of a starch (Genkina et al., 2007; Jane et al., 1999). According to these authors, the chains with DP < 10, which are unable to form double helices, might be located in crystalline areas, which result in imperfections in starch structure. These findings indicate that arrowroot starch with a smaller proportion of short chains has a crystalline structure with less imperfection than those of cassava and Peruvian carrot starches. X-ray diffraction and relative crystallinity The arrowroot starch displayed a CA-type X-ray pattern (Figure 2). Similar result was also found by Jyothi et al. (2010). The C-type pattern is a mixture of A- and B-type patterns and then it contains pure A and B polymorphs in different proportions. There are various kinds of C-type patterns, some resemble the A-type, some the B-type, and some are almost intermediate between the two. These C-types were discriminated as CA, CB, and CC types (Hizukuri, 1961). HMT caused a progressive alteration with treatment time in X-ray pattern, from CA to A-type in arrowroot starch that occurred due to a crystallite transformation from B-type to A-type during the treatment. According to Varatharajan et al. (2010), the differences between A and B polymorphs arise from water content and the way in which the double helix pairs are packed in the crystals. The lattice of the B-type has a large void where 36 water molecules are accommodated. This void is not
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Pepe et al.
Intensity
a
37.4 %
b 51.4 % c
100
200 50 100
53.4 %
d
0
0 0
0
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36.8 %
Viscosity (RVU)
300
5
10
15
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25
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10
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25
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30
Angle 2θ
Figure 2. X-ray diffraction pattern and relative crystallinity of native and HMT-modified arrowroot starches: (a) native, (b) 4 h HMT, (c) 8 h HMT, (d) 16 h HMT.
present in A-type structure that accommodates eight water molecules. The packing of double helices in the B-type starch is less compact and thus, during treatment, they would be more mobile and more prone to disruption than those of A-type starch. In this study, the change in the crystalline pattern of starch during treatment occurred due to dehydration of water molecules, followed by movement of a pair of double helices to the center of the channel of B-type crystallites, which changed from a less thermodynamically stable structure to a more stable A-type model (Moraes et al., 2014; Varatharajan et al., 2010; Zavareze and Dias, 2011). Changes in relative crystallinity after HTM are dependent upon the botanical source of starch and conditions used in the treatment (Zavareze and Dias, 2011). Relative crystallinity increased with treatment time from 36.8% in native starch to 53.4% in 16 h modified starch. Chen et al. (2015) also observed an increase in relative crystallinity of wheat starch modified by HMT at different moisture levels. This increase was expected because HMT leads to rearrangement of the starch molecules that increases interaction between them. However, Sui et al. (2015) observed that X-ray intensities increased but relative crystallinity decreased to a greater extent with increasing moisture content when normal and waxy maize starches were modified by HMT. This treatment also may promote displacement of the double-helical chains within the starch crystals, resulting in a crystalline matrix that is more organized than in native starch (Chen et al., 2015; Zavareze and Dias, 2011). Pasting properties The viscoamylographic profiles of the native and 2, 4, 8, and 16 h modified starches obtained from RVA
Figure 3. Viscosity profiles of native and HMT-modified arrowroot starches: (#) native, («) 2 h HMT, (*) 4 h HMT, () 8 h HMT, () 16 h HMT.
are shown in Figure 3. The native arrowroot starch was found to have a higher pasting temperature and lower pasting viscosities when compared to other root starches, such as Peruvian carrot (Moraes et al., 2013; Vieira and Sarmento, 2008) and cassava (Moraes et al., 2013) starches. High pasting temperatures and low viscosities suggest the presence of strong bonding forces within the granule (Peroni et al., 2006). HMT significantly affected the pasting behavior of the starches, which, independently of the treatment time, revealed a large decrease in peak viscosity; breakdown practically disappeared and pasting temperatures increased, indicating that the starch became more stable when exposed to heat and mechanical shearing. Similar results were found by Moraes et al. (2014), Pinto et al. (2015), Singh et al. (2011), and Yadav et al. (2013) for different starches modified by HMT. This treatment promotes the rearrangement of starch chains, which limits the ability of the granules to swell and reduces the amount of leached amylose, thus decreasing the pasting viscosity (Chen et al., 2015; Lawal, 2005; Pinto et al., 2015). The compaction of granular matter by vapor pressure force, as well as chemical bonding and the interactions that occur during HMT, might also be factors that influence the stability of starches exposed to HMT (Puncha-arnon and Uttapap, 2013). The treatment time mainly affected the pasting properties in the first 4 h. After 8 and 16 h of HMT treatment, there was a slight decrease in final viscosity and setback, and after 16 h of treatment, there was a decrease in peak viscosity. These results indicated that the longer treatments promote more rearrangement in the starch granules. 5
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Food Science and Technology International 0(0) Thermal properties
Endothermic rate flow (mW)
The arrowroot starch had high gelatinization temperatures (to, tp, tc) and H when compared to other root starches. The gelatinization temperature range of this starch varied from 62.4 to 76.2 C, and H was 15.3 J/g. Cassava and Peruvian carrot starches showed lower temperatures, whereas potato and sweet potato starches displayed higher gelatinization temperatures than arrowroot starch, when analyzed at the same conditions in previous studies (Moraes et al., 2013; Rocha et al., 2010). The branch chain length and branching degree of amylopectin, the proportions of amylose and amylopectin, and the architecture of the starch granule are the main factors that affect thermal properties of starch and may explain these differences. HMT caused significant changes in thermal properties of the starch. There was an increase in the gelatinization temperatures and a decrease in H of the
a b c d e
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Temperature (°C)
Figure 4. DSC curves of native and HMT-modified arrowroot starches: (a) native, (b) 2 h HMT, (c) 4 h HMT, (d) 8 h HMT, (e) 16 h HMT.
modified starches no matter which treatment time was used. There was also an increase in the gelatinization temperature ranges, and after 2 h of treatment, two transition peaks were observed (Figure 4). These results suggested that HMT increased the interaction between starch chains; therefore, higher temperatures were needed for disruption of the crystals. Moreover, the new structure formed had less homogeneous crystals melted at different temperatures, a finding which explains the two peaks observed in many samples. According to Cooke and Gidley (1992), H represents primarily the loss of double helix order rather than loss of crystallinity during gelatinization process. After HMT, the H of arrowroot starch decreased from 15.3 to 11.7 J/g indicating that the treatment may also promote an unwinding of double helices. Water absorption index, water solubility index, and swelling power and solubility at 90 C Native arrowroot starch had low water absorption index and water solubility index values (Table 1). HMT hardly altered these parameters. However, HMT caused a decrease in swelling power and solubility of the starch at 90 C, which suggest that the rearrangement of starch chains caused by HMT allowed for a realignment of bonding forces of the starch chains, thus changing its structure and crystallinity (Chung et al., 2009; Gunaratne and Hoover, 2002; Jacobs and Delcour, 1998). HMT promotes formation of ordered double helices, and in doing so, limits starch swelling and solubility, as suggested by Lawal (2005). According to Gunaratne and Hoover (2002) and Jyothi et al. (2010), HMT promotes additional interactions between amylose–amylose and amylose–amylopectin, which result in a denser granule structure that is partly responsible for the decrease in swelling power. Solubility at 90 C decreased after treatment; however, when the treatment time increased the solubility
Table 1. Water absorption and water solubility indices at 30 C, swelling power and solubility at 90 C of native and HMTmodified arrowroot starches Arrowroot starch
WAI (g/g)
WSI (%)
SP (g/g)
SOL (%)
Native 2 h HMT 4 h HMT 8 h HMT 16 h HMT
1.85 2.03 2.22 2.00 2.07
0.55 0.51 0.40 0.57 0.59
60.43 19.98 26.44 26.64 25.74
25.92 11.80 15.00 16.48 20.77
(0.01)b (0.24)ab (0.01)a (0.03)ab (0.03)ab
(0.09)ab (0.08)ab (0.01)b (0.06)a (0.02)a
(0.7)a (0.44)b (0.14)b (0.54)b (0.29)b
(0.94)a (0.53)d (0.20)c (0.92)c (0.90)b
Average of nine replicates followed by standard deviation. Values followed by the same letter in the same column are not significantly different by Tukey test (P > 0.05). SOL: solubility at 90 C; SP: swelling power; WAI: water absorption index; WAI: water solubility index.
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Pepe et al. also increased; a result that agrees with that obtained by Jyothi et al. (2010). Rheological characteristics Flow curves obtained from steady shearing revealed that all of the gels studied displayed a pseudoplastic behavior, i.e. they are gels in which apparent viscosity decreases as shear rate increases. The pseudoplastic or shear-thinning behavior can be confirmed by the values of the flow behavior index (n)—resulting from fitting Power Law (equation (1)) to the downward flow curves, which were lower than unity in all of the treatments studied (Table 2). HMT caused a decrease in the consistency index (K), which led to lower apparent viscosities (Figure 5). However, the behavior index increased under most of the conditions tested, showing that the flow properties of the starch gels became less dependent upon the imposed shear rate. The lower variation in the
Table 2. Consistency index (K), flow behavior index (n), and determination coefficient (R2) of gels from native and 4 h HMT arrowroot starch Treatment
K (Pa sn)
N
R2
Native Native acidified Native sterilized Treated Treated acidified Treated sterilized
16.18 5.82 7.85 5.69 0.56 2.86
0.38 0.52 0.42 0.51 0.63 0.53
0.984 0.997 0.989 0.995 0.998 0.997
(a)
apparent viscosity as the shear rate increased indicated that HMT decreased the pseudoplasticity of the gels studied. The rheological behavior observed in arrowroot starch gels confirmed the viscoamylograph profiles of the native and 4 h modified starches obtained from RVA (Figure 3), which indicate that, after treatment, the starch became more stable when exposed to mechanical shear. The rheological measurements under oscillatory shearing showed that HMT affected the storage (G0 ) and loss (G00 ) moduli obtained for gels from arrowroot starch (Figure 6). Gels from HMT-treated arrowroot starch, whether subjected to sterilization or acid conditions or not, revealed G0 and G00 levels that were higher than those of native starch gels. In addition, the values of G0 were only slightly dependent on frequency and were higher than G00 . This finding is consistent with the mechanical spectrum that is typical of a gel network. Jyothi et al. (2010) also observed that after HMT the arrowroot starch paste showed a similar behavior. Comparing the curves of the phase angle, tan d (Figure 6(e) and (f)), it is possible to observe that gels made of HTM starches were less frequency dependent, even when subjected to acid or thermal stress. These results suggest that HMT favored the strengthening of arrowroot starch gels and gave them greater resistance, particularly to acidification stress, conditions generally used in food industry.
CONCLUSIONS HMT caused a rearrangement of the amylose and amylopectin molecules in the starch granule, thus changing its physicochemical and rheological properties.
(b) 10
Apparent viscosity (Pa.s)
Apparent viscosity (Pa.s)
10
1
0.1
10
100
Shear rate (1/s)
1000
1
0.1
10
100
1000
Shear rate (1/s)
Figure 5. Apparent viscosity of gels from native and 4 h modified arrowroot starches, some of which were subjected to acidity or sterilization stress: (a) native, (b) 4 h HMT; (#) without stress; (*) acidified; (p) sterilized.
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Food Science and Technology International 0(0)
(a)
(b)
100
G' (Pa)
G' (Pa)
100
10
10
1
1 10
10
100
Frequency (rad/s)
(d) 100
G'' (Pa)
G'' (Pa)
(c) 100
10
1
10
1 10
100
10
Frequency (rad/s)
(e)
100
Frequency (rad/s)
100
Frequency (rad/s)
(f)
1
tan δ
tan δ
1
0.1
0.1 10
100
10
Frequency (rad/s)
100
Frequency (rad/s)
Figure 6. Storage modulus (G0 ), loss modulus (G00 ), and loss tangent (tan d) of gels from native and 4 h modified arrowroot starches, some of which were subjected to acidity or sterilization stresses: (a), (c), (e): native; (b), (d), (f): 4 h HMT; (#) without stress; () acidified; (m) sterilized.
These changes gave these starches increased stability against shearing and high temperatures, even when subjected to stress conditions of acidity or sterilization. Treatment times higher than 4 h did not increase the stability of starches against high temperatures and shearing, although they did increase their crystallinity. The crystalline structure with less imperfections and strong associative forces present in arrowroot starch contributed to the starch behavior after treatment. Increased stability of gels, high gelatinization temperature, low peak viscosity, and the absence of breakdown are interesting aspects in starch that need to be
considered during the processing of pumped and/or sterilized products. FUNDING The authors thank the Brazilian research development agency CNPq - Conselho Nacional de Desenvolvimento Cientı´ fico e Tecnolo´gico (National Council for Scientific and Technological Development) (grant number 476385/2010-5), for financial support.
DECLARATION OF CONFLICTING INTERESTS The authors declare that there is no conflict of interest.
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