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Dual modifications on the gelatinization, textural, and morphology properties of pea starch by sodium carbonate and Mesona chinensis polysaccharide
Food Hydrocolloids 102 (2020) 105601
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Dual modifications on the gelatinization, textural, and morphology properties of pea starch by sodium carbonate and Mesona chinensis polysaccharide Suchen Liu a, b, 1, Liuming Xie a, b, 1, Mingyue Shen a, b, Yuehuan Xiao a, b, Qiang Yu a, b, Yi Chen a, b, Jianhua Xie a, b, * a b
State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, 330047, China School of Food Science and Technology, Nanchang University, Nanchang, 330047, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Pea starch Mesona chinensis polysaccharide Sodium carbonate Morphology Circular dichroism
The effects of dual modifications on the gelatinization, textural, and morphology properties of pea starch by Na2CO3 and Mesona chinensis polysaccharide (MCP) were investigated. Results showed that Na2CO3 promoted granular swelling and disruption but decreased the rearrangement tendency of disordered starch fraction of PS during gelatinization. The addition of 0.05%–0.1% MCP slightly affected granular swelling and protected the integrity of starch granules of Na2CO3–PS. 0.2% MCP enhanced the retrogradation and recrystallization of gelatinized starch in the presence of Na2CO3. Near-UV circular dichroism spectra showed that adding Na2CO3 and MCP in PS resulted in a strong peak at 285 nm and a small trough at 310 nm in the spectra of MCP and PS. The peak intensity orders of samples were consistent with the reaggregation tendency, suggesting that the characteristic peak at 285 nm was closely related to the retrogradation degree of starch.
1. Introduction Starch is the predominant source of human dietary, and it not only occurred as the staple food, i.e. bread, noodles, pie, but also used as thickening, gelling, and texturizing agents in various formulated foods (Li, Jiang, Campbell, Blanco, & Jane, 2008; Zhang et al., 2018; Zhou, Ma, Yin, Hu, & Boye, 2019). Starch is a semi-crystalline consisting of alternating amorphous and crystalline lamellae growth rings, and the gelatinization of natural starch involves the disappearance of the crys talline structure of starch, expansion of particle volume expands, and the sharp increase in viscosity after the starch suspension is heated (Mat ignon & Tecante, 2017; Zhang, Lim, & Chung, 2019). The textural properties of starch-based food were determined in part by the gelati nization of starch, However, some natural starch gel products have some undesirable problems such as its syneresis, retrogradation, pH sensi tivity, and heating instability, which limit the application of starch (Zhou, Zhang, Chen, & Chen, 2017; Ren et al., 2020). Therefore, many ingredients (such as salts, gum, octenyl succinylation, polysaccharides and so on) were often used as conditioning agents to the modify textural
properties of starch (Ahmad & Williams, 1999; Chaisawang & Suphan tharika, 2005; Wang, He, Fu, Huang, & Zhang, 2016; Lv et al., 2018; Liu et al., 2018; Zhang et al., 2019; Yang, Gao, & Yang, 2020). The presence of salts affected the gelatinization peak temperature, gelatinization enthalpy, swelling properties, storage modulus, gel strength and gela tion rate constants, k, depending on the type of salt and the concentra tion (Ahmad & Williams, 1999). Chaisawang and Suphantharika (2005) found that xanthan and guar gum increased the RVA peak viscosity of cationic tapioca starch during pasting synergistically in different ways. Mesona chinensis polysaccharide (MCP) is an acidic non-starch polysaccharide with great gelling properties, and it can modify the textural properties via interacting with starch (Liu et al., 2018; Ren et al., 2020; Feng, Gu, & Jin, 2010). In the previous studies, the change of apparent properties of starch gels caused by MCP primarily attributed to the effect on the starch swelling and disruption in a granular level, and amylose leaching and hydrogen bonding in a molecular level (Feng et al., 2014; Liu et al., 2018; Yuris, Matia-Merino, Hardacre, Hindmarsh, & Goh, 2018). The interaction between MCP and starch was also affected by ions, such as Ca2þ and Naþ, which acted a role in magnifying
* Corresponding author. State Key Laboratory of Food Science and Technology, Nanchang University, No. 235 Nanjing East Road, Nanchang, 330047, Jiangxi, China. E-mail address: [email protected] (J. Xie). 1 These authors contributed equally to this work and are considered as co-first authors. https://doi.org/10.1016/j.foodhyd.2019.105601 Received 5 September 2019; Received in revised form 9 December 2019; Accepted 12 December 2019 Available online 18 December 2019 0268-005X/© 2019 Elsevier Ltd. All rights reserved.
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the promotion of granular swelling induced by MCP (Liu et al., 2019; Yuris et al., 2019). Na2CO3 was also widely used in the production of many traditional food products, such as tortillas, waxy rice dumplings and yellow alkaline noodles, to enhance the quality characteristics of color, flavor, and texture (Nor Nadiha, Fazilah, Bhat, & Karim, 2010). Moreover, Na2CO3 had significant influence on the pasting, textural, morphology properties of maize starch (Liu et al., 2019). However, research on the dual factors of Na2CO3 and MCP affect the physico chemical properties of pea starch is limited. In this study, the dual modification of addition of Na2CO3 and MCP on the gelatinization, textural, and morphology properties of pea starch (typical C-type starch) were investigated. In addition, the trans formation of ordered structure in the starch granules caused by Na2CO3 and MCP were also studied by X-ray diffraction (XRD) and circular di chroism (CD). This study may provide more evidence to explain how Na2CO3 affects the pea starch and pea starch-MCP systems and provide new insights into the modification of the textural properties of starchbased products.
tube, centrifuged at 4800 rpm for 10 min and collected the supernatant. Six mL NaOH (0.33 M) was added into 1 mL supernatant and heated in a water bath at 95 � C for 30 min, then cooled and centrifuged at 4800 rpm for 10 min. Five mL trichloroacetic acid (0.5%, v/v) was added in 0.1 mL supernatant and modified the pH within 5.0–6.0, then add 0.01 N iodine-potassium iodide (1.30 g I2 and 3.50 g KI dissolved in 100 mL distilled water) and reacted at room temperature for 30 min. The absorbance of sample was measured at 620 nm with amylose (from potato, Aladdin CO., Shanghai) as the standard and Na2CO3-MCP solu tions as the blanks. 2.5. Gel properties Gel properties analysis were consisted by textural, syneresis, and dynamic rheological experiments, to evaluate the apparent gel proper ties, water holding capacity and gel network strength, respectively. The samples were prepared as section 2.3 described. 2.5.1. Texture profile analysis (TPA) Textural properties of samples were determined by a texture analyzer (TA-XTplus, Stable Co., England). Test performed using 36R probe, the pre-test, test, and latter test speed were 2.0 mm/s, the test distance was 10.0 mm, the trigger force was 5 g and the trigger type was automatic.
2. Materials and methods 2.1. Materials Pea starch (PS, total starch: 97.61 � 0.32%, amylose content: 30.92%) was purchased from Dingcheng Food, Co. (Linyi, Shandong Province, China). The total starch content, amylose content was ob tained by spectrophotometric method (Jarvis & Jrl, 1993). MCP was extracted by hot water alkali method from dry Mesona chinensis herb (Xiaoshicheng, Ganzhou, Jiangxi Province, China) (Lin et al., 2017; Xie et al., 2010). The MCP contains 36.20% total sugar content, 16.60% uronic acid and 19.20% protein according to our pre vious study (Lin et al., 2017). Other chemicals used in this study were purchased from Sigma-Aldrich, Co. (St. Louis, MO, USA).
2.5.2. Syneresis analysis Syneresis test of samples were studied by the method of Majeed, Wani, and Hussain (2017) with some modifications. 20 g PS-MCP and Na2CO3-PS-MCP pastes were collected and weighted in the centrifuge tubes, then the gels were centrifuged in 4800 rpm for 10 min after cooling back to room temperature, the supernatant were collected and weighted. Syneresis ratio of samples was calculated by the flowing formula: 2.5.3. Dynamic rheological properties PS-MCP and Na2CO3-PS-MCP pastes were collected according to Section 2.3, then the pastes were cooling back to room temperature and placed for 12 h to stabilize gels. In the next step, dynamic rheological properties measurements of samples were carried out in the frequency range from 0.1 to 25 Hz at 1% strain by using the rheometer (ARES-G2, TA Instruments Inc., USA) equipped with a stainless steel parallel plate (40 mm diameter). The cooled pastes prepared by RVA were transferred onto the parallel and filled suffused the gap (0.5 mm), all the mea surements were performed in triplicate. And the steady shear mea surements were performed with a shear rate range from 0.01s 1 to 1000 s 1 at 25 � C. Storage modulus (G0 ) and loss modulus (G00 ) of were ob tained by system software to describe the dynamic rheological proper ties samples.
2.2. Preparation of PS-MCP and Na2CO3-PS-MCP suspensions 26.50 mg of Na2CO3 was accurately weighted and added into 25 mL distilled water and stirred for 30 min to prepare 0.01 M Na2CO3 solution. Then a MCP-Na2CO3 solution with MCP content from 0 to 0.2% was prepared. In the end, PS (6%, w/v) was added in Na2CO3-MCP solutions and then stirred for 30min to obtain the Na2CO3-PS-MCP suspensions. The suspensions were used for the following experiments. 2.3. Pasting properties The pasting of PS-MCP and Na2CO3-PS-MCP suspensions were car ried by Rapid Visco-Analyzer (RVA, Newport Scientific, NSW, Australia). RVA Standard 1 profile was used to perform the pasting ex periments. In briefly, the suspensions were stirring in 960 rpm at 50 � C held for 60 s, heated to 95 � C within 220 s and maintained for 160 s, then cooled back to 50 � C in the same rate of heating, then held at 50 � C for 30 min. Pasting parameters including peak viscosity (PV), through vis cosity (TV), final viscosity (FV), relative breakdown viscosity (BD, %), relative setback viscosity (SB) and onset temperature (PoT) were ob tained by RVA system software. The gelatinized samples were collected to perform the following determinations.
2.6. Confocal laser scanning microscopy (CLSM) MCP (0%, 0.05%, 0.1%, 0.2%; w/v) and Na2CO3 (0.01 M)-MCP (0%, 0.05%, 0.1%, 0.2%; w/v) solutions were prepared firstly as section 2.2, then PS (1%, w/v) was added in the solutions under stirring for 30 min and gelatinized by RVA Standard 1 profile. The gelatinized mixtures were dyed by 500 μL fluorescein 5-isothiocyanate (FITC) (0.1%, w/v) solution with stirring for 30 min and placed at room temperature for 12 h. The CLSM images of mixtures were observed by a confocal laser scanning microscopy (LSM 710, Carl Zeiss, Germany) with helium neon (He–Ne) laser pattern. The excitation wavelength and emission wave length were 488 nm and 525 nm, respectively. The CLSM images were processed with using the ZEN 2009 software (Carl Zeiss, Germany).
2.4. Amylose leaching analysis Leaching amylose content of samples was measured by iodine binding method (Kaufman, Wilson, Bean, Herald, & Shi, 2015). PS-MCP and Na2CO3-PS-MCP suspensions were gelatinized by Standard 1 profile, and interrupted at 0 s (room temperature, Stage 1), 160 s (70 � C, Stage 2), 284 s (95 � C, Stage 3), 432 s (95 � C, Stage 4) and 780 s (50 � C, Stage 5), respectively. The samples which gelatinized to varying degrees were immediately took out, then weighed and placed in a 50 mL centrifuge
2.7. X-ray diffraction analysis PS-MCP and Na2CO3-PS-MCP pastes were obtained by RVA Standard 2
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1 profile and freeze-dried by 80 � C lyophilizer (Labconco Co., USA). The XRD spectra of samples were obtained in an X-ray diffractometer (D8 Advance; Bruker Inc., Germany) by using Cu Kα (Li et al., 2018). The diffraction angle was scanned from 5 to 60� at a scanning rate of 1� /min. All the XRD spectra were processed with Jade 6.0 software.
gelatinization, water was absorbed by amorphous growth rings which led to swelling, and the swelling exerted a strong destabilizing effect on residual concluding semi-crystallinity and amorphous regions (Jenkins & Donald, 1998). Obviously, Na2CO3 played a role in intensifying destabilization and consequently accelerating swelling in the dispersion. MCP (0.05%–0.1%) did not shown significant effect on the PV and TV of Na2CO3-PS, but it increased the subsequent pasting viscosity significantly and increased the FV and SB. Hence, 0.05%–0.1% MCP could affect paste viscosity by promoting the reorganization of disor dered starch components, and this effect was more significant at high MCP concentration. However, the addition of 0.2% MCP not only increased the PV, TV and FV, but also increased BD and SB. It indicated that 0.2% MCP played a role in both granular swelling and remnant rearrangement of the Na2CO3-PS system. The improvement of MCP on starch remnants rearrangement have been reported in wheat starchMCP and maize starch-MCP systems, whereas the effects of MCP on starch swelling was often found in high concentration (0.2%) MCP (Liu et al., 2019; Yuris et al., 2018). The addition of MCP could interact with the leached starch fractions (mainly amylose) and promote the reorga nization of disordered starch components. However, the promotion of starch swelling might depend on various factors, such as MCP concen tration and starch gelatinization pattern. In addition, the pasting curves of Na2CO3-PS-0.1%/0.2% MCP mix tures exhibited the transient peak at 192 and 200 s. Similar transient peaks were also found in other starch-MCP systems, such as wheat starch, rice starch, and mung bean starch-MCP systems (Feng et al., 2014; Yuris, Goh, Hardacre, & Matia-Merino, 2017). It indicated that the high concentration of MCP played a role in starch swelling in the initial stage of pasting. The addition of high concentration of MCP could adjust the effect of Na2CO3 on the granular swelling during pasting (Liu et al., 2019). The high viscosity of MS-0.2% MCP may be due to the compe tition of water absorption from high amount of MCP. The rigidity of starch granules were improved, resulting in high viscosity. Moreover, a high concentration of MCP could form a hydration film, which was coated around the starch granules, thus increasing the effective volume and subsequently increasing the viscosity (Palabiyik a, Said Toker, Karaman, & Yildiz, 2017).
2.8. Near-UV circular dichroism analysis The circular dichroism (CD) test was carried using a Circular Di chroism Spectrometer (MOS-450/AF-CD) according to the method of Eren, Santos, and Campanella (2015) with some modification. PS-MCP and Na2CO3-PS-MCP pastes were prepared as section 2.2. 1 g gelati nized sample was took out and diluted in distilled water (1:10, w/w) under stirring for 30 min. The diluted sample was filtered through a 0.22 μm filter to obtain about 3 mL filtrate. Then a quartz cell with 1 mm optical path length was used for CD measurements of diluted samples. The test parameters were set as: temperature of 25 � C, circular dichroism spectrum wavelength range was 400 nm–250 nm, scanning speed was 100 nm/min, the data pitch and bandwidth were 1 nm, and the response sensitivity was 100 mdeg/cm. 2.9. Statistical analysis Data were presented as mean � SD in triplicate. The experiment results were analyzed by Tukey’s test (p < 0.05) using SPSS software (version 21.0). All the figures were performed by Origin Pro (version 8.0) software (Stat-Ease Inc., Minneapolis, USA) and Photoshop CC software (Adobe system Inc., USA). 3. Results and discussion 3.1. Pasting properties of MCP-starch suspensions The pasting properties of PS and Na2CO3-PS-MCP are displayed in Fig. 1 and Table 2. Pea starch has a typical gelatinization pattern in which its crystallinity is disrupted from central hilum to granular surface (Cai et al., 2013). Hence, the swelling of PS granules is inconspicuous until the outer lamellae is completely destroyed (Cai et al., 2013). Accordingly, the pasting curve of PS maintained an upward tendency and did not show an obvious pasting peak (Fig. 1). Compared with PS, the addition of Na2CO3 resulted in a significant increase in PV and TV and delayed onset temperature (PoT) from 75.00 � C to 76.60 � C (Table 2). It suggested that Na2CO3 could improve the resistance of raw granules (before gelatinization) to heat, and promote granular swelling and disruption after the initial crystalline disordering. In the initial
3.2. Amylose leaching Fig. 2 shows the leached amylose content of PS during pasting. Ac cording to the amylose distribution of PS, the amylose was primarily distributed in the central hilum, and a portion was distributed in the amorphous growth rings (Matignon & Tecante, 2017). The amylose started leached out as starch swelling and maintained a rapid speed under heating from 50 � C to 95 � C until the disruption involved the central hilum. Then, it maintained a steady trend until the pasting process was done. In the amylose leaching curve, we choose five points to the stop pasting process and analyze the change in amylose leaching induced by Na2CO3 and MCP in different stages. The addition of Na2CO3 and MCP played a role in impeding amylose leaching from stage 2, and no significant difference was observed be tween the samples in the presence or absence of MCP. According to the pasting curve of samples, the starch granules in all the samples did not swell in this stage, suggesting that this effect was induced by the inhi bition in the onset temperature of Na2CO3. After this stage, the Na2CO3PS-0.2% MCP suspension was highly gelatinized and had the highest viscosity that could not be centrifuged. Thus, no Na2CO3-PS-0.2% MCP gel date were presented in stages 3, 4 and 5 (Fig. 2). In stage 3, Na2CO3 had no significant effect in impeding amylose leaching. However, the presence of MCP significantly decreased the leached amylose content, and the effect was concentration dependent. In stages 4 and 5, both Na2CO3 and MCP showed significant effect on declining amylose leaching. Similar results were also found in wheat starch-MCP systems and starch-other polysaccharides (Funami et al., 2005; Lee, Baek, Cha, Park, & Lim, 2002; Yuris et al., 2017), the probably mechanism
Fig. 1. Pasting curves of PS and Na2CO3-PS-MCP suspensions, PS: pea starch, N-: Na2CO3, MCP: Mesona chinensis polysaccharide. 3
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Table 1 Textural parameters and syneresis of PS and Na2CO3-PS-MCP gels. Sample
Hardness (g)
Adhesiveness (g∙sec)
PS N-PS N-PS-0.05% MCP N-PS-0.1% MCP N-PS-0.2% MCP
696.60 � 12.23b 714.49 � 8.73b 791.26 � 26.65c 2039.88 � 44.90d 614.29 � 8.67a
407.91 � 10.67a 278.91 � 34.27c 271.4 � 43.21c 446.52 � 42.43a 333.79 � 44.27b
Springiness
Cohesiveness
Gumminess
Chewiness
Syneresis (%)
0.85 � 0.87 � 0.91 � 0.93 � 0.84 �
0.59 � 0.06c 0.28 � 0.06a 0.33 � 0.09 ab 0.32 � 0.02 ab 0.36 � 0.05b
408.8 � 29.38b 202.57 � 16.75a 249.83 � 24.46a 657.56 � 39.17c 220.91 � 19.29a
348.76 � 31.76c 176.53 � 11.49a 227.02 � 24.96b 612.02 � 7.22d 184.6 � 17.86a
48.42 � 1.39e 40.37 � 2.21d 34.30 � 3.64c 4.00 � 1.71b 0
0.04a 0.00a 0.05b 0.04b 0.02a
Data were presented as mean � SD in triplicate and the values in the same column with different letters are different significantly (p < 0.05). PS, pea starch; N-, Na2CO3; MCP, Mesona chinensis polysaccharide; PV, peak viscosity; TV, trough viscosity; FV, final viscosity; BD, breakdown viscosity; SB, setback viscosity; PoT, onset temperature of pasting curve.
process, the starch particles had not been swollen and the amylose had not been largely dissolved. In the later period of pasting, the increasing granular size and the improvement of starch remnants aggregation precipitated the increase of paste viscosity, and led to the decrease of leached amylose content.
Table 2 Pasting parameters of PS and Na2CO3-PS-MCP suspensions. Sample
PV (cP)
TV (cP)
FV (cP)
BD (%)
SB (%)
PoT (� C)
PS
193.67 � 2.65a
208.00 � 2.52a
290.67 � 4.16a
7.4 � 0.02a
75.00 � 0.15c
N-PS
393.33 � 20.55b
389.33 � 18.01b
443.67 � 14.57b
1.02 � 0.06d
N-PS0.05% MCP N-PS0.1% MCP N-PS0.2% MCP
411.00 � 25.10b
409.67 � 21.46b
568.33 � 24.69c
0.49 � 0.04c
391.67 � 4.62b
402.00 � 4.00b
663.00 � 11.53d
2.81 � 0.07b
28.44 � 0.07b 12.25 � 0.11a 28.03 � 0.51b 39.27 � 0.85c
488.00 � 1.73c
466.00 � 4.58c
870.00 � 7.00e
4.51 � 0.02e
46.44 � 0.61d
3.3. Gel properties
76.60 � 0.04d 71.85 � 0.22a 72.55 � 0.12b 72.60 � 0.03b
3.3.1. TPA The textural parameters of PS gel were changed by the addition of Na2CO3. Na2CO3 enlarged the gel hardness and springiness, but decreased the cohesiveness, gumminess and chewiness (Table 1). By Integration with granular swelling and disruption analysis, Na2CO3 can affect the swelling of starch granules, thus enhancing the gel strength and increasing the hardness. Meanwhile, the starch granules with high swelling degree always had lower particle strength due to lower gran ular integrity (Han et al., 2019). Therefore, the cohesiveness, gummi ness and chewiness were decreased. The hardness, springiness, cohesiveness, gumminess and chewiness were enhanced by the addition of 0.05–0.1% MCP, and this effect was increased with increasing MCP concentration. However, 0.2% MCP significantly deduced gel textural parameter in which the hardness, adhesiveness, springiness, cohesiveness, gumminess and chewiness were lower than those of PS (Table 1). During gelatinization, 0.2% MCP significantly improved starch swelling which was associated with the high degree disruption leading to the apparent decline in the unit strength of starch granules. The adhesiveness of Na2CO3-PS-0.2% MCP was in a medium level among all the samples, suggested that the high content starch remnants contributed to the visco properties of gels in a certain degree.
Data were presented as mean � SD in triplicate and the values in the same column with different letters are different significantly (p < 0.05). PS, pea starch; N-, Na2CO3; MCP, Mesona chinensis polysaccharide; PV, peak viscosity; TV, trough viscosity; FV, final viscosity; BD, breakdown viscosity; SB, setback viscosity; PoT, onset temperature of pasting curve.
primarily consisted of two parts; one assumes that polysaccharide could interact with the released amylose and form the polysaccharide-amylose complex and impeded the further amylose leaching (Yuris et al., 2017). Second, the promotion in starch swelling induced by polysaccharide or other substances increased the granular volume and viscosity, and it could hinder amylose release from granules to dispersion (Doblado- Maldonado, Gomand, Goderis, & Delcour, 2016). In the initial pasting
Fig. 2. Leached amylose content of mixed systems during pasting, (A): intercepted points in the Standard 1 profile and fitted curves of leached amylose content of PS, (B): leached amylose content of mixed system in different stages. S: stage, PS: pea starch, N-:Na2CO3, MCP: Mesona chinensis polysaccharide. 4
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3.3.2. Syneresis Syneresis, as an indicator to describe the water holding capacity of gels, is related to the starch chain length, molecular size and gel network structure (Falsafi et al., 2018). The values of syneresis showed that both Na2CO3 and MCP could improve the water holding capacity of PS gels (Table 1). It indicated that the effect on either starch swelling or reor ganization both contributed to the denser accumulation of starch rem nants, which can decrease the molecular mobility and induce the increase in steric hindrance, thus impeding water loss during centrifugation.
amylose segments, particle rigidity and packing density. Therefore, G0 and G00 increased as MCP concentration increased. Natobly, the variation trends of the tanδ of samples depended on the frequency. At low frequency, the tanδ of samples could be arranged as follows: Na2CO3-PS-0.2% MCP > Na2CO3-PS-0.1% MCP > Na2CO3-PS0.05% MCP > Na2CO3-PS > PS, indicating that the MCP and Na2CO3 primarily contributed to the visco-properties rather than the elasproperties. However, as the frequency increased, a contrast trend occurred after approximately 10 rad/s and enlarged under high fre quency. It suggested that the MCP and Na2CO3 could improve the stress of gel network at high frequency.
3.3.3. Dynamic rheological properties The dynamic rheological parameters of storage modulus (G0 ), loss modulus (G00 ) were often used to characterize the rigidity and tenacity of gel network (Xiao et al., 2019). The formation of gel network was closely related to the reorganization after pasting. In comparison with the PS gel, the sample added with Na2CO3 had lower G0 , G00 and tanδ. However, the G0 and G00 increased with addition of MCP in the dispersion. (Fig. 3 (A) and (B)). This was inconsistent with trend of textural parameters. Dynamic rheological experiment was more focused on the interaction force and linkage between molecules, compared with textural experi ment. Hence, the main factors affecting the dynamic rheological and textural properties were aggregation of double-helices and amorphous
3.4. CLSM CLSM is often used to observe the granule morphology in starch studies. In this study, the morphology change of PS granules induced by the addition of Na2CO3 and MCP in the onset and disrupted tempera tures, respectively, was observed at 70 � C and 95 � C. The starch granule size of all samples were increased after heating from 70 � C to 95 � C. In PS dispersion (Fig. 4 A and a), the granules did not completely gelatinize at 70 � C according to the granules only dyed by FITC at the edges. After heating to 95 � C, the FITC was strongly bound to the semi-disruptive granules and dyed around central hilum consequently. The addition of
Fig. 3. Dynamic rheological parameters of PS and Na2CO3-PS-MCP gels, A: Storage modulus (G0 ), B: loss modulus (G00 ), C: loss factor (tanδ); PS: pea starch, N-: Na2CO3, MCP: Mesona chinensis polysaccharide. 5
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Na2CO3 decreased the granular size at 70 � C, and increased starch disruption at 95 � C (Fig. 4 B and b). It indicated that the pasting analysis of Na2CO3 could improve the heat resistance before onset temperature and accelerate granular swelling and disruption once the crystalline disordering. In comparison with the Na2CO3-PS suspension, 0.05%– 0.1% MCP increased the granular size at 70 � C but declined the starch disruption at 95 � C, and the granule integrity was protected to a certain degree (Fig. 4 c and d). As the MCP concentration increased to 0.2%, the enhancement in starch swelling and disruption affected the granular size, and resulted in the irregular shapes and shrank edges of PS gran ules. This condition accounted for the decrease in hardness of Na2CO3 -PS-0.2% MCP gels.
3.6. CD According to the previous studies, starch gelatinization interactions concluding disorganization and reorganization was proceeding in a molecular level, i.e. double helices, single helix (Matignon & Tecante, 2017), and it reported that the starch gel network was consisted by the filamentous structure formed with double helices linked with amylose segment loops (Richardson, Kidman, Langton, & Hermansson, 2004). Meanwhile, the hydrocolloids added in the starch dispersion also affected starch properties. For PS system, the changes of amylose leaching and reorganization were significantly in the presence of Na2CO3 and MCP, whereas the interaction manner was unclear. Circular dichroism (CD) was often used to investigate the secondary structure of protein, such as α-helix and β-sheet (Li & Arakawa, 2019). It is also used to study the secondary structure of carbohydrates and indicate the order-disorder transition, but it could not directly confirm the certain linkage (Eren et al., 2015; Matsuda, Biyajima, & Sato, 2009). In this study, we tested the far-UV CD and near-UV CD simultaneously. Interesting ly, the far-UV CD spectra of samples did not show any fluc tuation, whereas the near-UV CD spectra showed peaks and troughs in a range of 400–250 nm. First, the near-UV CD spectrum PS showed a steady tendency, and this condition rarely occurs at long wavelength (>200 nm) according to the CD of natural carbohydrates (Fig. 5B). The spectrum of MCP showed a wide peak at 331 nm and a narrow trough at 266 nm, suggesting the existence of substituted π electrons in MCP, because the CD peaks of carbohydrates occurs beyond the wavelength within 200 nm only under the presence of substituents bearing π elec trons (Eren et al., 2015; Stevens, 1996). The addition of Na2CO3 in PS caused a strong peak at 285 nm and a small trough at 310 nm. The following addition of MCP also exhibited the same spectrum pattern but changed the intensity of N-PS systems. The near-UV CD spectrum peak intensity at 285 nm of N-PS and N-PS-MCP systems were followed the order as: Na2CO3-PS-0.2% MCP > Na2CO3-PS-0.05% MCP > Na2CO3-PS > Na2CO3-PS-0.1% MCP, and the trough intensity followed as: Na2CO3-PS > Na2CO3-PS-0.1% MCP > Na2CO3-PS-0.05% MCP > Na2CO3-PS-0.2% MCP. The peak intensity order highly corresponded to the degree of granular damage, and the trough intensity had a negative correlation with reaggregation tendency. The previous studies had re ported that the stronger peak and weaker trough in spectrum was accorded with ordered structure (Dentini, Crescenzi, & Blasi, 1984; Milas & Rinaudo, 1979). Therefore, the Na2CO3 added in the PS induced a disordered structure and the following MCP increased the ordered structure. It proved that the improvement of reorganization on account of MCP could promote the transformation from disordered to ordered
3.5. XRD The X-ray diffraction spectrum of PS indicated that PS is a typical Ctype starch, with strong diffraction peaks at 2θ values of 17.24� and 23.25� and weaker peaks at 2θ values of 5.72� and 15.23� (Polesi & Sarmento, 2011). The gelatinized PS (named as PS in Fig. 5A) showed passivated diffraction spectrum with a bread-like peak at 12.20� ¼ 2θ and some weak reflections at 2θ ¼ 5.72� , 17.24� , 22.05� , 23.87� . Ac cording to the previously studies (Matignon & Tecante, 2017; Reddy, Suriya, & Haripriya, 2013), the recrystallization occurred concomitant with retrogradation, resulting in the formation of polymer-rich phase, leading to the formation of B-type crystals, regardless of the origins and treatments of starches. This phenomenon was associated with the occurrence of B-type characteristic peaks in gelatinized PS sample. The XRD curve of PS was further passivated with addition of Na2CO3 and it only showed a single bread-like peak at 2θ ¼ 12.20� , indicating that the crystallnity melting was related to granular swelling degree. The addi tion of 0.05%–0.1% MCP in the N-PS system did not displayed signifi cant influence in the XRD pattern, whereas 0.2% MCP sharpened the XRD spectrum and exhibited some weak reflections at 2θ ¼ 5.63� , 17.09� , 22.07� , 24.24� . The intensity of characteristic peaks is distinctly corresponding to the crystalline proportion of starch (Bao, Li, Wu, & Ouyang, 2018). The crystalline structure in gelatinized starch was pri marily derived from the residual crystals which had not been destroyed in pasting and re-crystals formed during retrogradation (Matignon & Tecante, 2017). The strong peak intensity of gelatinized PS and Na2CO3-PS-0.2% MCP were primarily attributed to residual crystals and recrystallinity, respectively. The crystal proportion of Na2CO3 was significantly decreased by the accelerating ordered structure melting, and 0.2% MCP increased the diffraction peak intensity by enhancing reorganization of disordered starch components.
Fig. 4. CLSM imagine of PS and Na2CO3-PS-MCP dispersion; A, B, C, D and E are PS, N-PS, N-PS-0.05% MCP, N-PS-0.1% MCP and N-PS-0.2% MCP in 70 � C, respectively; the lowercase letters are the same sample in 95 � C corresponding to capital letters; PS: pea starch, N-: Na2CO3, MCP: Mesona chinensis polysaccharide. 6
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Fig. 5. X-ray diffraction spectra (A) and near-UV CD spectra (B) of PS and N-PS-MCP samples, PS: pea starch, N-: Na2CO3, MCP: Mesona chinensis polysaccharide.
structure.
Appendix A. Supplementary data
4. Conclusions
Supplementary data to this article can be found online at https://doi. org/10.1016/j.foodhyd.2019.105601.
In this study, the effects of dual modification of Na2CO3 and MCP on the gelatinization, textural, and morphology properties of PS were investigated. Na2CO3 delayed the onset gelatinization of PS in the initial pasting stage, and played an important role in promoting starch swelling and receding the starch reorganization of PS dusing pasting, resulting in the increase of onset temperature and decrease of granular integrity and crystalline intensity. The addition of 0.05%–0.1% MCP in the Na2CO3PS system protected its granular integrity, increased the reorganization of PS, and improved the textural properties and network strength of PS gel. The addition of 0.2% MCP and Na2CO3 both promoted starch swelling and disruption, and 0.2% MCP could significantly improve the starch reorganization in the presence of Na2CO3. Our results can enable further understanding of the effects of dual modification of Na2CO3 and MCP on the gelatinization, textural, and morphology properties of PS, as well as the full utilization of pea starch resources.
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Declaration of competing interest The authors declare no conflict of interest. CRediT authorship contribution statement Suchen Liu: Conceptualization, Methodology, Formal analysis, Investigation, Writing - original draft, Visualization, Data curation. Liuming Xie: Formal analysis, Writing - original draft, Data curation, Visualization. Mingyue Shen: Writing - review & editing. Yuehuan Xiao: Software. Qiang Yu: Writing - review & editing. Yi Chen: Writing - review & editing. Jianhua Xie: Validation, Resources, Writing - review & editing, Supervision. Acknowledgments This study was financial supported by National Natural Science Foundation of China (21962020), the Natural Science Foundation of Jiangxi Province, China (20182ACB21004; 20171BCB23022), and The National Youth Top-notch Talent Support Program of China.
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Food Hydrocolloids journal homepage: http://www.elsevier.com/locate/foodhyd
Dual modifications on the gelatinization, textural, and morphology properties of pea starch by sodium carbonate and Mesona chinensis polysaccharide Suchen Liu a, b, 1, Liuming Xie a, b, 1, Mingyue Shen a, b, Yuehuan Xiao a, b, Qiang Yu a, b, Yi Chen a, b, Jianhua Xie a, b, * a b
State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, 330047, China School of Food Science and Technology, Nanchang University, Nanchang, 330047, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Pea starch Mesona chinensis polysaccharide Sodium carbonate Morphology Circular dichroism
The effects of dual modifications on the gelatinization, textural, and morphology properties of pea starch by Na2CO3 and Mesona chinensis polysaccharide (MCP) were investigated. Results showed that Na2CO3 promoted granular swelling and disruption but decreased the rearrangement tendency of disordered starch fraction of PS during gelatinization. The addition of 0.05%–0.1% MCP slightly affected granular swelling and protected the integrity of starch granules of Na2CO3–PS. 0.2% MCP enhanced the retrogradation and recrystallization of gelatinized starch in the presence of Na2CO3. Near-UV circular dichroism spectra showed that adding Na2CO3 and MCP in PS resulted in a strong peak at 285 nm and a small trough at 310 nm in the spectra of MCP and PS. The peak intensity orders of samples were consistent with the reaggregation tendency, suggesting that the characteristic peak at 285 nm was closely related to the retrogradation degree of starch.
1. Introduction Starch is the predominant source of human dietary, and it not only occurred as the staple food, i.e. bread, noodles, pie, but also used as thickening, gelling, and texturizing agents in various formulated foods (Li, Jiang, Campbell, Blanco, & Jane, 2008; Zhang et al., 2018; Zhou, Ma, Yin, Hu, & Boye, 2019). Starch is a semi-crystalline consisting of alternating amorphous and crystalline lamellae growth rings, and the gelatinization of natural starch involves the disappearance of the crys talline structure of starch, expansion of particle volume expands, and the sharp increase in viscosity after the starch suspension is heated (Mat ignon & Tecante, 2017; Zhang, Lim, & Chung, 2019). The textural properties of starch-based food were determined in part by the gelati nization of starch, However, some natural starch gel products have some undesirable problems such as its syneresis, retrogradation, pH sensi tivity, and heating instability, which limit the application of starch (Zhou, Zhang, Chen, & Chen, 2017; Ren et al., 2020). Therefore, many ingredients (such as salts, gum, octenyl succinylation, polysaccharides and so on) were often used as conditioning agents to the modify textural
properties of starch (Ahmad & Williams, 1999; Chaisawang & Suphan tharika, 2005; Wang, He, Fu, Huang, & Zhang, 2016; Lv et al., 2018; Liu et al., 2018; Zhang et al., 2019; Yang, Gao, & Yang, 2020). The presence of salts affected the gelatinization peak temperature, gelatinization enthalpy, swelling properties, storage modulus, gel strength and gela tion rate constants, k, depending on the type of salt and the concentra tion (Ahmad & Williams, 1999). Chaisawang and Suphantharika (2005) found that xanthan and guar gum increased the RVA peak viscosity of cationic tapioca starch during pasting synergistically in different ways. Mesona chinensis polysaccharide (MCP) is an acidic non-starch polysaccharide with great gelling properties, and it can modify the textural properties via interacting with starch (Liu et al., 2018; Ren et al., 2020; Feng, Gu, & Jin, 2010). In the previous studies, the change of apparent properties of starch gels caused by MCP primarily attributed to the effect on the starch swelling and disruption in a granular level, and amylose leaching and hydrogen bonding in a molecular level (Feng et al., 2014; Liu et al., 2018; Yuris, Matia-Merino, Hardacre, Hindmarsh, & Goh, 2018). The interaction between MCP and starch was also affected by ions, such as Ca2þ and Naþ, which acted a role in magnifying
* Corresponding author. State Key Laboratory of Food Science and Technology, Nanchang University, No. 235 Nanjing East Road, Nanchang, 330047, Jiangxi, China. E-mail address: [email protected] (J. Xie). 1 These authors contributed equally to this work and are considered as co-first authors. https://doi.org/10.1016/j.foodhyd.2019.105601 Received 5 September 2019; Received in revised form 9 December 2019; Accepted 12 December 2019 Available online 18 December 2019 0268-005X/© 2019 Elsevier Ltd. All rights reserved.
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the promotion of granular swelling induced by MCP (Liu et al., 2019; Yuris et al., 2019). Na2CO3 was also widely used in the production of many traditional food products, such as tortillas, waxy rice dumplings and yellow alkaline noodles, to enhance the quality characteristics of color, flavor, and texture (Nor Nadiha, Fazilah, Bhat, & Karim, 2010). Moreover, Na2CO3 had significant influence on the pasting, textural, morphology properties of maize starch (Liu et al., 2019). However, research on the dual factors of Na2CO3 and MCP affect the physico chemical properties of pea starch is limited. In this study, the dual modification of addition of Na2CO3 and MCP on the gelatinization, textural, and morphology properties of pea starch (typical C-type starch) were investigated. In addition, the trans formation of ordered structure in the starch granules caused by Na2CO3 and MCP were also studied by X-ray diffraction (XRD) and circular di chroism (CD). This study may provide more evidence to explain how Na2CO3 affects the pea starch and pea starch-MCP systems and provide new insights into the modification of the textural properties of starchbased products.
tube, centrifuged at 4800 rpm for 10 min and collected the supernatant. Six mL NaOH (0.33 M) was added into 1 mL supernatant and heated in a water bath at 95 � C for 30 min, then cooled and centrifuged at 4800 rpm for 10 min. Five mL trichloroacetic acid (0.5%, v/v) was added in 0.1 mL supernatant and modified the pH within 5.0–6.0, then add 0.01 N iodine-potassium iodide (1.30 g I2 and 3.50 g KI dissolved in 100 mL distilled water) and reacted at room temperature for 30 min. The absorbance of sample was measured at 620 nm with amylose (from potato, Aladdin CO., Shanghai) as the standard and Na2CO3-MCP solu tions as the blanks. 2.5. Gel properties Gel properties analysis were consisted by textural, syneresis, and dynamic rheological experiments, to evaluate the apparent gel proper ties, water holding capacity and gel network strength, respectively. The samples were prepared as section 2.3 described. 2.5.1. Texture profile analysis (TPA) Textural properties of samples were determined by a texture analyzer (TA-XTplus, Stable Co., England). Test performed using 36R probe, the pre-test, test, and latter test speed were 2.0 mm/s, the test distance was 10.0 mm, the trigger force was 5 g and the trigger type was automatic.
2. Materials and methods 2.1. Materials Pea starch (PS, total starch: 97.61 � 0.32%, amylose content: 30.92%) was purchased from Dingcheng Food, Co. (Linyi, Shandong Province, China). The total starch content, amylose content was ob tained by spectrophotometric method (Jarvis & Jrl, 1993). MCP was extracted by hot water alkali method from dry Mesona chinensis herb (Xiaoshicheng, Ganzhou, Jiangxi Province, China) (Lin et al., 2017; Xie et al., 2010). The MCP contains 36.20% total sugar content, 16.60% uronic acid and 19.20% protein according to our pre vious study (Lin et al., 2017). Other chemicals used in this study were purchased from Sigma-Aldrich, Co. (St. Louis, MO, USA).
2.5.2. Syneresis analysis Syneresis test of samples were studied by the method of Majeed, Wani, and Hussain (2017) with some modifications. 20 g PS-MCP and Na2CO3-PS-MCP pastes were collected and weighted in the centrifuge tubes, then the gels were centrifuged in 4800 rpm for 10 min after cooling back to room temperature, the supernatant were collected and weighted. Syneresis ratio of samples was calculated by the flowing formula: 2.5.3. Dynamic rheological properties PS-MCP and Na2CO3-PS-MCP pastes were collected according to Section 2.3, then the pastes were cooling back to room temperature and placed for 12 h to stabilize gels. In the next step, dynamic rheological properties measurements of samples were carried out in the frequency range from 0.1 to 25 Hz at 1% strain by using the rheometer (ARES-G2, TA Instruments Inc., USA) equipped with a stainless steel parallel plate (40 mm diameter). The cooled pastes prepared by RVA were transferred onto the parallel and filled suffused the gap (0.5 mm), all the mea surements were performed in triplicate. And the steady shear mea surements were performed with a shear rate range from 0.01s 1 to 1000 s 1 at 25 � C. Storage modulus (G0 ) and loss modulus (G00 ) of were ob tained by system software to describe the dynamic rheological proper ties samples.
2.2. Preparation of PS-MCP and Na2CO3-PS-MCP suspensions 26.50 mg of Na2CO3 was accurately weighted and added into 25 mL distilled water and stirred for 30 min to prepare 0.01 M Na2CO3 solution. Then a MCP-Na2CO3 solution with MCP content from 0 to 0.2% was prepared. In the end, PS (6%, w/v) was added in Na2CO3-MCP solutions and then stirred for 30min to obtain the Na2CO3-PS-MCP suspensions. The suspensions were used for the following experiments. 2.3. Pasting properties The pasting of PS-MCP and Na2CO3-PS-MCP suspensions were car ried by Rapid Visco-Analyzer (RVA, Newport Scientific, NSW, Australia). RVA Standard 1 profile was used to perform the pasting ex periments. In briefly, the suspensions were stirring in 960 rpm at 50 � C held for 60 s, heated to 95 � C within 220 s and maintained for 160 s, then cooled back to 50 � C in the same rate of heating, then held at 50 � C for 30 min. Pasting parameters including peak viscosity (PV), through vis cosity (TV), final viscosity (FV), relative breakdown viscosity (BD, %), relative setback viscosity (SB) and onset temperature (PoT) were ob tained by RVA system software. The gelatinized samples were collected to perform the following determinations.
2.6. Confocal laser scanning microscopy (CLSM) MCP (0%, 0.05%, 0.1%, 0.2%; w/v) and Na2CO3 (0.01 M)-MCP (0%, 0.05%, 0.1%, 0.2%; w/v) solutions were prepared firstly as section 2.2, then PS (1%, w/v) was added in the solutions under stirring for 30 min and gelatinized by RVA Standard 1 profile. The gelatinized mixtures were dyed by 500 μL fluorescein 5-isothiocyanate (FITC) (0.1%, w/v) solution with stirring for 30 min and placed at room temperature for 12 h. The CLSM images of mixtures were observed by a confocal laser scanning microscopy (LSM 710, Carl Zeiss, Germany) with helium neon (He–Ne) laser pattern. The excitation wavelength and emission wave length were 488 nm and 525 nm, respectively. The CLSM images were processed with using the ZEN 2009 software (Carl Zeiss, Germany).
2.4. Amylose leaching analysis Leaching amylose content of samples was measured by iodine binding method (Kaufman, Wilson, Bean, Herald, & Shi, 2015). PS-MCP and Na2CO3-PS-MCP suspensions were gelatinized by Standard 1 profile, and interrupted at 0 s (room temperature, Stage 1), 160 s (70 � C, Stage 2), 284 s (95 � C, Stage 3), 432 s (95 � C, Stage 4) and 780 s (50 � C, Stage 5), respectively. The samples which gelatinized to varying degrees were immediately took out, then weighed and placed in a 50 mL centrifuge
2.7. X-ray diffraction analysis PS-MCP and Na2CO3-PS-MCP pastes were obtained by RVA Standard 2
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1 profile and freeze-dried by 80 � C lyophilizer (Labconco Co., USA). The XRD spectra of samples were obtained in an X-ray diffractometer (D8 Advance; Bruker Inc., Germany) by using Cu Kα (Li et al., 2018). The diffraction angle was scanned from 5 to 60� at a scanning rate of 1� /min. All the XRD spectra were processed with Jade 6.0 software.
gelatinization, water was absorbed by amorphous growth rings which led to swelling, and the swelling exerted a strong destabilizing effect on residual concluding semi-crystallinity and amorphous regions (Jenkins & Donald, 1998). Obviously, Na2CO3 played a role in intensifying destabilization and consequently accelerating swelling in the dispersion. MCP (0.05%–0.1%) did not shown significant effect on the PV and TV of Na2CO3-PS, but it increased the subsequent pasting viscosity significantly and increased the FV and SB. Hence, 0.05%–0.1% MCP could affect paste viscosity by promoting the reorganization of disor dered starch components, and this effect was more significant at high MCP concentration. However, the addition of 0.2% MCP not only increased the PV, TV and FV, but also increased BD and SB. It indicated that 0.2% MCP played a role in both granular swelling and remnant rearrangement of the Na2CO3-PS system. The improvement of MCP on starch remnants rearrangement have been reported in wheat starchMCP and maize starch-MCP systems, whereas the effects of MCP on starch swelling was often found in high concentration (0.2%) MCP (Liu et al., 2019; Yuris et al., 2018). The addition of MCP could interact with the leached starch fractions (mainly amylose) and promote the reorga nization of disordered starch components. However, the promotion of starch swelling might depend on various factors, such as MCP concen tration and starch gelatinization pattern. In addition, the pasting curves of Na2CO3-PS-0.1%/0.2% MCP mix tures exhibited the transient peak at 192 and 200 s. Similar transient peaks were also found in other starch-MCP systems, such as wheat starch, rice starch, and mung bean starch-MCP systems (Feng et al., 2014; Yuris, Goh, Hardacre, & Matia-Merino, 2017). It indicated that the high concentration of MCP played a role in starch swelling in the initial stage of pasting. The addition of high concentration of MCP could adjust the effect of Na2CO3 on the granular swelling during pasting (Liu et al., 2019). The high viscosity of MS-0.2% MCP may be due to the compe tition of water absorption from high amount of MCP. The rigidity of starch granules were improved, resulting in high viscosity. Moreover, a high concentration of MCP could form a hydration film, which was coated around the starch granules, thus increasing the effective volume and subsequently increasing the viscosity (Palabiyik a, Said Toker, Karaman, & Yildiz, 2017).
2.8. Near-UV circular dichroism analysis The circular dichroism (CD) test was carried using a Circular Di chroism Spectrometer (MOS-450/AF-CD) according to the method of Eren, Santos, and Campanella (2015) with some modification. PS-MCP and Na2CO3-PS-MCP pastes were prepared as section 2.2. 1 g gelati nized sample was took out and diluted in distilled water (1:10, w/w) under stirring for 30 min. The diluted sample was filtered through a 0.22 μm filter to obtain about 3 mL filtrate. Then a quartz cell with 1 mm optical path length was used for CD measurements of diluted samples. The test parameters were set as: temperature of 25 � C, circular dichroism spectrum wavelength range was 400 nm–250 nm, scanning speed was 100 nm/min, the data pitch and bandwidth were 1 nm, and the response sensitivity was 100 mdeg/cm. 2.9. Statistical analysis Data were presented as mean � SD in triplicate. The experiment results were analyzed by Tukey’s test (p < 0.05) using SPSS software (version 21.0). All the figures were performed by Origin Pro (version 8.0) software (Stat-Ease Inc., Minneapolis, USA) and Photoshop CC software (Adobe system Inc., USA). 3. Results and discussion 3.1. Pasting properties of MCP-starch suspensions The pasting properties of PS and Na2CO3-PS-MCP are displayed in Fig. 1 and Table 2. Pea starch has a typical gelatinization pattern in which its crystallinity is disrupted from central hilum to granular surface (Cai et al., 2013). Hence, the swelling of PS granules is inconspicuous until the outer lamellae is completely destroyed (Cai et al., 2013). Accordingly, the pasting curve of PS maintained an upward tendency and did not show an obvious pasting peak (Fig. 1). Compared with PS, the addition of Na2CO3 resulted in a significant increase in PV and TV and delayed onset temperature (PoT) from 75.00 � C to 76.60 � C (Table 2). It suggested that Na2CO3 could improve the resistance of raw granules (before gelatinization) to heat, and promote granular swelling and disruption after the initial crystalline disordering. In the initial
3.2. Amylose leaching Fig. 2 shows the leached amylose content of PS during pasting. Ac cording to the amylose distribution of PS, the amylose was primarily distributed in the central hilum, and a portion was distributed in the amorphous growth rings (Matignon & Tecante, 2017). The amylose started leached out as starch swelling and maintained a rapid speed under heating from 50 � C to 95 � C until the disruption involved the central hilum. Then, it maintained a steady trend until the pasting process was done. In the amylose leaching curve, we choose five points to the stop pasting process and analyze the change in amylose leaching induced by Na2CO3 and MCP in different stages. The addition of Na2CO3 and MCP played a role in impeding amylose leaching from stage 2, and no significant difference was observed be tween the samples in the presence or absence of MCP. According to the pasting curve of samples, the starch granules in all the samples did not swell in this stage, suggesting that this effect was induced by the inhi bition in the onset temperature of Na2CO3. After this stage, the Na2CO3PS-0.2% MCP suspension was highly gelatinized and had the highest viscosity that could not be centrifuged. Thus, no Na2CO3-PS-0.2% MCP gel date were presented in stages 3, 4 and 5 (Fig. 2). In stage 3, Na2CO3 had no significant effect in impeding amylose leaching. However, the presence of MCP significantly decreased the leached amylose content, and the effect was concentration dependent. In stages 4 and 5, both Na2CO3 and MCP showed significant effect on declining amylose leaching. Similar results were also found in wheat starch-MCP systems and starch-other polysaccharides (Funami et al., 2005; Lee, Baek, Cha, Park, & Lim, 2002; Yuris et al., 2017), the probably mechanism
Fig. 1. Pasting curves of PS and Na2CO3-PS-MCP suspensions, PS: pea starch, N-: Na2CO3, MCP: Mesona chinensis polysaccharide. 3
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Table 1 Textural parameters and syneresis of PS and Na2CO3-PS-MCP gels. Sample
Hardness (g)
Adhesiveness (g∙sec)
PS N-PS N-PS-0.05% MCP N-PS-0.1% MCP N-PS-0.2% MCP
696.60 � 12.23b 714.49 � 8.73b 791.26 � 26.65c 2039.88 � 44.90d 614.29 � 8.67a
407.91 � 10.67a 278.91 � 34.27c 271.4 � 43.21c 446.52 � 42.43a 333.79 � 44.27b
Springiness
Cohesiveness
Gumminess
Chewiness
Syneresis (%)
0.85 � 0.87 � 0.91 � 0.93 � 0.84 �
0.59 � 0.06c 0.28 � 0.06a 0.33 � 0.09 ab 0.32 � 0.02 ab 0.36 � 0.05b
408.8 � 29.38b 202.57 � 16.75a 249.83 � 24.46a 657.56 � 39.17c 220.91 � 19.29a
348.76 � 31.76c 176.53 � 11.49a 227.02 � 24.96b 612.02 � 7.22d 184.6 � 17.86a
48.42 � 1.39e 40.37 � 2.21d 34.30 � 3.64c 4.00 � 1.71b 0
0.04a 0.00a 0.05b 0.04b 0.02a
Data were presented as mean � SD in triplicate and the values in the same column with different letters are different significantly (p < 0.05). PS, pea starch; N-, Na2CO3; MCP, Mesona chinensis polysaccharide; PV, peak viscosity; TV, trough viscosity; FV, final viscosity; BD, breakdown viscosity; SB, setback viscosity; PoT, onset temperature of pasting curve.
process, the starch particles had not been swollen and the amylose had not been largely dissolved. In the later period of pasting, the increasing granular size and the improvement of starch remnants aggregation precipitated the increase of paste viscosity, and led to the decrease of leached amylose content.
Table 2 Pasting parameters of PS and Na2CO3-PS-MCP suspensions. Sample
PV (cP)
TV (cP)
FV (cP)
BD (%)
SB (%)
PoT (� C)
PS
193.67 � 2.65a
208.00 � 2.52a
290.67 � 4.16a
7.4 � 0.02a
75.00 � 0.15c
N-PS
393.33 � 20.55b
389.33 � 18.01b
443.67 � 14.57b
1.02 � 0.06d
N-PS0.05% MCP N-PS0.1% MCP N-PS0.2% MCP
411.00 � 25.10b
409.67 � 21.46b
568.33 � 24.69c
0.49 � 0.04c
391.67 � 4.62b
402.00 � 4.00b
663.00 � 11.53d
2.81 � 0.07b
28.44 � 0.07b 12.25 � 0.11a 28.03 � 0.51b 39.27 � 0.85c
488.00 � 1.73c
466.00 � 4.58c
870.00 � 7.00e
4.51 � 0.02e
46.44 � 0.61d
3.3. Gel properties
76.60 � 0.04d 71.85 � 0.22a 72.55 � 0.12b 72.60 � 0.03b
3.3.1. TPA The textural parameters of PS gel were changed by the addition of Na2CO3. Na2CO3 enlarged the gel hardness and springiness, but decreased the cohesiveness, gumminess and chewiness (Table 1). By Integration with granular swelling and disruption analysis, Na2CO3 can affect the swelling of starch granules, thus enhancing the gel strength and increasing the hardness. Meanwhile, the starch granules with high swelling degree always had lower particle strength due to lower gran ular integrity (Han et al., 2019). Therefore, the cohesiveness, gummi ness and chewiness were decreased. The hardness, springiness, cohesiveness, gumminess and chewiness were enhanced by the addition of 0.05–0.1% MCP, and this effect was increased with increasing MCP concentration. However, 0.2% MCP significantly deduced gel textural parameter in which the hardness, adhesiveness, springiness, cohesiveness, gumminess and chewiness were lower than those of PS (Table 1). During gelatinization, 0.2% MCP significantly improved starch swelling which was associated with the high degree disruption leading to the apparent decline in the unit strength of starch granules. The adhesiveness of Na2CO3-PS-0.2% MCP was in a medium level among all the samples, suggested that the high content starch remnants contributed to the visco properties of gels in a certain degree.
Data were presented as mean � SD in triplicate and the values in the same column with different letters are different significantly (p < 0.05). PS, pea starch; N-, Na2CO3; MCP, Mesona chinensis polysaccharide; PV, peak viscosity; TV, trough viscosity; FV, final viscosity; BD, breakdown viscosity; SB, setback viscosity; PoT, onset temperature of pasting curve.
primarily consisted of two parts; one assumes that polysaccharide could interact with the released amylose and form the polysaccharide-amylose complex and impeded the further amylose leaching (Yuris et al., 2017). Second, the promotion in starch swelling induced by polysaccharide or other substances increased the granular volume and viscosity, and it could hinder amylose release from granules to dispersion (Doblado- Maldonado, Gomand, Goderis, & Delcour, 2016). In the initial pasting
Fig. 2. Leached amylose content of mixed systems during pasting, (A): intercepted points in the Standard 1 profile and fitted curves of leached amylose content of PS, (B): leached amylose content of mixed system in different stages. S: stage, PS: pea starch, N-:Na2CO3, MCP: Mesona chinensis polysaccharide. 4
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3.3.2. Syneresis Syneresis, as an indicator to describe the water holding capacity of gels, is related to the starch chain length, molecular size and gel network structure (Falsafi et al., 2018). The values of syneresis showed that both Na2CO3 and MCP could improve the water holding capacity of PS gels (Table 1). It indicated that the effect on either starch swelling or reor ganization both contributed to the denser accumulation of starch rem nants, which can decrease the molecular mobility and induce the increase in steric hindrance, thus impeding water loss during centrifugation.
amylose segments, particle rigidity and packing density. Therefore, G0 and G00 increased as MCP concentration increased. Natobly, the variation trends of the tanδ of samples depended on the frequency. At low frequency, the tanδ of samples could be arranged as follows: Na2CO3-PS-0.2% MCP > Na2CO3-PS-0.1% MCP > Na2CO3-PS0.05% MCP > Na2CO3-PS > PS, indicating that the MCP and Na2CO3 primarily contributed to the visco-properties rather than the elasproperties. However, as the frequency increased, a contrast trend occurred after approximately 10 rad/s and enlarged under high fre quency. It suggested that the MCP and Na2CO3 could improve the stress of gel network at high frequency.
3.3.3. Dynamic rheological properties The dynamic rheological parameters of storage modulus (G0 ), loss modulus (G00 ) were often used to characterize the rigidity and tenacity of gel network (Xiao et al., 2019). The formation of gel network was closely related to the reorganization after pasting. In comparison with the PS gel, the sample added with Na2CO3 had lower G0 , G00 and tanδ. However, the G0 and G00 increased with addition of MCP in the dispersion. (Fig. 3 (A) and (B)). This was inconsistent with trend of textural parameters. Dynamic rheological experiment was more focused on the interaction force and linkage between molecules, compared with textural experi ment. Hence, the main factors affecting the dynamic rheological and textural properties were aggregation of double-helices and amorphous
3.4. CLSM CLSM is often used to observe the granule morphology in starch studies. In this study, the morphology change of PS granules induced by the addition of Na2CO3 and MCP in the onset and disrupted tempera tures, respectively, was observed at 70 � C and 95 � C. The starch granule size of all samples were increased after heating from 70 � C to 95 � C. In PS dispersion (Fig. 4 A and a), the granules did not completely gelatinize at 70 � C according to the granules only dyed by FITC at the edges. After heating to 95 � C, the FITC was strongly bound to the semi-disruptive granules and dyed around central hilum consequently. The addition of
Fig. 3. Dynamic rheological parameters of PS and Na2CO3-PS-MCP gels, A: Storage modulus (G0 ), B: loss modulus (G00 ), C: loss factor (tanδ); PS: pea starch, N-: Na2CO3, MCP: Mesona chinensis polysaccharide. 5
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Na2CO3 decreased the granular size at 70 � C, and increased starch disruption at 95 � C (Fig. 4 B and b). It indicated that the pasting analysis of Na2CO3 could improve the heat resistance before onset temperature and accelerate granular swelling and disruption once the crystalline disordering. In comparison with the Na2CO3-PS suspension, 0.05%– 0.1% MCP increased the granular size at 70 � C but declined the starch disruption at 95 � C, and the granule integrity was protected to a certain degree (Fig. 4 c and d). As the MCP concentration increased to 0.2%, the enhancement in starch swelling and disruption affected the granular size, and resulted in the irregular shapes and shrank edges of PS gran ules. This condition accounted for the decrease in hardness of Na2CO3 -PS-0.2% MCP gels.
3.6. CD According to the previous studies, starch gelatinization interactions concluding disorganization and reorganization was proceeding in a molecular level, i.e. double helices, single helix (Matignon & Tecante, 2017), and it reported that the starch gel network was consisted by the filamentous structure formed with double helices linked with amylose segment loops (Richardson, Kidman, Langton, & Hermansson, 2004). Meanwhile, the hydrocolloids added in the starch dispersion also affected starch properties. For PS system, the changes of amylose leaching and reorganization were significantly in the presence of Na2CO3 and MCP, whereas the interaction manner was unclear. Circular dichroism (CD) was often used to investigate the secondary structure of protein, such as α-helix and β-sheet (Li & Arakawa, 2019). It is also used to study the secondary structure of carbohydrates and indicate the order-disorder transition, but it could not directly confirm the certain linkage (Eren et al., 2015; Matsuda, Biyajima, & Sato, 2009). In this study, we tested the far-UV CD and near-UV CD simultaneously. Interesting ly, the far-UV CD spectra of samples did not show any fluc tuation, whereas the near-UV CD spectra showed peaks and troughs in a range of 400–250 nm. First, the near-UV CD spectrum PS showed a steady tendency, and this condition rarely occurs at long wavelength (>200 nm) according to the CD of natural carbohydrates (Fig. 5B). The spectrum of MCP showed a wide peak at 331 nm and a narrow trough at 266 nm, suggesting the existence of substituted π electrons in MCP, because the CD peaks of carbohydrates occurs beyond the wavelength within 200 nm only under the presence of substituents bearing π elec trons (Eren et al., 2015; Stevens, 1996). The addition of Na2CO3 in PS caused a strong peak at 285 nm and a small trough at 310 nm. The following addition of MCP also exhibited the same spectrum pattern but changed the intensity of N-PS systems. The near-UV CD spectrum peak intensity at 285 nm of N-PS and N-PS-MCP systems were followed the order as: Na2CO3-PS-0.2% MCP > Na2CO3-PS-0.05% MCP > Na2CO3-PS > Na2CO3-PS-0.1% MCP, and the trough intensity followed as: Na2CO3-PS > Na2CO3-PS-0.1% MCP > Na2CO3-PS-0.05% MCP > Na2CO3-PS-0.2% MCP. The peak intensity order highly corresponded to the degree of granular damage, and the trough intensity had a negative correlation with reaggregation tendency. The previous studies had re ported that the stronger peak and weaker trough in spectrum was accorded with ordered structure (Dentini, Crescenzi, & Blasi, 1984; Milas & Rinaudo, 1979). Therefore, the Na2CO3 added in the PS induced a disordered structure and the following MCP increased the ordered structure. It proved that the improvement of reorganization on account of MCP could promote the transformation from disordered to ordered
3.5. XRD The X-ray diffraction spectrum of PS indicated that PS is a typical Ctype starch, with strong diffraction peaks at 2θ values of 17.24� and 23.25� and weaker peaks at 2θ values of 5.72� and 15.23� (Polesi & Sarmento, 2011). The gelatinized PS (named as PS in Fig. 5A) showed passivated diffraction spectrum with a bread-like peak at 12.20� ¼ 2θ and some weak reflections at 2θ ¼ 5.72� , 17.24� , 22.05� , 23.87� . Ac cording to the previously studies (Matignon & Tecante, 2017; Reddy, Suriya, & Haripriya, 2013), the recrystallization occurred concomitant with retrogradation, resulting in the formation of polymer-rich phase, leading to the formation of B-type crystals, regardless of the origins and treatments of starches. This phenomenon was associated with the occurrence of B-type characteristic peaks in gelatinized PS sample. The XRD curve of PS was further passivated with addition of Na2CO3 and it only showed a single bread-like peak at 2θ ¼ 12.20� , indicating that the crystallnity melting was related to granular swelling degree. The addi tion of 0.05%–0.1% MCP in the N-PS system did not displayed signifi cant influence in the XRD pattern, whereas 0.2% MCP sharpened the XRD spectrum and exhibited some weak reflections at 2θ ¼ 5.63� , 17.09� , 22.07� , 24.24� . The intensity of characteristic peaks is distinctly corresponding to the crystalline proportion of starch (Bao, Li, Wu, & Ouyang, 2018). The crystalline structure in gelatinized starch was pri marily derived from the residual crystals which had not been destroyed in pasting and re-crystals formed during retrogradation (Matignon & Tecante, 2017). The strong peak intensity of gelatinized PS and Na2CO3-PS-0.2% MCP were primarily attributed to residual crystals and recrystallinity, respectively. The crystal proportion of Na2CO3 was significantly decreased by the accelerating ordered structure melting, and 0.2% MCP increased the diffraction peak intensity by enhancing reorganization of disordered starch components.
Fig. 4. CLSM imagine of PS and Na2CO3-PS-MCP dispersion; A, B, C, D and E are PS, N-PS, N-PS-0.05% MCP, N-PS-0.1% MCP and N-PS-0.2% MCP in 70 � C, respectively; the lowercase letters are the same sample in 95 � C corresponding to capital letters; PS: pea starch, N-: Na2CO3, MCP: Mesona chinensis polysaccharide. 6
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Fig. 5. X-ray diffraction spectra (A) and near-UV CD spectra (B) of PS and N-PS-MCP samples, PS: pea starch, N-: Na2CO3, MCP: Mesona chinensis polysaccharide.
structure.
Appendix A. Supplementary data
4. Conclusions
Supplementary data to this article can be found online at https://doi. org/10.1016/j.foodhyd.2019.105601.
In this study, the effects of dual modification of Na2CO3 and MCP on the gelatinization, textural, and morphology properties of PS were investigated. Na2CO3 delayed the onset gelatinization of PS in the initial pasting stage, and played an important role in promoting starch swelling and receding the starch reorganization of PS dusing pasting, resulting in the increase of onset temperature and decrease of granular integrity and crystalline intensity. The addition of 0.05%–0.1% MCP in the Na2CO3PS system protected its granular integrity, increased the reorganization of PS, and improved the textural properties and network strength of PS gel. The addition of 0.2% MCP and Na2CO3 both promoted starch swelling and disruption, and 0.2% MCP could significantly improve the starch reorganization in the presence of Na2CO3. Our results can enable further understanding of the effects of dual modification of Na2CO3 and MCP on the gelatinization, textural, and morphology properties of PS, as well as the full utilization of pea starch resources.
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Declaration of competing interest The authors declare no conflict of interest. CRediT authorship contribution statement Suchen Liu: Conceptualization, Methodology, Formal analysis, Investigation, Writing - original draft, Visualization, Data curation. Liuming Xie: Formal analysis, Writing - original draft, Data curation, Visualization. Mingyue Shen: Writing - review & editing. Yuehuan Xiao: Software. Qiang Yu: Writing - review & editing. Yi Chen: Writing - review & editing. Jianhua Xie: Validation, Resources, Writing - review & editing, Supervision. Acknowledgments This study was financial supported by National Natural Science Foundation of China (21962020), the Natural Science Foundation of Jiangxi Province, China (20182ACB21004; 20171BCB23022), and The National Youth Top-notch Talent Support Program of China.
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