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Effect of different Mesona chinensis polysaccharides on pasting, gelation, structural properties and in vitro digestibility of tapioca starch-Mesona chinensis polysaccharides gels
Food Hydrocolloids 99 (2020) 105327
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Effect of different Mesona chinensis polysaccharides on pasting, gelation, structural properties and in vitro digestibility of tapioca starch-Mesona chinensis polysaccharides gels
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Yuehuan Xiao, Suchen Liu, Mingyue Shen, Lian Jiang, Yanming Ren, Yu Luo, Jianhua Xie∗ State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, 330047, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Tapioca starch Mesona chinensis polysaccharides Pasting Gelation Structure In vitro digestibility
The effects of Mesona chinensis polysaccharides (MCP) obtained through cellulase-assisted (MCP-C) and sodium carbonate-assisted (MCP-S) extractions on the pasting, gelation, structural properties, and in vitro digestibility of tapioca starch (TS)-MCP gels were investigated. The pasting, rheological, gelation and structural properties of TS/MCPs were analyzed by rapid visco analysis (RVA), rheological analysis, texture analysis, X-ray diffraction, fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), respectively. And the digestibility extent of TS/MCPs was determined by an in vitro method. The expansion degree of starch granules, pasting viscosity, hardness, and the amount of amylose leached of TS were decreased after adding MCP-C and increased after adding MCP-S. TS/MCPs showed higher storage modulus (G′), higher short-range order and finer structure than that of TS. In addition, MCP-C and MCP-S decreased the content of rapidly digestible starch (RDS) of TS, especially when 0.5% MCP-C was added. Moreover, the slowly digestible starch (SDS) and resistant starch (RS) contents of TS/MCPs were positively correlated with the G′ and DO, thereby indicating that the strong and ordered gel network had a retardant impact on starch digestion.
1. Introduction Tapioca is a tuber food crop with extensive cultivation history and economic value in China. Its starch has high viscosity and is widely used as a thickener or gelling agent in the food industry (Chen, Fu, & Luo, 2015). However, its high viscosity and inherent formless gel state impede the mechanized production of tapioca starch (TS)-based products, thus leading to its limited applications. Many modification methods were developed to improve starch quality. These approaches include chemical, physical, and biological methods (Atichokudomchai & Varavinit, 2003; Xia et al., 2015; Han et al., 2012; Reddy, Lee, Lim, & Park, 2019). Among them, physical modification, such as complexation with other food-derived ingredients like protein (Yang, Zhong, Goff, & Li, 2019), phenolic compound (An, Bae, Han, Lee, & Lee, 2016) and polysaccharides (Liu, Li, Fan, Zhang, & Zhong, 2019a), is a green and environmentally friendly method. In particular, polysaccharides are safe and non-toxic because they come from plants living organisms, including in plants, body fluids of animals, bacteria, yeast and fungi (Shao, Chen, & Sun, 2013; Xie, Tang, Jin, Li, & Xie, 2016). Recent research has shown that polysaccharides can interact with TS to improve
the hardness, anti-shear ability, water retention ability and structural stability of gels (Russ, Zielbauer, Ghebremedhin, & Vilgis, 2016; Singh, Geveke, & Yadav, 2017; von Borries-Medrano, Jaime-Fonseca, & Aguilar-Méndez, 2019; Sheng et al., 2018). Mesona chinensis, a labiatae plant, can be mixed with starch to make black bean jelly (Lin et al., 2018). Mesona chinensis polysaccharide (MCP) is considered to be the major functional component of the herb form the gel with starch (Liu et al., 2019b). In our previous work, we obtained two kinds of MCP through cellulase-assisted (MCP-C) and sodium carbonate-assisted (MCP-S) extractions. The results of physicochemical, rheological and thermal experiments showed that molecular weight, apparent viscosity, storage modulus, and thermal stability were different; the total sugar, uronic acid, and protein contents of MCP-S were 32.28%, 29.52%, and 31.35%, respectively, whereas those of MCP-C were 29.37%, 23.21%, and 22.37%, correspondingly; the monosaccharide composition of MCP-S included arabinose, fucose, galactose, glucose, rhamnose, and xylose at a molar ratio of 0.32:0.87:0.82:6.24:0.11:0.34; meanwhile, the monosaccharide composition of MCP-C included arabinose, fucose, galactose, glucose, and mannose at a molar ratio of 0.24:0.92:0.55:10.7:0.32; and MCP-S had
∗ 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).
https://doi.org/10.1016/j.foodhyd.2019.105327 Received 10 May 2019; Received in revised form 21 August 2019; Accepted 21 August 2019 Available online 22 August 2019 0268-005X/ © 2019 Elsevier Ltd. All rights reserved.
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2.4. Rheological properties
the higher apparent viscosity and dynamic modulus than MCP-C at the same concentration (Xiao et al., 2019). Furthermore, Tang et al. (2017) found that MCP-C obtain the highest antioxidant activity than MCP obtained through hot-alkali (Na2CO3) and ultrasonic-assisted extractions. In recent years, many studies on the starch-MCP compounded system have been conducted. Liu et al. (2018) reported that the adding MCP reduces the gelatinization enthalpy (ΔH) and increases the pasting temperature and rheological properties (i.e., thixotropy, storage modulus) of wheat starch. MCP can interact with amylose extracted from starch granules and can change the molecular mobility of the water and carbohydrate populations of starch-MCP gels (Yuris et al., 2017, 2019a). The changes of gel properties after mixing maize and rice starches with MCP are also excellent (Feng, Ye, Zhuang, Fang, & Chen, 2012; Liu et al., 2019b). However, the effects of MCP-C and MCP-S on the functional and structural properties of TS-MCP gels have not been studied. In the present study, the effects of MCP-C and MCP-S on the pasting, gelation, structural properties and in vitro digestibility of TSMCP gels were investigated. Furthermore, the correlation between the selected inherent factors and in vitro digestibility parameters was analyzed.
Rheological measurement was carried out using a rheometer (ARESG2, TA Instruments Inc., USA) equipped with parallel plate (1000 μm gap, 40 mm diameter). Before the test, all samples were prepared by RVA and placed at room temperature for 20 h to complete hydration. Frequency sweep was performed from 0.99 rad/s to 157.08 rad/s (0.15–25 Hz) in linear viscoelastic region (1% oscillating strain, 25 °C) (Romero, Santra, Rose, & Zhang, 2017). The rheological parameters, storage modulus (G′) and loss modulus (G″) were recorded. 2.5. Gel strength and hardness 8 mL TS/MCPs gels were collected in the RVA test and transferred into 10 mL sample vials and kept at 4 °C for 20 h. Then, the vials were inverted for 1–2 min to assess the strength of the TS/MCPs gels. Flow behavior is not observed in the gel represents that it reaches the critical gel concentration Ccrit (Wang, Virgilio, Wood-Adams, & Heuzey, 2018a). Hardness analysis of TS/MCPs gels was according to a previous work with slight modifications (Wang et al., 2018b). The tests were performed using the texture analyzer (TA-XT plus, Stable Co., England) fitted with the P/0.5 probe. The test parameters were set as followed: pretest, test and post-test speeds were 2 mm/s, the test distance was 10.0 mm, the trigger force was 5 g and the trigger type was automatic. Each sample was evaluated three times.
2. Materials and methods 2.1. Materials Tapioca starch (TS) (amylose content: 26.43%) was purchased from Dingcheng Food, Co. (Linyi, Shandong Province, China), maize starch (MS) (amylose content: 30.67%) was purchased from Tianjin Honglu Food Co. (Tianjin, China) and pea starch (PS) (amylose content: 30.92%) was purchased from Jiangsu Xinliang Food Co. (Jiangsu China). And the amylose content was determined by spectrophotometric method (Jarvis & Walker, 1993). Mesona chinensis was purchased from XiaoShicheng, GanZhou, JiangXi. Porcine pancreatin and amyloglucosidase were obtained from Sigma-Aldrich, Inc. (St. Louis, MO). Ultra-pure water was provided by a Milli-Q water purification system (Millipore, USA). And all other chemicals were of analytical grade.
2.6. Swelling power and solubility Swelling power and solubility of all samples were determined as the method described by Paraginski et al. (2019). The starch (1%, w/v) was mixed with different MCPs (25 mL) in centrifuge tubes at different concentrations. Mixed solutions were heated at 95 °C for 30 min. Then, the gelatinized samples were cooled to room temperature, centrifuged at 4800 rpm for 30 min. Then, the supernatant was collected and dried at 105 °C to a constant. The solubility and swelling power were calculated according to Eqs. (3) and (4),
2.2. Preparation the mixtures of TS/MCPs
Solubility (%) = (WS/W) × 100%
(3)
MCP-C and MCP-S were extracted from Mesona chinensis herb, respectively (Xiao et al., 2019). Homogeneous sample solutions of 0.1%, 0.3%, and 0.5% MCP-C and MCP-S (25 mL, w/v) were prepared. Afterwards, each sample solution was added to TS (6%, w/v) and stirred to achieve uniform state.
Swelling power (g/g) = WP/W(1-S)
(4)
Where WS is the dried supernatant weight (g), W is the dried sample weight (g), WP is the precipitate weight (g) and S is the solubility (%). 2.7. X-ray diffraction analysis
2.3. Pasting properties
All samples were collected from RVA test, freeze-dried, cut into slices and used in X-ray diffraction (XRD) experiment. The samples were analyzed by an X-ray diffractometer (D8 Advance, Bruker Inc., Germany) with the 2θ (°) range of 5°–45° (Wang, Zhang, Fan, Yang, & Chen, 2019). The relative crystallinity (RC) was quantitatively estimated as a ratio of the crystalline area to the total area using MDI JADE 6.0 software, the total area included the crystalline and amorphous regions.
Mixed solutions were prepared as described above (section 2.2) and the pasting behavior of mixed solutions determined by the rapid visco analyzer (RVA, Newport Scientific, NSW, Australia). The heating process was programmed based on the method reported by Mishra and Rai (2006). Mixed solutions (25 mL) were held at 50 °C for 1 min, and were heated to 95 °C at 12.16 °C/min, held at 95 °C for 2.5 min before cooling to 50 °C at 12.16 °C/min and holding at 50 °C for 2 min. The constant shear rate of 160 rpm was used. The pasting parameters measured including peak viscosity (PV, cP), though viscosity (TV, cP), final viscosity (FV, cP), and pasting temperature (PT, °C). Relative breakdown viscosity (BV, %) and setback viscosity (SV, %) were introduced to intuitively reflect the properties change of solutions at pasting process (Palabiyik, Toker, Karaman, & Yildiz, 2017). Relative breakdown viscosity and setback viscosity were calculated using Eqs. (1) and (2), BV% = (PV-TV)/PV × 100%
(1)
SV% = (FV-TV)/FV × 100%
(2)
2.8. Short-range ordered structure Fourier transform infrared (FT-IR) spectra of samples were obtained at room temperature by a spectrometer (Nicolet 5700, USA) using the method reported by Miao, Zhang, Mu, and Jiang (2010). The absorbance height at 1047 cm−1, 1022 cm−1 and 995 cm−1 were recorded. 2.9. Scanning electron microscopy (SEM) Microstructure of TS/MCPs were observed by using the SEM (JSM2
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6701F, JFOL Ltd., Japan). The dried samples were cut to slices and sprayed with gold, prepared to perform the test at the voltage of 5.0 kV. 2.10. In vitro digestibility In vitro starch digestion was analyzed according to the method described by Englyst, Kingman, and Cummings (1992) with some modifications. Firstly, dried TS (300 mg) was gelatinized at 95 °C for 30 min with and without MCPs solutions (5 mL, ultra-pure water was added to the control group), and rapidly cooled to prevent the retrogradation of starch. Afterwards, 10 mL of sodium acetate buffer solution (0.1 M, pH 5.2) added to the all mixed solutions, and equilibrated at 37 °C for 5 min. Then, rotors and 10 mL of mixed enzyme solution (pancreatin and amyloglucosidase) added to it. Lastly, mixed solutions were incubated in an oscillating water bath at 37 °C. At different time points (20, 30, 60, 90, 120, and 180 min), 95% of ethanol was added at a volume ratio of 3:1 to stop enzymatic digestion, centrifuged (4800 rpm, 10 min). Then, the supernatant was collected and used to determine glucose content by the 3, 5-dinitrosalicylic acid (DNS) method (Miller, 1959). Percentage of hydrolyzed starch was calculated by multiplying a factor of 0.9 with the glucose content, hydrolysis rate and the content of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) were calculated using Eqs. (5)–(8):
Fig. 1. Pasting behavior of TS/MCPs determined by rapid visco analyzer.
pasting. The PV, TV, and FV of TS with MCP-S increased from 718.33 to 898.00 cP, 492.67 to 593.00 cP, and 716.33 to 907.00 cP, correspondingly (Table 1). These results were attributed to the swelling and rigidity of starch granules (Liu et al., 2019b). On the one hand, the pasting viscosity of TS increased after adding MCP-S, which competed for water absorption with TS, thereby improving the rigidity of starch granules. MCP-S also formed a film on the surface of swollen starch granules, thus increasing the volume of granules. On the other hand, the pasting viscosity of TS decreased after adding MCP-C addition, which has lower apparent viscosity than MCP-S. MCP-C can penetrate and form a complex in starch granules, thereby reducing water activity and limiting the expansion of granules (Xiao et al., 2019; Zhou et al., 2017). Furthermore, the ordered structure, crystallinity, molecular structure, and molecular weight of amylopectin had been reported to affect the pasting viscosity of starch (Kim, Woo, & Chung, 2018; Zheng et al., 2019). Relative breakdown viscosity (BV) can evaluate the stability of starch granules under shear and thermal environments (Liu et al., 2018). BV is related to PV, higher PV indicates the greater degree of swelling of granules, the degree of granules rupture and the leaching of amylose are more serious (Ma, Zhu, & Wang, 2019). Table 1 displays that the TS with MCP-S had higher BV than TS with MCP-C. Setback viscosity (SV) can characterize the ability of the re-aggregation of the swollen and broke starch granules during cooling (Sheng et al., 2018). In Table 1, relative SV decreased after adding MCP-C, thereby indicating that MCP-C inhibits the short-term retrogradation of TS by interacting with leached amylose (Ma et al., 2019). However, the SV of TS/MCP-S increased, which may be due to the amylose fragments were dissolved well, thereby resulting in promoting the aggregation of swollen granules and formation of stronger gel networks after adding MCP-S during cooling (Berski & Ziobro, 2018). In fact, the ability to promote short-term retrogradation of starch should be careful consideration in food applications because starch retrogradation is unexpected in most products. Hot paste stability index (HPI) represents the ability of the TS/MCPs to maintain 80% of PV value after reaching PV during heating. The HPI of TS/MCPs increased except when 0.5% MCP-S was added. The BV of TS with 0.5% MCP-S was highest among all samples, thereby indicating its instability during heating. The selection of a suitable type and concentration of MCPs will open a pathway to control the pasting behavior of TS.
Hydrolysis rate (%) = (Content of hydrolyzed glucose × 0.9)/ TS × 100% (5) RDS (%) = 0.9 × (G20-G0)/TS × 100%
(6)
SDS (%) = 0.9 × (G120-G20)/TS × 100%
(7)
RS (%) = 0.9 × (TS-RDS-SDS)/TS × 100%
(8)
Where TS is the total starch content of the sample (mg), G20 is the glucose content (mg) after 20 min hydrolysis, G0 is the free glucose content (mg), G120 is the glucose content (mg) after 120 min hydrolysis. 2.11. Statistical analysis All tests were determined at least in triplicate. Date were analyzed by SPSS software (version 21.0, SPSS Inc., Chicago, IL, USA). analysis of variance (ANOVA) and Tukey's test were used to compare differences among the mean values at 0.05 level of confidence. Images were drawn by Origin Pro software (version 8.0, Stat-Ease Inc., Minneapolis, MN, USA). 3. Results and discussion 3.1. Pasting properties In the pasting curve obtained using a rapid visco analyzer, pasting temperature (PT) represents the point at which viscosity started to rise. After reaching the PT, starch granules began to expand, and viscosity rapidly increased to a peak viscosity (PV). The PV represents the maximum swelling degree of starch granules during heating. Heating of samples was continued, thereby causing the starch granules to rupture and the viscosity to drop to through viscosity (TV) (von BorriesMedrano et al., 2019; Huang et al., 2017). During cooling, rearrangement between amylose and amylopectin resulted in increased viscosity and reached the final viscosity (FV) (Chen et al., 2015). The pasting curves and parameters of TS/MCPs are plotted in Fig. 1 and presented in Table 1, respectively. The PT of TS was 73.22 °C and increasing after adding MCPs.This result may be attributed to the reduction in water activity of starch-MCP-water system (Zhou, Zhang, Chen, & Chen, 2017). In comparison with the pure starch, TS added with MCP-C had a slightly decreased PV, TV, and FV, but the differences were insignificant (p > 0.05), whereas TS added with MCP-S, especially at 0.5% MCP-S, had significantly increased PV, TV, and FV during
3.2. Rheological properties The viscoelastic behavior of the TS/MCPs gels were determined at an angular frequency range of 0.99–157.08 rad/s at 25 °C. Fig. 2A and B plot the storage modulus (G′) and loss modulus (G″) curves of TS/MCPs gels. G′ and G″ are the representative parameters in dynamic rheology 3
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Table 1 Pasting parameters of TS/MCP-C and TS/MCP-S mixtures. Sample TS TS/0.1% TS/0.3% TS/0.5% TS/0.1% TS/0.3% TS/0.5%
MCP-C MCP-C MCP-C MCP-S MCP-S MCP-S
PV (cP)
TV (cP)
FV (cP)
PT (°C)
BV (%)
SV (%)
HPSI
718.33a 709.67a 706.00a 701.00a 759.33b 813.00c 898.00d
492.67a 498.33a 487.00a 487.33a 527.00b 554.00c 593.00d
716.33a 694.33a 683.67a 679.67a 766.00b 826.67c 907.00d
73.22a 73.78b 73.77 ab 74.33b 73.47 ab 74.08 ab 73.80 ab
31.42abc 29.77a 31.01abc 30.48 ab 30.61 ab 31.85bc 33.96d
31.22bc 28.23a 28.76a 28.3a 31.21bc 32.98cd 34.61d
56.79b 64.47de 65.06e 68.35f 60.24c 62.65cd 51.85a
PV, peak viscosity; TV, trough viscosity; FV, final viscosity; BV, relative breakdown; SV, relative setback; HPSI, hot pastes stability index and PT, pasting temperature. Values in columns not sharing the same letter are significantly different (p < 0.05).
(Zhang, Zhu, Tong, & Ren, 2012). In all cases, these values increased with frequency and concentration. And G′ were higher than G″, indicating that all mixed gels exhibited the typical gel-like behavior (Shao, Qiu, Chen, Zhu, & Sun, 2017). The G′ value of TS gel was 47.04 Pa at an angular frequency of 157.08 rad/s (25 Hz) and increased after adding MCPs. The increase in G′ value may be due to the following factors: (a) adding MCPs reduces the available water content of starch and increases the effective concentration of starch in per unit volume, thus facilitating the formation of a stable gel structure; and (b) is heat increases the swollen and ruptured starch granules and decreases the size of starch granules, thereby increasing the contact area between starch and MCPs. Furthermore, gelatinous MCPs can form a coat on the surface of swollen starch, thus increasing the rigidity of starch granules (Ma et al., 2019; Yuris, Matia-Merino, Hardacre, Hindmarsh, & Goh, 2018). The G′ values were higher in TS/MCP-S gels than in TS/MCP-C gels at low concentrations (0.1% and 0.3%) but lower at high concentration (0.5%). Among all TS/MCPs gels, TS with 0.5% MCP-S had the highest pasting viscosity and BV, thereby causing the granules rupture and decreasing the value of G'. Fig. 3. Gel images and flow behavior of samples. (A) Gel images of tapioca starch (TS), maize starch (MS), pea starch (PS), and TS mixed with 0.5% MCP-S. (B) The flow behavior of TS/MCPs after being flipped for 1 min, and from left to right were the TS, TS/MCP-C (0.1%, 0.3%, and 0.5%, w/v), TS/MCP-S (0.1%, 0.3%, and 0.5%, w/v), respectively. (C) The flow behavior of TS/MCPs after being flipped for 2 min, same order as above.
3.3. Gel strength and hardness The images of starch gels (i.e., TS and maize and pea starches) with the same concentration (6%, w/v) are demonstrated in Fig. 3A. Evidently, the gel formed by TS had a transparent, formless, weak structure in comparison with the two other starches. TS gel became black, agglomerate, and had no noticeable holes after adding 0.5% MCP-S. The effects of MCP-C and MCP-S on the flow behaviors of TS gel are exhibited in Fig. 3B and C. The TS/MCPs gels displayed different gelation behavior. All TS/MCPs gels had no obvious flow behavior, except when the 0.1% MCP-C was added after being flipped for 1 min. Afterwards, the TS gels with 0.1% MCP-S and 0.5% MCP-C exhibited flow behavior after being flipped for 2 min. Gel hardness is the peak stress observed during the compression
cycle (Nishinari & Fang, 2018; Nishinari, Fang, & Rosenthal, 2019) In Fig. 4, the hardness of the TS gel was 0.23 N. The hardness of TS/MCP-C gels declined, except at 0.3% (0.28 N). However, a significant increase in hardness was found in TS/MCP-S gels, and the highest hardness value (0.42 N) was obtained after adding 0.5% MCP-S. The results of gel strength and hardness tests on TS/MCPs gels were consistent with those of pasting viscosity. These results confirmed that the synergistic effect was stronger between TS and MCP-S than between TS and MCP-C.
Fig. 2. Storage modulus (G′) and loss modulus (G″) curves of TS/MCP-C (A) and TS/MCP-S (B). 4
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Fig. 4. TS/MCPs gels with 30 mm diameter and 30 mm height were compressed at the test speed was 2 mm/s, and the gel hardness values were recorded by texture analyzer.
Fig. 5. X-ray diffraction spectra of the TS/MCPs.
Moreover, adding MCP-S increased the rigidity of starch granules in the pasting experiment.
unchanged. Similar results were reported for the effects of pullulan on the crystallinity of TS (Sheng et al., 2018). The reason for the phenomenon was that MCP-C and MCP-S inhibit the long-term retrogradation of TS.
3.4. Swelling power and solubility 3.6. Short-range ordered structure The structural characteristics of starch are closely related to swelling power, solubility, crystallinity and short-range order (Zheng et al., 2019). Swelling power and solubility can characterize the water absorption capacity of starch granules and the extent of amylose leaching during swelling (Wang et al., 2017). Table 2 summarizes that the swelling power and solubility of TS gels was 11.56 g/g and 34.75%, respectively, at 95 °C. Although the values slightly decreased, adding MCP-C had no significant effect on these properties, thereby indicating that MCP-C can inhibit the swelling power of starch granules and leaching of amylose (Chen et al., 2015). Meanwhile, the swelling power and solubility of TS gels after adding 0.5% MCP-S was increased to 18.53 g/g and 40.87%, respectively. In the pasting experiment, MCP-C decreased the FV, BV and SV of TS, whereas MCP-S increases these properties. These differences are related to the differences in water absorption capacities and swelling power.
Fourier transform-infrared (FT-IR) spectroscopy could analyze the effects of MCP-C and MCP-S on the chain conformation, helicity, and double helical structure of TS. The ratio of the integrated peak area at 1047/1022 cm−1 and 1022/995 cm−1 could reveal the internal changes in degree of order (DO) and degree of double helix (DD), respectively (Zhou, Ma, Yin, Hu, & Boye, 2019). The IR ratio of 1047/ 1022 cm−1 and 1022/995 cm−1 of TS were 1.02 and 0.857, correspondingly (Table 2). The DO and DD values of TS/MCPs increased, thereby indicating that MCP-C and MCP-S can promote the formation of an ordered structure of TS, and the packing density of double helices become increasingly compact in the region near the starch granule surfaces upon reorientation. The results of short-range order were similar to that of rheological experiments. TS/MCP-C obtained a highest DO value than MCP-S at high concentration (0.5%), whereas the DO values of TS were lower with MCP-C than with MCP-S at low concentrations (0.1% and 0.3%). The results indicated that MCP-C penetrated into starch granules and assisted TS in forming an ordered and stable gel structure.
3.5. X-ray diffraction The X-ray diffraction patterns of all samples are presented in Fig. 5. Native TS had an A-type pattern with strong diffraction peaks at nearly 15° and 23° and double peaks at approximately 17° and 18° (Zhu et al., 2017). The relative crystallinity (RC) of native starch was 67.54%. The diffraction peak became lower and wider in starch than in the native starch after pasting. Moreover, the peak strength of TS/MCPs remained
3.7. SEM The images obtained through SEM exhibited that native TS granules were round and spherical with some irregular cracks on the surface
Table 2 Storage modulus, solubility, swelling power, DO, DD, and in vitro digestibility parameters of TS/MCPs. Sample
TS TS/0.1% TS/0.3% TS/0.5% TS/0.1% TS/0.3% TS/0.5%
MCP-C MCP-C MCP-C MCP-S MCP-S MCP-S
G′ (Pa)
Solubility (%)
Swelling power (g/g)
DO
DD
RDS (g/100 g starch)
SDS (g/100 g starch)
RS (g/100 g starch)
47.04a 47.11a 55.59c 67.02d 54.15b 56.20bc 66.57d
34.75 ab 33.26a 33.87a 35.22 ab 39.21 ab 37.82 ab 40.87b
11.56a 10.80a 10.50a 11.50a 14.86b 17.44bc 18.53c
1.02 1.02 1.04 1.08 1.05 1.06 1.06
0.86 0.87 0.92 0.90 0.89 0.93 0.91
15.11 g 12.11c 13.13d 11.02b 10.57a 13.41e 14.02f
9.92a 11.49 ab 10.83a 13.22b 13.51b 11.84 ab 12.05 ab
74.97c 76.40 g 76.04f 75.76d 75.92e 74.75b 73.92a
G′, the storage modulus at the angular frequency was 157.08 rad/s; DO, the ratio of 1047/1022 cm−1 by FT-IR; DD, the ratio of 1022/995 cm−1 by FT-IR; RDS, rapidly digestible starch; SDS, slowly digestible starch; RS, resistant starch. Different letters in the same column indicate a significant difference at p < 0.05. 5
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Fig. 6. SEM micrographs of TS/MCPs and native TS, respectively. (A) gelatinized TS; (a) native TS; (B–D) TS/MCP-C at different concentrations (0.1, 0.3, 0.5%); (b–d) TS/MCP-S at different concentrations (0.1%, 0.3%, 0.5%).
MCP-S during pasting, thereby resulting in increased accessibility of starch granules to digestive enzymes. The addition of MCP-C and MCP-S decreased the rapidly digestible starch (RDS) content and increased the slowly digestible starch (SDS) content, thereby indicating that MCPs can mitigate TS digestibility and help to reduce postprandial blood glucose and insulin levels (Ek, Wang, Brand-Miller, & Copeland, 2014). These results were similar to the study of the wheat starch mixed with MCP, it which the presence of MCP reduced starch digestion in fragmented gels (Yuris, Hardacre, Goh, & Matia-Merino, 2019b).
(Fig. 6a). These characteristics may be due to mechanical damage production. The surface structure of gelatinized TS was composed of some disordered cells whose cell walls had an obvious collapse (Fig. 6A, black circle area). Fig. 6 showed a “honeycomb” structure of TS/MCPs, and the number of fragments was less than that of TS. In TS after adding 0.5% MCP-C, the pore size of the cells were markedly reduced, and the cells were orderly and tightly connected to one another. Meanwhile, adding MCP-S did not significantly affect the pore size of cell but enhanced the thickness of the cell wall (Fig. 6c and d, black circle area). This phenomenon was especially observed in TS after adding 0.5% MCP-S.
3.9. Correlation analysis 3.8. In vitro digestibility
The results of correlation analysis between in vitro digestibility and the selected inherent factors of TS/MCPs complexes are summarized in Table 3. The RDS content of TS/MCPs was positively correlated with BV (r = 0.5916), SV (r = 0.4795), and hardness (r = 0.4555). The SDS and RS contents of TS/MCPs were positively correlated with G′ and DO (r > 0.50). These results indicated that the enhancement in rigidity and ordered degree of the gel were beneficial to mitigate the digestive ability of starch. Furthermore, the improvement provided an extensive reaction time for human body to adjust blood sugar and had an excellent effect in preventing diseases, such as diabetes.
Starch is an important source of energy for humans, and digestion is closely linked to human health (Chen et al., 2019). The hydrolysis rate curves of TS/MCPs obtained by simulating the digestion process of samples in the gastrointestinal tract are depicted in Fig. 7. The hydrolysis rate of TS was rapid in the first 60 min (17.71%) and was reduced after adding MCP-C and MCP-S. This condition might be due to the effect of viscosity. TS/MCP-S exhibited higher pasting viscosity than TS/MCP-C, The hydrolysis rate of TS after adding 0.5% MCP-S was the fastest in the first 60 min (19.09%) in all the mixed solutions. This result might be related to the high BV values and swelling power of TS/
Fig. 7. Enzymatic hydrolysis curves of the TS/MCP-C (A) and TS/MCP-S (B) during incubating at 37 °C for 0 min, 20 min, 30 min, 60 min, 90 min, 120 min, and 180 min. 6
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Table 3 The correlation analysis between in vitro digestibility parameters and the selected inherent factors of TS/MCPs.
RDS SDS RS
BV
SV
Hardness
G′
Solubility
Swelling power
DO
DD
0.5916** −0.1101 −0.0280
0.4795** 0.0100 −0.1821
0.4555* −0.1214 −0.2363
−0.2157 0.5700* 0.6694**
−0.0113 0.4937* −0.0087
0.1683 0.3275* 0.1201
−0.3670* 0.7376** 0.7638**
−0.1524 0.3250* 0.6113*
RDS, rapidly digestible starch; SDS, slowly digestible starch; RS, resistant starch; BV, relative breakdown; SV, relative setback; G′, the storage modulus at the angular frequency was 157.08 rad/s; DO, the ratio of 1047/1022 cm−1 by FT-IR; DD, the ratio of 1022/995 cm−1 by FT-IR. * and ** means the correlation are significant at the p < 0.05 and p < 0,01 levels, respectively.
4. Conclusions
Berski, W., & Ziobro, R. (2018). Pasting and gel characteristics of normal and waxy maize starch in glucose syrup solutions. Journal of Cereal Science, 79, 253–258. von Borries-Medrano, E., Jaime-Fonseca, M. R., & Aguilar-Méndez, M. A. (2019). Tapioca starch-galactomannan systems: Comparative studies of rheological and textural properties. International Journal of Biological Macromolecules, 122, 1173–1183. Chen, J., Chen, Y., Ge, H., Wu, C., Pang, J., & Miao, S. (2019). Multi-scale structure, pasting and digestibility of adlay (Coixlachryma-jobi L.) seed starch. Food Hydrocolloids, 89, 885–891. Chen, H. M., Fu, X., & Luo, Z. G. (2015). Effect of gum Arabic on freeze-thaw stability, pasting and rheological properties of tapioca starch and its derivatives. Food Hydrocolloids, 51, 355–360. Ek, K. L., Wang, S., Brand-Miller, J., & Copeland, L. (2014). Properties of starch from potatoes differing in glycemic index. Food & Function, 5(10), 2509–2515. Englyst, H. N., Kingman, S. 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Human oral processing and texture profile analysis parameters: Bridging the gap between the sensory evaluation and the instrumental measurements. Journal of Texture Studies, 1–12. Palabiyik, İ., Toker, O. S., Karaman, S., & Yildiz, Ö. (2017). A modeling approach in the interpretation of starch pasting properties. Journal of Cereal Science, 74, 272–278. Paraginski, R. T., Colussi, R., Dias, A. R. G., da Rosa Zavareze, E., Elias, M. C., & Vanier, N. L. (2019). Physicochemical, pasting, crystallinity, and morphological properties of starches isolated from maize kernels exhibiting different types of defects. Food Chemistry, 274, 330–336. Reddy, C. K., Lee, D. J., Lim, S. T., & Park, E. Y. (2019). Enzymatic debranching of starches from different botanical sources for complex formation with stearic acid. Food Hydrocolloids, 89, 856–863. Romero, H. M., Santra, D., Rose, D., & Zhang, Y. (2017). Dough rheological properties and texture of gluten-free pasta based on proso millet flour. 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In TS/MCP-C, pasting viscosity (PV, TV, FV, BV, and SV), gel strength and hardness decreased given the decreased swelling power and solubility of TS after adding MCP-C, thereby inhibiting the swelling of starch granules and limiting the leaching of amylose. Meanwhile, the pasting viscosity, gel strength, hardness, swelling power and solubility of TS increased after adding MCP-S. The results of rheological experiments and FT-IR spectroscopy confirmed that the elasticity and ordered structure of TS increased after adding MCP-C and MCP-S. MCP-C decreased the pore size of cell and MCP-S increased the thickness of the cell wall. These results suggested that MCP-C and MCP-S affect the pasting, gelation and structural properties of TS in different ways. MCPC inhibited the expansion of granules and leaching of amylose and assisted TS to form an ordered gel structure, whereas, MCP-S can enhance the hardness and strength of the gel by increasing the rigidity of starch granules. In additionally, the RDS content was reduced in accorance with the in vitro digestibility study of TS after adding MCP-C and MCPS, whereas the SDS and RS contents were increased. The SDS and RD contents exhibited a good correlation with G′, DO and DD. Based on the these results, it is concluded that the TS with MCP-C and MCP-S can form an arranged, compact and fine structure, which can effectively mitigate the digestibility of starch. The addition of MCP-C and MCP-S can distinctively affect the pasting viscosity, gel strength and hardness of TS and simultaneously enhances the gel network structure of TS. It means that TS mixed with MCP-C and MCP-S can satisfy the requirements of different gel-like starch foods and can expand its acceptability in the food industry. Conflicts of interest The authors declare that they have no conflict of interest. Acknowledgements This study was financial supported by the Program of the National Natural Science Foundation of China (31972034), the Natural Science Foundation of Jiangxi Province, China (20181ACB20013; 20171BCB23022), and the National Youth Top-notch Talent Support Program of China. Authors are thankful to Dr. Bing Xie and Dr. Peng Xu, The Center of Analysis and Testing, Nanchang University, China for XRD and SEM measurements. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.foodhyd.2019.105327. References An, J. S., Bae, I. Y., Han, S. I., Lee, S. J., & Lee, H. G. (2016). In vitro potential of phenolic phytochemicals from black rice on starch digestibility and rheological behaviors. Journal of Cereal Science, 70, 214–220. Atichokudomchai, N., & Varavinit, S. (2003). Characterization and utilization of acid modified cross-linked tapioca starch in pharmaceutical tablets. Carbohydrate Polymers, 53(3), 263–270.
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Shao, P., Chen, X., & Sun, P. (2013). In vitro antioxidant and antitumor activities of different sulfated polysaccharides isolated from three algae. International Journal of Biological Macromolecules, 62, 155–161. Shao, P., Qiu, Q., Chen, H., Zhu, J., & Sun, P. (2017). Physicochemical stability of curcumin emulsions stabilized by Ulva fasciata polysaccharide under different metallic ions. International Journal of Biological Macromolecules, 105, 154–162. Sheng, L., Li, P., Wu, H., Liu, Y., Han, K., Gouda, M., et al. (2018). Tapioca starch-pullulan interaction during gelation and retrogradation. LWT-Food Science and Technology, 96, 432–438. Singh, A., Geveke, D. J., & Yadav, M. P. (2017). Improvement of rheological, thermal and functional properties of tapioca starch by using gum Arabic. LWT-Food Science and Technology, 80, 155–162. Tang, W., Shen, M., Xie, J., Liu, D., Du, M., Lin, L., et al. (2017). Physicochemical characterization, antioxidant activity of polysaccharides from Mesona chinensis Benth and their protective effect on injured NCTC-1469 cells induced by H2O2. Carbohydrate Polymers, 175, 538–546. Wang, W., Shen, M., Liu, S., Jiang, L., Song, Q., & Xie, J. (2018b). Gel properties and interactions of Mesona blumes polysaccharide-soy protein isolates mixed gel: The effect of salt addition. Carbohydrate Polymers, 192, 193–201. Wang, C. S., Virgilio, N., Wood-Adams, P. M., & Heuzey, M. C. (2018a). A gelation mechanism for gelatin/polysaccharide aqueous complexes. Food Hydrocolloids, 79, 462–472. Wang, Y. R., Zhang, B., Fan, J. L., Yang, Q., & Chen, H. Q. (2019). Effects of sodium tripolyphosphate modification on the structural, functional, and rheological properties of rice glutelin. Food Chemistry, 281, 18–27. Wang, W., Zhou, H., Yang, H., Zhao, S., Liu, Y., & Liu, R. (2017). Effects of salts on the gelatinization and retrogradation properties of maize starch and waxy maize starch. Food Chemistry, 214, 319–327. Xiao, Y., Liu, S., Shen, M., Jiang, L., Ren, Y., Luo, Y., et al. (2019). Physicochemical, rheological and thermal properties of Mesona chinensis polysaccharides obtained by sodium carbonate assisted and cellulase assisted extraction. International Journal of Biological Macromolecules, 126, 30–36. Xia, W., Wang, F., Li, J., Wei, X., Fu, T., Cui, L., et al. (2015). Effect of high speed jet on the physical properties of tapioca starch. Food Hydrocolloids, 49, 35–41. Xie, J. H., Tang, W., Jin, M. L., Li, J. E., & Xie, M. Y. (2016). Recent advances in bioactive
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Effect of different Mesona chinensis polysaccharides on pasting, gelation, structural properties and in vitro digestibility of tapioca starch-Mesona chinensis polysaccharides gels
T
Yuehuan Xiao, Suchen Liu, Mingyue Shen, Lian Jiang, Yanming Ren, Yu Luo, Jianhua Xie∗ State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, 330047, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Tapioca starch Mesona chinensis polysaccharides Pasting Gelation Structure In vitro digestibility
The effects of Mesona chinensis polysaccharides (MCP) obtained through cellulase-assisted (MCP-C) and sodium carbonate-assisted (MCP-S) extractions on the pasting, gelation, structural properties, and in vitro digestibility of tapioca starch (TS)-MCP gels were investigated. The pasting, rheological, gelation and structural properties of TS/MCPs were analyzed by rapid visco analysis (RVA), rheological analysis, texture analysis, X-ray diffraction, fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), respectively. And the digestibility extent of TS/MCPs was determined by an in vitro method. The expansion degree of starch granules, pasting viscosity, hardness, and the amount of amylose leached of TS were decreased after adding MCP-C and increased after adding MCP-S. TS/MCPs showed higher storage modulus (G′), higher short-range order and finer structure than that of TS. In addition, MCP-C and MCP-S decreased the content of rapidly digestible starch (RDS) of TS, especially when 0.5% MCP-C was added. Moreover, the slowly digestible starch (SDS) and resistant starch (RS) contents of TS/MCPs were positively correlated with the G′ and DO, thereby indicating that the strong and ordered gel network had a retardant impact on starch digestion.
1. Introduction Tapioca is a tuber food crop with extensive cultivation history and economic value in China. Its starch has high viscosity and is widely used as a thickener or gelling agent in the food industry (Chen, Fu, & Luo, 2015). However, its high viscosity and inherent formless gel state impede the mechanized production of tapioca starch (TS)-based products, thus leading to its limited applications. Many modification methods were developed to improve starch quality. These approaches include chemical, physical, and biological methods (Atichokudomchai & Varavinit, 2003; Xia et al., 2015; Han et al., 2012; Reddy, Lee, Lim, & Park, 2019). Among them, physical modification, such as complexation with other food-derived ingredients like protein (Yang, Zhong, Goff, & Li, 2019), phenolic compound (An, Bae, Han, Lee, & Lee, 2016) and polysaccharides (Liu, Li, Fan, Zhang, & Zhong, 2019a), is a green and environmentally friendly method. In particular, polysaccharides are safe and non-toxic because they come from plants living organisms, including in plants, body fluids of animals, bacteria, yeast and fungi (Shao, Chen, & Sun, 2013; Xie, Tang, Jin, Li, & Xie, 2016). Recent research has shown that polysaccharides can interact with TS to improve
the hardness, anti-shear ability, water retention ability and structural stability of gels (Russ, Zielbauer, Ghebremedhin, & Vilgis, 2016; Singh, Geveke, & Yadav, 2017; von Borries-Medrano, Jaime-Fonseca, & Aguilar-Méndez, 2019; Sheng et al., 2018). Mesona chinensis, a labiatae plant, can be mixed with starch to make black bean jelly (Lin et al., 2018). Mesona chinensis polysaccharide (MCP) is considered to be the major functional component of the herb form the gel with starch (Liu et al., 2019b). In our previous work, we obtained two kinds of MCP through cellulase-assisted (MCP-C) and sodium carbonate-assisted (MCP-S) extractions. The results of physicochemical, rheological and thermal experiments showed that molecular weight, apparent viscosity, storage modulus, and thermal stability were different; the total sugar, uronic acid, and protein contents of MCP-S were 32.28%, 29.52%, and 31.35%, respectively, whereas those of MCP-C were 29.37%, 23.21%, and 22.37%, correspondingly; the monosaccharide composition of MCP-S included arabinose, fucose, galactose, glucose, rhamnose, and xylose at a molar ratio of 0.32:0.87:0.82:6.24:0.11:0.34; meanwhile, the monosaccharide composition of MCP-C included arabinose, fucose, galactose, glucose, and mannose at a molar ratio of 0.24:0.92:0.55:10.7:0.32; and MCP-S had
∗ 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).
https://doi.org/10.1016/j.foodhyd.2019.105327 Received 10 May 2019; Received in revised form 21 August 2019; Accepted 21 August 2019 Available online 22 August 2019 0268-005X/ © 2019 Elsevier Ltd. All rights reserved.
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2.4. Rheological properties
the higher apparent viscosity and dynamic modulus than MCP-C at the same concentration (Xiao et al., 2019). Furthermore, Tang et al. (2017) found that MCP-C obtain the highest antioxidant activity than MCP obtained through hot-alkali (Na2CO3) and ultrasonic-assisted extractions. In recent years, many studies on the starch-MCP compounded system have been conducted. Liu et al. (2018) reported that the adding MCP reduces the gelatinization enthalpy (ΔH) and increases the pasting temperature and rheological properties (i.e., thixotropy, storage modulus) of wheat starch. MCP can interact with amylose extracted from starch granules and can change the molecular mobility of the water and carbohydrate populations of starch-MCP gels (Yuris et al., 2017, 2019a). The changes of gel properties after mixing maize and rice starches with MCP are also excellent (Feng, Ye, Zhuang, Fang, & Chen, 2012; Liu et al., 2019b). However, the effects of MCP-C and MCP-S on the functional and structural properties of TS-MCP gels have not been studied. In the present study, the effects of MCP-C and MCP-S on the pasting, gelation, structural properties and in vitro digestibility of TSMCP gels were investigated. Furthermore, the correlation between the selected inherent factors and in vitro digestibility parameters was analyzed.
Rheological measurement was carried out using a rheometer (ARESG2, TA Instruments Inc., USA) equipped with parallel plate (1000 μm gap, 40 mm diameter). Before the test, all samples were prepared by RVA and placed at room temperature for 20 h to complete hydration. Frequency sweep was performed from 0.99 rad/s to 157.08 rad/s (0.15–25 Hz) in linear viscoelastic region (1% oscillating strain, 25 °C) (Romero, Santra, Rose, & Zhang, 2017). The rheological parameters, storage modulus (G′) and loss modulus (G″) were recorded. 2.5. Gel strength and hardness 8 mL TS/MCPs gels were collected in the RVA test and transferred into 10 mL sample vials and kept at 4 °C for 20 h. Then, the vials were inverted for 1–2 min to assess the strength of the TS/MCPs gels. Flow behavior is not observed in the gel represents that it reaches the critical gel concentration Ccrit (Wang, Virgilio, Wood-Adams, & Heuzey, 2018a). Hardness analysis of TS/MCPs gels was according to a previous work with slight modifications (Wang et al., 2018b). The tests were performed using the texture analyzer (TA-XT plus, Stable Co., England) fitted with the P/0.5 probe. The test parameters were set as followed: pretest, test and post-test speeds were 2 mm/s, the test distance was 10.0 mm, the trigger force was 5 g and the trigger type was automatic. Each sample was evaluated three times.
2. Materials and methods 2.1. Materials Tapioca starch (TS) (amylose content: 26.43%) was purchased from Dingcheng Food, Co. (Linyi, Shandong Province, China), maize starch (MS) (amylose content: 30.67%) was purchased from Tianjin Honglu Food Co. (Tianjin, China) and pea starch (PS) (amylose content: 30.92%) was purchased from Jiangsu Xinliang Food Co. (Jiangsu China). And the amylose content was determined by spectrophotometric method (Jarvis & Walker, 1993). Mesona chinensis was purchased from XiaoShicheng, GanZhou, JiangXi. Porcine pancreatin and amyloglucosidase were obtained from Sigma-Aldrich, Inc. (St. Louis, MO). Ultra-pure water was provided by a Milli-Q water purification system (Millipore, USA). And all other chemicals were of analytical grade.
2.6. Swelling power and solubility Swelling power and solubility of all samples were determined as the method described by Paraginski et al. (2019). The starch (1%, w/v) was mixed with different MCPs (25 mL) in centrifuge tubes at different concentrations. Mixed solutions were heated at 95 °C for 30 min. Then, the gelatinized samples were cooled to room temperature, centrifuged at 4800 rpm for 30 min. Then, the supernatant was collected and dried at 105 °C to a constant. The solubility and swelling power were calculated according to Eqs. (3) and (4),
2.2. Preparation the mixtures of TS/MCPs
Solubility (%) = (WS/W) × 100%
(3)
MCP-C and MCP-S were extracted from Mesona chinensis herb, respectively (Xiao et al., 2019). Homogeneous sample solutions of 0.1%, 0.3%, and 0.5% MCP-C and MCP-S (25 mL, w/v) were prepared. Afterwards, each sample solution was added to TS (6%, w/v) and stirred to achieve uniform state.
Swelling power (g/g) = WP/W(1-S)
(4)
Where WS is the dried supernatant weight (g), W is the dried sample weight (g), WP is the precipitate weight (g) and S is the solubility (%). 2.7. X-ray diffraction analysis
2.3. Pasting properties
All samples were collected from RVA test, freeze-dried, cut into slices and used in X-ray diffraction (XRD) experiment. The samples were analyzed by an X-ray diffractometer (D8 Advance, Bruker Inc., Germany) with the 2θ (°) range of 5°–45° (Wang, Zhang, Fan, Yang, & Chen, 2019). The relative crystallinity (RC) was quantitatively estimated as a ratio of the crystalline area to the total area using MDI JADE 6.0 software, the total area included the crystalline and amorphous regions.
Mixed solutions were prepared as described above (section 2.2) and the pasting behavior of mixed solutions determined by the rapid visco analyzer (RVA, Newport Scientific, NSW, Australia). The heating process was programmed based on the method reported by Mishra and Rai (2006). Mixed solutions (25 mL) were held at 50 °C for 1 min, and were heated to 95 °C at 12.16 °C/min, held at 95 °C for 2.5 min before cooling to 50 °C at 12.16 °C/min and holding at 50 °C for 2 min. The constant shear rate of 160 rpm was used. The pasting parameters measured including peak viscosity (PV, cP), though viscosity (TV, cP), final viscosity (FV, cP), and pasting temperature (PT, °C). Relative breakdown viscosity (BV, %) and setback viscosity (SV, %) were introduced to intuitively reflect the properties change of solutions at pasting process (Palabiyik, Toker, Karaman, & Yildiz, 2017). Relative breakdown viscosity and setback viscosity were calculated using Eqs. (1) and (2), BV% = (PV-TV)/PV × 100%
(1)
SV% = (FV-TV)/FV × 100%
(2)
2.8. Short-range ordered structure Fourier transform infrared (FT-IR) spectra of samples were obtained at room temperature by a spectrometer (Nicolet 5700, USA) using the method reported by Miao, Zhang, Mu, and Jiang (2010). The absorbance height at 1047 cm−1, 1022 cm−1 and 995 cm−1 were recorded. 2.9. Scanning electron microscopy (SEM) Microstructure of TS/MCPs were observed by using the SEM (JSM2
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6701F, JFOL Ltd., Japan). The dried samples were cut to slices and sprayed with gold, prepared to perform the test at the voltage of 5.0 kV. 2.10. In vitro digestibility In vitro starch digestion was analyzed according to the method described by Englyst, Kingman, and Cummings (1992) with some modifications. Firstly, dried TS (300 mg) was gelatinized at 95 °C for 30 min with and without MCPs solutions (5 mL, ultra-pure water was added to the control group), and rapidly cooled to prevent the retrogradation of starch. Afterwards, 10 mL of sodium acetate buffer solution (0.1 M, pH 5.2) added to the all mixed solutions, and equilibrated at 37 °C for 5 min. Then, rotors and 10 mL of mixed enzyme solution (pancreatin and amyloglucosidase) added to it. Lastly, mixed solutions were incubated in an oscillating water bath at 37 °C. At different time points (20, 30, 60, 90, 120, and 180 min), 95% of ethanol was added at a volume ratio of 3:1 to stop enzymatic digestion, centrifuged (4800 rpm, 10 min). Then, the supernatant was collected and used to determine glucose content by the 3, 5-dinitrosalicylic acid (DNS) method (Miller, 1959). Percentage of hydrolyzed starch was calculated by multiplying a factor of 0.9 with the glucose content, hydrolysis rate and the content of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) were calculated using Eqs. (5)–(8):
Fig. 1. Pasting behavior of TS/MCPs determined by rapid visco analyzer.
pasting. The PV, TV, and FV of TS with MCP-S increased from 718.33 to 898.00 cP, 492.67 to 593.00 cP, and 716.33 to 907.00 cP, correspondingly (Table 1). These results were attributed to the swelling and rigidity of starch granules (Liu et al., 2019b). On the one hand, the pasting viscosity of TS increased after adding MCP-S, which competed for water absorption with TS, thereby improving the rigidity of starch granules. MCP-S also formed a film on the surface of swollen starch granules, thus increasing the volume of granules. On the other hand, the pasting viscosity of TS decreased after adding MCP-C addition, which has lower apparent viscosity than MCP-S. MCP-C can penetrate and form a complex in starch granules, thereby reducing water activity and limiting the expansion of granules (Xiao et al., 2019; Zhou et al., 2017). Furthermore, the ordered structure, crystallinity, molecular structure, and molecular weight of amylopectin had been reported to affect the pasting viscosity of starch (Kim, Woo, & Chung, 2018; Zheng et al., 2019). Relative breakdown viscosity (BV) can evaluate the stability of starch granules under shear and thermal environments (Liu et al., 2018). BV is related to PV, higher PV indicates the greater degree of swelling of granules, the degree of granules rupture and the leaching of amylose are more serious (Ma, Zhu, & Wang, 2019). Table 1 displays that the TS with MCP-S had higher BV than TS with MCP-C. Setback viscosity (SV) can characterize the ability of the re-aggregation of the swollen and broke starch granules during cooling (Sheng et al., 2018). In Table 1, relative SV decreased after adding MCP-C, thereby indicating that MCP-C inhibits the short-term retrogradation of TS by interacting with leached amylose (Ma et al., 2019). However, the SV of TS/MCP-S increased, which may be due to the amylose fragments were dissolved well, thereby resulting in promoting the aggregation of swollen granules and formation of stronger gel networks after adding MCP-S during cooling (Berski & Ziobro, 2018). In fact, the ability to promote short-term retrogradation of starch should be careful consideration in food applications because starch retrogradation is unexpected in most products. Hot paste stability index (HPI) represents the ability of the TS/MCPs to maintain 80% of PV value after reaching PV during heating. The HPI of TS/MCPs increased except when 0.5% MCP-S was added. The BV of TS with 0.5% MCP-S was highest among all samples, thereby indicating its instability during heating. The selection of a suitable type and concentration of MCPs will open a pathway to control the pasting behavior of TS.
Hydrolysis rate (%) = (Content of hydrolyzed glucose × 0.9)/ TS × 100% (5) RDS (%) = 0.9 × (G20-G0)/TS × 100%
(6)
SDS (%) = 0.9 × (G120-G20)/TS × 100%
(7)
RS (%) = 0.9 × (TS-RDS-SDS)/TS × 100%
(8)
Where TS is the total starch content of the sample (mg), G20 is the glucose content (mg) after 20 min hydrolysis, G0 is the free glucose content (mg), G120 is the glucose content (mg) after 120 min hydrolysis. 2.11. Statistical analysis All tests were determined at least in triplicate. Date were analyzed by SPSS software (version 21.0, SPSS Inc., Chicago, IL, USA). analysis of variance (ANOVA) and Tukey's test were used to compare differences among the mean values at 0.05 level of confidence. Images were drawn by Origin Pro software (version 8.0, Stat-Ease Inc., Minneapolis, MN, USA). 3. Results and discussion 3.1. Pasting properties In the pasting curve obtained using a rapid visco analyzer, pasting temperature (PT) represents the point at which viscosity started to rise. After reaching the PT, starch granules began to expand, and viscosity rapidly increased to a peak viscosity (PV). The PV represents the maximum swelling degree of starch granules during heating. Heating of samples was continued, thereby causing the starch granules to rupture and the viscosity to drop to through viscosity (TV) (von BorriesMedrano et al., 2019; Huang et al., 2017). During cooling, rearrangement between amylose and amylopectin resulted in increased viscosity and reached the final viscosity (FV) (Chen et al., 2015). The pasting curves and parameters of TS/MCPs are plotted in Fig. 1 and presented in Table 1, respectively. The PT of TS was 73.22 °C and increasing after adding MCPs.This result may be attributed to the reduction in water activity of starch-MCP-water system (Zhou, Zhang, Chen, & Chen, 2017). In comparison with the pure starch, TS added with MCP-C had a slightly decreased PV, TV, and FV, but the differences were insignificant (p > 0.05), whereas TS added with MCP-S, especially at 0.5% MCP-S, had significantly increased PV, TV, and FV during
3.2. Rheological properties The viscoelastic behavior of the TS/MCPs gels were determined at an angular frequency range of 0.99–157.08 rad/s at 25 °C. Fig. 2A and B plot the storage modulus (G′) and loss modulus (G″) curves of TS/MCPs gels. G′ and G″ are the representative parameters in dynamic rheology 3
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Table 1 Pasting parameters of TS/MCP-C and TS/MCP-S mixtures. Sample TS TS/0.1% TS/0.3% TS/0.5% TS/0.1% TS/0.3% TS/0.5%
MCP-C MCP-C MCP-C MCP-S MCP-S MCP-S
PV (cP)
TV (cP)
FV (cP)
PT (°C)
BV (%)
SV (%)
HPSI
718.33a 709.67a 706.00a 701.00a 759.33b 813.00c 898.00d
492.67a 498.33a 487.00a 487.33a 527.00b 554.00c 593.00d
716.33a 694.33a 683.67a 679.67a 766.00b 826.67c 907.00d
73.22a 73.78b 73.77 ab 74.33b 73.47 ab 74.08 ab 73.80 ab
31.42abc 29.77a 31.01abc 30.48 ab 30.61 ab 31.85bc 33.96d
31.22bc 28.23a 28.76a 28.3a 31.21bc 32.98cd 34.61d
56.79b 64.47de 65.06e 68.35f 60.24c 62.65cd 51.85a
PV, peak viscosity; TV, trough viscosity; FV, final viscosity; BV, relative breakdown; SV, relative setback; HPSI, hot pastes stability index and PT, pasting temperature. Values in columns not sharing the same letter are significantly different (p < 0.05).
(Zhang, Zhu, Tong, & Ren, 2012). In all cases, these values increased with frequency and concentration. And G′ were higher than G″, indicating that all mixed gels exhibited the typical gel-like behavior (Shao, Qiu, Chen, Zhu, & Sun, 2017). The G′ value of TS gel was 47.04 Pa at an angular frequency of 157.08 rad/s (25 Hz) and increased after adding MCPs. The increase in G′ value may be due to the following factors: (a) adding MCPs reduces the available water content of starch and increases the effective concentration of starch in per unit volume, thus facilitating the formation of a stable gel structure; and (b) is heat increases the swollen and ruptured starch granules and decreases the size of starch granules, thereby increasing the contact area between starch and MCPs. Furthermore, gelatinous MCPs can form a coat on the surface of swollen starch, thus increasing the rigidity of starch granules (Ma et al., 2019; Yuris, Matia-Merino, Hardacre, Hindmarsh, & Goh, 2018). The G′ values were higher in TS/MCP-S gels than in TS/MCP-C gels at low concentrations (0.1% and 0.3%) but lower at high concentration (0.5%). Among all TS/MCPs gels, TS with 0.5% MCP-S had the highest pasting viscosity and BV, thereby causing the granules rupture and decreasing the value of G'. Fig. 3. Gel images and flow behavior of samples. (A) Gel images of tapioca starch (TS), maize starch (MS), pea starch (PS), and TS mixed with 0.5% MCP-S. (B) The flow behavior of TS/MCPs after being flipped for 1 min, and from left to right were the TS, TS/MCP-C (0.1%, 0.3%, and 0.5%, w/v), TS/MCP-S (0.1%, 0.3%, and 0.5%, w/v), respectively. (C) The flow behavior of TS/MCPs after being flipped for 2 min, same order as above.
3.3. Gel strength and hardness The images of starch gels (i.e., TS and maize and pea starches) with the same concentration (6%, w/v) are demonstrated in Fig. 3A. Evidently, the gel formed by TS had a transparent, formless, weak structure in comparison with the two other starches. TS gel became black, agglomerate, and had no noticeable holes after adding 0.5% MCP-S. The effects of MCP-C and MCP-S on the flow behaviors of TS gel are exhibited in Fig. 3B and C. The TS/MCPs gels displayed different gelation behavior. All TS/MCPs gels had no obvious flow behavior, except when the 0.1% MCP-C was added after being flipped for 1 min. Afterwards, the TS gels with 0.1% MCP-S and 0.5% MCP-C exhibited flow behavior after being flipped for 2 min. Gel hardness is the peak stress observed during the compression
cycle (Nishinari & Fang, 2018; Nishinari, Fang, & Rosenthal, 2019) In Fig. 4, the hardness of the TS gel was 0.23 N. The hardness of TS/MCP-C gels declined, except at 0.3% (0.28 N). However, a significant increase in hardness was found in TS/MCP-S gels, and the highest hardness value (0.42 N) was obtained after adding 0.5% MCP-S. The results of gel strength and hardness tests on TS/MCPs gels were consistent with those of pasting viscosity. These results confirmed that the synergistic effect was stronger between TS and MCP-S than between TS and MCP-C.
Fig. 2. Storage modulus (G′) and loss modulus (G″) curves of TS/MCP-C (A) and TS/MCP-S (B). 4
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Fig. 4. TS/MCPs gels with 30 mm diameter and 30 mm height were compressed at the test speed was 2 mm/s, and the gel hardness values were recorded by texture analyzer.
Fig. 5. X-ray diffraction spectra of the TS/MCPs.
Moreover, adding MCP-S increased the rigidity of starch granules in the pasting experiment.
unchanged. Similar results were reported for the effects of pullulan on the crystallinity of TS (Sheng et al., 2018). The reason for the phenomenon was that MCP-C and MCP-S inhibit the long-term retrogradation of TS.
3.4. Swelling power and solubility 3.6. Short-range ordered structure The structural characteristics of starch are closely related to swelling power, solubility, crystallinity and short-range order (Zheng et al., 2019). Swelling power and solubility can characterize the water absorption capacity of starch granules and the extent of amylose leaching during swelling (Wang et al., 2017). Table 2 summarizes that the swelling power and solubility of TS gels was 11.56 g/g and 34.75%, respectively, at 95 °C. Although the values slightly decreased, adding MCP-C had no significant effect on these properties, thereby indicating that MCP-C can inhibit the swelling power of starch granules and leaching of amylose (Chen et al., 2015). Meanwhile, the swelling power and solubility of TS gels after adding 0.5% MCP-S was increased to 18.53 g/g and 40.87%, respectively. In the pasting experiment, MCP-C decreased the FV, BV and SV of TS, whereas MCP-S increases these properties. These differences are related to the differences in water absorption capacities and swelling power.
Fourier transform-infrared (FT-IR) spectroscopy could analyze the effects of MCP-C and MCP-S on the chain conformation, helicity, and double helical structure of TS. The ratio of the integrated peak area at 1047/1022 cm−1 and 1022/995 cm−1 could reveal the internal changes in degree of order (DO) and degree of double helix (DD), respectively (Zhou, Ma, Yin, Hu, & Boye, 2019). The IR ratio of 1047/ 1022 cm−1 and 1022/995 cm−1 of TS were 1.02 and 0.857, correspondingly (Table 2). The DO and DD values of TS/MCPs increased, thereby indicating that MCP-C and MCP-S can promote the formation of an ordered structure of TS, and the packing density of double helices become increasingly compact in the region near the starch granule surfaces upon reorientation. The results of short-range order were similar to that of rheological experiments. TS/MCP-C obtained a highest DO value than MCP-S at high concentration (0.5%), whereas the DO values of TS were lower with MCP-C than with MCP-S at low concentrations (0.1% and 0.3%). The results indicated that MCP-C penetrated into starch granules and assisted TS in forming an ordered and stable gel structure.
3.5. X-ray diffraction The X-ray diffraction patterns of all samples are presented in Fig. 5. Native TS had an A-type pattern with strong diffraction peaks at nearly 15° and 23° and double peaks at approximately 17° and 18° (Zhu et al., 2017). The relative crystallinity (RC) of native starch was 67.54%. The diffraction peak became lower and wider in starch than in the native starch after pasting. Moreover, the peak strength of TS/MCPs remained
3.7. SEM The images obtained through SEM exhibited that native TS granules were round and spherical with some irregular cracks on the surface
Table 2 Storage modulus, solubility, swelling power, DO, DD, and in vitro digestibility parameters of TS/MCPs. Sample
TS TS/0.1% TS/0.3% TS/0.5% TS/0.1% TS/0.3% TS/0.5%
MCP-C MCP-C MCP-C MCP-S MCP-S MCP-S
G′ (Pa)
Solubility (%)
Swelling power (g/g)
DO
DD
RDS (g/100 g starch)
SDS (g/100 g starch)
RS (g/100 g starch)
47.04a 47.11a 55.59c 67.02d 54.15b 56.20bc 66.57d
34.75 ab 33.26a 33.87a 35.22 ab 39.21 ab 37.82 ab 40.87b
11.56a 10.80a 10.50a 11.50a 14.86b 17.44bc 18.53c
1.02 1.02 1.04 1.08 1.05 1.06 1.06
0.86 0.87 0.92 0.90 0.89 0.93 0.91
15.11 g 12.11c 13.13d 11.02b 10.57a 13.41e 14.02f
9.92a 11.49 ab 10.83a 13.22b 13.51b 11.84 ab 12.05 ab
74.97c 76.40 g 76.04f 75.76d 75.92e 74.75b 73.92a
G′, the storage modulus at the angular frequency was 157.08 rad/s; DO, the ratio of 1047/1022 cm−1 by FT-IR; DD, the ratio of 1022/995 cm−1 by FT-IR; RDS, rapidly digestible starch; SDS, slowly digestible starch; RS, resistant starch. Different letters in the same column indicate a significant difference at p < 0.05. 5
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Fig. 6. SEM micrographs of TS/MCPs and native TS, respectively. (A) gelatinized TS; (a) native TS; (B–D) TS/MCP-C at different concentrations (0.1, 0.3, 0.5%); (b–d) TS/MCP-S at different concentrations (0.1%, 0.3%, 0.5%).
MCP-S during pasting, thereby resulting in increased accessibility of starch granules to digestive enzymes. The addition of MCP-C and MCP-S decreased the rapidly digestible starch (RDS) content and increased the slowly digestible starch (SDS) content, thereby indicating that MCPs can mitigate TS digestibility and help to reduce postprandial blood glucose and insulin levels (Ek, Wang, Brand-Miller, & Copeland, 2014). These results were similar to the study of the wheat starch mixed with MCP, it which the presence of MCP reduced starch digestion in fragmented gels (Yuris, Hardacre, Goh, & Matia-Merino, 2019b).
(Fig. 6a). These characteristics may be due to mechanical damage production. The surface structure of gelatinized TS was composed of some disordered cells whose cell walls had an obvious collapse (Fig. 6A, black circle area). Fig. 6 showed a “honeycomb” structure of TS/MCPs, and the number of fragments was less than that of TS. In TS after adding 0.5% MCP-C, the pore size of the cells were markedly reduced, and the cells were orderly and tightly connected to one another. Meanwhile, adding MCP-S did not significantly affect the pore size of cell but enhanced the thickness of the cell wall (Fig. 6c and d, black circle area). This phenomenon was especially observed in TS after adding 0.5% MCP-S.
3.9. Correlation analysis 3.8. In vitro digestibility
The results of correlation analysis between in vitro digestibility and the selected inherent factors of TS/MCPs complexes are summarized in Table 3. The RDS content of TS/MCPs was positively correlated with BV (r = 0.5916), SV (r = 0.4795), and hardness (r = 0.4555). The SDS and RS contents of TS/MCPs were positively correlated with G′ and DO (r > 0.50). These results indicated that the enhancement in rigidity and ordered degree of the gel were beneficial to mitigate the digestive ability of starch. Furthermore, the improvement provided an extensive reaction time for human body to adjust blood sugar and had an excellent effect in preventing diseases, such as diabetes.
Starch is an important source of energy for humans, and digestion is closely linked to human health (Chen et al., 2019). The hydrolysis rate curves of TS/MCPs obtained by simulating the digestion process of samples in the gastrointestinal tract are depicted in Fig. 7. The hydrolysis rate of TS was rapid in the first 60 min (17.71%) and was reduced after adding MCP-C and MCP-S. This condition might be due to the effect of viscosity. TS/MCP-S exhibited higher pasting viscosity than TS/MCP-C, The hydrolysis rate of TS after adding 0.5% MCP-S was the fastest in the first 60 min (19.09%) in all the mixed solutions. This result might be related to the high BV values and swelling power of TS/
Fig. 7. Enzymatic hydrolysis curves of the TS/MCP-C (A) and TS/MCP-S (B) during incubating at 37 °C for 0 min, 20 min, 30 min, 60 min, 90 min, 120 min, and 180 min. 6
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Table 3 The correlation analysis between in vitro digestibility parameters and the selected inherent factors of TS/MCPs.
RDS SDS RS
BV
SV
Hardness
G′
Solubility
Swelling power
DO
DD
0.5916** −0.1101 −0.0280
0.4795** 0.0100 −0.1821
0.4555* −0.1214 −0.2363
−0.2157 0.5700* 0.6694**
−0.0113 0.4937* −0.0087
0.1683 0.3275* 0.1201
−0.3670* 0.7376** 0.7638**
−0.1524 0.3250* 0.6113*
RDS, rapidly digestible starch; SDS, slowly digestible starch; RS, resistant starch; BV, relative breakdown; SV, relative setback; G′, the storage modulus at the angular frequency was 157.08 rad/s; DO, the ratio of 1047/1022 cm−1 by FT-IR; DD, the ratio of 1022/995 cm−1 by FT-IR. * and ** means the correlation are significant at the p < 0.05 and p < 0,01 levels, respectively.
4. Conclusions
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In TS/MCP-C, pasting viscosity (PV, TV, FV, BV, and SV), gel strength and hardness decreased given the decreased swelling power and solubility of TS after adding MCP-C, thereby inhibiting the swelling of starch granules and limiting the leaching of amylose. Meanwhile, the pasting viscosity, gel strength, hardness, swelling power and solubility of TS increased after adding MCP-S. The results of rheological experiments and FT-IR spectroscopy confirmed that the elasticity and ordered structure of TS increased after adding MCP-C and MCP-S. MCP-C decreased the pore size of cell and MCP-S increased the thickness of the cell wall. These results suggested that MCP-C and MCP-S affect the pasting, gelation and structural properties of TS in different ways. MCPC inhibited the expansion of granules and leaching of amylose and assisted TS to form an ordered gel structure, whereas, MCP-S can enhance the hardness and strength of the gel by increasing the rigidity of starch granules. In additionally, the RDS content was reduced in accorance with the in vitro digestibility study of TS after adding MCP-C and MCPS, whereas the SDS and RS contents were increased. The SDS and RD contents exhibited a good correlation with G′, DO and DD. Based on the these results, it is concluded that the TS with MCP-C and MCP-S can form an arranged, compact and fine structure, which can effectively mitigate the digestibility of starch. The addition of MCP-C and MCP-S can distinctively affect the pasting viscosity, gel strength and hardness of TS and simultaneously enhances the gel network structure of TS. It means that TS mixed with MCP-C and MCP-S can satisfy the requirements of different gel-like starch foods and can expand its acceptability in the food industry. Conflicts of interest The authors declare that they have no conflict of interest. Acknowledgements This study was financial supported by the Program of the National Natural Science Foundation of China (31972034), the Natural Science Foundation of Jiangxi Province, China (20181ACB20013; 20171BCB23022), and the National Youth Top-notch Talent Support Program of China. Authors are thankful to Dr. Bing Xie and Dr. Peng Xu, The Center of Analysis and Testing, Nanchang University, China for XRD and SEM measurements. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.foodhyd.2019.105327. References An, J. S., Bae, I. Y., Han, S. I., Lee, S. J., & Lee, H. G. (2016). In vitro potential of phenolic phytochemicals from black rice on starch digestibility and rheological behaviors. Journal of Cereal Science, 70, 214–220. Atichokudomchai, N., & Varavinit, S. (2003). Characterization and utilization of acid modified cross-linked tapioca starch in pharmaceutical tablets. Carbohydrate Polymers, 53(3), 263–270.
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