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Kinetic modeling of the ultrasonic-assisted extraction of polysaccharide from Nostoc commune and physicochemical properties analysis
International Journal of Biological Macromolecules 128 (2019) 421–428
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International Journal of Biological Macromolecules journal homepage: http://www.elsevier.com/locate/ijbiomac
Kinetic modeling of the ultrasonic-assisted extraction of polysaccharide from Nostoc commune and physicochemical properties analysis Yonggang Wang a,⁎,1, Jichao Liu a,b,1, Xiaofeng Liu a,⁎, Xuan Zhang a, Ye Xu a, Feifan Leng a, M.O. Avwenagbiku a a b
School of Life Science and Engineering, Lanzhou University of Technology, Lanzhou 730050, PR China School of Food and Biological Engineering, Shaanxi University of Science and Technology, Xi'an 710021, PR China
a r t i c l e
i n f o
Article history: Received 10 March 2018 Received in revised form 16 December 2018 Accepted 26 December 2018 Available online 17 January 2019 Keywords: Kinetic modeling Ultrasonic-assisted extraction polysaccharide Nostoc commune Vauch
a b s t r a c t Based on the theory of extraction and diffusion of Chinese herbal medicine, the dynamic model of ultrasonicassisted extraction process of polysaccharide from Nostoc commune Vauch. was established according to the second law of Fick, and further verified at different solid-liquid ratio (1/40–1/80 g/mL), temperature (313.15–353.15 K), ultrasonic power (240–600 W) and extraction time (0–25 min), the dynamic parameters including rate constant and relative extraction rate were respectively analyzed. The rate constant (k) gradually increased with the increase of temperature at different solid-liquid ratio. The maximum concentration of polysaccharide (NCVP) from N. commune was obtained with an optimal extraction condition at solid-liquid ratio of 1:50, extraction temperature of 353.15 K, ultrasonic power of 540 W and extraction time of 25 min. NCVP, the non reducing sugar with typical infrared spectrum characteristics of polysaccharide, dissolves in water but not dissolved in ethanol, acetone and petroleum ether and displays a good stability and smooth surface. The results provide the basis for NCVP in depth theoretical study of polysaccharide extraction processing. © 2019 Elsevier B.V. All rights reserved.
1. Introduction Nostoc commune Vauch. (NCV) is an edible terrestrial and N2-fixing blue-green algae, belongs to a photosynthetic prokaryote, and mainly distribute in the desert, polar and other special circumstances [1,2]. In China, NCV is a popular food with more content of protein, microelements, Vitamin C, and other nutrients [3–6]. Chinese Pharmacopoeia and more studies indicate that the extracts from NCV could prevent fatty liver, nyctalopia, kidney stones, and heart diseases, and showed multi-antioxidant, antitumor activities and antitumor and antibacterial activities [7–15]. NCV can secrete large amounts of extracellular polysaccharides to adapt to the harsh environment [13–15]. Studies have shown that polysaccharides, an important type of natural biopolymers, possess various nutritional values and health functions [16–18]. NCV is rich in water-soluble polysaccharides, and the present study demonstrates that polysaccharides from NCV could be potentially used for macrophage activation and consequently inhibiting leukemic cell growth and induced monocytic/macrophagic differentiation [8–11,13–15]. Many extraction techniques including hot-water extraction, microwave-assisted extraction, and ultrasonic-assisted extraction have been applied to obtain higher yields of polysaccharides. Hot⁎ Corresponding authors. E-mail addresses: [email protected] (Y. Wang), [email protected] (X. Liu). 1 Co-first author: Yonggang Wang and Jichao Liu.
https://doi.org/10.1016/j.ijbiomac.2018.12.247 0141-8130/© 2019 Elsevier B.V. All rights reserved.
water extraction process involved in heating or boiling as the conventional extraction technology [19], which exhibited inherent shortcomings of high-energy consumption, more extraction time consuming and limited polysaccharide production [20–22]. To overcome these drawbacks of hot water extraction method, the application of new technologies in the extraction of polysaccharides has been concerned by the food, pharmacological and chemical scientists in recent years. Ultrasound-assisted extraction (UAE) has been recognized as an environment-friendly extraction technique with strong advantages of extraction yield, lower energy input and shorter extraction time due to the acoustic cavitations [23–25]. In recent years, several mathematical models like pseudo first-order model, diffusion model, Weibull-type model, Saeman's model and two site kinetic model have been employed to simulate the extraction process of polysaccharides in the solid-liquid extraction system [26–30]. Mathematical modeling is a tool to facilitate the design, optimization and control of the processes, and extraction rates of the target compounds depends on the different operating experimental conditions [31,32]. These models are attracted to more researchers to optimize all these process variables for the best utilization of energy, time, raw material and/or solvent [26,27]. Now, there already have been some studies on the extraction and activity of polysaccharide from NCV [10–12]. The aim of this study was to use mathematical modeling and experiments to investigate the mass transfer of polysaccharides (NCVP) from NCV in the ultrasonic extraction process, and to unravel the effects of solid-
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liquid ratio, extraction temperature, ultrasonic power and extraction time on the extraction yield or concentration of NCVP. A suitable kinetic model with ultrasound-assisted extraction was established based on the second law of Fick, the extraction conditions were also optimized for obtaining the maximum yield or concentration of NCVP. Meanwhile, the physicochemical properties analysis, surface morphology and functional group structure of NCVP were studied, respectively. The data presented in this study provide evidence for the potential applications of NCVP in the food or pharmaceutical industries. 2. Materials and methods 2.1. Materials preparation NCV used in the study was purchased from local supermarket in Lanzhou city of China. It was dried at 60 °C and crushed to fine power of diameter 0.178 mm. All reagents were of analytical grade. 2.2. Ultrasound-assisted NCVP extraction The ultrasound-assisted extraction was carried out in a thermostatic ultrasonic processor (KQ-600DB, Kunshan Ultrasonic Instruments Co., Ltd., Jiangsu, China). The sonotrode can change the ultrasonic power from 240 to 600 W. Moreover, this extractor was equipped with an automatic temperature controlling system. The powder of NCV (5.0 g) was mixed with distilled water in a 500 mL reaction vessel during the ultrasound-assisted extraction. The extraction temperature was controlled by an automatic temperature controlling system. At the end of extraction, the crude extracts were centrifuged at 4000 rpm for 10 min to separate the liquid extracts from the solid residue. After the liquid extracts were condensed to 40 mL, the concentrate was further mixed with ethanol at final concentration of 80% (V/V) to precipitate overnight at 4 °C. The precipitates were further performed to remove proteins using Sevag method [33], dialyzed with 3500 Da dialysis bags and freeze-dried, giving the crude NCVP. for studying the physical and chemical properties and structures.
The effects of solid-liquid ratio, extraction temperature, ultrasonic power and extraction time on the extraction concentrations of NCVP were investigated in the present study. For the effect of solid-liquid ratio, it was performed at five different levels of 1:40, 1:50, 1:60, 1:70 and 1:80 (g/mL) while the ultrasonic power was set at 240, 300, 420, 560 and 600 W, respectively. To explore the effects of ultrasonic power and extraction temperature, sonication was carried out at five levels of 240, 300, 420, 560 and 600 W, meanwhile the extraction temperature (Kelvin temperature, K) was set at 313.15, 323.15, 333.15, 343.15 and 353.15 K. For all experiments, the extraction time was set at six levels of 5, 10, 15, 20, 25 and 30 min. The phenol-sulfuric acid method was employed to determine the polysaccharide content for each experiment [34]. 2.3. Kinetic models of NCVP extraction for UAE The ultrasonic-assisted NCVP extraction is a solid-liquid extraction process, which involved in the mass transfer process from intracellular to the solvent. It is generally believed that the internal diffusion of solute is the key step in the process of extraction. In the present study, the unsteady state diffusion model based on the Fick's second law is employed to investigate the kinetic process of NCVP by UAE method. In order to analyze the extraction process using this model, some assumptions need to be made as follows: (a) The shape of the NCV particle keeps almost constancy during the whole extraction process of NCVP and the mass transfer resistance of the particle surface can be neglected. (b) In any sample interval, the particle of NCV is distributed uniformly. Meanwhile, the diffusion of NCVP is carried out in the radial direction from the inside of the particle, and the mass concentration is uniform. Assuming the spherical radius of the particle is R. According to the Fick's second law, formula (1) can be described.
2
2
2
∂C ∂ C ∂ C ∂ C ¼ Ds 2 þ 2 þ 2 ∂t ∂ x ∂ y ∂ z
! ð1Þ
Fig. 1. The yield of NCVP using ultrasound-assisted extraction method with different solid-liquid ratio (A), ultrasonic power (B) and temperature (C). (Error bars for SD at n = 3).
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where ∂C is mass concentration gradient different with time, Ds is diffu∂t 2 2 2 sion coefficient, ∂ 2C, ∂ 2C, ∂ 2C is a mass concentration gradient on x, y, and Z ∂ x ∂ y ∂ z axes, respectively. 2
The particles of NCV are regards as spherical, the formula Δ2 C ¼ ∂ 2C
where C∞ is the mass equilibrium concentration of NCVP, mg/mL; C0 is the initial mass concentration, mg/mL, and t is the extraction time, min. The higher order term of the mass concentration distribution tends to zero, n = 1, the formula (4) can be transformed to the Eq. (5).
∂ x
2
2
∂ y
∂ z
þ ∂ 2C þ ∂ 2C could be converted to the formula (2):
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ðC ∞ −C Þ=ðC ∞ −C 0 Þ ¼
i 6 h exp −π2 Ds t=R2 2 π
ð5Þ
2
Δ2 C ¼
∂ C 2 ∂C þ ; ∂r 2 r ∂r
ð2Þ
and we defined mass concentration (f) was equal to the mass concentration of NCVP at the distance of r (mm) from the ball surface into the center of particles at a given extraction time (t, min). Hence, 2
∂f ∂ f ¼ Ds 2 ∂t ∂r
ð3Þ
In the model, boundary condition is r = 0, f = 0, r = R, and R is the particle radius (mm). Formula (1) can also be converted by Fourier transformation [35] as written below: ðC ∞ −C Þ=ðC ∞ −C 0 Þ ¼
∞ n h io 6 X exp −ðnπ=RÞ2 Ds t π2 n¼1
ð4Þ
The Eq. (5) also can be converted to the logarithmic Eq. (6). ln ½ðC ∞ Þ=ðC ∞ −C Þ ¼ kt þ ln π2 C ∞ =6ðC ∞ −C Þ
ð6Þ
where k is the second-order extraction rate constant, and k = π2Ds/R2, the initial mass concentration of NCVP (C0) is zero, relative extraction rate (y) is described as follow: y¼
C ∞ −C C∞
And the Eq. (6) further is transformed to the formula (7). y¼
6 expð−ktÞ π2
ð7Þ
Fig. 2. Relationship between ln[C∞ / C∞ − C] and extraction time under different solid-liquid ratios and ultrasonic power (A: 1:40 g/mL, B: 1:50 g/mL, C: 1:60 g/mL, D: 1:70 g/mL, E: 1:80 g/mL).
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Fig. 3. Relative raffinate rate versus time for different ultrasonic powers (A: 1:40 g/mL, B: 1:50 g/mL, C: 1:60 g/mL, D: 1:70 g/mL, E: 1:80 g/mL).
In above mentioned formulas, the relationship between the extraction time, temperature, solid-liquid ratio and the concentration of NCVP could be described as the formulas (6) and (7).
determined by a thermogravimetric analyzer (STA449C, Netzsch, Germany) as described by Chen et al. [17]. The pyrolysis, combustion melting point and enthalpy change were recorded and analyzed.
2.4. Determination of thermodynamic parameters
2.5. Physical and chemical properties
The thermodynamic properties including thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) of NCVP were
Solubility of NCVP in different solvents (water, ethanol, acetone and ether) was determined, and the physical and chemical properties
Fig. 4. The relationship between half-life (t1/2) and extraction power (P) and the relationship between the diffusion coefficient (Ds) and extraction power (P) in the ultrasonic extraction process of NCVP (A: relationship between t1/2 and P; B: relationship between Ds and P).
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(Potassium iodide reaction, Ninhydrin reaction, Fehling reaction, viscosity, optical activity, sulfate ion content and uronic acid content) of NCVP also were analyzed, respectively. 2.6. Structural characteristics of NCVP Scanning electron microscopy (SEM, Kevex JSM-5600LV, USA) and atomic force microscopy (AFM, Nano Scope III A, Digital Instrument, USA) was used to examine the surface texture while the functional group structure of NCVP was determined by Fourier Transform Infrared Spectrometer (FTIR, Nicolet, USA).
Table 1 Basic physical and chemical properties of NCVP. Groups
Reaction
Result
Solubility in different solvents
Water Ethanol Acetone Ether I-KI Ninhydrin reaction Fehling reaction Optical activity Specific rotatory power 298.15 K 313.15 K 333.15 K 353.15 K 373.15 K
+ − − − + − − −0.022 −46.2 0.642# 0.638# 0.634# 0.635# 0.611#
Chemical properties Optical activity and specific rotatory power Thermal stability
2.7. Statistical analysis All the experimental data represented as the mean value ± standard deviation (SD) from at least three replicates. The experimental data were used to fit to the kinetic models by linear regression (Origin 8.5, Origin Lab. Corp.), the model constants and the correlation coefficients (R2) was calculated. 3. Results and discussion 3.1. Ultrasound-assisted extraction of NCVP Fig. 1 showed the effects of ultrasonic power and solid-liquid ratio on the mass concentration of NCVP. When fixed the extraction temperature at 333.15 K, the concentrations increased rapidly with UAE time in the early period (10–30 min) and then descend in later period. As shown in Fig. 1, both ultrasound power and solid-liquid ratio had significant effects on the yield of NCVP, suggesting these two variables were the crucial factors for the extraction of NCVP. For the effects of ultrasound power, higher yield of NCVP was obtained with the increasing of ultrasound power (Fig. 1). As seen below, Fig. 1(A) indicated that the extraction temperature and extraction power were at 343.15 K and 420 W respectively. The total extraction at 30 min interval was performed every 5 min. From the longitudinal direction, at the same extraction time, an increase in the solid-liquid ratio resulted in increased NCVP yield. From the lateral direction, an increase in the extraction time from 25 to 30 min didn't bring about any significant difference in the NCVP yield. When the solid-liquid ratio reaches 1:50, the yield of NCVP continued to increase, and became stable at a point. As a result of this, the optimum solidliquid ratio and extraction time was determined to be 1:50 and 25 min respectively. For the effect of solid-liquid ratio, an increase of the solid-liquid ratio from the beginning 1:50 gives a slight decrease in the concentration of NCVP. The decrease of NCVP concentrations after 30 min of extraction as shown in Fig. 1 may be attributed to the degradation of NCVP extracted into the liquid by the mechanical force from acoustic cavitations. Fig. 1(B) indicated the solid-liquid ratio to be 1:50, the extraction temperature was 343.15 K and the yield of NCVP was investigated under different extraction powers. At the same extraction time, with increasing ultrasonic power, the diffusion rate of the NCVP is higher. However, when the ultrasonic power is greater than 540 W, the yield of NCVP is no longer apparently increased and kept stable. Therefore, the optimum ultrasonic power is determined to be 540 W. It can also be deduced from Fig. 1(B) that an increase of extracting ultrasonic power gradually resulted in an increase in the yield of NCVP from 0 to 25 min. More than 25 min, the concentration of NCVP decreased, possibly due to the effect of ultrasonic cavitations. This conclusion has also been reported in the literature [19,22,24]. Literature survey revealed that the diffusion of polysaccharides is commonly accompanied by their degradation in the process of ultrasonic-assisted extraction. Fig. 1(C) showed solid-liquid ratio and extraction power to be 1:50 and 420 W respectively and yields of NCVP were obtained at different extraction temperatures. At the same extraction time, an increasing
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Note: The value marked with # is the absorbance at 495 nm according to the phonel-sulfate method in the thermal stability analysis.
temperature also resulted in a yield increase of NCVP. However, when the temperature is higher than 343.15 K, the yield did not significantly increase. At the same extraction temperature, the yield of NCVP increased with the extension of extraction time until 25 min. Therefore, the optimal extraction temperature and time was chosen to be 343.15 K and 25 min, and the following dynamic modeling was established in 0–25 min with an interval of 5 min.
3.2. Kinetic models for UAE The concentration of NCVP was measured under the different experimental combination with the solid-liquid ratio, temperature, ultrasound power and time as shown in sTable 1. The kinetic model was verified by the data, and the kinetic parameters such as extraction rate constant, relative extraction yield, half life and effective diffusion coefficient were obtained. Fig. 2 and sTable 2 showed the linear regression results of the concentration of NCVP extracted by ultrasonic method under different material liquid ratio and power. Fig. 2 and sTable 2 also indicated that the regression model curves fitted the experimental data very well. According to the experimental data obtained under the extraction conditions with different solid-liquid ratio and ultrasonic power, when the temperature fixed at 333.15 K, the corresponding regressed kinetic constants were obtained and listed in sTable 2.
Fig. 5. Viscosity of the different concentration of NCVP at 296.15 K (Error bars for SD at n = 3).
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Fig. 6. Microscopic characterization of NCVP (A and B are SEM images of NCVP; C and D are AFM images of NCVP).
Figs. 1, 2, 3, 4 and sTable 2 showed the complete data information including the linear regression results of NCVP under the different solidliquid ratio and ultrasonic power (Supporting information). Fig. 2 showed the relationship between ln[C∞ / C∞ − C] and extraction time at different solid-liquid ratios and power, and the regression equations for ln[C∞ / C∞ − C] and extraction time at different solidliquid ratios and ultrasonic powers in sTable 2. As seen in Fig. 2, at any solid-liquid ratio, as the extraction time increases, the value of ln[C∞ / C∞ − C] gradually increased which was directly proportional to time, indicating ln[C∞ / C∞ − C] had a linear dependence on extraction time. At any solid-liquid ratio and arbitrary ultrasonic power, the R2 value of the
regression equation of ln[C∞ / C∞ − C] and extraction time was greater than 0.9. The value of R2 reflected a high degree of fit between the value ln[C∞ / C∞ − C] and the variable time. The particles of NCV were not soaked in water before extraction, so there was C0 = 0, setting relative extraction rate y = (C∞ − C) / C∞. By using the data in sTable 1, y was used as the ordinate and extraction time (t) was used as the abscissa. A well linear correlation was found between relative extraction rate and extraction time with the correlation coefficient R2 of greater than 0.9 as shown in Fig. 3 and sTable 2. Fig. 3 displayed that as the extraction time increases, the relative extraction rate monotonically decreases at any solid-liquid ratio, which was
Fig. 7. FT-IR (A) and thermal gravimetric and DSC analysis curve (B) of NCVP.
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exponentially related to the extraction time. When the extraction time was about 25 min, the relative extraction rate gradually approaches 0, indicating that the NCVP in the particles of NCV was gradually extracted completely after 25 min. And the regression equations and the corresponding rate constants were exhibited in sTable 3 according to the exponential model, indicating that the ultrasonic extraction process of NCVP was also described with the exponential model in good relating linear at different solid-liquid ratios and ultrasonic powers. Fig. 4 exhibited the relationship of half-life (t1/2), the diffusion coefficient (Ds) and extraction power (P). The value of t1/2 can be calculated t1/2 = ln2/k. With the increase of extraction power, the half-life of the NCVP extraction decreases gradually at different solid-liquid ratio and showed good linear relation (Fig. 4A). The effective diffusion coefficient also can be calculated by the equation k = π2Ds/R2 under different solidliquid ratio, and the curve displayed in Fig. 4B between the diffusion coefficient (Ds) and extraction power (P), obtained the better linear relativity. The results indicated the higher power can accelerate the effective diffusion of NCVP and shorten the extraction time [19,22]. However, the half-life and diffusion coefficient did not show some regularity at different solid-liquid ratio with a certain extraction power, which can be attributed to the assumed particles of NCV remaining unchanged. In fact, in actual operation, the cell wall of NCV particles will be damaged or become expanded duo to the ultrasonic cavitation action [24]. 3.3. Physical and chemical properties As can be seen from Table 1, the NCVP was dissolved in the same volume of different solvents, placed at room temperature for a period of time, and NCVP dissolved in water but not soluble in ethanol and other organic solvents. Meanwhile, the I-KI reaction was negative, indicating that NCVP was non starch. Triketohydrindene reaction was negative, manifesting that NCVP does not contain proteins, peptides or amino acids. Fehling's reaction was negative, showing that NCVP belongs to the non reducing sugar. Table 1 showed the average value of optical activity of NCVP were −0.023 at 23.5 °C, and the specific optical rotation values of NCVP was −48.3. According to the regression equation of standard curve y = 0.7772x + 0.0058 (R2 = 0.9869), the content of sulfate ion in NCVP was 2.04%. The content of uronic acid in NCVP calculated by the regression equation of the standard curve (y = 0.5023x − 0.0608, R2 = 0.9720) was 35.12%. The thermal stability of NCVP also can be seen in Table 1, and the absorption value of NCVP has little change until 80 °C, indicating that NCVP has good thermal stability and can be heat-degradation over 80 °C. As shown in Fig. 5, the viscosity of different concentration of NCVP were determined at 23.5 °C with the speed of 60 r/min by the digital viscometer (SNB-2, China), an increase in the concentration of NCVP resulted in an increase of the viscosity of NCVP and reached at 0.062 pa·s at the concentration of 0.9 mg/mL. 3.4. Representational structure Fig. 6 showed a SEM image and an AFM image of NCVP while Fig. 6 (A) and (B) displayed the scanning electron microscope results. At 50 times magnification, the NCVP were cellular extension. At magnification of 300 times, a smooth surface was chosen to obtain the microscopic information of polysaccharide aggregates. There was a large gap between the molecules of NCVP, which showed that there existed repulsion force between the polysaccharide molecules and the folds of the smooth surface were less. Fig. 6(C) and (D) showed that the molecular arrangement of polysaccharides was not close, and the size was different. There were a large number of molecular globular aggregates and a small amount of dispersion, the NCVP molecule was about 80 nm in height, the width was about 2.5 μm, and the area was about 6.25 μm2.
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According to Fig. 7(A), the FT-IR spectrum of NCVP was the absorption line of typical polysaccharide, which showed a strong absorption peak at 3600–3200 (3442.37) cm−1, indicating a strong polysaccharide molecule or intermolecular hydrogen. 2923.604 cm−1 was the characteristic peak of CH3, CH2 in the NCVP. 1384.662 cm−1 was the bending vibration absorption peak of C\\H, and the stretching vibration of C\\H and the vibration of CH constituted the characteristic peak of carbohydrate [36]. 1150–950 (1035.604) cm−1 was the pyranose ring within the ether bond (C\\O\\C) due to stretching vibration. 970–800 (804.184) cm−1 range had an absorption peak, indicating that it had a weak C\\O\\C stretching vibration [37]. According to Fig. 7(B), the peak area was −102.6 J/g, and the enthalpy of the thermal effect was −102.6 J, indicating the reaction was exothermic reaction. It can be seen from the figure that the reaction starting point and end point was 245.6 °C (518.75 K) and 309.2 °C (582.35 K), respectively. Therefore, the reaction width was 63.6 °C (336.75 K). And the NCVP at 287.4 °C (560.55 K) was the fastest weight loss. According to the DTA curve, the whole reaction process was exothermic indicating that the pyrolysis reaction smoothly proceeded and the total energy absorbed by chemical bonds is less than the total energy released by the formation of new bonds. 4. Conclusions In the present work, a reliable kinetic model was established to describe the real extraction process of NCVP from NCV during ultrasound-assisted extraction, and the kinetic parameters were calculated. Using this model, an optimal extraction condition was obtained, which includes 353.15 K of extraction temperature, 540 W of ultrasonic power, 25 min of extraction time and 1:50 of solid-liquid ratio, and the NCVP, a non-reducing polysaccharide, was obtained with good water solubility and thermal stability. The surface morphology of NCVP was smooth and contained fewer folds. Acknowledgement This research was supported by National Natural Science Foundation of China (No. 31460032, 81660581) and the Youth Talent Support Program of Lanzhou University of Technology (No. 2018). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.ijbiomac.2018.12.247. References [1] M. Potts, B.A. Whitton, The Ecology of Cyanobatacteria [M], Kluwer Academic Publishers, Netherlands, 2000 465–504. [2] S. Jensena, B.O. Petersen, S. Omarsdottira, B.S. Paulsen, J.Ø. Duus, E.S. Olafsdottir, Structural characterization of a complex heteroglycan from the cyanobacterium Nostoc commune, Carbohydr. Polym. 91 (2013) 370–376, https://doi.org/10.1016/j. carbpol.2012.08.063. [3] S.J. Guo, S.H. Shan, X.T. Jin, Z.W. Li, Z.Y. Li, L.Q. Zhao, Q. An, W. Zhang, Water stress proteins from Nostoc commune Vauch. exhibit anti-colon cancer activities in vitro and in vivo, J. Agr. Food Chem. 63 (1) (2015) 150–159. [4] Y. Diao, H.B. Han, D.F. Zhang, J.P. Zhou, Z.J. Yang, Determination of nine microelements in Nostoc commune Vauch. by ICP-AES, Adv. Mater. Res. 518–523 (2012) 5020–5023, https://doi.org/10.4028/www.scientific.net/AMR.518-523.5020. [5] W.P. Zhang, M.A. Ya-Ge, C.J. Yang, S.L. Zhao, P.M. Yang, Comparative on nutritional components in wild and cultivated of Nostoc commune Vauch, Food Res Dev 37 (15) (2016) 44–48 , (In Chinese) https://doi.org/10.3969/j.issn.1005-6521.2016. 15.001. [6] J. Chen, L. Zhao, J. Xu, R. Yang, S. He, X. Yan, Determination of oxidized scytonemin in Nostoc commune Vauch. cultured on different conditions by high performance liquid chromatography coupled with triple quadrupole mass spectrometry, J. Appl. Phycol. 25 (4) (2013) 1001–1007, https://doi.org/10.1007/s10811-012-9914-1. [7] S.K. Chai, B. Kim, T.X. Pham, Y. Yue, C.L. Weller, T.P. Carr, Y.K. Park, J.Y. Lee, Hypolipidemic effect of a blue-green alga (Nostoc commune) is attributed to its nonlipid fraction by decreasing intestinal cholesterol absorption in C57BL/6J mice, J. Med. Food 18 (11) (2015) 1214–1222, https://doi.org/10.1089/jmf.2014.0121.
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Contents lists available at ScienceDirect
International Journal of Biological Macromolecules journal homepage: http://www.elsevier.com/locate/ijbiomac
Kinetic modeling of the ultrasonic-assisted extraction of polysaccharide from Nostoc commune and physicochemical properties analysis Yonggang Wang a,⁎,1, Jichao Liu a,b,1, Xiaofeng Liu a,⁎, Xuan Zhang a, Ye Xu a, Feifan Leng a, M.O. Avwenagbiku a a b
School of Life Science and Engineering, Lanzhou University of Technology, Lanzhou 730050, PR China School of Food and Biological Engineering, Shaanxi University of Science and Technology, Xi'an 710021, PR China
a r t i c l e
i n f o
Article history: Received 10 March 2018 Received in revised form 16 December 2018 Accepted 26 December 2018 Available online 17 January 2019 Keywords: Kinetic modeling Ultrasonic-assisted extraction polysaccharide Nostoc commune Vauch
a b s t r a c t Based on the theory of extraction and diffusion of Chinese herbal medicine, the dynamic model of ultrasonicassisted extraction process of polysaccharide from Nostoc commune Vauch. was established according to the second law of Fick, and further verified at different solid-liquid ratio (1/40–1/80 g/mL), temperature (313.15–353.15 K), ultrasonic power (240–600 W) and extraction time (0–25 min), the dynamic parameters including rate constant and relative extraction rate were respectively analyzed. The rate constant (k) gradually increased with the increase of temperature at different solid-liquid ratio. The maximum concentration of polysaccharide (NCVP) from N. commune was obtained with an optimal extraction condition at solid-liquid ratio of 1:50, extraction temperature of 353.15 K, ultrasonic power of 540 W and extraction time of 25 min. NCVP, the non reducing sugar with typical infrared spectrum characteristics of polysaccharide, dissolves in water but not dissolved in ethanol, acetone and petroleum ether and displays a good stability and smooth surface. The results provide the basis for NCVP in depth theoretical study of polysaccharide extraction processing. © 2019 Elsevier B.V. All rights reserved.
1. Introduction Nostoc commune Vauch. (NCV) is an edible terrestrial and N2-fixing blue-green algae, belongs to a photosynthetic prokaryote, and mainly distribute in the desert, polar and other special circumstances [1,2]. In China, NCV is a popular food with more content of protein, microelements, Vitamin C, and other nutrients [3–6]. Chinese Pharmacopoeia and more studies indicate that the extracts from NCV could prevent fatty liver, nyctalopia, kidney stones, and heart diseases, and showed multi-antioxidant, antitumor activities and antitumor and antibacterial activities [7–15]. NCV can secrete large amounts of extracellular polysaccharides to adapt to the harsh environment [13–15]. Studies have shown that polysaccharides, an important type of natural biopolymers, possess various nutritional values and health functions [16–18]. NCV is rich in water-soluble polysaccharides, and the present study demonstrates that polysaccharides from NCV could be potentially used for macrophage activation and consequently inhibiting leukemic cell growth and induced monocytic/macrophagic differentiation [8–11,13–15]. Many extraction techniques including hot-water extraction, microwave-assisted extraction, and ultrasonic-assisted extraction have been applied to obtain higher yields of polysaccharides. Hot⁎ Corresponding authors. E-mail addresses: [email protected] (Y. Wang), [email protected] (X. Liu). 1 Co-first author: Yonggang Wang and Jichao Liu.
https://doi.org/10.1016/j.ijbiomac.2018.12.247 0141-8130/© 2019 Elsevier B.V. All rights reserved.
water extraction process involved in heating or boiling as the conventional extraction technology [19], which exhibited inherent shortcomings of high-energy consumption, more extraction time consuming and limited polysaccharide production [20–22]. To overcome these drawbacks of hot water extraction method, the application of new technologies in the extraction of polysaccharides has been concerned by the food, pharmacological and chemical scientists in recent years. Ultrasound-assisted extraction (UAE) has been recognized as an environment-friendly extraction technique with strong advantages of extraction yield, lower energy input and shorter extraction time due to the acoustic cavitations [23–25]. In recent years, several mathematical models like pseudo first-order model, diffusion model, Weibull-type model, Saeman's model and two site kinetic model have been employed to simulate the extraction process of polysaccharides in the solid-liquid extraction system [26–30]. Mathematical modeling is a tool to facilitate the design, optimization and control of the processes, and extraction rates of the target compounds depends on the different operating experimental conditions [31,32]. These models are attracted to more researchers to optimize all these process variables for the best utilization of energy, time, raw material and/or solvent [26,27]. Now, there already have been some studies on the extraction and activity of polysaccharide from NCV [10–12]. The aim of this study was to use mathematical modeling and experiments to investigate the mass transfer of polysaccharides (NCVP) from NCV in the ultrasonic extraction process, and to unravel the effects of solid-
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liquid ratio, extraction temperature, ultrasonic power and extraction time on the extraction yield or concentration of NCVP. A suitable kinetic model with ultrasound-assisted extraction was established based on the second law of Fick, the extraction conditions were also optimized for obtaining the maximum yield or concentration of NCVP. Meanwhile, the physicochemical properties analysis, surface morphology and functional group structure of NCVP were studied, respectively. The data presented in this study provide evidence for the potential applications of NCVP in the food or pharmaceutical industries. 2. Materials and methods 2.1. Materials preparation NCV used in the study was purchased from local supermarket in Lanzhou city of China. It was dried at 60 °C and crushed to fine power of diameter 0.178 mm. All reagents were of analytical grade. 2.2. Ultrasound-assisted NCVP extraction The ultrasound-assisted extraction was carried out in a thermostatic ultrasonic processor (KQ-600DB, Kunshan Ultrasonic Instruments Co., Ltd., Jiangsu, China). The sonotrode can change the ultrasonic power from 240 to 600 W. Moreover, this extractor was equipped with an automatic temperature controlling system. The powder of NCV (5.0 g) was mixed with distilled water in a 500 mL reaction vessel during the ultrasound-assisted extraction. The extraction temperature was controlled by an automatic temperature controlling system. At the end of extraction, the crude extracts were centrifuged at 4000 rpm for 10 min to separate the liquid extracts from the solid residue. After the liquid extracts were condensed to 40 mL, the concentrate was further mixed with ethanol at final concentration of 80% (V/V) to precipitate overnight at 4 °C. The precipitates were further performed to remove proteins using Sevag method [33], dialyzed with 3500 Da dialysis bags and freeze-dried, giving the crude NCVP. for studying the physical and chemical properties and structures.
The effects of solid-liquid ratio, extraction temperature, ultrasonic power and extraction time on the extraction concentrations of NCVP were investigated in the present study. For the effect of solid-liquid ratio, it was performed at five different levels of 1:40, 1:50, 1:60, 1:70 and 1:80 (g/mL) while the ultrasonic power was set at 240, 300, 420, 560 and 600 W, respectively. To explore the effects of ultrasonic power and extraction temperature, sonication was carried out at five levels of 240, 300, 420, 560 and 600 W, meanwhile the extraction temperature (Kelvin temperature, K) was set at 313.15, 323.15, 333.15, 343.15 and 353.15 K. For all experiments, the extraction time was set at six levels of 5, 10, 15, 20, 25 and 30 min. The phenol-sulfuric acid method was employed to determine the polysaccharide content for each experiment [34]. 2.3. Kinetic models of NCVP extraction for UAE The ultrasonic-assisted NCVP extraction is a solid-liquid extraction process, which involved in the mass transfer process from intracellular to the solvent. It is generally believed that the internal diffusion of solute is the key step in the process of extraction. In the present study, the unsteady state diffusion model based on the Fick's second law is employed to investigate the kinetic process of NCVP by UAE method. In order to analyze the extraction process using this model, some assumptions need to be made as follows: (a) The shape of the NCV particle keeps almost constancy during the whole extraction process of NCVP and the mass transfer resistance of the particle surface can be neglected. (b) In any sample interval, the particle of NCV is distributed uniformly. Meanwhile, the diffusion of NCVP is carried out in the radial direction from the inside of the particle, and the mass concentration is uniform. Assuming the spherical radius of the particle is R. According to the Fick's second law, formula (1) can be described.
2
2
2
∂C ∂ C ∂ C ∂ C ¼ Ds 2 þ 2 þ 2 ∂t ∂ x ∂ y ∂ z
! ð1Þ
Fig. 1. The yield of NCVP using ultrasound-assisted extraction method with different solid-liquid ratio (A), ultrasonic power (B) and temperature (C). (Error bars for SD at n = 3).
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where ∂C is mass concentration gradient different with time, Ds is diffu∂t 2 2 2 sion coefficient, ∂ 2C, ∂ 2C, ∂ 2C is a mass concentration gradient on x, y, and Z ∂ x ∂ y ∂ z axes, respectively. 2
The particles of NCV are regards as spherical, the formula Δ2 C ¼ ∂ 2C
where C∞ is the mass equilibrium concentration of NCVP, mg/mL; C0 is the initial mass concentration, mg/mL, and t is the extraction time, min. The higher order term of the mass concentration distribution tends to zero, n = 1, the formula (4) can be transformed to the Eq. (5).
∂ x
2
2
∂ y
∂ z
þ ∂ 2C þ ∂ 2C could be converted to the formula (2):
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ðC ∞ −C Þ=ðC ∞ −C 0 Þ ¼
i 6 h exp −π2 Ds t=R2 2 π
ð5Þ
2
Δ2 C ¼
∂ C 2 ∂C þ ; ∂r 2 r ∂r
ð2Þ
and we defined mass concentration (f) was equal to the mass concentration of NCVP at the distance of r (mm) from the ball surface into the center of particles at a given extraction time (t, min). Hence, 2
∂f ∂ f ¼ Ds 2 ∂t ∂r
ð3Þ
In the model, boundary condition is r = 0, f = 0, r = R, and R is the particle radius (mm). Formula (1) can also be converted by Fourier transformation [35] as written below: ðC ∞ −C Þ=ðC ∞ −C 0 Þ ¼
∞ n h io 6 X exp −ðnπ=RÞ2 Ds t π2 n¼1
ð4Þ
The Eq. (5) also can be converted to the logarithmic Eq. (6). ln ½ðC ∞ Þ=ðC ∞ −C Þ ¼ kt þ ln π2 C ∞ =6ðC ∞ −C Þ
ð6Þ
where k is the second-order extraction rate constant, and k = π2Ds/R2, the initial mass concentration of NCVP (C0) is zero, relative extraction rate (y) is described as follow: y¼
C ∞ −C C∞
And the Eq. (6) further is transformed to the formula (7). y¼
6 expð−ktÞ π2
ð7Þ
Fig. 2. Relationship between ln[C∞ / C∞ − C] and extraction time under different solid-liquid ratios and ultrasonic power (A: 1:40 g/mL, B: 1:50 g/mL, C: 1:60 g/mL, D: 1:70 g/mL, E: 1:80 g/mL).
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Fig. 3. Relative raffinate rate versus time for different ultrasonic powers (A: 1:40 g/mL, B: 1:50 g/mL, C: 1:60 g/mL, D: 1:70 g/mL, E: 1:80 g/mL).
In above mentioned formulas, the relationship between the extraction time, temperature, solid-liquid ratio and the concentration of NCVP could be described as the formulas (6) and (7).
determined by a thermogravimetric analyzer (STA449C, Netzsch, Germany) as described by Chen et al. [17]. The pyrolysis, combustion melting point and enthalpy change were recorded and analyzed.
2.4. Determination of thermodynamic parameters
2.5. Physical and chemical properties
The thermodynamic properties including thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) of NCVP were
Solubility of NCVP in different solvents (water, ethanol, acetone and ether) was determined, and the physical and chemical properties
Fig. 4. The relationship between half-life (t1/2) and extraction power (P) and the relationship between the diffusion coefficient (Ds) and extraction power (P) in the ultrasonic extraction process of NCVP (A: relationship between t1/2 and P; B: relationship between Ds and P).
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(Potassium iodide reaction, Ninhydrin reaction, Fehling reaction, viscosity, optical activity, sulfate ion content and uronic acid content) of NCVP also were analyzed, respectively. 2.6. Structural characteristics of NCVP Scanning electron microscopy (SEM, Kevex JSM-5600LV, USA) and atomic force microscopy (AFM, Nano Scope III A, Digital Instrument, USA) was used to examine the surface texture while the functional group structure of NCVP was determined by Fourier Transform Infrared Spectrometer (FTIR, Nicolet, USA).
Table 1 Basic physical and chemical properties of NCVP. Groups
Reaction
Result
Solubility in different solvents
Water Ethanol Acetone Ether I-KI Ninhydrin reaction Fehling reaction Optical activity Specific rotatory power 298.15 K 313.15 K 333.15 K 353.15 K 373.15 K
+ − − − + − − −0.022 −46.2 0.642# 0.638# 0.634# 0.635# 0.611#
Chemical properties Optical activity and specific rotatory power Thermal stability
2.7. Statistical analysis All the experimental data represented as the mean value ± standard deviation (SD) from at least three replicates. The experimental data were used to fit to the kinetic models by linear regression (Origin 8.5, Origin Lab. Corp.), the model constants and the correlation coefficients (R2) was calculated. 3. Results and discussion 3.1. Ultrasound-assisted extraction of NCVP Fig. 1 showed the effects of ultrasonic power and solid-liquid ratio on the mass concentration of NCVP. When fixed the extraction temperature at 333.15 K, the concentrations increased rapidly with UAE time in the early period (10–30 min) and then descend in later period. As shown in Fig. 1, both ultrasound power and solid-liquid ratio had significant effects on the yield of NCVP, suggesting these two variables were the crucial factors for the extraction of NCVP. For the effects of ultrasound power, higher yield of NCVP was obtained with the increasing of ultrasound power (Fig. 1). As seen below, Fig. 1(A) indicated that the extraction temperature and extraction power were at 343.15 K and 420 W respectively. The total extraction at 30 min interval was performed every 5 min. From the longitudinal direction, at the same extraction time, an increase in the solid-liquid ratio resulted in increased NCVP yield. From the lateral direction, an increase in the extraction time from 25 to 30 min didn't bring about any significant difference in the NCVP yield. When the solid-liquid ratio reaches 1:50, the yield of NCVP continued to increase, and became stable at a point. As a result of this, the optimum solidliquid ratio and extraction time was determined to be 1:50 and 25 min respectively. For the effect of solid-liquid ratio, an increase of the solid-liquid ratio from the beginning 1:50 gives a slight decrease in the concentration of NCVP. The decrease of NCVP concentrations after 30 min of extraction as shown in Fig. 1 may be attributed to the degradation of NCVP extracted into the liquid by the mechanical force from acoustic cavitations. Fig. 1(B) indicated the solid-liquid ratio to be 1:50, the extraction temperature was 343.15 K and the yield of NCVP was investigated under different extraction powers. At the same extraction time, with increasing ultrasonic power, the diffusion rate of the NCVP is higher. However, when the ultrasonic power is greater than 540 W, the yield of NCVP is no longer apparently increased and kept stable. Therefore, the optimum ultrasonic power is determined to be 540 W. It can also be deduced from Fig. 1(B) that an increase of extracting ultrasonic power gradually resulted in an increase in the yield of NCVP from 0 to 25 min. More than 25 min, the concentration of NCVP decreased, possibly due to the effect of ultrasonic cavitations. This conclusion has also been reported in the literature [19,22,24]. Literature survey revealed that the diffusion of polysaccharides is commonly accompanied by their degradation in the process of ultrasonic-assisted extraction. Fig. 1(C) showed solid-liquid ratio and extraction power to be 1:50 and 420 W respectively and yields of NCVP were obtained at different extraction temperatures. At the same extraction time, an increasing
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Note: The value marked with # is the absorbance at 495 nm according to the phonel-sulfate method in the thermal stability analysis.
temperature also resulted in a yield increase of NCVP. However, when the temperature is higher than 343.15 K, the yield did not significantly increase. At the same extraction temperature, the yield of NCVP increased with the extension of extraction time until 25 min. Therefore, the optimal extraction temperature and time was chosen to be 343.15 K and 25 min, and the following dynamic modeling was established in 0–25 min with an interval of 5 min.
3.2. Kinetic models for UAE The concentration of NCVP was measured under the different experimental combination with the solid-liquid ratio, temperature, ultrasound power and time as shown in sTable 1. The kinetic model was verified by the data, and the kinetic parameters such as extraction rate constant, relative extraction yield, half life and effective diffusion coefficient were obtained. Fig. 2 and sTable 2 showed the linear regression results of the concentration of NCVP extracted by ultrasonic method under different material liquid ratio and power. Fig. 2 and sTable 2 also indicated that the regression model curves fitted the experimental data very well. According to the experimental data obtained under the extraction conditions with different solid-liquid ratio and ultrasonic power, when the temperature fixed at 333.15 K, the corresponding regressed kinetic constants were obtained and listed in sTable 2.
Fig. 5. Viscosity of the different concentration of NCVP at 296.15 K (Error bars for SD at n = 3).
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Fig. 6. Microscopic characterization of NCVP (A and B are SEM images of NCVP; C and D are AFM images of NCVP).
Figs. 1, 2, 3, 4 and sTable 2 showed the complete data information including the linear regression results of NCVP under the different solidliquid ratio and ultrasonic power (Supporting information). Fig. 2 showed the relationship between ln[C∞ / C∞ − C] and extraction time at different solid-liquid ratios and power, and the regression equations for ln[C∞ / C∞ − C] and extraction time at different solidliquid ratios and ultrasonic powers in sTable 2. As seen in Fig. 2, at any solid-liquid ratio, as the extraction time increases, the value of ln[C∞ / C∞ − C] gradually increased which was directly proportional to time, indicating ln[C∞ / C∞ − C] had a linear dependence on extraction time. At any solid-liquid ratio and arbitrary ultrasonic power, the R2 value of the
regression equation of ln[C∞ / C∞ − C] and extraction time was greater than 0.9. The value of R2 reflected a high degree of fit between the value ln[C∞ / C∞ − C] and the variable time. The particles of NCV were not soaked in water before extraction, so there was C0 = 0, setting relative extraction rate y = (C∞ − C) / C∞. By using the data in sTable 1, y was used as the ordinate and extraction time (t) was used as the abscissa. A well linear correlation was found between relative extraction rate and extraction time with the correlation coefficient R2 of greater than 0.9 as shown in Fig. 3 and sTable 2. Fig. 3 displayed that as the extraction time increases, the relative extraction rate monotonically decreases at any solid-liquid ratio, which was
Fig. 7. FT-IR (A) and thermal gravimetric and DSC analysis curve (B) of NCVP.
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exponentially related to the extraction time. When the extraction time was about 25 min, the relative extraction rate gradually approaches 0, indicating that the NCVP in the particles of NCV was gradually extracted completely after 25 min. And the regression equations and the corresponding rate constants were exhibited in sTable 3 according to the exponential model, indicating that the ultrasonic extraction process of NCVP was also described with the exponential model in good relating linear at different solid-liquid ratios and ultrasonic powers. Fig. 4 exhibited the relationship of half-life (t1/2), the diffusion coefficient (Ds) and extraction power (P). The value of t1/2 can be calculated t1/2 = ln2/k. With the increase of extraction power, the half-life of the NCVP extraction decreases gradually at different solid-liquid ratio and showed good linear relation (Fig. 4A). The effective diffusion coefficient also can be calculated by the equation k = π2Ds/R2 under different solidliquid ratio, and the curve displayed in Fig. 4B between the diffusion coefficient (Ds) and extraction power (P), obtained the better linear relativity. The results indicated the higher power can accelerate the effective diffusion of NCVP and shorten the extraction time [19,22]. However, the half-life and diffusion coefficient did not show some regularity at different solid-liquid ratio with a certain extraction power, which can be attributed to the assumed particles of NCV remaining unchanged. In fact, in actual operation, the cell wall of NCV particles will be damaged or become expanded duo to the ultrasonic cavitation action [24]. 3.3. Physical and chemical properties As can be seen from Table 1, the NCVP was dissolved in the same volume of different solvents, placed at room temperature for a period of time, and NCVP dissolved in water but not soluble in ethanol and other organic solvents. Meanwhile, the I-KI reaction was negative, indicating that NCVP was non starch. Triketohydrindene reaction was negative, manifesting that NCVP does not contain proteins, peptides or amino acids. Fehling's reaction was negative, showing that NCVP belongs to the non reducing sugar. Table 1 showed the average value of optical activity of NCVP were −0.023 at 23.5 °C, and the specific optical rotation values of NCVP was −48.3. According to the regression equation of standard curve y = 0.7772x + 0.0058 (R2 = 0.9869), the content of sulfate ion in NCVP was 2.04%. The content of uronic acid in NCVP calculated by the regression equation of the standard curve (y = 0.5023x − 0.0608, R2 = 0.9720) was 35.12%. The thermal stability of NCVP also can be seen in Table 1, and the absorption value of NCVP has little change until 80 °C, indicating that NCVP has good thermal stability and can be heat-degradation over 80 °C. As shown in Fig. 5, the viscosity of different concentration of NCVP were determined at 23.5 °C with the speed of 60 r/min by the digital viscometer (SNB-2, China), an increase in the concentration of NCVP resulted in an increase of the viscosity of NCVP and reached at 0.062 pa·s at the concentration of 0.9 mg/mL. 3.4. Representational structure Fig. 6 showed a SEM image and an AFM image of NCVP while Fig. 6 (A) and (B) displayed the scanning electron microscope results. At 50 times magnification, the NCVP were cellular extension. At magnification of 300 times, a smooth surface was chosen to obtain the microscopic information of polysaccharide aggregates. There was a large gap between the molecules of NCVP, which showed that there existed repulsion force between the polysaccharide molecules and the folds of the smooth surface were less. Fig. 6(C) and (D) showed that the molecular arrangement of polysaccharides was not close, and the size was different. There were a large number of molecular globular aggregates and a small amount of dispersion, the NCVP molecule was about 80 nm in height, the width was about 2.5 μm, and the area was about 6.25 μm2.
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According to Fig. 7(A), the FT-IR spectrum of NCVP was the absorption line of typical polysaccharide, which showed a strong absorption peak at 3600–3200 (3442.37) cm−1, indicating a strong polysaccharide molecule or intermolecular hydrogen. 2923.604 cm−1 was the characteristic peak of CH3, CH2 in the NCVP. 1384.662 cm−1 was the bending vibration absorption peak of C\\H, and the stretching vibration of C\\H and the vibration of CH constituted the characteristic peak of carbohydrate [36]. 1150–950 (1035.604) cm−1 was the pyranose ring within the ether bond (C\\O\\C) due to stretching vibration. 970–800 (804.184) cm−1 range had an absorption peak, indicating that it had a weak C\\O\\C stretching vibration [37]. According to Fig. 7(B), the peak area was −102.6 J/g, and the enthalpy of the thermal effect was −102.6 J, indicating the reaction was exothermic reaction. It can be seen from the figure that the reaction starting point and end point was 245.6 °C (518.75 K) and 309.2 °C (582.35 K), respectively. Therefore, the reaction width was 63.6 °C (336.75 K). And the NCVP at 287.4 °C (560.55 K) was the fastest weight loss. According to the DTA curve, the whole reaction process was exothermic indicating that the pyrolysis reaction smoothly proceeded and the total energy absorbed by chemical bonds is less than the total energy released by the formation of new bonds. 4. Conclusions In the present work, a reliable kinetic model was established to describe the real extraction process of NCVP from NCV during ultrasound-assisted extraction, and the kinetic parameters were calculated. Using this model, an optimal extraction condition was obtained, which includes 353.15 K of extraction temperature, 540 W of ultrasonic power, 25 min of extraction time and 1:50 of solid-liquid ratio, and the NCVP, a non-reducing polysaccharide, was obtained with good water solubility and thermal stability. The surface morphology of NCVP was smooth and contained fewer folds. Acknowledgement This research was supported by National Natural Science Foundation of China (No. 31460032, 81660581) and the Youth Talent Support Program of Lanzhou University of Technology (No. 2018). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.ijbiomac.2018.12.247. References [1] M. Potts, B.A. Whitton, The Ecology of Cyanobatacteria [M], Kluwer Academic Publishers, Netherlands, 2000 465–504. [2] S. Jensena, B.O. Petersen, S. Omarsdottira, B.S. Paulsen, J.Ø. Duus, E.S. Olafsdottir, Structural characterization of a complex heteroglycan from the cyanobacterium Nostoc commune, Carbohydr. Polym. 91 (2013) 370–376, https://doi.org/10.1016/j. carbpol.2012.08.063. [3] S.J. Guo, S.H. Shan, X.T. Jin, Z.W. Li, Z.Y. Li, L.Q. Zhao, Q. An, W. Zhang, Water stress proteins from Nostoc commune Vauch. exhibit anti-colon cancer activities in vitro and in vivo, J. Agr. Food Chem. 63 (1) (2015) 150–159. [4] Y. Diao, H.B. Han, D.F. Zhang, J.P. Zhou, Z.J. Yang, Determination of nine microelements in Nostoc commune Vauch. by ICP-AES, Adv. Mater. Res. 518–523 (2012) 5020–5023, https://doi.org/10.4028/www.scientific.net/AMR.518-523.5020. [5] W.P. Zhang, M.A. Ya-Ge, C.J. Yang, S.L. Zhao, P.M. Yang, Comparative on nutritional components in wild and cultivated of Nostoc commune Vauch, Food Res Dev 37 (15) (2016) 44–48 , (In Chinese) https://doi.org/10.3969/j.issn.1005-6521.2016. 15.001. [6] J. Chen, L. Zhao, J. Xu, R. Yang, S. He, X. Yan, Determination of oxidized scytonemin in Nostoc commune Vauch. cultured on different conditions by high performance liquid chromatography coupled with triple quadrupole mass spectrometry, J. Appl. Phycol. 25 (4) (2013) 1001–1007, https://doi.org/10.1007/s10811-012-9914-1. [7] S.K. Chai, B. Kim, T.X. Pham, Y. Yue, C.L. Weller, T.P. Carr, Y.K. Park, J.Y. Lee, Hypolipidemic effect of a blue-green alga (Nostoc commune) is attributed to its nonlipid fraction by decreasing intestinal cholesterol absorption in C57BL/6J mice, J. Med. Food 18 (11) (2015) 1214–1222, https://doi.org/10.1089/jmf.2014.0121.
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