LWT - Food Science and Technology 60 (2015) 124e130
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Nanocapsules of b-carotene: Thermal degradation kinetics in a scraped surface heat exchanger (SSHE) lez-Reza a, b, D. Quintanar-Guerrero c, J.J. Flores-Minutti b, R.M. Gonza rrez-Cortez a, b, M.L. Zambrano-Zaragoza a, * E. Gutie a n, Universidad Nacional Auto noma de M n y Tecnologías Facultad de Estudios Superiores Cuautitla exico, Laboratorio de Procesos de Transformacio neTeoloyucan, San Sebastia n Xhala, Cuautitla n Izcalli, Edo de M Emergentes en Alimentos, Km 2.5 Carretera Cuautitla exico, CP.54714, Mexico b n, Universidad Nacional Auto noma de M Facultad de Estudios Superiores Cuautitla exico, Departamento de Ingeniería y Tecnología, Laboratorio n Izcalli C.P. 54745, Edo de M Experimental Multidisciplinario, Ingeniería en Alimentos, Av. 1o de mayo s/n Cuautitla exico, Mexico c n, Universidad Nacional Auto noma de M Facultad de Estudios Superiores Cuautitla exico, Laboratorio de Posgrado en Tecnología Farmac eutica, Av. 1o de n Izcalli C.P. 54745, Edo de M mayo s/n Cuautitla exico, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 April 2014 Received in revised form 19 August 2014 Accepted 2 September 2014 Available online 16 September 2014
Response surface methodology was used to optimize the conditions of thermal degradation of b-carotene nanocapsules in a scraped surface heat exchanger. The variables studied were volumetric flow (2.4 10 6e4.8 10 6 m3/s), steam pressure (49e147 kPa), and rotor speed (10.4e31.2 s 1). Results showed that the experimental data could be adequately fitted into a second-order polynomial model with multiple regression coefficients (R2) of 0.842e0.977, and that the variables with the greatest significance in the degradation of the b-carotene were steam pressure and volumetric flow (p < 0.05). The responses analyzed were loss of b-carotene and changes in the degradation rate (k) and activation energy (Ea). The highest process conditions obtained for thermal degradation prevention were 4.4 10 6 m3/s of volumetric flow, steam pressure at 98 kPa, and a rotor speed of 38.29 s 1, with optimum values of k ¼ 0.049 min 1, Ea ¼ 171.49 kJ/mol, and loss of nanoencapsulated b-carotene ¼ 6.93%. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Heat treatment b-carotene Nanocapsules Emulsification-diffusion Food nanotechnology
1. Introduction Scraped surface heat exchangers (SSHE) are used in a wide variety of applications in the chemical, pharmaceutical and food industries, especially for different kinds of unit operations (eg. freezing, sterilization, pasteurization, cooling, crystallization, etc.). High viscosities and non-Newtonian behaviors of processed fluids are often encountered in this field, which tend to complicate their handling and reduce heat transfer rates in the processing equipment (Yataghene, Fayolle, & Legrand, 2009; Yataghene, Francine, & Jack, 2011). The study of rheological properties of nanoparticles in the heating treatments is very important. In the SSHE, the study of rotor speed is a key parameter for the efficiency evaluation in the nez-Colmenero, 2014; thermal process (Bou, Cofrades, & Jime Russell, Burmester, & Winch, 1997). Thermal treatments of foods in SSHE are primarily intended to inactivate pathogens and deteriorative microorganisms. Unfortunately, such sensory food
* Corresponding author. Tel.: þ52 5556231999x39406; fax: þ52 5556232077. E-mail addresses: luz.zambrano@unam.mx, maryluz97@yahoo.com.mx (M.L. Zambrano-Zaragoza). http://dx.doi.org/10.1016/j.lwt.2014.09.020 0023-6438/© 2014 Elsevier Ltd. All rights reserved.
properties as color, texture and nutritional value may also tend to suffer degradation during such processes. Kinetic models are essential for the design, evaluation and optimization of new processes implemented to ensure maximum quality factors in food (D'Addio, Carotenuto, Di Natale, & Nigro, 2011; Dutta, Dutta, Raychaudhuri, & Chakraborty, 2006). The b-carotene is now widely used as an additive in the food industry to improve the color of certain foods and beverages. Studies show that it has high antioxidant activity, in addition to beneficial health functions, such as preventing and/or protecting against cancer, cardiovascular diseases and colorectal adenomas (Qiu, Chen, & Li, 2009; Ramoneda, Ponce-Cevallos, Buera, & Elizalde, 2011; Yuan, Gao, Mao, & Zhao, 2008) Due to their highly unsaturated structure, carotenoids are prone to degradation by temperature during processing and storage (Achir, Randrianatoandro, Bohuon, Laffargue, & Avallone, 2010). The current demand for functional foods is increasing and the benefits provided by these kinds of ingredients, including increased physiological functions, have both positive impacts on human health and commercial implications. Specifically, nanoemulsions and colloidal particles (eg. nanocrystals, nanoparticles, etc.) used as micronutrient systems (pharmafoods), and certain nutraceuticals, are having important effects on the
lez-Reza et al. / LWT - Food Science and Technology 60 (2015) 124e130 R.M. Gonza
development of improved products and multifunctional systems (Lesmes & McClements, 2009; Onwulata, 2013). Nanotechnology is now set to impact the food industry at all stages of processing, right from primary production at the farming level, and has been shown to improve the functionality of some emerging technologies, such as edible films for food applications (Zambrano-Zaragoza et al., 2014). Generally speaking, nanoparticles are defined as solid colloidal particles that include two forms: nanospheres and nanocapsules (Mora-Huertas, Fessi, & Elaissari, 2010; Zambrano-Zaragoza et al., 2013). According to mann, Doelker, and Fessi (1998), prepaQuintanar-Guerrero, Alle ration of nanocapsules (NCs) by the Emulsification-Diffusion Method (EDM) allows lipophilic active substance nanoencapsulation. The experimental procedure performed to achieve this requires three phases: organic, aqueous and dilution. EDM is an excellent choice for the preparation of nanosystems since it results in the development of safe, functional food dispersions (FDA, 2007; rrez-Cortez, & Quintanar-Guerrero, Zambrano-Zaragoza, Gutie ~ oz, 2012). The structure of NCs is ideal for develMendoza-Mun oping foods that contain b-carotene as a functional ingredient and for modifying the physical characteristics of the original material in order to improve sensory qualities and/or increase nutritional content (Bouchemal, Briancon, Perrier, & Fessi, 2004; Mirhosseini, Tan, Hamid, & Yusof, 2008). Response surface methodology (RSM) consists of a group of mathematical and statistical techniques based on the fit of empirical models from experimental data obtained with an experimental design. Toward this objective, linear or square polynomial functions are employed to describe the system studied and, consequently, to explore (modeling and displacing) experimental conditions until its optimization. Desirability function (D) allows to the analyst find the experimental conditions (factor levels) to reach, simultaneously, the optimal value for all the evaluated variables, including the researcher's priorities during the optimization procedure (Bezerra, Santelli, Oliveira, Villar, & Escaleira, 2008; Vera Candioti, De Zan, C amara, & Goicoechea, 2014). In the present study, the degradation of b-carotene nanoencapsulated and supported in model fluid (CMC dispersion 0.5 g/ 100 g) was analyzed as effect of heat treatment in a scraped surface heat exchanger. Degradation rate (k) and activation energy (Ea) were evaluated and are discussed in relation to the loss of b-carotene at the end of the thermal process. 2. Materials and methods 2.1. Materials Poly-3-caprolactone
(PCL)
(Molecular
Weight
~80
kDa,
r ¼ 1.147 g/cm3 at 25 C) was obtained from SigmaeAldrich® (USA).
The stabilizing agent was Pluronic®, F-127 (Poloxamer 407, PF-127) xico). b-carotene (99%) and sunflower oil (r ¼ 0.921 g/cm3 (BASF, Me at 25 C), supplied by SigmaeAldrich® (USA), was used as the oily core. The partially water-miscible solvent was ethyl acetate (EA), HPLC grade, provided by Fermont (Mexico). This solvent was selected due to its low toxicity (ICH class: 3). Distilled water was of Milli-Q quality (Millipore®, USA, Bedfore, MD). Carboxymethylcellulose was obtained from Amtex Gelycel®. All other reagents were of analytical grade and were used without further purification.
125
2.3. Particle size (PS), polydispersion index (PDI) and zeta potential (z) PS distribution and PDI were determined by the laser light scattering technique at a fixed angle of 273 and 25 C, using a Zsizer 4 (Zetasizer Nano Series Malvern Ltd., UK). The dispersion was diluted in Milli-Q® water, according to the volume frequency histogram for the system, with and without CMC. The z was evaluated by electrophoretic motion using as reference standard polystyrene dispersions (z ¼ 55 mV), this parameter measures the degree of repulsion between adjacent particles. The optimal z index is >j30j, considered a physically stable system. All measurements were performed in triplicate at 25 C.
2.4. Morphological studies The NCs were purified by four ultracentrifugations (45,000 g for 60 min at 5 C) in order to eliminate the excess stabilizer. One droplet of this concentrated suspension was then spread on a glass surface and dried and prepared according, Zambrano-Zaragoza, ~ o-Tostado, Gutie rrez-Cortez, QuintanarMercado-Silva, Castan Guerrero (2011), and then observed under a high vacuum scanning electron microscope (LV-SEM, JSM 5600 LV) at a resolution of 5 nm. 2.5. Preparation and thermal conductivity of a fluid model with NCs Dispersion of the CMC (0.5 g/100 g) was prepared at 25 C by stirring at 63 s 1 (Arde Barinco Inc., New Jersey); then a quantity equivalent to 70 mg/mL of b-carotene in nanocapsules was added. This dispersion was used as a fluid model for the thermal treatment study. Thermal conductivity was determined by a KD2 Pro® Thermal Properties Analyzer (Decagon Devices Inc., USA) using a KS-1 sensor model, before and after the thermal treatment. All measurements were performed in triplicate at 25 C. 2.6. b-carotene kinetic modeling An SSHE (Armfield® LTD FT25C, England) was used to evaluate the thermal treatment of the b-carotene nanocapsules. The bcarotene contained in the thermal output from the SSHE process was determined by spectrophotometry using a Cintra 10 UVeVisible (GBC Scientific Equipment, Australia) at l ¼ 480 nm previously calibrated with CMC dispersion (0.5 g/100 g) in order to avoid errors due to the absorbancy of the carrier. All measurements were performed in triplicate at 25 C. b-carotene concentrations were determined on the basis of a previously elaborated calibration curve in intervals of 20 mg/mL in distilled water in range of 0e200 mg/mL ([b carotene NCs] ¼ Absorbance/0.0152). The concentration changes in the nanoencapsulated b-carotene during the thermal process as modeled by a first-order kinetic reaction model can be represented as follows (Eq. (1)):
C ¼ kt ln C0
(1)
2.2. Nanocapsules preparation NCs were produced by the Emulsification-Diffusion Method (EDM), described in detail elsewhere (Quintanar-Guerrero et al., 1998), according to the performance optimization proposed by rrez-Cortez, Castan ~ oZambrano-Zaragoza, Mercado-Silva, Gutie Tostado, and Quintanar-Guerrero (2011) for food applications.
where C0 is the initial concentration of b-carotene (mg/mL) at time zero; C is the concentration of b-carotene (mg/mL) at time t; k ¼ the temperature-dependent rate constant (min 1); and t is the holding time (min). The effect of temperature in relation to steam pressure was calculated by a first order kinetic constant using the Arrhenius equation (Eq. (2)):
lez-Reza et al. / LWT - Food Science and Technology 60 (2015) 124e130 R.M. Gonza
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"
k ¼ kref
Ea exp R
1 1 T Tref
!# (2)
where T is the absolute temperature; Tref is the absolute reference temperature; kref is the reaction rate constant at the reference temperature; Ea is the activation energy; and R is the universal gas constant. 2.7. Experimental design Response surface methodology (RSM) was used to study the effect of the independent variables ei.e., volumetric flow (X1), steam pressure (X2), and rotor speed (X3) on the b-carotene degradation rate (Y1), activation energy (Y2), and loss of b-carotene (Y3). A second-order, central composite rotatable design (CCRD) was set up to conduct 20 experiments (six axial points, eight factorial points, and six central points) with a ¼ 1.68719. A secondorder polynomial equation was used to express the response variables as a function of the independent variables, as follows:
Yi ¼ b0 þ b1 X1 þ b2 X2 þ b3 X3 þ b11 X12 þ b22 X22 þ b33 X33 þ b12 X1 X2 þ b13 X1 X3 þ b23 X2 X3
(3)
where Yi represents the response variables; b0 is a constant; and bi, bii and bij are the linear, quadratic, and interactive coefficients, respectively. The coded and uncoded independent variables used in the RSM design are listed in Table 1. All experiments were carried out considering three replications and in random order (Myers & Montgomery, 2002). The coefficients of the response surface equation were determined, and an analysis of variance (ANOVA) was performed to evaluate any significant differences between the independent variables using MINITAB® release 14 (Minitab Inc., PA, USA). 2.8. Optimization The optimum conditions for the thermal treatment of b-carotene nanocapsules were determined by applying a desirability function (D) (Vera Candioti et al., 2014) using MINITAB® release 14. Loss of b-carotene and k were the minimized responses, while Ea was maximized. The factors considered were: (X1) volumetric flow; (X2) steam pressure; and (X3) rotor speed. The differences in the findings in relation to the expected optimization values were evaluated at a ¼ 0.05 to analyze the results. 3. Results and discussion
good integration of b-carotene and PCL in a capsular architecture (Quintanar-Guerrero et al., 1998; Mora-Huertas et al., 2010). 3.1.1. Particle size and polydispersion index Fig. 1 represents the distribution of the PS and PDI of the bcarotene nanocapsules, with and without CMC as the polysaccharide support. It reveals that the addition of CMC did not modify the PS of the colloidal system, as there was no significant difference in the PS of 191 nm for the NCs and 209 nm for the NCs/ CMC, while the PDI increased from 0.165 to 0.304 upon adding CMC as a support for the nanocapsules. This variation is most likely due to the formation of a layer of coating around the NCs effectuated by the polysaccharide (CMC). Mora-Huertas et al. (2010) have reported similar results for NCs formed by EDM with a mean PS of 250e650 nm. These PDI values suggest that nanocapsule dispersion had a narrow distribution. For b-carotene nanocapsules, Zambrano-Zaragoza et al. (2011) reported a PDI of 0.076, but a PDI of 0.15 for DL-a-tocopherol nanocapsules for use as food additives. 3.1.2. Zeta potential The z obtained was 34.20 mV, suggesting a stable dispersion iz-Abajo, with a low probability of physical aggregation. Sa lez-Ferrero, Moreno-Ruiz, Romo-Hualde, and Gonza lezGonza Navarro (2013) reported that nanoparticles formed with b-carotene have a lower zeta potential of 34 mV. Since z is a measure of the degree of repulsion between similarly-charged particles in the dispersion, colloids with a high z (either positive or negative) are electrically-stabilized (Zambrano-Zaragoza et al., 2011). 3.1.3. Morphological studies Fig. 2a shows a micrograph that corresponds to the b-carotene nanocapsules. It shows that the distribution and PS of the NCs is homogeneous with a few aggregates. Fig. 2b shows the capsular structure that consists of an oily core (b-carotene) surrounded by a thin envelope (PCL). The PS and dispersion index obtained coincided with the laser light scattering. 3.2. Fitting models Table 2 shows representative experimental lots of heat treatment in the SSHE. These results reveal that experiments 10 and 11 were those with the lowest loss of b-carotene and thus correspond to the extreme points of the model. The largest loss of nanoencapsulated b-carotene occurred under the conditions of steam pressure 180.5 kPa, rotor speed 20.8 s 1, and volumetric flow
3.1. Nanocapsule characterization Once prepared, the nanocapsules were characterized by particle size, b-carotene encapsulation, and density, in order to confirm their formation. This assessment established that the degree of encapsulation achieved was at least 76%, and that the density range was 1.019 ± 0.02 g/cm3, indicative of an efficient encapsulation and Table 1 Uncoded and coded independent variables used in RMS design. Coded variables Uncoded variables
Coded levels 1.68 1
X1 X2 X3
6
3
Volumetric flow 10 (m /s) 1.58 Steam pressure (kPa) 15.6 Rotor speed (s 1) 3.30
0
1
1.68
2.40 3.60 4.80 5.62 49.0 98.0 147.0 180.5 10.4 20.8 31.2 38.29
Fig. 1. Distribution particle size of nanocapsules of b-carotene previously to heat treatment. ( ) NCs, ( ) NCs/CMC.
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Fig. 2. Micrographs of b-carotene nanocapsules at a) 10,000 and b) 25,000 .
3.6 10 6 m3/s, which means that the use of a nanoencapsulated system results in increased b-carotene protection that greatly reduces the amount of NCs that needs to be added during the formulation of a product that will be subjected to a thermal process. Table 3 shows the ANOVA for the coefficients of the polynomial regression model and reflects the influence of the factors studied on the function of the experimental data. According to the lack-offit test, which represents the behavior of the experimental data at the limits of the experimental design, it adequately described the influence of the factors analyzed on the independent variables (Myers & Montgomery, 2002). The regression coefficients for the R2 responses were analyzed with the following results: 0.963 for k (min 1); 0.981 for Ea (kJ/mol); and 0.866 for the loss of b-carotene (%). According to Mune, Minka, and Mbome (2008), these values are suitable for the modeling process. The analysis of variance (ANOVA) makes it possible to determine the influence of the coefficients on the response variables (Table 3). For the degradation rate all terms were significant (p 0.05), except for the quadratic term of the rotor speed and the interaction between volumetric flow and rotor speed. For Ea, the rotor speed did not influence the thermal process (p > 0.48). With regards to the quadratic terms obtained, those with the highest values were
steam pressure (p 0.05), and the interaction of volumetric flow and rotor speed (p < 0.05) for the responses analyzed. 3.3. Degradation rate (k) of NCs Fig. 3a shows the effect of volumetric flow rate and rotor speed on the degradation rate of b-carotene nanocapsules. The terms that directly influenced the k of the NCs were all linear terms of the model (p 0.05), while the least significant one was the quadratic of the rotor speed (p 0.372). This finding suggests that there is a significant curvature (minimum) around the central to the axial points of the quadratic model (Fig. 3a) with a value of k ¼ 0.02 min 1 when volumetric flow is 4.8 10 6 m3/s and steam pressure is 49 kPa. Chen & Huang (1998) reported degradation rates for b-carotene in the range of 0.001e0.026 min 1 in intervals of heating to 50e150 C. Also, Achir et al. (2010) reported values for the thermal degradation of b-carotene at 120 C of 0.132 min 1. This allows us to infer that the poly-3-caprolactone used as the polymer in the formation of nanocapsules has a significant effect in terms of decreasing b-carotene degradation, according to the results obtained at the higher constant; i.e., above 0.026 min 1, at the central and axial points of the model. The degradation rate increased
Table 2 Batch mean analysis of thermal degradation of nanocapsules of b-carotene. Batch no.
Volumetric flow 10 6 (m3/s)
Steam pressure (kPa)
Rotor speed (s 1)
k (min 1)
7 15 20 10 16 11 6 9 17 12 4 8 5 18 13 19 3 14 2 1
2.40 3.60 3.60 5.62 3.60 3.60 4.80 1.58 3.60 3.60 4.80 4.80 2.40 3.60 3.60 3.60 2.40 3.60 4.80 2.40
147 98 98 98 98 15.60 49 98 98 180.54 147 147 49 98 98 98 147 98 49 49
31.20 20.80 20.80 20.80 20.80 20.80 31.20 20.80 20.80 20.80 10.40 31.20 31.20 20.80 3.31 20.80 10.40 38.29 10.40 10.40
0.07 0.03 0.04 0.07 0.03 0.03 0.03 0.04 0.03 0.12 0.09 0.11 0.03 0.03 0.02 0.04 0.04 0.03 0.03 0.04
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.001 0.003 0.006 0.004 0.005 0.001 0.004 0.004 0.059 0.003 0.006 0.010 0.003 0.007 0.002 0.004 0.006 0.002 0.004 0.010
Ea (kJ/mol) 153.68 183.98 164.15 148.78 180.49 159.77 180.71 179.90 176.85 112.33 122.13 114.91 178.04 175.82 185.95 166.48 175.34 175.87 153.03 165.20
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.950 1.975 1.536 3.633 1.631 0.888 0.650 0.300 3.246 1.888 1.362 0.838 2.556 0.168 1.225 1.161 1.462 1.784 0.762 3.796
Loss (%) 25.85 10.37 10.21 7.05 10.74 10.18 4.73 14.23 10.09 29.92 15.02 13.33 12.44 11.10 6.52 9.96 11.43 11.03 5.54 18.67
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.497 0.473 0.745 0.431 0.990 0.391 0.272 0.211 0.746 0.626 0.130 0.426 0.612 0.299 0.482 0.930 0.612 0.667 0.416 0.567
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Table 3 ANOVA and regression coefficients on response variables in function studied factors. k (min 1)
Term
Coef
b0 b1 b2 b3 b11 b22 b33 b12 b13 b23
a
R2 R2-adj
Ea (kJ/mol) p-value
0.030 0.011a 0.024a 0.005a 0.008a 0.015a 8.35E 4ns 0.013a 0.002ns 0.006a 0.963 0.956
0.000 0.000 0.000 0.000 0.000 0.000 0.372 0.000 0.177 0.000
Coef
Loss (%) p-value
a
183.10 11.26a 13.97a 0.39ns 7.37a 17.37a 1.51a 10.31a 3.66a 8.68a 0.981 0.978
0.000 0.000 0.000 0.485 0.000 0.000 0.007 0.000 0.000 0.000
Coef
p-value a
10.41 3.06a 4.21a 0.972a 0.09ns 3.42a 0.57ns 1.49a 1.33a 2.47s 0.866 0.842
0.000 0.000 0.000 0.014 0.804 0.000 0.132 0.004 0.010 0.000
b0 ¼ Regression coefficient bi ¼ Lineal coefficient bii ¼ Quadratics coefficients bij ¼ Interaction coefficients. a
Significant term (p < 0.05). not significant term (p > 0.05).
ns
directly with steam pressure (temperature). The least squares equation for the second order degradation rate (Y1) of significant terms is as follows:
k ¼ 0:18 5:7 104 X1 1:8 10 3 X2 þ 5:7 109 X11 þ 6:3 10 6 X22 þ 223:65X12 þ 1:2 10 5 X23 (4) 3.4. Activation energy (Ea) Fig. 3b shows the response surface for Ea according to changes in the kinetic constants for degradation and the temperature of bcarotene in the NCs. It reveals a significant effect of rotor speed and volumetric flow on the axial points of the model. The factors that directly influenced the Ea of the NCs of b-carotene were the linear terms of volumetric flow and steam pressure (p 0.0), while the least significant was the lineal term of rotor speed (p 0.485). According to Demiray, Tulek, and Yilmaz (2013), the Ea for bcarotene is 40.2 kJ/mol when temperature increases from 70 to 80 C and this, in turn, is more greatly affected on other temperature scales. In this study, the temperatures reached were between 80 and 93 C, with greater Ea for the NCs. This suggests that the biopolymer (poly-3-caprolactone) used in the formation of the NCs confers thermal resistance to b-carotene, which correlates with that shown in degradation kinetics. According to studies by Aparicio-Ruiz, Mínguez-Mosquera, and Gandul-Rojas (2011), the average Ea for b-carotene is 62 kJ/mol, since according with S aiz-Abajo et al. (2013) the degree of protection depends on component of the protective layer., Achir et al. (2010) reported values for Ea of 154 ± 21 kJ/mol for the degradation of b-carotene in palm olein and Vegetaline® oil with similar ~ a, values for NCs at the central points of the model. Spada, Noren Marczak, and Tessaro (2012) and Ramoneda et al. (2011) indicate that kinetic modeling for microencapsulated b-carotene corresponds to first order degradation kinetics, and that a high density of the polymer utilized as a function of its molecular weight produces the encapsulation of lipophilic agents. The polymer support of the fluid model (CMC) suggests a double encapsulation system model, such that Ea achieves higher values than those reported for untreated b-carotene encapsulation. The second order least squares equation for the activation energy (Y2) in significant terms is as follows:
Ea ¼ 29:14 þ 3:9 107 X1 þ 1:12X2 5:1 1012 X11 7:2 10 3 X22 1:7 105 X12 þ 2:9 105 X13
(5)
Fig. 3. Response surface for a) degradation rate (k) as a function of volumetric flow and rotor speed, b) activation energy (Ea) as a function of volumetric flow and rotor speed and c) loss of b-carotene nanocapsules as a function of steam pressure and rotor speed.
The thermal conductivity obtained for the fluid model was 0.59 W/m C before and after subjection to the heat treatment without changes for addition of NCs to the dispersion of CMC (thermal conductivity of NCs ¼ 0.56 W/m C at 20 C). This indicates that the system with the nanocapsules incorporated is thermally stable, and was not affected by the shearing action or velocity of the blades of the scraped surface heat exchanger
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(Lee & Irvine, 1997). The thermal conductivity of CMC in a mixture with sodium is in the interval of 0.60e0.68 W/m C (Broniarz-Press & Pralat, 2009). This is consistent with the current study. The changes in the Ea are attributed to steam pressure and volumetric flow, showing good stability for the submicronic system according to values obtained of zeta potential and thermal conductivity before and after of heat treatment. 3.5. Loss of b-carotene Fig. 3c shows the response surface of the independent variables studied. A direct effect of steam pressure on the loss of nanoencapsulated b-carotene was found from the central points to the axial points due to the rotational speed of the blades of the SSHE, whose function is to homogenize the temperature of the product inside the cylinders of the apparatus. A synergistic effect occurred at the minimum axial points of the steam pressure and maximums of rotor speed. The minimum and maximum losses of b-carotene were 10% and 30%, respectively. According to research by Marx, Stuparic, Schieber, and Carle (2003), the specific fractions of bcarotene can be quantified spectrophotometrically to give dependable results when the measurement of the continuous phase (oil) is very low. Emin, Mayer-Miebach, and Schuchmann (2012) reported a minimal loss of b-carotene of about 30% in the extrusion process, regardless of temperature (130e170 C). The present study shows that the maximum loss of b-carotene is approximately 30% and that minimum retention is around 70%, leading to the inference that nanoencapsulation provides properties of heat resistance to antioxidant compounds such as b-carotene. The factors that directly influence the loss of NCs of b-carotene are all linear terms of the model (p 0.05), while the least significant is the quadratic of the volumetric flow (p 0.804). Eq. (6) is the second order model for the loss of b-carotene (Y3) in significant terms:
response goals (Vera Candioti et al., 2014). The optimal process conditions obtained for the thermal degradation of b-carotene nanocapsules were 4.4 10 6 m3/s of volumetric flow, steam pressure of 98 kPa, and rotor speed of 38.29 s 1, with optimum values of k ¼ 0.049 min 1 and Ea ¼ 171.5 kJ/mol, with a loss of nanoencapsulated b-carotene of 6.93%.
Loss ¼ 32:3 3:3 106 X1 0:39X2 þ 0:22X3 þ 1:4 10 3 X22
4. Conclusions
þ 2:5 104 X12 þ 0:48 10 3 X23 (6) A contrast to these results was obtained by performing a comparative study under the same operating conditions, but using unencapsulated b-carotene (Table 4). This resulted in a decrease in the loss of b-carotene to a minimum of 30%; thus reaffirming that the nanoencapsulation of antioxidant agents provides properties of thermal resistance in thermal processes. 3.6. Optimization Optimization was carried out by first superimposing the contour plots for the degradation rate, activation energy and loss of nanoencapsulated b-carotene as a function of volumetric flow and steam pressure at a constant rotor speed (31.2 s 1) (Fig. 4). A numerical procedure was applied to predict the exact optimum level of the independent variables leading to the desirable function (D ¼ 1) Table 4 Batch mean analysis of loss of b-carotene unencapsulated and encapsulated in the thermal treatment. Batch no.
Volumetric flow 10 6 (m3/s)
Steam pressure (kPa)
Rotor speed (s 1)
Unencapsulated (%)
Encapsulated (%)
7 10 11
2.4 5.6 3.6
147 98 15.6
31.2 20.8 20.8
58.54 ± 2 55.42 ± 1 58.92 ± 1
25.85 ± 0.497 7.05 ± 0.431 10.18 ± 0.391
Fig. 4. Superimposed contour plot of steam pressure as a function of volumetric flow at a fixed rotor speed of 31.2 s 1. ( 5 and 15) loss of b-carotene (%), ( 160 and 180) Ea (kJ/mol), ( 0.04 and 0.06) k (min 1).
The present study shows that the second-order polynomial model fits in terms of describing and predicting the responses of the kinetic parameters and the loss of nanoencapsulated b-carotene. Nanoencapsulation provides an additional protector effect that impedes the degradation of thermolabile compounds in a thermal process. This effect is attributed to the presence of the membrane film formed around the oily core. These findings indicate that the use of nanotechnology can improve the retention of bcarotene in thermal processes, and that the potential use of nanoencapsulation can be applied easily to other antioxidant agents for other processes (eg. blanching, sterilization, UHT, etc.) Acknowledgments The authors acknowledge the financial support for this work from PAPIIT: IT231511 and IT200814 of DGAPA and Investigation Internal Project PIAPIC06. We would like to thank M. en I. Alicia del pez for taking the micrographs of the nanocapsules. Real Lo References Achir, N., Randrianatoandro, V. A., Bohuon, P., Laffargue, A., & Avallone, S. (2010). Kinetic study of b-carotene and lutein degradation in oils during heat treatment. European Journal of Lipid Science and Technology, 112(3), 349e361. Aparicio-Ruiz, R., Mínguez-Mosquera, M. I., & Gandul-Rojas, B. (2011). Thermal degradation kinetics of lutein, b-carotene and b-cryptoxanthin in virgin olive oils. Journal of Food Composition and Analysis, 24(6), 811e820. Bezerra, M. A., Santelli, R. E., Oliveira, E. P., Villar, L. S., & Escaleira, L. A. (2008). Response surface methodology (RSM) as a tool for optimization in analytical chemistry. Talanta, 76(5), 965e977.
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