Production, characterization and controlled release studies of biodegradable polymer microcapsules incorporating neem seed oil by spray drying

Food Packaging and Shelf Life 18 (2018) 131–139

Contents lists available at ScienceDirect

Food Packaging and Shelf Life journal homepage: www.elsevier.com/locate/fpsl

Production, characterization and controlled release studies of biodegradable polymer microcapsules incorporating neem seed oil by spray drying Kanyarat Sittipummongkol, Chiravoot Pechyen

T

⁎

Division of Materials and Textile Technology, Faculty of Science and Technology, Thammasat University, Patumthani, 12120, Thailand

A R T I C LE I N FO

A B S T R A C T

Keywords: Microcapsules Azadirachtin Insecticides Polyvinyl alcohol Gum arabic Whey protein isolate Maltodextrin

Azadirachtin is a biologically active constituent of neem seed oil, exhibiting medicinal and pesticidal properties. This work reports on the encapsulation of neem seed oil extract within three different polymeric shells: polyvinyl alcohol (PVA), gum arabic (GA) and whey protein isolate/maltodextrin (WPI/MD), using spray drying. The obtained, roughly spherical microcapsules had average sizes of 28.84 ± 11.86 μm, 32.43 ± 13.06 μm, and 52.88 ± 17.33 μm (obtained from PVA, GA, and WPI/MD, respectively). Fourier transform infrared spectroscopy confirmed the presence of the core and shell components, in addition to surface functional groups. Encapsulation efficiencies for neem seed oil proved higher in smaller microcapsules, although efficiency values of 60–92% were obtained in all cases. In vitro release of neem seed oil from the microcapsules followed the Ritger–Peppas model, as governed by Fickian diffusion. From these results, the association of botanical insecticides within biopolymer cores offer considerable potential for increasing agricultural production levels, and reducing impacts on the environment and human health.

1. Introduction

& Maji, 2009a,b). Microencapsulation is a process of enveloping the core material, e.g. vitamin, essential oil, or drug, in a protective shell material. Biopolymers are ideal shell materials due to their ability to degrade under the influence of the environment, leaving only non-toxic residues. Of these, poly (vinyl alcohol) has been utilized previously due to its water solubility, biodegradability, and film forming ability (Bachtsi & Kiparissides, 1996; Pal, Banthia, & Majumdar, 2007). Gum arabic has also been used as a shell material as it is a good emulsifier, has sufficient viscosity, can be easily solubilized in water, and is capable of forming polymeric films (Kaasgaard & Keller, 2005; Krishnan, Kshirsagar, & Singhal, 2005). Maltodextrin, despite having poor emulsifying properties, shows good film forming ability and can be combined with protein or starch to produce shell material (Madene, Jacquot, & Scher, 2006). Whey protein isolate has also been used in combination with maltodextrin because of its good emulsification and antioxidant properties (Kim & Morr, 1996). The aim of the present contribution is to investigate the potential of gum arabic, poly (vinyl alcohol), and whey protein isolate/maltodextrin as spray dryable shell materials for microencapsulation of neem seed oil. Determination of morphologies and assessments of chemical and physical properties for all microcapsules were undertaken. Release profiles of neem seed oil from all microcapsules were

Due to the negative perception of people towards synthetic chemicals, especially in relation to toxicity, bio-based compounds are gaining attention as raw materials for industrial sectors supporting infrastructure, medical and pharmaceutical technology, and agricultural product development. The concepts of sustainable development and wellbeing have been integrated into the agricultural sector, through organic farming. The scope of organic farming includes biological pest control, mixed cropping and the fostering of insect predators (Geiger, Bengtsson, & Berendse, 2010). Replacement of synthetic chemicals (i.e. pesticides) with those derived from nature remains at the heart of the organic farming philosophy. One of the most effective strategies in organic farming focuses on the use of bioactive compounds as insect repellents (Dayan, Cantrell, & Duke, 2009). Neem seed oil contains azadiractin as its main bioactive component, a compound having efficient insect repellent and insecticidal properties (Kari, Isa, Marleena, Heikki, & Dionyssios, 2011). However, neem seed oil as a liquid has limited lifetime in soil, and is typically sensitive to light, temperature, and microorganisms, leading to its rapid degradation soon after spraying. To address these issues and allow for controlled release and higher efficiency, microencapsulation may be a promising approach due to its simplicity and flexibility (Devi

⁎

Corresponding author. E-mail address: [email protected] (C. Pechyen).

https://doi.org/10.1016/j.fpsl.2018.09.001 Received 13 December 2017; Received in revised form 28 May 2018; Accepted 17 September 2018 2214-2894/ © 2018 Published by Elsevier Ltd.

Food Packaging and Shelf Life 18 (2018) 131–139

K. Sittipummongkol, C. Pechyen

was evaporated using a rotary evaporator (V-850, Buchi, Switzerland). The quantity of neem seed oil thus obtained represents the unbound surface oil in the powder sample. To calculate the total oil content, 4 g of microcapsule powder was added to 80 mL of dichloromethane/methanol (3:2) (Koç, Güngör, & Zungur, 2015). The mixture was homogenized at 300 rpm for 15 min, mixed with 16 mL of water, and then shaken vigorously at 300 rpm for 15 min. The combined water/methanol layer containing the shell residue was removed, and the neem oil was recovered from the dichloromethane layer using a rotary evaporator (V-850, Buchi, Switzerland), and subsequently weighed. All samples were analyzed for total oil content in duplicate. From the above data, the encapsulation efficiency (% EE) was calculated using Eq. (1) below;

obtained using the total immersion method. 2. Materials and methods 2.1. Materials Neem seed oil (from Azadirachta indica) was purchased from Wasan Product, Co. Ltd. Thailand. Food grade gum arabic, and maltodextrin were purchased from Petrochemical Cor., Co. Ltd, (Thailand). Analytical grades of poly (vinyl alcohol) and whey protein isolate were purchased from Chemical Supply, Co. Ltd and Bodybuilding Warehouse, Co. Ltd. Thailand, respectively. Tween 80 (cationic surfactant) was purchased from Chemical Cor, Co. Ltd. Hexane, dichloromethane, and methanol (analytical grade) were purchased from Labscan (Asia) (Thailand). All chemical reagents were used as received without any further purification.

Total oil content − Surface oil Total oil content

content

× 100

(1)

2.2. Preparation of emulsions 2.5. In vitro release of neem seed oil Shell emulsions were prepared from either polyvinyl alcohol (PVA, 3 g), gum arabic (GA, 20 g), or whey protein isolate mixed maltodextrin (WPI/MD, 20 g), as shown in Fig. 1. Each polymeric shell material was dissolved, in separate experiments, in 80 ml of DI water and the solution left overnight. Following this, 2 g of Tween 80 was poured into the solution. In another vial, neem seed oil was dispersed in 20 ml of DI water for 30 min. After adding the polymeric shell material solution into the neem seed oil dispersion, the mixture was then stirred at 1200 rpm for 30 min. In all preparations, the ratio of neem seed oil to shell material was maintained at 1:2.

Microcapsule powder (10 mg) was added to a dialysis bag, and the sample immersed in a solution (30 mL) of 0.1% tween 80 in DI water. At certain time intervals (between 0–4320 min), 0.5 mL aliquots were removed for analysis; these were replaced each time with the same volume of fresh release medium. Neem seed oil release was monitored using UV–vis spectrophotometry (Synergy H1 microplate reader, BioTek®) at 254 nm for each aliquot, with cumulative release being calculated per gram of microcapsule powder. From the above results, the neem seed oil release transport mechanism was analyzed and found to conform to the Ritger–Peppas model (Korsmeyer & Peppas, 1981; Kumbar, Kulkarni, & Dave, 2001; Riyajan & Sakdapipanich, 2009b), as expressed in Eq. (2) below;

2.3. Fabrication of microcapsules via spray drying The prepared emulsions were spray dried (SDE-50 EURO, Euro Best Technology Co., Ltd., Thailand) with the emulsion being pump fed into the dryer prior to being atomized in the drying chamber. Evaporation of liquid from the sample droplets occurred on contact with the drying air. The feed flow rate was fixed at 50 L/h, with the inlet drying air temperature used for dry which PVA and GA were 175 °C and WPI/MD was 120 °C, with an outlet drying air temperature of PVA, GA and WPI/MD were 90 °C the method was followed by (Kim et al., 2013). The obtained spray dried powders were kept in sealed bags prior to further study.

Where Mt is the cumulative neem seed oil release at release time t, M∞ is the cumulative release at an infinite time, k is the release rate constant, and n is the release exponent. A value of n < 0.43 is characteristic of Fickian diffusion, n = 1.0 corresponds to case II diffusion, and 0.43 < n < 0.85 is indicative of non-Fickian release (Maderuelo, Zarzuelo, & Lanao, 2011; Siepmann & Peppas, 2001).

2.4. Determination of encapsulation efficiency

2.6. Characterization of microcapsules

The amount of surface oil (non-encapsulated neem seed oil) in spray dried powders was quantified following the method proposed by Calvo, Hernández, and Lozano (2010), with some modifications (Calvo et al., 2010). To extract the free oil, microcapsule powder (4 g) was dispersed in 25 mL of hexane and homogenized at 100 rpm for 5 min at 39 °C. After filtering the suspension (Whatman No.1 filter paper) the filtrate

2.6.1. Scanning electron microscopy The morphologies of core-shell materials were investigated using FE-SEM (Hitachi, S-4800) at an acceleration voltage of 2 kV. Prior to investigation, samples were stored in desiccators to limit the effects of humidity. Each sample was placed on carbon tape, and then sputtered with gold particles before visualization.

Mt = kt n M∞

(2)

2.6.2. Zeta potential Zeta potential measurements of core-shell materials were undertaken using a dynamic light scattering system operating in the particle analyzer. All measurements utilized suspensions prepared in DI water as a dispersion medium. 2.6.3. UV–vis spectrophotometry A UV–vis spectrophotometer (Synergy H1 microplate reader, BioTek®) equipped with a transmittance accessory was used to record the electronic spectra of samples over a wavelength range of 200–1000 nm. 2.6.4. FTIR spectroscopy ATR-FTIR measurements were performed using a Perkin Elmer USA spectrophotometer. All FTIR absorption spectra were recorded in the

Fig. 1. Schematic diagram depicting formation of neem seed oil loaded microcapsules. 132

Food Packaging and Shelf Life 18 (2018) 131–139

K. Sittipummongkol, C. Pechyen

650 cm−1–4000 cm−1 range at a resolution of ± 4 cm−1, over 32 scans.

3.2. Zeta-potential measurements

2.6.5. Thermogravimetric analysis (TGA) Thermal properties of the microencapsulated samples and shell materials were analyzed using thermo gravimetric analysis (NETZSCH TG 209F3 TGA209F3-0364-L), with thermograms being obtained from 30 °C to 700 °C at a heating rate of 5 °C/min.

Zeta-potential measurements are useful in providing an indication of particle, or colloidal, stability. Highly negative, or highly positive zeta-potentials are indicative of well stabilized particle systems, whereas values close to zero reflect lower stability towards aggregation. Normally, for particles to be stable in water zeta potential values of above +30 or below −30 mV are required (Choi, Ryu, Kwak, & Ko, 2010). Table 1 displays the zeta potential values of neem seed oil loaded microcapsules. Notably, the zeta-potential values of the obtained microcapsules are strongly negative (below −30 mV in all cases) implying that the microcapsules form stable aqueous dispersions. These data are in agreement with the FTIR results, which suggest that the presence of surface hydroxyl groups reflects hydrogen bonding of the microcapsules with water, and are responsible for the negative surface charges.

2.7. Statistical analysis Data were expressed as the mean ± standard deviation (SD). Data were analyzed using one way analysis of variance (ANOVA), followed by independent-sample t-test (SPSS 19.0, Chicago, U.S.A.). A p value < 0.05 was considered as statistically significant. 3. Results and discussion

3.3. SEM analysis and particle size 3.1. ATR-FTIR spectroscopy The morphologies of neem seed oil loaded PVA, GA and WPI/MD microcapsules are displayed in Fig. 4. All particles are roughly spherical in shape although variations in size are evident. When comparing the surfaces of the microcapsules, those having WPI/MD as a shell material appear roughest while those based on PVA exhibit the smoothest surface texture. The roughness of the WPI/MD surfaces might be due to their tendencies to absorb polar moieties (Hundre et al., 2015). Surface defects, including pores and bumps found in the shells made from GA and WPI/MD, were probably a result of uneven drying (Klinkesorn, Sophanodora, & Chinachoti, 2006) and fast evaporation of liquid from the microcapsule emulsion during the spray drying process (Al-Ismail, El-Dijani, & Al-Khatib, 2016). Surface pores may also originate from uneven shrinkage during the last stage of drying (Buma, 1971). The average sizes of neem seed oil loaded PVA, neem seed oil loaded GA, and neem seed oil loaded WPI/MD particles were 28.84 ± 11.86, 32.43 ± 13.06, and 52.88 ± 17.33 μm, respectively. All microcapsule types showed a broad size distribution. This phenomenon is governed by the centrifugal force of the homogenizer, such that at distances further from the center larger microcapsules are generated because of smaller forces being exerted on the oil droplets (Bagle, Jadhav, & Gite, 2013). The greater average diameter of neem seed oil loaded WPI/MD relative to other microcapsules may be a result of weak core-shell interactions, as neem seed oil is hydrophobic while the WPI/MD shell surface is appreciably hydrophilic due to the presence of polar protein/ carbohydrate moieties (Fig. 5).

The release of neem seed oil from a matrix-type delivery system may be controlled by diffusion, erosion or a combination of both. Homogeneous and heterogeneous erosion are both detectable. Heterogeneous erosion occurs when degradation is confined to a thin layer at the surface of the delivery system, whereas homogenous erosion is a result of degradation occurring at a uniform rate throughout the polymer matrix (Fig. 2). Infrared spectroscopy confirmed the presence of the core, and the shell components of each of the prepared microcapsules. Fig. 3 highlights ATR-FTIR spectra of neem seed oil encapsulated in three different polymeric shells. Comparison between the spectra of each chemical composition and the corresponding microcapsule were made clear using dashed lines. The ATR-FTIR spectra of neem seed oil show characteristic peaks at 2853 cm−1 (CeH stretching), 1744 cm−1 (C]O stretching), 1239 cm−1 (CeO stretching), and 721 cm−1 (CeH Bending) (Devi & Maji, 2009a). Peaks attributable to PVA appear at 3308 cm−1 (OeH stretching), 2911 cm−1 (CeH stretching) and 1733 cm−1 (C]O stretching) (Sullad, Manjeshwar, & Aminabhavi, 2010). Other peaks at 3287 cm−1 (OeH stretching), 2911 cm−1 (CeH stretching) and 1599 cm−1 (C]O stretching) due to GA (Nayak, Das, & Maji, 2012), 3275 cm−1 (NeH stretching), 2927 cm−1 (CeH stretching) and 1630 cm−1 (C]O stretching) from WPI (Hundre, Karthik, & Anandharamakrishnan, 2015) and 3308 cm−1 (OeH stretching), 2926 cm−1 (CeH stretching) and 1642 cm−1 (C]O stretching) from MD, are also evident. In all cases, the neem seed oil loaded microcapsules showed characteristic peaks for both shell, and core components. Enlargement of OeH stretching peak at about 3300 cm−1 of the microcapsules might be ascribed to heat-induced oxidation of the shell material during the spray-drying process.

3.4. Neem seed oil encapsulation efficiency Spray-dried microcapsules were obtained from emulsions containing a 1:2 mass ratio of neem seed oil to polymeric shell material.

Fig. 2. Schematic representation of the controlled release system (a) neem seed oil loaded microcapsule (b) diffusion of water into microcapsules (c) release of neem seed oil from the partly dissolved microcapsule shell. 133

Food Packaging and Shelf Life 18 (2018) 131–139

K. Sittipummongkol, C. Pechyen

Fig. 3. ATR- FTIR spectra of a.1 Neem seed oil, a.2 PVA shell, a.3 Neem seed oil loaded- PVA microcapsules, b.1 Neem seed oil, b.2 GA shell, b.3 Neem seed oil loaded-GA microcapsules, c.1 Neem seed oil, c.2 WPI shell, c.3 MD shell, c.4 Neem seed oil loaded- WPI/MD microcapsules.

Fig. 4. SEM micrographs of neem seed oil encapsulated by (a) PVA; (b) GA; and (c) WPI/MD.

Table 1 Particle size, zeta potential of encapsulation material and Encapsulation Efficiency (%EE). Polymer:oil

Ratio

Size (μm)*

Zeta potential (mV)*

%EE*

PVA:Neem seed oil GA:Neem seed oil WPI/MD:Neem seed oil

2:1 2:1 2:1

28.84 ± 11.86ab 32.43 ± 13.06ab 52.88 ± 17.33ac

−39.9 ± 5.5bc −36.8 ± 3.1ac −52.0 ± 9.5ad

92.94 ± 3.87ab 89.59 ± 1.45ab 60.70 ± 2.73bc

* Scores presented as mean ± standard error. A–d: different latters indicates significant different materials (P < 0.05). 134

Food Packaging and Shelf Life 18 (2018) 131–139

K. Sittipummongkol, C. Pechyen

Fig. 5. Schematic diagram of neem seed oil encapsulated with (a) PVA; (b) GA; and (c) WPI/MD.

135

Food Packaging and Shelf Life 18 (2018) 131–139

K. Sittipummongkol, C. Pechyen

Table 2 Values of kinetic parameter for releasing mechanism of neem seed oil from neem seed oil-encapsulated microcapsules. Shell materials

Range min

n

k min−1

r2

PVA GA WPI/MD

10−360 10−360 10−360

0.1917 0.2776 0.2349

2.6113 2.2874 2.5826

0.9711 0.9732 0.9723

in chitosan nanoparticles (Hosseini, Zandi, & Rezaei, 2013). At any given submersion time point, the cumulative amount of neem seed oil released from WPI/MD capsules was higher than that of GA, and PVA capsules, with the greater affinity of neem seed oil with PVA being a likely explanation for the higher retention level. Moreover, the presence of pores and cracks on the microcapsule surfaces may facilitate solvent diffusion into the microcapsules, resulting in enhanced oil release rates (Moreau & Rosenberg, 1993). On the other hand, smooth microcapsule surfaces proved beneficial in preventing oil loss (Hwang, Kim, & Wee, 2006), as the absence of cracks retards permeation of solvent into the core (Barros Fernandes, Borges, & Botrel, 2014). These previous findings are consistent with the observations reported here, and provide an explanation for the order (WPI/MD > GA > PVA) of release rates of neem seed oil from microcapsules comprised of different polymeric shells. The kinetics describing the release behavior of neem seed oil from microcapsules were consistent with the Ritger–Peppas model, for the first 60% of release data (Chime & Onunkwo, 2013). The release of neem seed oil from the microcapsules can be calculated by plotting ln (Mt/M) versus ln t, affording a linear relationship. Table 2 summarizes kinetic parameters for the cumulative release of neem seed oil from PVA, GA, and WPI/MD capsules. From these, the R2 values of neem seed oil encapsulated by PVA, and those encapsulated by GA and WPI/ MD reflect this linearity. The release mechanism can be elucidated from the n values, which represent the release exponent. The diffusion exponent values of neem seed oil loaded PVA, neem seed oil loaded GA, and neem seed oil loaded WPI/MD (0.1917, 0.2776, and 0.2349, respectively) indicated that release occurred via Fickian diffusion, the molecular diffusion of neem seed oil due to a chemical potential gradient. Polymer shells are partially solubilized in water at 30 °C due to the presence of surface hydroxyl (PVA, GA, WPI/MD), and amino groups (WPI). Over time, the loss of structural integrity allows for oil egress via diffusion under the influence of a chemical potential gradient (Singhvi & Singh, 2011).

Fig. 6. In vitro release of neem seed oil from PVA, GA and WPI/MD microcapsules.

The encapsulation efficiency (% EE, Table 1), as calculated using Eq. (1), was found to be 92.94 ± 3.81, 89.59 ± 1.45, and 60.70 ± 2.73% for microcapsules composed of PVA, GA, and WPI/MD shells, respectively. These results are consistent with past studies highlighting the influence of shell material type on encapsulation efficiency (Porras-Saavedra, Palacios-González, & Lartundo-Rojas, 2015; Turchiuli, Munguia, & Sanchez, 2014). The calculated %EE values show an inverse correlation to capsule size, with smaller microcapsules (PVA, GA) likely exhibiting stronger interactions between the shell component and the oil core. Employing PVA as a shell material resulted in the smallest capsules; these also exhibit the highest %EE values. GA and WPI/MD, having an abundance of polar groups on their peripheries, are more hydrophilic and accordingly may associate more weakly with the hydrophobic oil component than PVA. This factor may account for the lower %EE of these capsules, and rationalize their larger average sizes as indicated by SEM imaging (Buma, 1971; Tan, Chan, & Heng, 2005).

3.5. In vitro release studies of neem seed oil from microcapsules The in vitro release profiles of neem seed oil from PVA, GA and WPI/ MD microcapsules are shown in Fig. 6, and depend on the shell material, morphology, and the degree of microcapsule solubility. From these results, cumulative release can be expressed as two distinct stages. The initial 500 min are defined by a burst release phase, where quantities of neem seed oil released were approximately 40, 50, and 58% of the total for microcapsules derived from PVA, GA, and WPI/MD, respectively. During this stage, release of neem seed oil occurred via diffusion through the microcapsule walls. The subsequent stage (up to 4320 min) is defined by more gradual release, accounting for approximately 50, 65%, and 79% of the total for PVA, GA, and WPI/MD capsules, respectively. Initial burst release originates from leaching of neem seed oil located near the capsule walls. As no crosslinking exists between polymer chains comprising the shell, the shell dissolution rate is very fast and the oil in close proximity to the wall could quickly diffuse out (Forim & Costa, 2013; Riyajan & Sakdapipanich, 2009a). The droplet forming ability of core compounds is determined by its interfacial tension in Tween 80-water. Droplet formation controls microstructure in microencapsulation. Shell structures on hydrophilic surfaces were considered to have intermediate interfacial tension leading to stable droplet forming ability in DI water. With decreased hydrophobicity in DI water, the shell structures with comparably higher hydrophobicity transformed from spheres to connected and fused spheres because of increased interfacial tension that lowers droplet stability. More hydrophobic compounds did not form droplets in DI water. The results herein are similar to those documented for encapsulated oregano essential oil

3.6. Thermal properties of neem seed oil encapsulated within PVA, GA and WPI/MD capsules The TGA thermograms of neem seed oil loaded microcapsules (PVA, GA and WPI/MD) are shown in Fig. 7. TGA analysis of the polymers showed that degradation takes place in three steps for PVA (Fig. 7a), and in four well-differentiated steps for GA, and mixed WPI/MD (Fig. 7b and c). Initial weight loss due to moisture content occurs between 50–100 °C for all shell polymer types. PVA and neem seed oil loaded PVA microcapsules exhibited around 20% weight loss at 300 °C and 305 °C, respectively, and 50% weight loss at 343 °C, and 361 °C, respectively. WPI/MD and GA capsules contain higher initial moisture contents compared to PVA capsules; this affinity for water can be attributed to the greater number of hydrogen bonding carboxyl (in polysaccharides and oligosaccharide) groups making up these polymers (Felix, Birchal, & Botrel, 2017). The TGA thermogram for PVA (Fig. 7a) exhibits three mass loss zones which correspond to the degradation of polymer components. After water loss, polymer decomposition occurred starting at 315 °C (reflecting about 60% mass loss), arising from decomposition of side chains in the PVA structure. The second smaller step at 420 °C can be attributed to degradation of the PVA backbone. At 136

Food Packaging and Shelf Life 18 (2018) 131–139

K. Sittipummongkol, C. Pechyen

Fig. 7. TGA thermograms of encapsulated neem seed oil within different polymer shells (a) PVA; (b) GA; and (c) WPI/MD (left : Weight loss (%), right : Derivative weight (%/min)).

255, 264, 246 and 257 °C, respectively, and 50% at 301, 325, 319 and 334 °C, respectively. The third phase of degradation from 370 °C to 420 °C, representing an average weight loss of 30 ± 2%, relates to the degradation of the remaining components. At 700 °C (experiment end) the samples had lost approximately four-fifths of the initial mass, resulting in a residual mass of about 20 ± 3%. This high thermal stability, with resultant high solid residue content, may be due to the complex and heterogeneous polysaccharide structure in these polymer

700 °C, the remaining residue accounts for approximately 29.5% of the initial mass (Kumar, Koltypin, & Cohen, 2000). In the GA and WPI/MD thermograms (Fig. 7b and c) the weight remains constant until polysaccharide decomposition commences (around 210 °C), which continues until 300 °C with a weight loss of ∼45%. Slowly, a progressive carbonized structure was formed as the temperature increased further and GA, neem seed oil loaded GA microcapsules, WPI/MD, and neem seed oil loaded WPI/MD microcapsules weight loss values were 20% at 137

Food Packaging and Shelf Life 18 (2018) 131–139

K. Sittipummongkol, C. Pechyen

shell materials. Comparing the TGA thermograms of the shell polymers in their pristine forms with those of the microcapsules allows the effects of neem seed oil on the thermal stability of the polymeric shells to be understood. Interestingly, once incorporated in the microcapsules, the shell polymers exhibited a slower thermal decomposition than their pristine forms. Devi and co-workers (Pal et al., 2007) demonstrated that pure neem seed oil displayed a weight loss of 20% and 50% at 315 °C and 375 °C, respectively, indicating that neem seed oil itself shows better thermal stability than all shell materials used in this work. When fabricated into the core-shell structure, the oil component slightly enhanced the thermal stability of the polymeric shell materials.

Biological and Chemical Sciences, 4, 97–103. Choi, K. O., Ryu, J., Kwak, H. S., & Ko, S. (2010). Spray-dried conjugated linoleic acid encapsulated with Maillard reaction products of whey proteins and maltodextrin. Food Science and Biotechnology, 19, 957–965. Dayan, F. E., Cantrell, C. L., & Duke, S. O. (2009). Natural products in crop protection. Bioorganic & Medicinal Chemistry, 17, 4022–4034. Devi, N., & Maji, T. K. (2009a). Effect of crosslinking agent on neem (Azadirachta indica A. Juss.) seed oil (NSO) encapsulated microcapsules of κ-carrageenan and chitosan polyelectrolyte complex. Journal of Macromolecular Science Part A Pure and Applied Chemistry, 46, 1114–1121. Devi, N., & Maji, T. K. (2009b). A novel microencapsulation of neem (Azadirachta indica A. Juss.) seed oil (NSO) in polyelectrolyte complex of κ‐carrageenan and chitosan. Journal of Applied Polymer Science, 113, 1576–1583. Felix, P. H., Birchal, V. S., & Botrel, D. A. (2017). Physicochemical and thermal stability of microcapsules of cinnamon essential oil by spray drying. Journal of Food Processing and Preservation, 41, 1–9. Forim, M. R., & Costa, E. S. (2013). Development of a new method to prepare nano-/ microcapsules loaded with extracts of Azadirachta indica, their characterization and use in controlling Plutella xylostella. Journal of Agricultural and Food Chemistry, 61, 9131–9139. Geiger, F., Bengtsson, J., & Berendse, F. (2010). Persistent negative effects of pesticides on biodiversity and biological control potential on European farmland. Basic and Applied Ecology, 11, 97–105. Hosseini, S. F., Zandi, M., & Rezaei, M. (2013). Two-step method for encapsulation of oregano essential oil in chitosan nanoparticles: Preparation, characterization and in vitro release study. Carbohydrate Polymers, 95, 50–56. Hundre, S. Y., Karthik, P., & Anandharamakrishnan, C. (2015). Effect of whey protein isolate and β-cyclodextrin wall systems on stability of microencapsulated vanillin by spray–freeze drying method. Food Chemistry, 174, 16–24. Hwang, J. S., Kim, J. N., & Wee, Y. J. (2006). Preparation and characterization of melamine-formaldehyde resin microcapsules containing fragrant oil. Biotechnology and Bioprocess Engineering: BBE, 11, 332–336. Kaasgaard, T., & Keller, D. (2005). Chitosan coating improves retention and redispersibility of freeze-dried flavor oil emulsions. Journal of Agricultural and Food Chemistry, 58, 2446–2454. Kari, T., Isa, L., Marleena, H., Heikki, S., & Dionyssios, P. (2011). In M. Stoytcheva (Ed.). Use of botanical pesticides in modern plant protection, pesticides in the modern world pesticides use and managementInTech (Chapter 12). Kim, Y. D., & Morr, C. V. (1996). Microencapsulation properties of gum arabic and several food proteins: Spray-dried orange oil emulsion particles. Journal of Agricultural and Food Chemistry, 44, 1314–1320. Kim, I. H., Han, J., Na, J. H., Chang, P. S., Chung, M. S., Park, K. H., et al. (2013). Insect‐resistant food packaging film development using cinnamon oil and microencapsulation technologies. Journal of Food Science, 78(2), E229–E237. Klinkesorn, U., Sophanodora, P., & Chinachoti, P. (2006). Characterization of spray-dried tuna oil emulsified in two-layered interfacial membranes prepared using electrostatic layer-by-layer deposition. Food Research International, 39, 449–457. Koç, M., Güngör, Ö., & Zungur, A. (2015). Microencapsulation of extra virgin olive oil by spray drying: Effect of wall materials composition, process conditions, and emulsification method. Food and Bioprocess Technology, 8, 301–318. Korsmeyer, R. W., & Peppas, N. A. (1981). Effect of the morphology of hydrophilic polymeric matrices on the diffusion and release of water soluble drugs. Journal of Membrane Science, 9, 211–227. Krishnan, S., Kshirsagar, A. C., & Singhal, R. S. (2005). The use of gum arabic and modified starch in the microencapsulation of a food flavoring agent. Carbohydrate Polymers, 62, 309–315. Kumar, R. V., Koltypin, Y., & Cohen, Y. S. (2000). Preparation of amorphous magnetite nanoparticles embedded in polyvinyl alcohol using ultrasound radiation. Journal of Materials Chemistry B, 10, 1125–1129. Kumbar, S. G., Kulkarni, A. R., & Dave, A. M. (2001). Encapsulation efficiency and release kinetics of solid and liquid pesticides through urea formaldehyde crosslinked starch, guar gum, and starch guar gum matrices. Journal of Applied Polymer Science, 82, 2863–2866. Madene, A., Jacquot, M., & Scher, J. (2006). Flavour encapsulation and controlled release—a review. International Journal of Food Science & Technology, 41, 1–21. Maderuelo, C., Zarzuelo, A., & Lanao, J. M. (2011). Critical factors in the release of drugs from sustained release hydrophilic matrices. Journal of Controlled Release, 154, 12–19. Moreau, D. L., & Rosenberg, M. (1993). Microstructure and fat extractability in microcapsule based on whey proteins or mixtures of whey proteins and lactose. Food Structure, 12(6), 457–468. Nayak, A. K., Das, B., & Maji, R. (2012). Calcium alginate/gum arabic beads containing glibenclamide: Development and in vitro characterization. International Journal of Biological Macromolecules, 51, 1070–1078. Pal, K., Banthia, A. K., & Majumdar, D. K. (2007). Preparation and characterization of polyvinyl alcohol-gelatin hydrogel membranes for biomedical applications. AAPS PharmSciTech, 8, 142–146. Porras-Saavedra, J., Palacios-González, E., & Lartundo-Rojas, L. (2015). Microstructural properties and distribution of components in microcapsules obtained by spraydrying. Journal of Food Engineering, 152, 105–112. Riyajan, S. A., & Sakdapipanich, J. T. (2009a). Encapsulated neem extract containing Azadiractin-A within hydrolyzed poly (vinyl acetate) for controlling its release and photodegradation stability. Chemical Engineering Journal, 152, 591–597. Riyajan, S. A., & Sakdapipanich, J. T. (2009b). Development of a controlled release neem capsule with a sodium alginate matrix, crosslinked by glutaraldehyde and coated with natural rubber. Polymer Bulletin, 63, 609–622. Siepmann, J., & Peppas, N. A. (2001). Mathematical modeling of controlled drug delivery.

4. Conclusions Neem seed oil, a botanical insecticide, was successfully encapsulated within three different biopolymer shells, with spray drying affording core shell microcapsules. ATR-FTIR spectra of the neem seed oil loaded PVA, GA, and WPI/MD microcapsules confirmed the presence of both neem seed oil, and shell materials. Morphological investigations indicated that the obtained microcapsules were roughly spherical, with hydrophilic WPI/MD shell material affording the largest capsule sizes on average. The zeta potential values of all microcapsules were highly negative, implying good aqueous dispersion stability. Immersion studies in water indicated that, over time, partial shell dissolution occurred, allowing core leaching. The release characteristics of neem seed oil from all microcapsules showed two distinct stages, an initial stage corresponding to rapid release and a second, more gradual release profile. The kinetics of the release behavior obeyed the Ritger–Peppas model, with Fickian diffusion accounting for the release mechanism irrespective of the shell materials as confirmed by the diffusion exponent values. The ease of fabrication, biodegradability, and favorable release behavior of these microcapsules may drive their application in new areas related to organic farming, such as insect repellent coatings for plastic mulch, and in biodegradable insecticidal plant pots. Acknowledgements The authors gratefully acknowledge financial support from the National Research Council of Thailand and the Plastics Institute of Thailand. We also acknowledge the Laboratory of Organic Synthesis, Chulabhorn Research Institute and the center for advanced studies in Materials and Packaging TU, Faculty of Science and Technology, Thammasat University. References Al-Ismail, K., El-Dijani, L., & Al-Khatib, H. (2016). Effect of microencapsulation of vitamin C with gum arabic, whey protein isolate and some blends on its stability. Journal of Scientific and Industrial Research, 75(3), 176–180. Bachtsi, A. R., & Kiparissides, C. (1996). Synthesis and release studies of oil-containing poly(vinyl alcohol) microcapsules prepared by coacervation. Journal of Controlled Release, 38, 49–58. Bagle, A. V., Jadhav, R. S., & Gite, V. V. (2013). Controlled release study of phenol formaldehyde microcapsules containing neem oil as an insecticide. International Journal of Polymeric Materials, 62, 421–425. Barros Fernandes, R. V., Borges, S. V., & Botrel, D. A. (2014). Gum arabic/starch/maltodextrin/inulin as wall materials on the microencapsulation of rosemary essential oil. Carbohydrate Polymers, 101, 524–532. Buma, T. J. (1971). Free fat in spray-dried whole milk. 8. The relation between free-fat content and particle porosity of spray-dried whole milk. (Accessed 30 March 2018) http://agris. fao.org/agris-search/search.do;jsessionid= D40DCC1E593F394A8636E92FF2EAA012?request_locale=es&recordID= US201302396506&sourceQuery=&query=&sortField=&sortOrder=& agrovocString=&advQuery=¢erString=&enableField=/. Calvo, P., Hernández, T., & Lozano, M. (2010). Microencapsulation of extra‐virgin olive oil by spray‐drying: Influence of wall material and olive quality. European Journal of Lipid Science and Technology: EJLST, 112, 852–858. Chime, S. A., & Onunkwo, G. C. (2013). Kinetics and mechanisms of drug release from swellable and non swellable matrices: A review. Research Journal of Pharmaceutical

138

Food Packaging and Shelf Life 18 (2018) 131–139

K. Sittipummongkol, C. Pechyen

Tan, L. H., Chan, L. W., & Heng, P. W. (2005). Effect of oil loading on microspheres produced by spray drying. Journal of Microencapsulation, 22, 253–259. Turchiuli, C., Munguia, M. J., & Sanchez, M. H. (2014). Use of different supports for oil encapsulation in powder by spray drying. Advanced Powder Technology, 255, 103–108.

Advanced Drug Delivery Reviews, 48, 137–138. Singhvi, G., & Singh, M. (2011). Review: In-vitro drug release characterization models. International Journal of Pharmaceutical Sciences and Research, 2, 77–84. Sullad, A. G., Manjeshwar, L. S., & Aminabhavi, T. M. (2010). Controlled release of theophylline from interpenetrating blend microspheres of poly (vinyl alcohol) and methyl cellulose. Journal of Applied Polymer Science, 116, 1226–1235.

139