Encapsulation of Retinyl Palmitate with a Mixture of Cyclodextrins and Maltodextrins by the Kneading Method

Abstract

In this study, encapsulation of retinyl palmitate using the kneading method was investigated. The wall materials tested were mixtures of one of three naturally occurring cyclodextrins (CDs) and maltodextrin (MD) at low moisture content, and the MDs varied in their dextrose equivalent (DE) values. The retention and stability of retinyl palmitate encapsulated in a matrix prepared from a combination of α-CD and MD (DE = 11) were superior to those observed for all other combinations of CDs and MDs (DE = 17.5, 28, and47). The stabilities of the encapsulated retinyl palmitate fitted Avrami's equation. The rate constants of the MDs with low DE values were lower than those of MDs with high DE values. The degradation rate of the encapsulated retinyl palmitate depended on the MD content, possibly because high MD content suppressed oxygen diffusion into the wall material. In the α-CD/MD matrix, the MD content was a more important factor than the α-CD content for the stability of retinyl palmitate.

Introduction

Retinoids are natural and synthetic derivatives of vitamin A. The most common forms of vitamin A precursors present in food are retinol and retinyl esters, which are stored as esters of fatty acids, predominantly as retinyl palmitate (ester of retinol and palmitate) (Tanumihardjo, 2011). Retinoids are essential nutrients for animals, affecting lipid and protein metabolism and endocrine system regulation. The chemical stability of retinoids, including retinyl palmitate, is strongly dependent on chemical and environmental factors such as the solvent, temperature, and oxygen availability (Ji and Seo, 1999). The protection offered by dietary vitamin A has been well established (Loveday and Singh, 2008; Sauvant et al., 2012); thus, enhancing retinoid stability by encapsulation has been extensively investigated. Gonnet et al. (2010) reviewed new trends in the encapsulation of liposoluble vitamins, including the encapsulation of vitamin A in the food industry. Encapsulation is an important method for protecting unstable compounds from damage due to oxidation and other degradative processes (Gonnet et al., 2010). The materials used for the encapsulation of vitamin A have been classified according to the stability of the constructs, which include solid particles, molecular complexes, emulsions, and liposomes (Sauvant et al., 2012). Molecular complexes of retinoids with cyclodextrins (CDs), proteins, and chitosan have been well studied. Retinoid-CD complexes are usually prepared by mixing the retinoids with CD in an aqueous solution (Gonnet et al., 2010; Lin et al., 2007), but this is not an easy procedure. A γ-CD/retinol complex with the required composition is commercially available (Regiert, 2009); however, its synthesis requires vigorous stirring for 72h at 50°C under a N₂ atmosphere (Moldenhauer et al., 1999). Lin et al. (2000) improved complex solubility and stability using a method for the preparation of a 2-hydroxypropyl-β-CD (HP-β-CD)/all-trans-retinoic acid complex that involved shaking the suspension under ambient temperature (24°C) for 8 d. Furthermore, Yoshida et al. (1999) tested the stability of retinol in emulsions and found that after 4 weeks at 50°C in O/W, W/O, and O/W/O emulsions, the percentage of retinol remaining was 32.3%, 45.7%, and 56.9%, respectively. However, the emulsions contained only 0.1% retinol. Singh and Das (1998) studied the properties of retinol and retinyl palmitate intercalated in phosphatidylcholine liposomes. In general, spray-drying is commonly used to encapsulate food ingredients with solid particles (Gharsallaoui et al., 2007), and many encapsulated powders are manufactured by emulsification of substrates with surfactants in maltodextrin (MD) solutions and spray-drying the resulting mixtures. The efficacies of three different processes, namely, spray-drying, drum-drying, and freeze-drying, were studied and evaluated with reference to the retention of β-carotene. Pure β-carotene encapsulated with maltodextrin (dextrose equivalent [DE] value of 25) exhibited the least degradation upon freeze-drying (approximately 8%), followed by spray-drying (11%) and then drum-drying (14%) (Desobry et al., 1997). Complexation with cyclodextrins offers the following benefits: alteration of the solubility profile of the guest compound; stability against the effects of light, heat, and oxidation; masking of undesirable physiological effects; and reduction in volatility (Hedges, 1998). Hutin et al. (2004) investigated the process of CD complexation during kneading. Carbohydrate polymers are the most commonly used encapsulating material and are preferred over proteins and lipids. The encapsulating carbohydrates generally used, such as MD and gum arabic, belong to the polysaccharide category (Murugesan and Orsat, 2012). MDs are formed by the partial hydrolysis of starch with acids or enzymes, and are characterized in terms of DEs, where the DE value is a measure of the extent/ degree of starch hydrolysis. The matrices formed by MDs are important for encapsulation (Madene, 2006).

Kneading is an encapsulation method in which a homogenous paste of the excipient materials is prepared in a mixer or mortar with the addition of small quantities of water. This step is followed by the gradual addition of the guest material to the paste, with continuous kneading to attain a suitable consistency, followed by drying of the paste (Ghosh et al., 2011). Kneading is a typical processing step in the preparation of host-guest complexes containing CDs, and many elementary studies have described such methods for encapsulating the oils of flavoring agents. Furuta et al. (1994) performed encapsulation of the essential oil d-limonene by kneading it with CDs and MDs that have low moisture content. The complex-encapsulated profiles of selected volatiles were investigated after kneading for various periods, and no significant differences were found between the compositional properties of the resulting powdered complexes, which were obtained using a vacuum oven and different spray-drying methods (Bhandari et al., 1999). Asceno et al. (2011) investigated the complexation of tretinoin and dimethyl-β-CD using various inclusion methods such as coevaporation, freeze-drying, spray-drying, and kneading. Although kneading has been adequately studied in the food industry, to our knowledge, no research has been performed on kneading for the encapsulation of retinyl palmitate, and no studies have described the encapsulation of retinyl palmitate in a matrix prepared by combining CDs and MDs.

In this study, retinyl palmitate powder was encapsulated by kneading it with a matrix comprising CD and MD with low moisture content. We used three types of CDs (α, β, and γ) and MD components with various DE values as excipients in order to investigate their effect on the stability of retinyl palmitate.

Materials and Methods

Materials Retinyl palmitate (> 95.0%; no stabilizer) was purchased from Riken Vitamin Co., Ltd. (Tokyo, Japan). MDs were purchased from the following companies: MDs made from tapioca with DE values of 11 ± 1 and 18 ± 2 were obtained from Matsutani Chemical Industry Co., Ltd. (Hyogo, Japan); MD made from corn with a DE value of 28 ± 2 was obtained from Miekaryou Co., Ltd. (Mie, Japan); and MD made from corn with a DE value of 47 ± 3 was obtained from Nihon Shokuhin Kako Co., Ltd. (Tokyo, Japan). α-, β-, and γ-CD were purchased from Cyclochem Co., Ltd. (Tokyo, Japan). The chemicals used in the analysis were of analytical grade and were purchased from Wako Pure Chemical Industry, Ltd. (Osaka, Japan).

Preparation of CD and MD powders loaded with retinyl palmitate The slurries used to evaluate the influence of CD type and DE value of MD were composed of 12% retinyl palmitate, 59% MD, 14% CD, and 15% (w/w) water. Seventy grams of CDs and 295 g of MDs were moistened with 75 g of distilled water and mixed uniformly in the kneader (PMV-1H; Irie Shoukai Co., Ltd., Tokyo, Japan) for approximately 20 min. The mixture was preheated and maintained at a constant temperature of 50°C before adding retinyl palmitate in order to avoid solidification of the retinyl palmitate during kneading. After 60 g of retinyl palmitate was preheated and melted at 70°C, the kneader was spun at 68 rpm. For an accurate determination of the retinyl palmitate content with respect to kneading time, kneaded wet test samples were acquired at 0, 10, 20, 30, and 80 min and were immediately frozen. Subsequently, the samples were vacuum-dried (SVD-12S; ISUZU Seisakusho Co., Ltd., Niigata, Japan) at 40°C and 11 Pa for 24 h and then pulverized with a mortar and pestle to generate powdered samples, which were passed through a sieve (pore size, 212 μm) (Micro Vibro Sifter M-2; Tsutui Scientific Instruments Co., Ltd., Tokyo, Japan) and maintained at −30°C until used.

Stability test for powder-encapsulated retinyl palmitate The stability of retinyl palmitate in the powdered test samples was analyzed after preparing the samples as follows: kneaded wet mixture samples (after 80 min of kneading) were acquired and were immediately frozen. The samples were then vacuum-dried at 40°C and 11 Pa for 24 h and pulverized with a mortar and pestle. The resulting powdered samples were passed through a sieve (pore size, 212 μm) and were weighed into a vial. The vial was maintained at 60°C for a predefined time (d). The encapsulated retinyl palmitate content was quantified by weighing each of the powdered samples (5 mg) into vials and dissolving them in 0.5 mL of distilled water. The resulting solution was sonicated for 3 min, followed by the addition of 4 mL of ethanol and a further 3 min of sonication. After centrifuging the mixtures at 3000 rpm for 10 min, the supernatants were diluted 20-fold. The absorbance of the diluted supernatants was measured at 325 nm with a spectrophotometer (V-560; Jasco Corporation, Tokyo, Japan) and quantified by extrapolation on a linear calibration curve obtained previously using diluted retinyl palmitate samples.

Scanning electron microscopy (SEM) analysis of powders A scanning electron microscope (JSM 6060; JEOL Co., Ltd., Tokyo, Japan) was used to observe the morphological features of the powders at 400-fold magnification. The powders were placed on SEM stubs with double-sided adhesive tape (Nisshin EM Co., Ltd., Tokyo, Japan), and the specimens were coated with Pt-Pd using a Model MSP-1S magnetron sputter coater (Vacuum Device Inc., Tokyo, Japan). The coated samples were analyzed at an operational voltage of 20 kV.

Results and Discussion

Effects of CD type and DE value of MD on retinyl palmitate content in vacuum-dried powders The retinyl palmitate content in powders consisting of various ratios of CD and MD with different DE values was evaluated after kneading for various times (Fig. 1). As the kneading time increased, the content of retinyl palmitate in the powders tended to increase. After an 80-min kneading time, the amount of retinyl palmitate in powders consisting of MD (DE = 11) and α-, β-, and γ-CD was 0.120, 0.117, and 0.08 g/g powder, respectively. When MDs with DE values of 11 and 28 were used, the amount of retinyl palmitate in the powders containing γ-CD was less than 35% of that in the samples containing α-CD. Thus, α-CD was able to encapsulate retinyl palmitate, but γ-CD was not. The retinyl palmitate content appeared to be affected to a greater extent by the type of CD than by the DE value or kneading time. However, analysis of the powders containing α-CD showed that MDs with a lower DE value incorporated more retinyl palmitate into the powders than those with a higher DE value. This result indicates that the selection of MD as a matrix is appropriate for the encapsulation of retinyl palmitate. Here, the retinyl palmitate, CD, and MD content in kneading slurries was the same. MD with a low DE has a higher viscosity (Dokić P. L.et al., 2004); therefore, CD-MD mixtures containing MD with a low DE require high torque for kneading. Dokić et al. (2004) investigated the effect of the DE value of MD on the droplet size of sunflower oil emulsions. They reported that lower DE values favored the formation of smaller droplets because of higher continuous-phase viscosities. With respect to the kneading and vacuum-drying methods, these physical properties of the matrix may affect the encapsulation of oily compounds in the matrix wall materials, thereby affecting the encapsulation efficiency.

The effect of retinyl palmitate content in powders with different ratios of α-CD and MD (DE = 11) on the encapsulation rate is shown in Fig. 2, wherein the solid lines represent the calculated line using the following first order rate equation (1):   

where C (g/g powder) represents the retinyl palmitate content in the sample at time t_m (min), k (1/min) represents the encapsulation rate constant, and C₀ (g/g powder) represents the maximum content. The lines satisfactorily fitted the experimental results, indicating that the encapsulation time-courses were correlated by the first order reaction. The coefficients of determination (r2) ranged from 0.76 to 0.94. Neoh et al. (2006) investigated the encapsulation behavior for carbon dioxide encapsulation into α-CD and estimated the encapsulation characteristics using the first-order reaction equation. The parameter k values calculated by equation (1) for the different compositions of α-CD and MD (DE = 11) are listed in Table 1. Unexpectedly, the content of retinyl palmitate did not increase at a higher ratio of CD to retinyl palmitate; the k value was highest at the lowest CD to retinyl palmitate ratio. These results suggest that the encapsulation rate may depend on the concentration of MD in the powder.

Fig. 1.

Effect of the type of CD and MD (DE value) on retinyl palmitate content during kneading. ●, DE = 11; Δ, DE = 17.5; ■, DE = 28; and ◊, DE = 47. (a) α-CD; and (b) β;-CD (DE = 11 and 17.5) and γ-CD (DE = 28).

Fig. 2.

Effect of kneading time on retinyl palmitate content during kneading. The molar ratios of α-CD to retinyl palmitate used were ●, 0.32; Δ, 0.64; ▲, 0.96; and □, 1.26.

Duchene et al. (1999) studied the loading of steroids into isobutyl cyanoacrylate nanoparticles with HP-β-CD and found that the loading capacity of the nanoparticles increased in the presence of HP-β-CD. The authors suggested that lipophilic drugs cannot be dissolved in sufficient concentrations in the polymerization medium. Furthermore, they proposed that the loading depends on the drug dissolved in the polymerization medium and the partition coefficient of the drug between the polymer and medium. The authors concluded that CD can increase the loading capacity of carriers (Duchene et al., 1999). Trichard et al. (2007) reported the construction of minispheres made of α-CD/oil for the encapsulation of isotretinoin. Notably, even though isotretinoin does not fit within the α-CD cavity, the encapsulation efficiency was found to be particularly high (93% ± 7%), and 0.35% isotretinoin exhibited good stability in the minispheres for at least 4 months. The protection extended by α-CD/oil beads is not due to the formation of an inclusion complex (Trichard et al., 2007). Moreover, carbohydrates cannot be used as wall materials in the absence of a surface-active wall constituent because they generally have no emulsification properties (Bangs and Reineccius, 1988). Thus, the results of the present study indicate that the role of CD presumably lies in changing the partition coefficient of retinyl palmitate and that CD may act as an emulsifier in the MD slurry. Furthermore, the inclusion complex formed by retinyl palmitate into α-CD might not strongly stabilize the retinyl palmitate in the MD-CD mixture during kneading.

Observation of the surfaces of powders containing α-CD and MDs with different DE values The structures of powders made from α-CD and MDs with DEs of 11, 17.5, and 28 were observed by SEM (Fig. 3). The surfaces of the powders made from MDs with a higher DE value were more shattered and rougher than those made from MDs with a lower DE value. It appears that powders containing MDs with a higher DE value are more fragile than those containing MDs with a lower DE value. Desobry et al. (1999) reported the addition of mono- and disaccharides to MDs to reduce the pore size in the MD network and limit oxygen diffusion. Using this method, β-carotene was better retained in a matrix having MD (DE = 25), which consisted of MD (DE = 4) with glucose, than MD (DE = 4) alone (Desobry et al., 1999). Moreau and Rosenberg (1996, 1998) reported that the permeability of the wall matrix to oxygen is affected by porosity and the oxidative stability of the core material. Our results corroborate that the structure of the powders may affect the oxidative stability of encapsulated retinyl palmitate.

Influence of the type of CD and DE value of MD on the stability of retinyl palmitate in vacuum-dried powders The stability profiles of retinyl palmitate in powders containing α-, β-, or γ-CDs and MDs with DEs of 11, 17.5, or 28 at 60°C showed that a mixture of α-CD and MD exhibited greater stability than mixtures containing β- or γ-CD (Fig. 4). Further, MDs with a lower DE value stabilized the encapsulated retinyl palmitate more effectively than those with a higher DE value, which suggests that the content and stability of retinyl palmitate in the powder containing a mixture of α-CD and MD were higher than those containing β- and γ-CD. These results do not concur with those obtained for the interaction of retinoid with CDs reported previously. Yap et al. (2005) reported that HP-β-CD was more effective than α-CD in increasing the aqueous solubility of 13-cis-retinoic acid. Moldenhauer et al.(1999) demonstrated that the stabilizing effect on retinol was clearly more pronounced for the γ-CD complex than for β-CD. Our results suggest that the properties of retinyl palmitate encapsulated in mixtures of CD and MD by the kneading method were different from those observed using other methods.

Table 1. Slurry composition and encapsulation rate (k) for the kneading experiments.

	Slurry composition (%)
α-CD retinyl palmitate(molar ratio)	Retinyl palmitate	α-CD	MD (DE= 11)	Water	k (1/min)
	0.32	12	7	66		15	0.49
0.64	12	14	59	15	0.43
0.96	12	28	45	15	0.31
1.26	12	42	31	15	0.13

Fig. 3.

Scanning electron microscopy (SEM) images of samples prepared from α-CDs and MDs with different DE values. (a) DE = 11, (b) DE = 17.5, (c) DE = 28.

Fig. 4.

Effect of the type of CD and MD (DE value) on the stability of retinyl palmitate encapsulated in the powder at 60°C. ●, DE = 11; Δ, DE = 17.5; and ■, DE = 28. (a) α-CD; and (b) β-CD (DE = 11 and 17.5) and γ-CD (DE = 28).

The stability profiles of retinyl palmitate for various ratios of α-CD and MD (DE = 11) at 60° suggest that the powder containing a 0.32 molar ratio of α-CD to retinyl palmitate had the highest stability (Fig. 5). At 14 d, the retinyl palmitate content decreased with an increase in the molar ratio of α-CD to retinyl palmitate, which suggests that the MD in the wall matrix is more effective at protecting retinyl palmitate from heat degradation than the inclusion complex formed from CD and retinyl palmitate.

Fig. 5.

Stability of retinyl palmitate in the kneaded powder at 60 °C. The molar ratios of α-CD/retinyl palmitate are ●, 0.32; Δ, 0.64; ▲, 0.96; and , 1.26.

Wagner and Warthesen (1995) reported that hydrolyzed starch with a DE value of 36.5 was superior to hydrolyzed starch with DE values of 4, 15, or 25 for improving the retention of α- and β-carotene in spray-dried encapsulated carrot powder during storage. On the other hand, Bangs and Reineccius (1981) reported that increasing the DE value of MD decreased the retention of the volatiles during spray-drying. MDs with a lower DE have lower oxygen diffusion coefficients than MDs with a higher DE. Our results suggest that the stability of retinyl palmitate may depend on the diffusion coefficient of oxygen.

The solid lines in Figs. 4 and 5 represent the calculated lines using Avrami's equation (2):   

where R (−) represents the retention of retinyl palmitate in the samples with various CD/retinyl palmitate molar ratios at time t_d (d), A (1/d) is the apparent rate constant, and n (−) is a parameter indicating the stability mechanism. Avrami's equation is applicable to the determination of the flavor release rate for flavor/CD complexes. The parameter n relates to the release mechanism and when n < 1, the molecular diffusion of flavor is rate-limited (Yoshii et al., 2001). The value of n was determined to be 0.6, which indicates that the stability of retinyl palmitate in the powders fitted satisfactorily to Avrami's equation. The stability of retinyl palmitate was assumed to be controlled almost completely by the molecular diffusion of oxygen. The degradation rate constant A values for differing ratios of CDs and MDs to retinyl palmitate are listed in Table 2. The rate constant A increased with an increasing molar ratio of α-CD to retinyl palmitate, and with increasing DE values of MD. The rate constant A in the powders containing α-CD and MD (DE = 11) was found to be lower than those in the powders containing β- and γ-CD. Yoshii et al. (2001) reported that the retention of emulsified ethyl butyrate during spray was dependent on the concentration of MD. The suppression of oxygen diffusion by MD might enhance the protection of retinyl palmitate.

Table 2. Apparent rate constant A calculated according to Avrami' equation for different ratios of CD to retinyl palmitate.

α-CD/Retinyl palmitate (molar ratio)	CD	MD (DE)	A × 103(1/d)
0.32	α-CD	11	8.0
0.64	α-CD	11	9.4
0.96	α-CD	11	19.3
1.28	α-CD	11	73.2
0.64	α-CD	17.5	10.3
0.64	α-CD	28	47.4
0.64	β-CD	11	39.2
0.64	β-CD	17.5	28.1
0.64	γ-CD	11	318.0

Conclusion

The results of this study indicate that for retinyl palmitate, α-CD and MD with low DE values can provide effective protection at a practical concentration when encapsulated by the kneading method in the food industry. Furthermore, the kneading method generates porous particles with superior solubility and produces large particles more easily than the spray-drying method. In this study, the stabilization of retinyl palmitate improved with a decreasing molar ratio of CD to retinyl palmitate. The stability of retinyl palmitate is affected by molecular diffusion. We infer that MD with a low DE value has an effect on the structure of the powders because it affects their solidness, thus suppressing the diffusion of oxygen to a greater extent than when the DE value is low. Furthermore, the amount of MD also influenced the suppression of diffusion. Our results also suggest that α-CD improves the dispersion of retinyl palmitate into the MD matrix, although α-CD cannot easily form inclusion complexes with retinyl palmitate. Moreover, our results are also applicable to solid powders of encapsulated materials, which do not fit into the cavities of CDs.

References

•  Ascenso  A.  Guedes  R.,  Bernardino  R.,  Diogo  H.,  Carvalho  FA.,  Santos  NC.,  Silva  AM., and  Marques  HC. (2011). Complexation and full characterization of the tretinoin and dimethyl-β-cyclodextrin complex. AAPS PharmSciTech, 12, 553-563.
•  Bangs  W. E. and  Reineccius  G. A. (1981). Influence of dryer infeed matrices on the retention of volatile flavor compounds during spray drying. J. Food Sci., 47, 254-259.
•  Bangs  W. E. and  Reineccius  G. A. (1988). Corn starch derivatives: possible wall materials for spray-dried flavor manufacture. In “Flavor encapsulation”, ed. by Reineccius G. A. and Risch S. J., Am. Chem. Soc., Washington, pp. 12-28.
•  Bhandari  B. R.,  D'Arcy  B. R., and  Padukka  I. (1999). Encapsulation of lemon oil by paste method using β-cyclodextrin. J. Agric. Food Chem., 47, 5194-5197.
•  Desobry  S. A.,  Netto  F. M., and  Labuza  T. P. (1997). Comparison of spray-drying, drum-drying and freeze-drying for β-carotene encapsulation and preservation. J. Food Sci., 62, 1158-1162.
•  Desobry  S. A.,  Netto  F. M., and  Labuza  T. P. (1999). Influence of maltodextrin systems at an equivalent 25DE on encapsulated β-carotene loss during storage. J. Food Process. Preserv., 23, 39-55.
•  Dokić  P. L.,  Jakovljevic  J., and  Dokić  P. P. (2004). Relation between viscous characteristics and dextrose equivalent of maltodextrins. Starch, 56, 520-525.
•  Dokić  P. P.,  Dokić  P. L.,  Sovilj  V. J., and  Katona  J. M. (2004). Influence of maltodextrin dextrose equivalent value on rheological and dispersion properties of sunflower oil in water emulsions. Acta Periodica Technol., 35, 17-24.
•  Duchêne  D.,  Ponchel  G., and  Wouessidjewe  D. (1999). Cyclodextrins in targeting application to nanoparticles. Adv. Drug Deliv. Rev., 36, 29-40.
•  Furuta  T. and  Yoshii  H. (1994). Powdery encapsulation of d-limonene by kneading with mixed powders of β-cyclodextrin and maltodextrin at low water content. Biosci. Biotechol. Biochem., 58, 847-850.
•  Gharsallaoui  A.,  Roudaut  G.,  Chambin  O.,  Voilley  A., and  Saurel  R. (2007). Applications of spray-drying in microencapsulation of food ingredients: An overview. Food Res. Int., 40, 1107-1121.
•  Ghosh  A.,  Biswas  S., and  Ghosh  T. (2011). Preparation and evaluation of silymarin β-cyclodextrin molecular inclusion complexes. J. Young Pharm., 3, 205-210.
•  Gonnet  M.,  Lethuaut  L., and  Boury  F. (2010). New trends in encapsulation of liposoluble vitamins. J. Control Release, 146, 276-290.
•  Hedges  A. R. (1998). Industrial applications of cyclodextrins. Chem. Rev., 98, 2035-2044.
•  Hutin  S.,  Chamayou  A.,  Avan  J. L.,  Paillard  B.,  Baron  M.,  Couarraze  G., and  Bougaret  J. (2004). Drug substance-cyclodextrin complexation. Pharm. Technol., 28, 112-124.
•  Ji  H. G. and  Seo  B. (1999). Retinol at 5% in a cream: its stability, efficacy and effect. Cosmet. Toiletries, 114, 61-68.
•  Lin  H. S.,  Chean  C. S.,  Ng  Y. Y.,  Chan  S. Y., and  Ho  P. C. (2000). 2-Hydroxypropyl-β-cyclodextrin increases aqueous solubility and photostability of all-trans-retinoic acid. J. Clin. Pharm. Ther., 25, 265-269.
•  Lin  H. S.,  Leong  W. W. Y.,  Yang  J. A.,  Lee  P.,  Chan  S. Y., and  Ho  P. C. (2007). Biopharmaceutics of 13-cis-retinoic acid (isotretinoin) formulated with modified β-cyclodextrins. Int. J. Pharm., 341, 238-245.
•  Loveday  S. M. and  Singh  H. (2008). Recent advances in technologies for vitamin A protection in foods. Trend Food Sci. Technol., 19, 657-668.
•  Madene  A.,  Jacquot  M.,  Scher  J., and  Desobry  S. (2006). Flavour encapsulation and controlled release — a review. Int. J. Food Sci. Technol., 41, 1-21.
•  Moldenhauer  J. P.,  Regiert  M., and  Wimmer  T. (1999). Complexes of γ-cyclodextrin and retinol or retinol derivatives, processes for their preparation and their use. US Patent 5,985,296, Nov. 16.
•  Moreau  D. L. and  Rosenberg  M. (1996). Oxidative stability of anhydrous milkfat microencapsulated in whey proteins. J. Food Sci., 61, 39-43.
•  Moreau  D. L. and  Rosenberg  M. (1998). Porosity of whey protein-based microcapsules containing anhydrous milkfat measured by gas displacement pycnometry. J. Food Sci., 63, 1-5.
•  Murugesan  R. and  Orsat  V. (2012). Spray drying for the production of nutraceutical ingredients—A review. Food Bioprocess. Technol., 5, 3-14.
•  Neoh  T. L.,  Yoshii  H., and  Furuta  T. (2006). Encapsulation and release characteristics of carbon dioxide in α-cyclodextrin. J. Incl. Phenom. Macro., 56, 125-133.
•  Regiert  M. (2009). Retinol complexes with γ-cyclodextrin. SOFW-J., 135, 12-20.
•  Sauvant  P.,  Cansell  M.,  Sassi  A. H., and  Atgié  C. (2012). Vitamin A enrichment: caution with encapsulation strategies used for food applications. Food Res. Int., 46, 469-479.
•  Singh  A. K. and  Das  J. (1998). Liposome encapsulated vitamin A compounds exhibit greater stability and diminished toxicity. Biophys. Chem., 73, 155-162.
•  Tanumihardjo  S. A. (2011). Vitamin A: biomarkers of nutrition for development. Am. J. Clin. Nutr., 94, 658S-65S.
•  Trichard  L.,  Fattal  E.,  Besnard  M., and  Bochot  A. (2007). α-Cyclodextrin/ oil beads as a new carrier for improving the oral bioavailability of lipophilic drugs. J. Control Release, 122, 47-53.
•  Wagner  L. A. and  Warthesen  J. J. (1995). Stability of spray-dried encapsulated carrot carotenes. J. Food Sci., 60, 1048-1053.
•  Yap  K. L.,  Liu  X.,  Thenmozhiyal  J. C., and  Ho  P. C. (2005). Characterization of the 13-cis-retinoic acid/cyclodextrin inclusion complexes by phase solubility, photostability, physicochemical and computational analysis. Eur. J. Pharm. Sci., 25, 49-56.
•  Yoshida  K.,  Sekine  T.,  Matsuzaki  F.,  Yanaki  T., and  Yamaguchi  M. (1999). Stability of vitamin A in oil-in-water-in-oil-type multiple emulsions. J. Am. Oil Chem. Soc., 76, 1-6.
•  Yoshii  H.,  Soottitantawat  A.,  Liu  X. D.,  Atarashi  T.,  Furuta  T.,  Aishima  S.,  Ohgawara  M., and  Linko  P. (2001). Flavor release from spray-dried maltodextrin/gum arabic or soy matrices as a function of storage relative humidity. Innov. Food Sci. Emerg. Technol., 2, 55-61.