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Influence of emulsion and powder size on the stability of encapsulated d -limonene by spray drying
Innovative Food Science and Emerging Technologies 6 (2005) 107 – 114 www.elsevier.com/locate/ifset
Influence of emulsion and powder size on the stability of encapsulated d-limonene by spray drying Apinan Soottitantawata, Fanny Bigeardb, Hidefumi Yoshiia, Takeshi Furutaa,*, Masaaki Ohkawarac, Pekka Linkod a
Department of Biotechnology, Tottori University, 4-101, Minami, Koyama, Tottori, 680-8552, Japan b ENSBANA, Universite de Bourgogne, Dijon, France c Ohkawara Kakouki Co. Ltd., Yokohama 224-0053, Japan d Department of Chemical Technology, Helsinki University of Technology, P.O. Box 6100 HUT, Espoo, Finland Received 20 August 2004; accepted 29 September 2004
Abstract The microencapsulation of d-limonene by spray drying was investigated with respect to the effects of emulsion droplet size, powder particle size, as well as to the effects of various kinds of matrices (gum arabic, maltodextrin, and modified starch) on its stability. It was realized by studying release characteristics and oxidative stability during storage. The release and the oxidation decreased deeply with an increase in powder and emulsion particle size for gum arabic and maltodextrin materials. Further, the distributions of emulsion size in the powder showed an increase in the fraction of large emulsion droplets and changed to a bimodal distribution. However, the modified starch HI-CAP 100 showed a higher stability of encapsulated d-limonene than the others. The influence of powder and emulsion size on its encapsulated flavor as well as the change in the emulsion size during storage could not be observed. D 2004 Elsevier Ltd. All rights reserved. Keywords: Microencapsulation; Spray drying; Release; Oxidation stability Industrial relevance: Spray drying is a common and useful unit operation for microencapsulation of food ingredients. Data on emulsion droplet size and on powder size on product stability provide conflicting results which makes a systematic study regarding these factors highly relevant. The data suggest that an optimal size of flavour powder should be selected for high retention during spray drying, stability during storage and for the ability to control release of flavour.
1. Introduction Microencapsulation of flavors is of great importance in the flavoring and food industries. This is a technique of encapsulation of flavors in liquid form in a carrier matrix in order to obtain a dry flavor powder, which is easy to handle because of the solid state. The capsules (5–300 Am in diameter) can be made of sugars, gums, proteins, polysaccharides, lipids and synthetic polymers. The advantages of this technology are not only in providing protection against degradative reactions and preventing the loss of flavor, but also in giving the controlled release function of * Corresponding author. Tel.: +81 857 315273; fax: +81 857 31 0881. E-mail address: [email protected] (T. Furuta). 1466-8564/$ - see front matter D 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ifset.2004.09.003
flavors during food processing and storage. The most common way to realize the microencapsulation of flavors is spray drying, which is the transformation of a feed from a fluid state (solution, dispersion, emulsion) to dried particulate form. Spray drying is divided into different steps: atomization, mixing of sprayed liquid and air, evaporation of water and separation of product. Before spray drying, one more step is necessary to transform feed liquid into powder: emulsification of flavors into small emulsion droplets within a carrier solution (O/W emulsion) by a homogenizer. Then the emulsion is fed into the spray dryer and transformed into droplets by an atomizer, followed by dehydrating in a hot air. Numerous studies have been conducted to evaluate the retention of flavor during spray drying and the shelf life of the spray-dried powder.
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Recently, Soottitantawat, Yoshii, Furuta, Ohkawara, and Linko (2003) has reported the influence of emulsion size on the retention during spray drying of soluble and insoluble flavor. The smaller emulsion size showed the higher retention than the large emulsion size especially for the insoluble flavor. On the other hand, the retention had a maximum at the optimum value of a mean emulsion size for the soluble flavor. Further, they also reported small droplets of flavor embedded in the shell of the wall matrix inside the powder, confirming the observations by other researchers (Chang, Scire, & Jacobs, 1988; Finney, Buffo, & Reineccius, 2002; Kim & Morr, 1996; Reineccius, Ward, Whorton, & Andon, 1995; Rosenberg & Young, 1993; Sheu & Rosenberg, 1995). In addition, the stability and release characteristics of encapsulated flavors from the powder are important for estimating the shelf life of the flavor, as well as for the controlled release applications in food (Anandaraman & Reineccius, 1986; Bertolini, Siani & Grosso, 2001; Soottitantawat et al., 2004; Whorton, 1995; Whorton & Reineccius, 1995; Yoshii et al., 2001). The wall materials still present a limited capacity against oxidation, since the most wall materials used act as semipermeable membranes. Concerning to the study on the effect of the emulsion size on the shelf life of encapsulated orange oil flavor, Risch and Reineccius (1988) showed a longer shelf life of larger feed emulsion size. However, in the same manner for the shelf life of encapsulated fatty acid, Ishido, Hakamata, Minemoto, Adachi, and Matsuno (2002) has recently reported a lower oxidation rate of linoleic acid encapsulated in maltodextrin for the smaller size of feed emulsion. According to these contrasting views, data concerning the influence of emulsion size on the shelf life of product are scare and somewhat confusing. The opposite was also reported in the case of emulsion liquid (Lethuaut, Me´tro, & Genoi, 2002) which was explained by the large surface area for the small emulsion size resulting in the higher oxidation. On the other hand, the number of lipid molecules per small droplet also decreases and the amount of surface-active compounds adsorbed at the interface might be increased. This limits initiation and propagation resulting in the lower oxidation. In the same manner, the effect of emulsion size on the encapsulated flavor in the matrix could be explained. However, other factors also should affect the shelf life of encapsulated flavors. As Chang et al. (1988) reported on the effect of the powder particle size, the larger size exhibited a more protective effect against oxidation. From theses points, the powder morphology and the arrangement as well as the size of emulsion droplets inside the shell of the powder seem to be important for the stability of the encapsulated flavors. Therefore, the objective of this work was to evaluate the influence of emulsion droplet size and the powder size on the stability of the encapsulated d-limonene. The morphology of the powder and the changing of emulsion droplet size during storage were also investigated.
2. Materials and methods 2.1. Materials d-Limonene and gum arabic (GA) were purchased from Nacalai Tesque (Kyoto, Japan). Maltodextrin with ca. 20 DE (MD, Amycol No.1) and modified starch (HI-CAP 100) were obtained from Nippon Starch Chemicals (Osaka, Japan) and National NSC (Tokyo, Japan), respectively. The organic chemicals used in the analyses were of analytical grade. 2.2. Preparation of encapsulated d-limonene spray-dried powder The carrier solution was prepared by dissolving the solid powders in warm distilled water. The carrier solution was composed of 20% w/w GA or 20% w/w HI-CAP 100 or the mixture of 10% w/w of GA and 10% w/w of additive wall materials MD. Then d-limonene was added to the solution as model flavor. In an attempt to create different particle sizes of emulsion, the mass ratio of amount of d-limonene to emulsifier, and the ways of the homogenization were controlled as shown in Fig. 1. A low solid concentration was used because it was easier to control the size of emulsion. To prepare emulsion of large droplet size (LE), d-limonene was added to the solution at the mass ratio to emulsifier (GA or HICAP 100) of 3:1 and then homogenized by using a Polytron homogenizer (PT-10, Kinematica, Littau, Switzerland) at dial 8 for 3 min. Then, the remaining carrier solution was added to the emulsion to make up the mass ratio of the amount of dlimonene to the total wall materials to 1:4. On the other hand, to
Fig. 1. Schematic procedure for creating small and large size emulsion.
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make a smaller emulsion droplet (SE), d-limonene was added to the carrier solution to produce a flavor mass ratio to wall materials of 1–4. The mixture was homogenized by using a Polytron homogenizer (PT-6100, Kinematica) at 8000 rpm for 3 min and then passed through the Microfluidizer (model 110T, Microfluidics, Newton, MA) at 12,000 psig (82.8 MPa). To transform to the powder, the emulsion was spray dried in an Ohkawara-L8 spray dryer (Ohkawara Kakouki, Yokohama, Japan) as describe in the previous work (Soottitantawat et al., 2003, 2004; Yoshii et al., 2001). The operational conditions of the spray drying were: air inlet temperature of 200 8C, air outlet temperature of 110F10 8C, feed rate of 45 mL/min and air flow rate of 110 kg/h. The rotational speed of the atomizer was controlled at 10,000, 20,000, and 30,000 rev/min to produce the large powder (LP), medium powder (MP), and small powder (SP), respectively. 2.3. Emulsion droplet size analysis d-Limonene droplet size distribution of the feed liquid emulsions were analyzed using a laser scattering particle size analyzer (SALD-3000A, Shimadzu, Kyoto, Japan). At the point of the measurement, the emulsion was further diluted to less than 0.02% w/w to prevent multiple scattering effects. The drop size distribution was expressed as volume distribution and defined as the average emulsion size, D 43 (McClements, 1999; Soottitantawat et al., 2003). The specific surface area, SSA, was calculated with the volume-surface average emulsion diameter, D 32 (Linare`s, Larre´, & Popineau, 2001; McClements, 1999) P P zi D4i z D3 6 Pi i i2 ; SSA ¼ D43 ¼ Pi ; D ¼ 32 3 D z D z D 32 i i i i i i where D 43 is the average emulsion size, D 32 is the volumesurface average emulsion diameter, z i is the number of droplets of diameter D i , and SSA is the specific surface area. Each sample was analyzed in duplicate, and the data were presented as an average. d-Limonene droplet size in the powder after spray drying was measured from the reconstituted emulsion. The powder was reconstituted to 10% w/w of encapsulated powder by dissolving 0.2 g of powder in 1.8 ml of distilled water at a room temperature with a magnetic stirrer for 30 min. Subsequently, the distribution of emulsion droplet were measured in the same manner as above. 2.4. Powder particle size analysis The size distribution of the spray-dried powders was determined by dispersing them in 2-methyl-1-propanol and analyzing by the laser light scattering method with a batch cell unit (SALD-2000A, Shimadzu). The average particle size and the specific surface area were reported as explained above. Each sample was analyzed in duplicate and the data were reported as an average.
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2.5. Surface oil determination The method for determining the surface oil content was explained in the previous work (Soottitantawat et al., 2003). One tenth of a gram of powder was washed in 2 ml of hexane containing the internal standard cyclohexanone, 1 Al/ml, in a glass bottle. The mixtures were slowly mixed on a rotary shaker for the optimum time of 30 s at ambient temperature. The solvent was then filtered. d-Limonene content in the organic phase was measured by gas chromatography. The results were the average of the duplicates in each sample. 2.6. Morphological characterization by scanning electron microscopy (SEM) The external and internal structure of the encapsulated powder were studied by SEM (JSM 5800, JEOL, Tokyo, Japan). The powders were placed on the SEM stubs using a two-sided adhesive tape (Nisshin EM, Tokyo, Japan) and then analyzed at 15 kV acceleration voltage after Pt–Pd sputtering by MSP-1S magnetron sputter coater (Vacuum Device, Tokyo, Japan). The internal structure was investigated as described in our previous work (Soottitantawat et al., 2003). 2.7. The stability of spray-dried d-limonene The stability of encapsulated d-limonene was defined as the release and the oxidation of d-limonene as reported in our previous work (Soottitantawat et al., 2004). About 0.1 g of the spray-dried powder was weighed and spread as a thin layer in a 15 ml (20f48 mm) glass bottle, and stored in a 51F5% RH and 50 8C desiccator. At this condition the highest release and oxidation rate were observed (Soottitantawat et al., 2004) without the change of external structure of the particles, since it is close to the glass transition point of the capsule matrices. Fifteen sample bottles were placed in a desiccator to study the release and oxidation kinetics for 25 or 30 days. At fixed time intervals, the bottles were removed from the desiccator in order to extract and measure the residual amounts of d-limonene and the oxide compounds by heat extraction method as described in our previous work (Soottitantawat et al., 2004). The retention of d-limonene was defined as the ratio of the remaining amount of d-limonene to the initial one. The amount of the oxide compound was expressed by the mass ratio of the oxide to the retained d-limonene. Avrami’s equation (Weibull distribution function), was applied to the release time-courses of the encapsulated dlimonene as reported in the previous work (Soottitantawat et al., 2004; Yoshii et al., 2001). R ¼ exp½ ðkt Þn where R is the retention of d-limonene, t is the storage time, k is the release rate constant, and n is a parameter
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Table 1 Properties of encapsulated d-limonene after spray drying Type of carrier solid
Samplea
Emulsion size (Am)
Reconstituted emulsion (Am)
SSA of reconstituted emulsion (m2/m3)
Powder size (Am)
SSA of powder (m2/m3)
Retention during spray drying (%)
Surface oil (%)
GA
LELP LEMP LESP SELP SEMP SESP LELP LEMP LESP SELP SEMP SESP LELP LEMP LESP SELP SEMP SESP
3.16 2.91 3.01 0.81 0.80 0.80 3.37 3.26 3.20 0.84 0.90 1.04 2.12 2.38 2.10 0.66 0.68 0.67
3.42 2.83 2.53 1.14 0.86 0.90 4.09 2.97 2.87 0.84 1.19 1.73 2.16 1.95 1.60 0.69 0.71 0.70
3.16 3.10 3.37 6.08 7.88 7.69 3.27 3.39 3.33 7.88 5.74 4.28 3.24 3.69 4.42 9.50 9.00 9.17
70 51 31 61 54 32 65 47 24 60 46 27 60 35 23 57 38 23
0.10 0.17 0.66 0.12 0.16 0.43 0.11 0.19 0.95 0.12 0.20 0.68 0.12 0.26 0.37 0.13 0.25 0.36
82 97 95 99 99 99 95 91 87 100 98 93 79 74 80 94 92 89
3.19 6.81 5.96 1.06 2.75 2.89 0.72 0.56 0.45 0.44 0.68 0.72 1.25 0.63 1.28 0.43 0.39 0.46
GA and MD (1:1)
HI-CAP 100
a
LE: large emulsion size, SE: small emulsion size, LP: large powder size, MP: medium powder size, SP: small powder size.
representing the release mechanism. Furthermore, since the amount of limonene oxide and carvone increased linearly with time during the initial period, the apparent oxidation rate constants were calculated on the basis of the zero order kinetic reaction scheme (Soottitantawat et al., 2004). In addition, the changes of emulsion droplets in the powder during storage were also investigated. The encapsulated dlimonene powders were reconstituted and the size was measured as described above.
3. Results and discussion 3.1. The physical properties and the surface oil content of the spray-dried powder Six types of the spray-dried powders for each carrier solution were prepared in various combinations of the emulsion size and the powder size, in order to investigate the effects on the stability of d-limonene during storage. The small powder size (25–30 Am: SP), medium powder size (40–50 Am: MP) and large powder size (60–70 Am: LP)
were prepared by controlling the rotational speed of atomizer at 10,000, 20,000, and 30,000 rpm, respectively. Two types of the reconstituted emulsion size were categorized as a large emulsion (2.5–4 Am: LE) and a small emulsion (~1 Am: SE). The physical properties of the spraydried d-limonene powders, such as the reconstituted emulsion size, powder size, the surface oil content, and the flavor retention were shown in Table 1. d-Limonene retention during spray drying was defined as the ratio of the d-limonene in the powder to the 0.25 kg d-limonene/kg dried solid of the feed emulsion. Flavor retention in all systems was higher than 80%. In all wall material systems of powder size as controlled with the rotational speed of atomizer seemed to have a less important effect on the flavor retention, as compared to the influence of emulsion size as shown in Table 1. As mentioned by Chang et al. (1988), the large atomized droplets have reduced surface area to volume ratio which would result in better d-limonene retention, but it also takes a longer time for film formation around the large atomized droplets in the drying process. The longer was the time necessary for the film formation, the greater was the loss of volatile flavors.
Fig. 2. External structure of encapsulated d-limonene powder for the small powder of about 30 Am and the small emulsion of about 1 Am. Wall materials: (a) GA, (b) Blend GA-MD, (c) HICAP-100.
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observed for the GA wall material systems. The larger emulsion size showed a higher surface oil content than the smaller emulsion, as reported by Soottitantawat et al. (2003). However, no important effects on the surface oil content were found in the powder size to the surface oil content. The outer structure of encapsulated d-limonene powders in the wall materials, GA, blend GA-MD, and HICAP 100 are shown in Fig. 2a, b, and c, respectively. Both groove and smooth powder surfaces were observed. However, the smooth surface of powder was observed more in the HICAP 100 wall materials than with the others. 3.2. Effect of the powder particles size on stability of encapsulated flavor powder In the previous works (Soottitantawat et al., 2004), the stability of encapsulated d-limonene was indicated by using
Fig. 3. Effect of powder and reconstituted emulsion size on the parameters of Avrami’s equation for the d-limonene encapsulated powder stored at 51% RH and 50 8C. (a) Release rate constant, k, (b) release mechanism factor, n. o., GA; 5n, blend of GA-MD; DE, HI-CAP 100. Filled symbols represent a large reconstituted emulsion and unfilled symbols for a small reconstituted emulsion. The error bars indicate 95% confidence level.
The flavor retention is higher for the small emulsion than large emulsion. As described in our previous work (Soottitantawat et al., 2003), the evaporation of flavor seems to be easier with large emulsion size during atomization. The larger emulsion droplets were sheared into smaller droplets. Wall materials of GA and modified starch HI-CAP 100, which have good emulsifier properties, showed no important effects on the flavor retention in the comparison to the effect of the emulsion size. GA showed a higher flavor retention at the same size of emulsion droplets when compare to other wall materials. Even though, HICAP 100 was easier to use in order to make fine emulsion droplets. The retaining of d-limonene on the powder surface (percent of surface oil) was defined as the ratio of dlimonene on the surface to the total flavor in the powder. As shown in the Table 1, higher surface oil content was
Fig. 4. Effect of powder and reconstituted emulsion size on the formation rate constant of the d-limonene encapsulated powder stored at 51% RH and 50 8C. (a) Formation of limonene oxide, (b) formation of carvone. o., GA; 5n, blend of GA-MD; DE, HI-CAP 100. Filled symbols represent a large reconstituted emulsion and unfilled symbols for a small reconstituted emulsion. The error bars indicate 95% confidence level.
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Fig. 5. Change in distribution of reconstituted emulsion during storage at 51% RH and 50 8C for the small powders of about 30 Am and small emulsion size of about 1 Am. Wall materials: (a) GA, (b) Blend GA-MD, (c) HI-CAP 100. 5, 0 day; o, 7 day; D, 14 day; q, 21 day; R , 28 day.
the release rate and the oxidation rate. Limonene oxide and carvone were chosen as indicators of the oxidation. Therefore, the release rate constant and release mechanisms parameter were calculated by fitting the release time courses of d-limonene as shown in Fig. 3 with the Avrami’s equation as mentioned before in the function of powder size. The apparent oxidation rate constant were also calculated by using zero order kinetic reaction schemes fitting with the formation time courses of limonene oxide and carvone as shown in Fig. 4 against the powder size. In Fig. 3a, when GA and blend GA-MD were used as wall materials, the small powder size showed a higher release rate constant than the large powder. The oxidation rate constant also decreased with an increase in powder size as shown in Fig. 4a and b. The larger size of encapsulated dlimonene powder showed a longer product shelf life. This can be explained by the reduced surface area to volume ratio of the large powder as shown by the SSA values of powder in the Table 1, resulting in the decrease in the effective surface area for d-limonene to release and react with oxygen. However, for HI-CAP 100 wall materials, the effect of the powder size on the stability could not be observed, particularly in the release rate constant. Furthermore, the lower release and the oxidation rate constants were observed than with the GA or blend GA-MD as wall
materials. The higher stability of HI-CAP 100 might be a result of the morphology during spray drying. As shown in Fig. 2, the smooth surface area of HI-CAP 100 powders was observed comparing to other wall materials. In the same powder size, the effective surface area of the smooth surface powder is lower than the groove surface powder resulting in the lower release and oxidation rate of encapsulated dlimonene. Further, it might also be a result of a unique polymer structure of HI-CAP 100 with a dextrose equivalent of 32–37 (National Starch and Chemical, 1999). Furthermore, in Fig. 3b, most of n values are in the range of 0.30– 0.80 which shows that the release should be controlled by the diffusion mechanism. This agrees well with the results of the previous work (Soottitantawat et al., 2004; Yoshii et al., 2001). In addition, the distribution and average reconstituted emulsion size during storage were also measured to study the stability of the encapsulated d-limonene as shown in Figs. 5 and 6. In Fig. 5a and b, the change in the distribution of reconstituted emulsion size was reported for GA and blend GA-MD wall materials, respectively. The distributions showed an increase in the fraction of large emulsion droplet and a change to a bimodal distribution. On the other hands, the change in the distribution of emulsion size in HICAP 100 could not be observed as shown in Fig. 5c. These
Fig. 6. Change in mean reconstituted emulsion size during storage at 51% RH and 50 8C for the small initial reconstituted emulsion size (SE) of about 1 Am. Wall materials: (a) GA, (b) Blend GA-MD, (c) HI-CAP 100. 5, Small powder (SP); D, Medium powder (MP); o, Large powder (LP).
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results supported the higher stability of encapsulated dlimonene in HI-CAP 100 wall materials than in the others as explained above. The changes in average reconstituted emulsion size were also investigated as a function of powder size during storage in Fig. 6. In Fig. 6a and b, the smaller powder size showed a higher emulsion size increasing rate than the larger powder size for GA and blend GA-MD as wall materials. These observations also agreed with the fact that the large powders were shown to exhibit a better protection against oxidation for the encapsulated d-limonene. However, for HI-CAP 100, the change in average reconstituted emulsion size for all powder sizes could not be observed as also shown in Fig. 6c. These results agreed with the powder size had almost no effect on the stability of encapsulated d-limonene HI-CAP 100 powder. This is likely to result from the high stability of encapsulated dlimonene in HI-CAP 100, and could overcome the powder size effect. Furthermore, SEM was also used to the internal structure of encapsulated d-limonene for the different powder sizes as shown in Fig. 7 for GA with the large size emulsion. dLimonene droplets were located in the form of small droplets embedded in the shell of wall matrix as shown in Fig. 7a, b, and c. A thicker shell matrix was observed in the large powder. On the other hand, for the small powder the thinner shell matrix and the higher concentration of dlimonene droplet were observed especially near the inner and outer surface of the shell. d-Limonene droplet, located near the surface of the powder, should be easier to release or react with the outside oxygen. These observations could be used to explain why the smaller powder showed a lower stability in addition to the larger effective surface area of the small powder. 3.3. Effect of the reconstituted emulsion size on stability of encapsulated d -limonene powder The effect of the reconstituted emulsion size on the stability of encapsulated d-limonene was also studied as shown in Figs. 3 and 4. The filled symbols represent a large reconstituted emulsion and unfilled symbols represent a small reconstitute emulsion. The small reconstituted emulsion size showed the higher release rate and oxidation rates
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Fig. 8. Change in mean reconstituted emulsion size during storage at 51% RH and 50 8C for the large initial reconstituted emulsion size (LE) of about 2 Am of HI-CAP 100 wall materials. 5, Small powder (SP); D, Medium powder (MP); o, Large powder (LP).
constant than the larger emulsion size in the GA and blend GA-MD wall materials. This indicates the larger size of dlimonene in powder showed a longer shelf life of the products. As mentioned above, this could be explained by the higher effective surface area of the small emulsion droplet to release and to react with the oxygen. The results are in an agreement with those of Risch and Reineccius (1988) but in a conflict with those of Ishido et al. (2002). As mentioned by Lethuaut et al. (2002), the decrease of oxidation rate of the small emulsion size should come from the decrease of the lipid molecules and increase of surface active compounds that could limit the initiation and propagation of the chain reaction. From Ishido et al. (2002), a fatty acid was used as core material of which oxidation mechanism should be composed of the chain reaction. That could explain the higher stability of smaller emulsion droplet in the matrix materials. However, in Risch and Reineccius (1988) and in the present work, d-limonene was used as model flavor which has a zero order kinetic of the oxidation reaction as mentioned in the materials and methods section. The reaction is not dependent on the concentration of the reactant d-limonene. Therefore, the effective surface area should control the oxidation rate of
Fig. 7. Microstructure of encapsulated d-limonene powder when blend GA-MD was used as wall materials for the large reconstituted emulsion size (LE). (a) Small powder (SP); (b) Medium powder (MP); (c) Large powder (LP).
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encapsulated d-limonene in the wall matrix. The calculated surface area, SSA, of the small emulsion size is 2 times larger than the large emulsion size as shown in Table 1. That is why the higher stability of large reconstituted emulsion droplet was reported. However, for HI-CAP 100, the effect of the emulsion size on the stability could not be observed. These results also agreed with the unchanged of mean reconstituted emulsion size during storage in both case of a small emulsion size and large emulsion size as shown in Figs. 6c and 8, respectively. These should be from the high stability of encapsulated d-limonene in HI-CAP 100 as discussed above, which can overcome the effect of emulsion droplet size.
4. Conclusions The powder size showed the influence on the stability of the encapsulated flavor in addition to the powder properties such as the bulk volume and the flowability of powder. The powder size distribution from the spray drying could be effectively controlled by changing the rotational speed of the centrifugal atomizer. The large powder size showed the higher stability and lower release of encapsulated flavor than the small powder size. Furthermore, in addition to the effect of emulsion droplet size on the retention during spray drying (Soottitantawat et al., 2003), the emulsion size also affected to the stability of encapsulated flavor powder. The small flavor size in the powder showed the lower stability than the large size of flavor especially for the simple zero order kinetic oxidation of flavor (d-limonene), even though the smaller size of emulsion can give the higher retention during the spray drying (Soottitantawat et al., 2003). Therefore, the optimal size of flavor in the powder should be recommended for both of the high retention during spray drying and its stability during storage as well as the ability to control the release of flavor.
Acknowledgements This study was partly supported by the Grant-in-Aid for Scientific Research (No. 15580108) from the Ministry of Education, Science, and Culture of Japan. We also acknowledge Nippon NSC (Tokyo, Japan) and Nippon Starch Chemicals (Osaka, Japan) for their kind gift of HI-CAP 100 and MD, respectively.
References Anandaraman, S., & Reineccius, G. A. (1986). Stability of encapsulated orange peel oil. Food Technology, 40, 88 – 93.
Bertolini, A. C., Siani, A. C., & Grosso, C. R. (2001). Stability of monoterpenes encapsulated in gum arabic by spray-drying. Journal of Agricultural and Food Chemistry, 49, 780 – 785. Chang, Y. I., Scire, J., & Jacobs, B. (1988). Effect of particle and microstructure properties on encapsulated orange oil. In S. J. Risch, & G. A. Reineccius (Eds.), Flavor encapsulation. ACS Symp. Ser. No., vol. 370 (pp. 87 – 102). Finney, J., Buffo, R., & Reineccius, G. A. (2002). Effect of type of atomization and processing temperatures on the physical properties and stability of spray-dried flavors. Journal of Food Science, 67(3), 1108 – 1114. Ishido, E., Hakamata, K., Minemoto, Y., Adachi, S., & Matsuno, R. (2002). Oxidation Process of Linoleic acid encapsulated with a polysaccharide by spray drying. Food Science and Technology Research, 8(1), 85 – 88. Kim, Y. D., & Morr, C. V. (1996). Microencapsultaion properties of gum arabic and several food proteins: spray-dried orange oil emulsion particles. Journal of Agricultural and Food Chemistry, 44, 1314 – 1320. Lethuaut, L., Me´tro, F., & Genoi, C. (2002). Effect of droplet size on lipid oxidation rate of oil-in-water emulsions stabilized by protein. Journal of the American Chemical Society, 5, 425 – 430. Linare`s, E., Larre´, C., & Popineau, Y. (2001). Freeze- or spray-dried gluten hydrolysateds: 2. Effect of emulsification process on droplet size and emulsion stability. Journal of Food Engineering, 48, 137 – 146. McClements, D. J. (1999). In F. M. Clydesdale (Ed.), Food Emulsions, Contemporary food science. Washinton, DC7 CRC Press. National Starch and Chemical. (1999). Product data sheet: HI-CAP 100. National Starch and Chemical, A Member of the ICI Group, Manchester, UK. Reineccius, G. A., Ward, F. M., Whorton, C., & Andon, S. A. (1995). Development in gum acacias for the encapsulation flavors.. In S. J. Risch, & G. A. Reineccius (Eds.), Encpasulation and controlled release of food ingredients. ACS Symp. Ser. No., vol. 590 (pp. 161 – 168). Risch, S. J., & Reineccius, G. A. (1988). Spray-dried orange oil: Effect of emulsion size on flavor retention and shelf stability. In S. J. Risch, & G. A. Reineccius (Eds.), Flavor encapsulation. ACS Symp. Ser. No., vol. 370 (pp. 67 – 77). Rosenberg, M., & Young, S. L. (1993). Whey proteins as microencapsulating agents: micro-encapsulation of anhydrous milkfat-structure evaluation. Food Structure, 12, 31 – 41. Sheu, T. Y., & Rosenberg, M. (1995). Microencapsulation by spray drying ethyl caprylate in whey protein and carbohydrate wall systems. Journal of Food Science, 60(1), 98 – 103. Soottitantawat, A., Yoshii, H., Furuta, T., Ohgawara, M., Forssell, P., Partanen, R., et al. (2004). Effect of water activity on the release characteristics and oxidative stability of d-limonene encapsulated by spray drying. Journal of Agricultural and Food Chemistry, 52, 1269 – 1276. Soottitantawat, A., Yoshii, H., Furuta, T., Ohgawara, M., & Linko, P. (2003). Microencapsulation by spray drying: Influence of emulsion size on the retention of volatile compounds. Journal of Food Science, 68, 2256 – 2262. Whorton, C. (1995). Factors influencing volatile release from encapsulation matrices. In S. J. Risch, & G. A. Reineccius (Eds.), Encpasulation and controlled release of food ingredients. ACS Symp. Ser. No., vol. 590 (pp. 134 – 142). Whorton, C., & Reineccius, G. A. (1995). Evaluation of the mechanisms associated with the release of encapsulated flavor materials from maltodextrin matrices. In S. J. Risch, & G. A. Reineccius (Eds.), Encpasulation and controlled release of food ingredients. ACS Symp. Ser. No., vol. 590 (pp. 143 – 160). Yoshii, H., Soottitantawat, A., Liu, X. D., Atarashi, T., Furuta, T., Aishima, S., et al. (2001). Flavor release from spray dried maltodextrin/gum arabic or soy matrices as a function of storage relative humidity. Innovative Food Science and Emerging Technologies, 2, 55 – 61.
Influence of emulsion and powder size on the stability of encapsulated d-limonene by spray drying Apinan Soottitantawata, Fanny Bigeardb, Hidefumi Yoshiia, Takeshi Furutaa,*, Masaaki Ohkawarac, Pekka Linkod a
Department of Biotechnology, Tottori University, 4-101, Minami, Koyama, Tottori, 680-8552, Japan b ENSBANA, Universite de Bourgogne, Dijon, France c Ohkawara Kakouki Co. Ltd., Yokohama 224-0053, Japan d Department of Chemical Technology, Helsinki University of Technology, P.O. Box 6100 HUT, Espoo, Finland Received 20 August 2004; accepted 29 September 2004
Abstract The microencapsulation of d-limonene by spray drying was investigated with respect to the effects of emulsion droplet size, powder particle size, as well as to the effects of various kinds of matrices (gum arabic, maltodextrin, and modified starch) on its stability. It was realized by studying release characteristics and oxidative stability during storage. The release and the oxidation decreased deeply with an increase in powder and emulsion particle size for gum arabic and maltodextrin materials. Further, the distributions of emulsion size in the powder showed an increase in the fraction of large emulsion droplets and changed to a bimodal distribution. However, the modified starch HI-CAP 100 showed a higher stability of encapsulated d-limonene than the others. The influence of powder and emulsion size on its encapsulated flavor as well as the change in the emulsion size during storage could not be observed. D 2004 Elsevier Ltd. All rights reserved. Keywords: Microencapsulation; Spray drying; Release; Oxidation stability Industrial relevance: Spray drying is a common and useful unit operation for microencapsulation of food ingredients. Data on emulsion droplet size and on powder size on product stability provide conflicting results which makes a systematic study regarding these factors highly relevant. The data suggest that an optimal size of flavour powder should be selected for high retention during spray drying, stability during storage and for the ability to control release of flavour.
1. Introduction Microencapsulation of flavors is of great importance in the flavoring and food industries. This is a technique of encapsulation of flavors in liquid form in a carrier matrix in order to obtain a dry flavor powder, which is easy to handle because of the solid state. The capsules (5–300 Am in diameter) can be made of sugars, gums, proteins, polysaccharides, lipids and synthetic polymers. The advantages of this technology are not only in providing protection against degradative reactions and preventing the loss of flavor, but also in giving the controlled release function of * Corresponding author. Tel.: +81 857 315273; fax: +81 857 31 0881. E-mail address: [email protected] (T. Furuta). 1466-8564/$ - see front matter D 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ifset.2004.09.003
flavors during food processing and storage. The most common way to realize the microencapsulation of flavors is spray drying, which is the transformation of a feed from a fluid state (solution, dispersion, emulsion) to dried particulate form. Spray drying is divided into different steps: atomization, mixing of sprayed liquid and air, evaporation of water and separation of product. Before spray drying, one more step is necessary to transform feed liquid into powder: emulsification of flavors into small emulsion droplets within a carrier solution (O/W emulsion) by a homogenizer. Then the emulsion is fed into the spray dryer and transformed into droplets by an atomizer, followed by dehydrating in a hot air. Numerous studies have been conducted to evaluate the retention of flavor during spray drying and the shelf life of the spray-dried powder.
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Recently, Soottitantawat, Yoshii, Furuta, Ohkawara, and Linko (2003) has reported the influence of emulsion size on the retention during spray drying of soluble and insoluble flavor. The smaller emulsion size showed the higher retention than the large emulsion size especially for the insoluble flavor. On the other hand, the retention had a maximum at the optimum value of a mean emulsion size for the soluble flavor. Further, they also reported small droplets of flavor embedded in the shell of the wall matrix inside the powder, confirming the observations by other researchers (Chang, Scire, & Jacobs, 1988; Finney, Buffo, & Reineccius, 2002; Kim & Morr, 1996; Reineccius, Ward, Whorton, & Andon, 1995; Rosenberg & Young, 1993; Sheu & Rosenberg, 1995). In addition, the stability and release characteristics of encapsulated flavors from the powder are important for estimating the shelf life of the flavor, as well as for the controlled release applications in food (Anandaraman & Reineccius, 1986; Bertolini, Siani & Grosso, 2001; Soottitantawat et al., 2004; Whorton, 1995; Whorton & Reineccius, 1995; Yoshii et al., 2001). The wall materials still present a limited capacity against oxidation, since the most wall materials used act as semipermeable membranes. Concerning to the study on the effect of the emulsion size on the shelf life of encapsulated orange oil flavor, Risch and Reineccius (1988) showed a longer shelf life of larger feed emulsion size. However, in the same manner for the shelf life of encapsulated fatty acid, Ishido, Hakamata, Minemoto, Adachi, and Matsuno (2002) has recently reported a lower oxidation rate of linoleic acid encapsulated in maltodextrin for the smaller size of feed emulsion. According to these contrasting views, data concerning the influence of emulsion size on the shelf life of product are scare and somewhat confusing. The opposite was also reported in the case of emulsion liquid (Lethuaut, Me´tro, & Genoi, 2002) which was explained by the large surface area for the small emulsion size resulting in the higher oxidation. On the other hand, the number of lipid molecules per small droplet also decreases and the amount of surface-active compounds adsorbed at the interface might be increased. This limits initiation and propagation resulting in the lower oxidation. In the same manner, the effect of emulsion size on the encapsulated flavor in the matrix could be explained. However, other factors also should affect the shelf life of encapsulated flavors. As Chang et al. (1988) reported on the effect of the powder particle size, the larger size exhibited a more protective effect against oxidation. From theses points, the powder morphology and the arrangement as well as the size of emulsion droplets inside the shell of the powder seem to be important for the stability of the encapsulated flavors. Therefore, the objective of this work was to evaluate the influence of emulsion droplet size and the powder size on the stability of the encapsulated d-limonene. The morphology of the powder and the changing of emulsion droplet size during storage were also investigated.
2. Materials and methods 2.1. Materials d-Limonene and gum arabic (GA) were purchased from Nacalai Tesque (Kyoto, Japan). Maltodextrin with ca. 20 DE (MD, Amycol No.1) and modified starch (HI-CAP 100) were obtained from Nippon Starch Chemicals (Osaka, Japan) and National NSC (Tokyo, Japan), respectively. The organic chemicals used in the analyses were of analytical grade. 2.2. Preparation of encapsulated d-limonene spray-dried powder The carrier solution was prepared by dissolving the solid powders in warm distilled water. The carrier solution was composed of 20% w/w GA or 20% w/w HI-CAP 100 or the mixture of 10% w/w of GA and 10% w/w of additive wall materials MD. Then d-limonene was added to the solution as model flavor. In an attempt to create different particle sizes of emulsion, the mass ratio of amount of d-limonene to emulsifier, and the ways of the homogenization were controlled as shown in Fig. 1. A low solid concentration was used because it was easier to control the size of emulsion. To prepare emulsion of large droplet size (LE), d-limonene was added to the solution at the mass ratio to emulsifier (GA or HICAP 100) of 3:1 and then homogenized by using a Polytron homogenizer (PT-10, Kinematica, Littau, Switzerland) at dial 8 for 3 min. Then, the remaining carrier solution was added to the emulsion to make up the mass ratio of the amount of dlimonene to the total wall materials to 1:4. On the other hand, to
Fig. 1. Schematic procedure for creating small and large size emulsion.
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make a smaller emulsion droplet (SE), d-limonene was added to the carrier solution to produce a flavor mass ratio to wall materials of 1–4. The mixture was homogenized by using a Polytron homogenizer (PT-6100, Kinematica) at 8000 rpm for 3 min and then passed through the Microfluidizer (model 110T, Microfluidics, Newton, MA) at 12,000 psig (82.8 MPa). To transform to the powder, the emulsion was spray dried in an Ohkawara-L8 spray dryer (Ohkawara Kakouki, Yokohama, Japan) as describe in the previous work (Soottitantawat et al., 2003, 2004; Yoshii et al., 2001). The operational conditions of the spray drying were: air inlet temperature of 200 8C, air outlet temperature of 110F10 8C, feed rate of 45 mL/min and air flow rate of 110 kg/h. The rotational speed of the atomizer was controlled at 10,000, 20,000, and 30,000 rev/min to produce the large powder (LP), medium powder (MP), and small powder (SP), respectively. 2.3. Emulsion droplet size analysis d-Limonene droplet size distribution of the feed liquid emulsions were analyzed using a laser scattering particle size analyzer (SALD-3000A, Shimadzu, Kyoto, Japan). At the point of the measurement, the emulsion was further diluted to less than 0.02% w/w to prevent multiple scattering effects. The drop size distribution was expressed as volume distribution and defined as the average emulsion size, D 43 (McClements, 1999; Soottitantawat et al., 2003). The specific surface area, SSA, was calculated with the volume-surface average emulsion diameter, D 32 (Linare`s, Larre´, & Popineau, 2001; McClements, 1999) P P zi D4i z D3 6 Pi i i2 ; SSA ¼ D43 ¼ Pi ; D ¼ 32 3 D z D z D 32 i i i i i i where D 43 is the average emulsion size, D 32 is the volumesurface average emulsion diameter, z i is the number of droplets of diameter D i , and SSA is the specific surface area. Each sample was analyzed in duplicate, and the data were presented as an average. d-Limonene droplet size in the powder after spray drying was measured from the reconstituted emulsion. The powder was reconstituted to 10% w/w of encapsulated powder by dissolving 0.2 g of powder in 1.8 ml of distilled water at a room temperature with a magnetic stirrer for 30 min. Subsequently, the distribution of emulsion droplet were measured in the same manner as above. 2.4. Powder particle size analysis The size distribution of the spray-dried powders was determined by dispersing them in 2-methyl-1-propanol and analyzing by the laser light scattering method with a batch cell unit (SALD-2000A, Shimadzu). The average particle size and the specific surface area were reported as explained above. Each sample was analyzed in duplicate and the data were reported as an average.
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2.5. Surface oil determination The method for determining the surface oil content was explained in the previous work (Soottitantawat et al., 2003). One tenth of a gram of powder was washed in 2 ml of hexane containing the internal standard cyclohexanone, 1 Al/ml, in a glass bottle. The mixtures were slowly mixed on a rotary shaker for the optimum time of 30 s at ambient temperature. The solvent was then filtered. d-Limonene content in the organic phase was measured by gas chromatography. The results were the average of the duplicates in each sample. 2.6. Morphological characterization by scanning electron microscopy (SEM) The external and internal structure of the encapsulated powder were studied by SEM (JSM 5800, JEOL, Tokyo, Japan). The powders were placed on the SEM stubs using a two-sided adhesive tape (Nisshin EM, Tokyo, Japan) and then analyzed at 15 kV acceleration voltage after Pt–Pd sputtering by MSP-1S magnetron sputter coater (Vacuum Device, Tokyo, Japan). The internal structure was investigated as described in our previous work (Soottitantawat et al., 2003). 2.7. The stability of spray-dried d-limonene The stability of encapsulated d-limonene was defined as the release and the oxidation of d-limonene as reported in our previous work (Soottitantawat et al., 2004). About 0.1 g of the spray-dried powder was weighed and spread as a thin layer in a 15 ml (20f48 mm) glass bottle, and stored in a 51F5% RH and 50 8C desiccator. At this condition the highest release and oxidation rate were observed (Soottitantawat et al., 2004) without the change of external structure of the particles, since it is close to the glass transition point of the capsule matrices. Fifteen sample bottles were placed in a desiccator to study the release and oxidation kinetics for 25 or 30 days. At fixed time intervals, the bottles were removed from the desiccator in order to extract and measure the residual amounts of d-limonene and the oxide compounds by heat extraction method as described in our previous work (Soottitantawat et al., 2004). The retention of d-limonene was defined as the ratio of the remaining amount of d-limonene to the initial one. The amount of the oxide compound was expressed by the mass ratio of the oxide to the retained d-limonene. Avrami’s equation (Weibull distribution function), was applied to the release time-courses of the encapsulated dlimonene as reported in the previous work (Soottitantawat et al., 2004; Yoshii et al., 2001). R ¼ exp½ ðkt Þn where R is the retention of d-limonene, t is the storage time, k is the release rate constant, and n is a parameter
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Table 1 Properties of encapsulated d-limonene after spray drying Type of carrier solid
Samplea
Emulsion size (Am)
Reconstituted emulsion (Am)
SSA of reconstituted emulsion (m2/m3)
Powder size (Am)
SSA of powder (m2/m3)
Retention during spray drying (%)
Surface oil (%)
GA
LELP LEMP LESP SELP SEMP SESP LELP LEMP LESP SELP SEMP SESP LELP LEMP LESP SELP SEMP SESP
3.16 2.91 3.01 0.81 0.80 0.80 3.37 3.26 3.20 0.84 0.90 1.04 2.12 2.38 2.10 0.66 0.68 0.67
3.42 2.83 2.53 1.14 0.86 0.90 4.09 2.97 2.87 0.84 1.19 1.73 2.16 1.95 1.60 0.69 0.71 0.70
3.16 3.10 3.37 6.08 7.88 7.69 3.27 3.39 3.33 7.88 5.74 4.28 3.24 3.69 4.42 9.50 9.00 9.17
70 51 31 61 54 32 65 47 24 60 46 27 60 35 23 57 38 23
0.10 0.17 0.66 0.12 0.16 0.43 0.11 0.19 0.95 0.12 0.20 0.68 0.12 0.26 0.37 0.13 0.25 0.36
82 97 95 99 99 99 95 91 87 100 98 93 79 74 80 94 92 89
3.19 6.81 5.96 1.06 2.75 2.89 0.72 0.56 0.45 0.44 0.68 0.72 1.25 0.63 1.28 0.43 0.39 0.46
GA and MD (1:1)
HI-CAP 100
a
LE: large emulsion size, SE: small emulsion size, LP: large powder size, MP: medium powder size, SP: small powder size.
representing the release mechanism. Furthermore, since the amount of limonene oxide and carvone increased linearly with time during the initial period, the apparent oxidation rate constants were calculated on the basis of the zero order kinetic reaction scheme (Soottitantawat et al., 2004). In addition, the changes of emulsion droplets in the powder during storage were also investigated. The encapsulated dlimonene powders were reconstituted and the size was measured as described above.
3. Results and discussion 3.1. The physical properties and the surface oil content of the spray-dried powder Six types of the spray-dried powders for each carrier solution were prepared in various combinations of the emulsion size and the powder size, in order to investigate the effects on the stability of d-limonene during storage. The small powder size (25–30 Am: SP), medium powder size (40–50 Am: MP) and large powder size (60–70 Am: LP)
were prepared by controlling the rotational speed of atomizer at 10,000, 20,000, and 30,000 rpm, respectively. Two types of the reconstituted emulsion size were categorized as a large emulsion (2.5–4 Am: LE) and a small emulsion (~1 Am: SE). The physical properties of the spraydried d-limonene powders, such as the reconstituted emulsion size, powder size, the surface oil content, and the flavor retention were shown in Table 1. d-Limonene retention during spray drying was defined as the ratio of the d-limonene in the powder to the 0.25 kg d-limonene/kg dried solid of the feed emulsion. Flavor retention in all systems was higher than 80%. In all wall material systems of powder size as controlled with the rotational speed of atomizer seemed to have a less important effect on the flavor retention, as compared to the influence of emulsion size as shown in Table 1. As mentioned by Chang et al. (1988), the large atomized droplets have reduced surface area to volume ratio which would result in better d-limonene retention, but it also takes a longer time for film formation around the large atomized droplets in the drying process. The longer was the time necessary for the film formation, the greater was the loss of volatile flavors.
Fig. 2. External structure of encapsulated d-limonene powder for the small powder of about 30 Am and the small emulsion of about 1 Am. Wall materials: (a) GA, (b) Blend GA-MD, (c) HICAP-100.
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observed for the GA wall material systems. The larger emulsion size showed a higher surface oil content than the smaller emulsion, as reported by Soottitantawat et al. (2003). However, no important effects on the surface oil content were found in the powder size to the surface oil content. The outer structure of encapsulated d-limonene powders in the wall materials, GA, blend GA-MD, and HICAP 100 are shown in Fig. 2a, b, and c, respectively. Both groove and smooth powder surfaces were observed. However, the smooth surface of powder was observed more in the HICAP 100 wall materials than with the others. 3.2. Effect of the powder particles size on stability of encapsulated flavor powder In the previous works (Soottitantawat et al., 2004), the stability of encapsulated d-limonene was indicated by using
Fig. 3. Effect of powder and reconstituted emulsion size on the parameters of Avrami’s equation for the d-limonene encapsulated powder stored at 51% RH and 50 8C. (a) Release rate constant, k, (b) release mechanism factor, n. o., GA; 5n, blend of GA-MD; DE, HI-CAP 100. Filled symbols represent a large reconstituted emulsion and unfilled symbols for a small reconstituted emulsion. The error bars indicate 95% confidence level.
The flavor retention is higher for the small emulsion than large emulsion. As described in our previous work (Soottitantawat et al., 2003), the evaporation of flavor seems to be easier with large emulsion size during atomization. The larger emulsion droplets were sheared into smaller droplets. Wall materials of GA and modified starch HI-CAP 100, which have good emulsifier properties, showed no important effects on the flavor retention in the comparison to the effect of the emulsion size. GA showed a higher flavor retention at the same size of emulsion droplets when compare to other wall materials. Even though, HICAP 100 was easier to use in order to make fine emulsion droplets. The retaining of d-limonene on the powder surface (percent of surface oil) was defined as the ratio of dlimonene on the surface to the total flavor in the powder. As shown in the Table 1, higher surface oil content was
Fig. 4. Effect of powder and reconstituted emulsion size on the formation rate constant of the d-limonene encapsulated powder stored at 51% RH and 50 8C. (a) Formation of limonene oxide, (b) formation of carvone. o., GA; 5n, blend of GA-MD; DE, HI-CAP 100. Filled symbols represent a large reconstituted emulsion and unfilled symbols for a small reconstituted emulsion. The error bars indicate 95% confidence level.
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Fig. 5. Change in distribution of reconstituted emulsion during storage at 51% RH and 50 8C for the small powders of about 30 Am and small emulsion size of about 1 Am. Wall materials: (a) GA, (b) Blend GA-MD, (c) HI-CAP 100. 5, 0 day; o, 7 day; D, 14 day; q, 21 day; R , 28 day.
the release rate and the oxidation rate. Limonene oxide and carvone were chosen as indicators of the oxidation. Therefore, the release rate constant and release mechanisms parameter were calculated by fitting the release time courses of d-limonene as shown in Fig. 3 with the Avrami’s equation as mentioned before in the function of powder size. The apparent oxidation rate constant were also calculated by using zero order kinetic reaction schemes fitting with the formation time courses of limonene oxide and carvone as shown in Fig. 4 against the powder size. In Fig. 3a, when GA and blend GA-MD were used as wall materials, the small powder size showed a higher release rate constant than the large powder. The oxidation rate constant also decreased with an increase in powder size as shown in Fig. 4a and b. The larger size of encapsulated dlimonene powder showed a longer product shelf life. This can be explained by the reduced surface area to volume ratio of the large powder as shown by the SSA values of powder in the Table 1, resulting in the decrease in the effective surface area for d-limonene to release and react with oxygen. However, for HI-CAP 100 wall materials, the effect of the powder size on the stability could not be observed, particularly in the release rate constant. Furthermore, the lower release and the oxidation rate constants were observed than with the GA or blend GA-MD as wall
materials. The higher stability of HI-CAP 100 might be a result of the morphology during spray drying. As shown in Fig. 2, the smooth surface area of HI-CAP 100 powders was observed comparing to other wall materials. In the same powder size, the effective surface area of the smooth surface powder is lower than the groove surface powder resulting in the lower release and oxidation rate of encapsulated dlimonene. Further, it might also be a result of a unique polymer structure of HI-CAP 100 with a dextrose equivalent of 32–37 (National Starch and Chemical, 1999). Furthermore, in Fig. 3b, most of n values are in the range of 0.30– 0.80 which shows that the release should be controlled by the diffusion mechanism. This agrees well with the results of the previous work (Soottitantawat et al., 2004; Yoshii et al., 2001). In addition, the distribution and average reconstituted emulsion size during storage were also measured to study the stability of the encapsulated d-limonene as shown in Figs. 5 and 6. In Fig. 5a and b, the change in the distribution of reconstituted emulsion size was reported for GA and blend GA-MD wall materials, respectively. The distributions showed an increase in the fraction of large emulsion droplet and a change to a bimodal distribution. On the other hands, the change in the distribution of emulsion size in HICAP 100 could not be observed as shown in Fig. 5c. These
Fig. 6. Change in mean reconstituted emulsion size during storage at 51% RH and 50 8C for the small initial reconstituted emulsion size (SE) of about 1 Am. Wall materials: (a) GA, (b) Blend GA-MD, (c) HI-CAP 100. 5, Small powder (SP); D, Medium powder (MP); o, Large powder (LP).
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results supported the higher stability of encapsulated dlimonene in HI-CAP 100 wall materials than in the others as explained above. The changes in average reconstituted emulsion size were also investigated as a function of powder size during storage in Fig. 6. In Fig. 6a and b, the smaller powder size showed a higher emulsion size increasing rate than the larger powder size for GA and blend GA-MD as wall materials. These observations also agreed with the fact that the large powders were shown to exhibit a better protection against oxidation for the encapsulated d-limonene. However, for HI-CAP 100, the change in average reconstituted emulsion size for all powder sizes could not be observed as also shown in Fig. 6c. These results agreed with the powder size had almost no effect on the stability of encapsulated d-limonene HI-CAP 100 powder. This is likely to result from the high stability of encapsulated dlimonene in HI-CAP 100, and could overcome the powder size effect. Furthermore, SEM was also used to the internal structure of encapsulated d-limonene for the different powder sizes as shown in Fig. 7 for GA with the large size emulsion. dLimonene droplets were located in the form of small droplets embedded in the shell of wall matrix as shown in Fig. 7a, b, and c. A thicker shell matrix was observed in the large powder. On the other hand, for the small powder the thinner shell matrix and the higher concentration of dlimonene droplet were observed especially near the inner and outer surface of the shell. d-Limonene droplet, located near the surface of the powder, should be easier to release or react with the outside oxygen. These observations could be used to explain why the smaller powder showed a lower stability in addition to the larger effective surface area of the small powder. 3.3. Effect of the reconstituted emulsion size on stability of encapsulated d -limonene powder The effect of the reconstituted emulsion size on the stability of encapsulated d-limonene was also studied as shown in Figs. 3 and 4. The filled symbols represent a large reconstituted emulsion and unfilled symbols represent a small reconstitute emulsion. The small reconstituted emulsion size showed the higher release rate and oxidation rates
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Fig. 8. Change in mean reconstituted emulsion size during storage at 51% RH and 50 8C for the large initial reconstituted emulsion size (LE) of about 2 Am of HI-CAP 100 wall materials. 5, Small powder (SP); D, Medium powder (MP); o, Large powder (LP).
constant than the larger emulsion size in the GA and blend GA-MD wall materials. This indicates the larger size of dlimonene in powder showed a longer shelf life of the products. As mentioned above, this could be explained by the higher effective surface area of the small emulsion droplet to release and to react with the oxygen. The results are in an agreement with those of Risch and Reineccius (1988) but in a conflict with those of Ishido et al. (2002). As mentioned by Lethuaut et al. (2002), the decrease of oxidation rate of the small emulsion size should come from the decrease of the lipid molecules and increase of surface active compounds that could limit the initiation and propagation of the chain reaction. From Ishido et al. (2002), a fatty acid was used as core material of which oxidation mechanism should be composed of the chain reaction. That could explain the higher stability of smaller emulsion droplet in the matrix materials. However, in Risch and Reineccius (1988) and in the present work, d-limonene was used as model flavor which has a zero order kinetic of the oxidation reaction as mentioned in the materials and methods section. The reaction is not dependent on the concentration of the reactant d-limonene. Therefore, the effective surface area should control the oxidation rate of
Fig. 7. Microstructure of encapsulated d-limonene powder when blend GA-MD was used as wall materials for the large reconstituted emulsion size (LE). (a) Small powder (SP); (b) Medium powder (MP); (c) Large powder (LP).
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encapsulated d-limonene in the wall matrix. The calculated surface area, SSA, of the small emulsion size is 2 times larger than the large emulsion size as shown in Table 1. That is why the higher stability of large reconstituted emulsion droplet was reported. However, for HI-CAP 100, the effect of the emulsion size on the stability could not be observed. These results also agreed with the unchanged of mean reconstituted emulsion size during storage in both case of a small emulsion size and large emulsion size as shown in Figs. 6c and 8, respectively. These should be from the high stability of encapsulated d-limonene in HI-CAP 100 as discussed above, which can overcome the effect of emulsion droplet size.
4. Conclusions The powder size showed the influence on the stability of the encapsulated flavor in addition to the powder properties such as the bulk volume and the flowability of powder. The powder size distribution from the spray drying could be effectively controlled by changing the rotational speed of the centrifugal atomizer. The large powder size showed the higher stability and lower release of encapsulated flavor than the small powder size. Furthermore, in addition to the effect of emulsion droplet size on the retention during spray drying (Soottitantawat et al., 2003), the emulsion size also affected to the stability of encapsulated flavor powder. The small flavor size in the powder showed the lower stability than the large size of flavor especially for the simple zero order kinetic oxidation of flavor (d-limonene), even though the smaller size of emulsion can give the higher retention during the spray drying (Soottitantawat et al., 2003). Therefore, the optimal size of flavor in the powder should be recommended for both of the high retention during spray drying and its stability during storage as well as the ability to control the release of flavor.
Acknowledgements This study was partly supported by the Grant-in-Aid for Scientific Research (No. 15580108) from the Ministry of Education, Science, and Culture of Japan. We also acknowledge Nippon NSC (Tokyo, Japan) and Nippon Starch Chemicals (Osaka, Japan) for their kind gift of HI-CAP 100 and MD, respectively.
References Anandaraman, S., & Reineccius, G. A. (1986). Stability of encapsulated orange peel oil. Food Technology, 40, 88 – 93.
Bertolini, A. C., Siani, A. C., & Grosso, C. R. (2001). Stability of monoterpenes encapsulated in gum arabic by spray-drying. Journal of Agricultural and Food Chemistry, 49, 780 – 785. Chang, Y. I., Scire, J., & Jacobs, B. (1988). Effect of particle and microstructure properties on encapsulated orange oil. In S. J. Risch, & G. A. Reineccius (Eds.), Flavor encapsulation. ACS Symp. Ser. No., vol. 370 (pp. 87 – 102). Finney, J., Buffo, R., & Reineccius, G. A. (2002). Effect of type of atomization and processing temperatures on the physical properties and stability of spray-dried flavors. Journal of Food Science, 67(3), 1108 – 1114. Ishido, E., Hakamata, K., Minemoto, Y., Adachi, S., & Matsuno, R. (2002). Oxidation Process of Linoleic acid encapsulated with a polysaccharide by spray drying. Food Science and Technology Research, 8(1), 85 – 88. Kim, Y. D., & Morr, C. V. (1996). Microencapsultaion properties of gum arabic and several food proteins: spray-dried orange oil emulsion particles. Journal of Agricultural and Food Chemistry, 44, 1314 – 1320. Lethuaut, L., Me´tro, F., & Genoi, C. (2002). Effect of droplet size on lipid oxidation rate of oil-in-water emulsions stabilized by protein. Journal of the American Chemical Society, 5, 425 – 430. Linare`s, E., Larre´, C., & Popineau, Y. (2001). Freeze- or spray-dried gluten hydrolysateds: 2. Effect of emulsification process on droplet size and emulsion stability. Journal of Food Engineering, 48, 137 – 146. McClements, D. J. (1999). In F. M. Clydesdale (Ed.), Food Emulsions, Contemporary food science. Washinton, DC7 CRC Press. National Starch and Chemical. (1999). Product data sheet: HI-CAP 100. National Starch and Chemical, A Member of the ICI Group, Manchester, UK. Reineccius, G. A., Ward, F. M., Whorton, C., & Andon, S. A. (1995). Development in gum acacias for the encapsulation flavors.. In S. J. Risch, & G. A. Reineccius (Eds.), Encpasulation and controlled release of food ingredients. ACS Symp. Ser. No., vol. 590 (pp. 161 – 168). Risch, S. J., & Reineccius, G. A. (1988). Spray-dried orange oil: Effect of emulsion size on flavor retention and shelf stability. In S. J. Risch, & G. A. Reineccius (Eds.), Flavor encapsulation. ACS Symp. Ser. No., vol. 370 (pp. 67 – 77). Rosenberg, M., & Young, S. L. (1993). Whey proteins as microencapsulating agents: micro-encapsulation of anhydrous milkfat-structure evaluation. Food Structure, 12, 31 – 41. Sheu, T. Y., & Rosenberg, M. (1995). Microencapsulation by spray drying ethyl caprylate in whey protein and carbohydrate wall systems. Journal of Food Science, 60(1), 98 – 103. Soottitantawat, A., Yoshii, H., Furuta, T., Ohgawara, M., Forssell, P., Partanen, R., et al. (2004). Effect of water activity on the release characteristics and oxidative stability of d-limonene encapsulated by spray drying. Journal of Agricultural and Food Chemistry, 52, 1269 – 1276. Soottitantawat, A., Yoshii, H., Furuta, T., Ohgawara, M., & Linko, P. (2003). Microencapsulation by spray drying: Influence of emulsion size on the retention of volatile compounds. Journal of Food Science, 68, 2256 – 2262. Whorton, C. (1995). Factors influencing volatile release from encapsulation matrices. In S. J. Risch, & G. A. Reineccius (Eds.), Encpasulation and controlled release of food ingredients. ACS Symp. Ser. No., vol. 590 (pp. 134 – 142). Whorton, C., & Reineccius, G. A. (1995). Evaluation of the mechanisms associated with the release of encapsulated flavor materials from maltodextrin matrices. In S. J. Risch, & G. A. Reineccius (Eds.), Encpasulation and controlled release of food ingredients. ACS Symp. Ser. No., vol. 590 (pp. 143 – 160). Yoshii, H., Soottitantawat, A., Liu, X. D., Atarashi, T., Furuta, T., Aishima, S., et al. (2001). Flavor release from spray dried maltodextrin/gum arabic or soy matrices as a function of storage relative humidity. Innovative Food Science and Emerging Technologies, 2, 55 – 61.