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form a stable emulsion. The emulsion is then fed into a spray dryer where it is converted to a dried particle.
Microencapsulation is the technique by which the Numerous wall materials or encapsulating agents are sensitive ingredients are packed within a coating or wall available for food application. Gums arabic, hydrolyzed material. The wall material protects the sensitive ingredient starches, and emulsifying starches are most commonly used (or core) against adverse reaction, prevents the loss of as wall materials (Kenyon, 1995; Reineccius, 1988; Shahidi volatile ingredient, and controls release of the ingredient & Han, 1993). Some proteins such as whey proteins (Risch, 1993; Shahidi & Han, 1993). In addition, micro- (Sheu & Rosenberge, 1995), sodium caseinate (Hogan, encapsulation can convert liquids into free- owing powers, McNamee, Riordan, & Sullivan, 2001), and gelatin which are easy to handle. (Bruschi, Cardoso, Lucchesi, & Gremiao, 2003) are also Microencapsulation has found many applications in used as wall materials. Typically, the effective wall food industry. Important applications are to coat color- materials for spray drying should have functional proper- ants, avors, vitamins, and other sensitive food ingredients ties, including good emulsification, film forming, high in order to increase their shelf life (Dziezak, 1988; Shahidi solubility, low viscosity at high concentrations and low cost & Han, 1993). Various techniques are employed to properties (Reineccius, 1988; Trubiani & Lacourse, 1988). microencapsulate food ingredients. Spray-drying is the Gum arabic, a natural plant exudates polysaccharide of most often used technique in the food industry (Gibbs, acacia, is a well-known effective wall material for many Kermasha, Alli, & Mulligan, 1999; Reineccius, 1988). In years and is still the good choice as wall material due to its this process, the sensitive ingredient was mixed or stable emulsion and good volatile retention. Problems homogenized in a solution containing wall material to associated with the use of gum arabic in microencapsula- tion are high cost and limited supply. Emulsifying starches are starches derivatives with lipophilic group, i.e.emulsification properties (Trubiani & Lacourse, 1988). (Bangkok, Thailand). Modified tapioca starch was However, emulsifying starches have some limitations. They prepared according to the method described in exhibit poor avor protection against oxidation and have Section 2.2 in the laboratory of Department of Food off avor (Reineccius, 1988). Krishnan, Kshrisagar, and Science and Technology of Thammasat University Singhal (2003) studied the efficacy of succinylated waxy (Pathumthani, Thailand). Trans-b-carotene (powder) was maize starch, maltodextrin and gum arabic as wall obtained from Sigma Chemical Company (St. Louis, materials for encapsulation of cardamom oleoresin by USA). All other chemicals used in this study were of spray drying. They reported that succinylated waxy maize analytical grade.
Starch and maltodextrin had a lower protection to cardamom oleoresin during storage as compared to gum 2.2. Sample preparation arabic.
Maltodextrins are hydrolyzed starches produced by partially hydrolysis of starch with acid or enzymes. Acid modified tapioca starch was prepared from Hydrolyzed starches have the advantages of being low native tapioca starch according to the procedure of cost, bland in avor, and good avor protection against Loksuwan (2005) (Thailand Petty Patent No. 2146). oxidation. Hydrolyzed starches are reported to improve Tapioca starch was added to 3 N H2 SO4 in a ratio of shelf life of orange oil (Anandaraman & Reineccius, 1986) 1:5 w/v. The mixture was stirred magnetically for 3 h at and carrot carotene (Wagner & Warthesen, 1995). These 60 1C. After hydrolysis the starch slurry was cooled and authors also reported that storage stability of core neutralized with saturated Na2 CO3 . The acid modified materials increa sed as hydrolyzed starches DE increased. starch was filtered, washed with three volumes of distilled Problems associate with the use of hydrolyzed starches in water, followed with 100 ml ethanol (95%). The starch microencapsulation are lack of emulsification properties was then dried at 70 1C for overnight. The dried starch and poor avor retention (Reineccius, 1988). Many was ground using a laboratory blender. Prior to micro- researches have used hydrolyzed starches in conjunction encapsulation, the modified starch was suspended in with other wall materials or emulsifying agents to improve distilled water (29% w/w) and heated under steam pressure their emulsifying characteristics. Mixtures of maltodextrins for 5 min to obtain gelatinized starch paste. Pure trans- or corn syrup solids with whey proteins were reported as b-carotene was added to the gelatinized starch paste in a effective wall materials for microencapsulation of ethyl ratio of 1:580 w/w, on dry starch basis. The mixture was caprylate (Sheu & Rosenberge, 1995). Barbosa, Borsarelli, then homogenized to obtain an aqueous emulsion and Mercadante (2005) reported that maltodextrin with (feed liquid) and immediately fed to the spray-dryer emulsifier Tween 80 had the ability to encapsulate a higher (Armfield FT 30, Armfield Technical Education Co., amount of bixin than maltodextrin alone. A blend of gum Hampsshier, England). The inlet and outlet air tempera- arabic: maltodextrins: modified starch at a 4/6:1/6:1/6 ture were maintained at 17075and9575 1C, respectively.
Was reported to provide a better protection of cardamom Experiments were performed in triplicate. The spray-dried oleoresin than gum arabic (Krishnan, Bhosale, & Singhal, powders were collected, kept in plastic bags wrapped with 2005). aluminum foil and stored in desiccators containing silica Preliminary study in our laboratory has shown that the gel at room temperature.efficacy of acid modified starch for encapsulation required Solution of maltodextrin (29% w/w) and native tapiocathe starch pre-swelling and gelatinization. This can be starch (20% w/w, due to limit of viscosity) in distilled waterachieved by autoclaving of the modified starch slurry under were used for comparison study. Pure trans-b-carotene wassteam pressure. This process results in formation of starch added to maltodextrin and native tapioca starch solutionspaste. The objective of this study was to evaluate the in the ratio of 1:580 and 1:400 w/w, on dry basis, potential of acid modified tapioca starch after treated with respectively. The homogenization and spray drying wereheat under steam pressure as wall materials for encapsula- performed in the similar manner above. tion of b-carotene. The microstructure and physicochem- ical properties of encapsulated powder were investigated. 2.3.Determination of dextrose equivalent (DE) andThese results were compared to those of its native starch viscosity and commercial maltodextrin.
DE of modified starch produced by acid hydrolysis was2. Material and methods determined using the method of Lane and Eynon (1923). Viscosity (cps) of samples was measured using Brook-2.1. Materials field Digital Viscometer (Model DV-II+, Brookfield Engineering Laboratories, Inc., Stoughton, USA). Solu- Native tapioca starch was purchased from local market tions of modified tapioca starch (29% w/w), native starch (Thailand). The moisture content was about 8%. (20% w/w), and maltodextrin (29% w/w) in distilled water Moisture content was determined according to the method were prepared. The samples were then placed in a water described in Section 2.9. Maltodextrin (Star-Dri 240-S, DE bath with gently stirred. The viscosity was measured when 24) was a gift from Burley Jucker Specialties Ltd. the temperature of sample reached 80 1C.
Particle size distribution of the samples was measured using an AquaLab (CS2, USA).The particle size distributions of the spray dried powders were determined using Laboratory test sieve (AS 200 digit, 2.10. Statistical analysis ASTME 11, Retsch, Germany). The data reported in all tables are average of triplicate
Optical microscope determinations. Analysis of the data was carried out using ANOVA (SPSS program version 10.0 for Windows).An optical microscope (Polarizing Microscope Axios- Differences between means were tested using the Duncan's kop-po, Zeiss) was used to investigate the feed liquids multiple range tests at Po0.05.before spray drying and the spray dried powders. Thepicture was taken at 200 magnification.
Results and discussion
Scanning electron microscopy 3.1. Dextrose equivalent (DE) and viscosity Scanning electron microscope (SEM) (JEOL JSM-6301F, DE is a measure of degree of hydrolysis of starch Jeol Ltd., Tokyo, Japan) was used to study the morpholo- molecule, which related to reducing sugar production. The gical properties of the spray-dried powders. Powder particles low DE value means lower amount of reducing sugar produced. The modified starch obtained in this investiga- were attached to the SEM stubs of 10 0 diameter using a two- sided adhesive tape. The samples were then sputter coated tion had DE value of 2, indicating that degree of hydrolysis with gold and examined at 500 ,1000 , and 1500 was very low. This means that the acid-modified starch magnifications. An acceleration potential of 5 kV was used obtained in this investigation contained less amount of low during micrograph. molecular weight sugar than maltodextrin with DE value of 24. In other words, this modified starch contained many
Analysis of total and surface carotene of spray-dried amylose molecules with shorter chain length, as the result powder of acid hydrolysis.
Results from the measurement of viscosity showed that. The method of Desobry, Netto, and Labuza (1997) with at 29% w/w maltodextrin had lower viscosity (13.8 cps) slight modification was used to analyze the total carotene than modified tapioca starch (133.8 cps). At 29% the native and surface carotene. starch solution was too viscous to measure its viscosity.Total carotene: Powder (50 mg) was weighed into the Therefore, the viscosity of native starch was measured at 125 ml- ask, dispersed in water (2.5 ml) and extracted with 20% w/w, which was found to be 31,880 cps. hexane (25 ml). After shaking (500 rpm) for 30 min at room temperature, the hexane fraction was measured at 454 nm
Particle size distribution with spectrophotometer.
Surface carotene: Powder (50 mg) was weighed into the The particle size distributions of spray-dried powders or ask and extracted with 25 ml hexane. After shaking at microcapsules using Laboratory test sieve are shown in 100 rpm for 15 s, sample was centrifuged at 1000g for. The weight percent data were plotted against the 1 min. The supernatant was measured at 454 nm with particle diameter in microns. Modified tapioca starch had spectrophotometer. wider particle size distribution, toward the smaller diameters, as compared to its native starch and maltodex-
Cold water solubility of spray-dried powders trin. The most predominant diameters for modified tapioca starch were 75-150 m (55.8%), for native starch were The method of Singh and Singh (2003) with slight 106-250 m (69.7%) and for maltodextrin were 106-250 m modification was used to analyze cold water solubility of (80.0%). The larger powder particle sizes of maltodextrin spray dried powders. One gram of powder was mixed with can be explained by agglomeration or caking of powder 100 ml of water using a magnetic stirrer at room temperature particles, which were observed in this sample. for 30 min. A 30-ml aliquot of starch solution was transferred to a 50-ml centrifuge tube and centrifuged (Hettich 3.3. Optical microscope Zentrifugal Universal 16R, German) at speed 430g for 15 min. A 10-ml aliquot of the supernatant was evaporated Light micrographs of feed liquids and spray-dried on a steam bath and dried in an oven at 110 1C for overnight.
Determination of moisture content and water activity als. The modified tapioca starch showed disintegration of some granules; only a few starch granules still exhibited The moisture content of the samples was measured maltese cross as compared with the native starch. This by hot air oven at 105 1C for 16 h. The water activity result indicated that steam pressure treatment caused changes in granular structure of acid modified starch. In the case of maltodextrin, completely disintegration of starch granules was observed.
SEM of spray-dried powder Spray-dried powders prepared from modified tapioca starch, native tapioca starch, and maltodextrin were observed for granular structure using SEM . Results clearly showed significant differences in size and shape. Microcapsules from modified tapioca starch showed spherical shape with extensive dented surface, while those from native tapioca starch showed drying process (Rosenberg, Kopelman, & Talmon, 1985, rounded shape, smooth surface with no obvious dents. 1990). The extensive dented surfaces of modified tapioca Modified tapioca starch had granules size ranging from o5 starch was probably attributed to starch granule disrupted to 30 mm, while native tapioca starch had more homo- resulted in more susceptible to shrinkage during the drying geneous granules ranging in size from 2 to 18 mm. stages. The SEM micrograph of spray-dried maltodextrin Formation of dented surfaces of spray-dried particles was showed spherical shapes with smooth and some dented attributed to the shrinkage of the particles during the surfaces, and a more heterogeneous size, which mainly