O-STARCH-10 Effect of maltodextrin on core retention and microencapsulation efficiency of encapsulated soy oil Plengsuree Thiengnoi 1, Moshe Rosenberg 2 and Manop Suphantharika 1 1 Department of Biotechnology, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand 2 Department of Food Science and Technology, University of California, Davis, CA 95616, USA Abstract Soy oil which is rich in polyunsaturated fatty acids is one of a few non-fish oils containing linolenic acid (an omega-3 fatty acid) that has been shown to prevent heart disease. However, soy oil is susceptible to oxidative deterioration and its use in dry foods is limited because of its liquid form. Microencapsulation of soy oil is an alternative choice for application of soy oil by converting it into dry and stable powder. Soy oil was microencapsulated in wall system using spray-drying process. The mixture of soy protein isolate (SPI) and maltodextrin with different DE (Dextrose Equivalent) values were evaluated as microencapsulating agents or wall materials. An effect of maltodextrin types (7.5DE, 18DE and 24DE) on core retention and microencapsulation efficiency (MEE) was determined. The core retention was not related to DE value in all systems, except for condition of 5% protein concentration/25% core load indicated that the core retention was not affected by the type of maltodextrin. The effect of DE value on MEE showed that MEE was significantly influenced by DE value of the maltodextrin. MEE increased when DE value increased in all cases. The results indicated that combination of soy protein isolate and carbohydrate potentially used as microencapsulating agents for encapsulation of lipids. Introduction Microencapsulation is the process by which small particles of solid, liquid or gas are packed within secondary materials to from a microcapsule (1). The material that is coated or entrapped is called core material, active, fill or internal phase. The material that forms the structures around the core is called wall material, carrier, membrane, shell or coating material. The microcapsule may range in diameter from sub-micron to several millimeters and can be designed to have a variety of structures. The structure of the microcapsules can be a single-particle structure in which core material is completely surrounded by a uniform wall material. It can also be multiwalled structure in which the wall layers can have the same or quite different composition (2, 9). The microencapsulation may be used to facilitate the processing of an ingredient or food product, or to improve its quality when deliver to the consumer. The microencapsulation protects the core ingredient from the environment or from undesirable interactions with other ingredients during processing and allows controlled release at the appropriate time (1). There are many techniques that are used to microencapsulate food ingredients such as, spray drying, spray chilling, extrusion, etc. A selection of method depends on the core and wall materials properties, controlled release mechanism, the capsule morphology and particle size required. The spray drying technique is the most commonly used microencapsulation method in the food industries and is also economical and flexible that produces products of good quality (1, 12). 137
The objective of this study was to investigate the functionality of soy protein isolate in wall systems containing 2.5 and 5% (w/w) soy protein isolate, 15 and 17.5% maltodextrins with different dextrose equivalents or DE values (MDE 7.5DE, MDE 18DE and MDE 24DE) that were used for encapsulation of lipids at loading ratio ranging 25 and 50% (w/w). The effect of maltodextrin types on the core retention and microencapsulation efficiency (MEE) was determined. Materials and Methods 1. Materials Soy protein isolate (SPI) (Prolisse, Cargill, Inc., Minneapolis, CA, USA.) contained 90.3% protein on dry basis. Maltodextrins with DE values of 7.5, 18 and 24 (Cerestar USA Inc., Hammond, IN, USA.) and soy oil (Costco, Vacaville, CA, USA.). 2. Emulsion preparation Wall solutions were prepared in deionized water that contained 20% (w/w) solids consisting of combinations of SPI and a maltodextrin at ratios of 75 and 87.5% (w/w). First of all, soy protein isolate was dissolved in deionized water containing sodium azide (0.02% w/v) into the SPI solution. This solution was adjusted to ph 7 and maltodextrin was added to SPI solution for dissolving. A soy oil was emulsified into the wall solutions at a proportion of 25 and 50% (w/w). Afterthat, the emulsification was carried out in two stages. First, a coarse emulsion was prepared by using an Ultra Turrax T25 basic homogenizer (IKA Labortechnik (Germany) operates at 22,000 rpm for 30 s. And then, a fine emulsion was prepared by using a PANDA 2K homogenizer (Niro Soavi S.P.A, PARMA (Italy)) operates at 50MPa for 4 successive passes. 3. Spray dryer An emulsion was spray dried using an APV Anhydro Laboratory Spray Dryer. (APV Anhydro A/S, Soborg, Denmark). The dryer had an evaporation rate of 7.5 kg/h and a chamber diameter of 1 m. The height, width and length were 2.6, 1.2 and 1.3 m, respectively. Drying was carried out in the concurrent mode. Centrifugal atomizer that operated at 50,000 rpm was used in order to atomize the emulsions. In all cases the inlet and exit temperatures were kept at 160±5 C and 80±5 C, respectively. All the powders were collected from the bottom of the dryer s cyclone and were kept in glass jars in desiccators at 25 C. 4. Core retention Core retention was defined as the ratio (expressed as percentage) of the amount of oil that exists in the capsule to the amount of oil that the emulsion contains Core retention (%) = % of oil net * 100 % of oil in emulsion The amount of oil that exists in the capsule was defined as oil content in the sample. Sample (about 1 g) of powder was placed into 50-ml tube containing 2 ml of ethanol (Fisher Scientific, Pittsburgh, PA). Then, 10-ml mixture of 37% HCl (Fisher Scientific, Pittsburgh, PA) and water at 25:11 (v/v) ratio was added into the tube. A mixture was heated at 100 C until it became dark brown color, cooled to room temperature. The mixture was added 10-ml ethanol and then transferred into Mojonnier fat extraction flask. Lipids were first extracted using a mixture of 25-ml 138
ethyl ether and 25-ml petroleum ether and then a mixture of 15-ml ethyl ether and 15- ml petroleum ether was used for additional 2 successive extraction steps. The mixture were combined, the solvent was removed at 100 C, the solvent-free extracts were dried at 100 C under vacuum for 30 min. Afterthat, the solvent-free extracts were cooled to room temperature in a desiccator and the extracted fat was determined gravimetrically (4). 5. Microencapsulation efficiency (MEE) MEE represents the proportion of oil that was not available to the extracting solvent (petroleum ether) under the test conditions. In order to calculate the MEE, the amount of core that could be extracted (surface oil), at standard conditions, had to be determined. The surface oil defines as the amount of core that could be extracted by solvent. One gram of dry capsules was weighed into an extraction flask; 25ml petroleum ether (Sigma Chemical Co.) was added to the flask.the extraction flask was placed on a Garver shaker (model 360; Garver Mfg., Union City, IN), The extraction was carried out for 5, 15 and 30 min at 25 C. The mixture was filtered (GN- 6; Gelman Science, Ann Arbor, MI), the solvent was evaporated over a water bath at 70 C, and the solvent-free extracts was dried at 100 C under vacuum for 30 min. The amount of extracted fat was then determined gravimetrically (11). MEE defined, in percentage, as (100% % surface oil) Results and Discussion 1. Core retention A core retention during microencapsulation by spray drying is affected by the properties and composition of the emulsion, and by the influence of atomization and drying conditions (3, 6, 7, 10). In order to understand the main factors that affect the core retention, it is important to understand the different phases during spray drying process. The first phase can be described as a steady-state process or a constant rate phase during water is removed, by a hot air, from the surface of the drying particles. Once a moisture content at the surface drops below saturation, an outer surface starts to dry until a crust is formed and signals the beginning of the second phase of spray drying, that is, a decreasing rate phase. A driving force that determined a drying rate during the first stage is the moisture content of the hot air and its flow rate around the drying particles. The second phase of the spray drying process is controlled by the rate of water diffusion from interior parts of the particle to the surface. This stage is influenced by the hindered diffusivity of water through the wall matrix. It has to be noted that due to the formation of moisture gradient from the surface of the drying particle inward, the drying rate during this stage exhibits an exponential decrease with time (5, 6). The high drying rates lead to rapid crust formation around the drying particles and then, the core retention increases. It has been suggested that core losses occur mainly prior to the formation of the dry crust, at the end of the constant drying rate phase of spray drying (6). Table 2 shows the effect of maltodextrin types on the core retention. Results indicated that the effect of DE values on the core retention was significantly varied. These differences could be explained by a variety of reason. It could be explained as the difference of maltodextrin molecular weight. A higher DE value presents a smaller molecular weight than a lower DE values. The higher core retention at the lower DE 139
value was due to the higher viscosity of emulsion, with the lower DE value, led to slower drying rate, its influence on an internal mixing was more significant. The higher viscosity limited the internal mixing and thus promoted the core retention. Nevertheless, the higher core retention at the higher DE value was affected as carbohydrate enhances the drying rate and thus, led to a rapid formation of dry crust and therefore, to increase the core retention (8). Table 2 The effect of the maltodextrin types on the core retention Maltodextrin types %SPI and core load (DE value) Core retention (%) 2.5% ISP / 25% core 7.5 83.35 ± 1.55 b 18 82.69 ± 1.81 b 24 89.99 ± 2.12 a 2.5% ISP / 50% core 7.5 86.76 ± 1.81 a 18 79.59 ± 1.73 b 24 89.21 ± 1.94 a 5% ISP / 25% core 7.5 84.88 ± 0.82 a 18 83.05 ± 1.52 a 24 86.44 ± 6.68 a 5% ISP / 50% core 7.5 86.29 ± 5.12 a 18 89.97 ± 2.79 a 24 78.67 ± 3.12 b 2. Microencapsulation efficiency (MEE) MEE is defined as the proportion of core, included in a unit mass of dry microcapsules that could not be extracted by solvent, at standardized extraction conditions. The proportion of core that could be extracted by the solvent was defined as surface oil or surface core (3, 8). Prolisse MEE (%) 100 90 80 70 60 50 40 0 5 10 15 20 25 DE value 2.5/25c 2.5/50c 5/25c 5/50c Figure 1 The effect of the types of maltodextrin on the MEE. Changes, with types of maltodextrin, in MEE obtained with microcapsules prepared with different formulation. Systems are denoted by %ISP/core load in formulation. 140
An effect of DE values on MEE presented in Figure 1. Results of MEE indicated that MEE was significantly influenced by the DE values of maltodextrin, in a range of 71.44%-96.85%. In all cases, MEE obtained with capsules containing the higher DE values was higher than that exhibited by capsules containing the lower DE values. The effect of DE values on MEE could be explained due to the differences in molecular weight of the carbohydrate constituents of the maltodextrins. It has been reported that low molecular weight carbohydrates form an amorphous, glass-like phase during spray drying. This phase has been indicated to fill all the spaces between the protein and core constituents of the capsule, thus acting like a hydrophilic sealant (3, 8). Conclusion Wall systems consisting of a mixture of soy protein isolate and maltodextrin were effective for soy oil microencapsulation by spray drying. The maltodextrin types affected a core retention and microencapsulation efficiency (MEE) of encapsulated soy oil because of the molecular weight. The higher DE values containing the smaller molecular weight than the lower DE values that affected a drying rate of powder particles. Results indicated that the effect of DE values on the core retention was significantly varied, but this effect on MEE was related to the DE values. Acknowledgements This research is partially supported by Commission on Higher Education, Ministry of Education, Thailand. References 1. Augustin, M. A., Sanguansri, L., Margetts, C. & Young, B. (2001). Microencapsulation of food ingredients. Food Australia, 53, 220-223. 2. Gibbs, B. F., Kermasha, S., Alli, I., & Mulligan, C. N. (1999). Encapsulation in the food industry: a review. International journal of food science and nutrition, 50, 213-224. 3. Moreau, D. L. & Rosenberg, M. (1993). Microstructure and fat extractability in microcapsules based on whey proteins or mixtures of whey proteins and lactose. Food Structure, 12, 457-468. 4. Nielsen, S. S. (1998). Food analysis. (2 nd Ed.) (pp. 207-208). Gaithersburg, Maryland: Aspen Publishers, Inc. 5. Reineccius, G. A. (1988). Spray drying of food flavors. In G. A. Reineccius & S. J. Risch (Eds.), Flavor encapsulation, (pp. 55-66). Washington DC: American Chemical Society. 6. Rosenberg, M., Kopelman, I. J., & Talmon, Y. (1990). Factors affecting retention in spray drying microencapsulation of volatile materials. Journal of Agriculture and Food Chemistry, 38, 1288-1294. 7. Rosenberg, M. & Young, S. L. (1993). Whey proteins as microencapsulating agents. Microencapsulation of anhydrous milkfat Structure evaluation. Food Structure, 12, 31-41. 141
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