Chapter 13
Evaluation of the Mechanisms Associated with the Release of Encapsulated Flavor Materials from Maltodextrin Matrices
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Colleen Whorton and Gary A. Reineccius Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108
In order to evaluate the mechanisms associated with the controlled delivery of encapsulated flavoring materials, maltodextrins and corn syrup solids of Dextrose Equivalent (DE) 10, 15, 20, 25, and 36 were spray-dried with a mixture of odd-numbered carbon aldehydes C-3 to C-11 at a level of 0.1% of the total mixture solids. Samples were equilibrated at 20°C at water activities ranging from 0.00 to 0.75. A gas chromatographic (GC) static headspace method was utilized to evaluate flavor diffusion over time as a function of volatile molecular weight and the rate of flavor exhaustion from the encapsulated powders. The effects of carrier D E , equilibration time and temperature, and sample water activity (a ) were also evaluated. Results were correlated with the glass transition temperature and collapse of each powder and with morphological changes observed by scanning electron microscopy (SEM). w
For many years, conventional methods of encapsulation such as spray-drying and extrusion have been the primary means of converting liquid flavors to a dry form for food applications. However, recent advances in the production technology of products such as microwave entrees, snacks and desserts; intermediate moisture foods such as cereal fruit fillings and fruit leathers; chewing gums, candy and confectionery; and dried beverage mixes have created a need for the development of flavors for these products which have controlled or sustained release properties. Although the pharmaceutical industry has successfully utilized such techniques in the manufacture of their products for a number of years, cost constraints have severely limited widespread application of these technologies in the food and flavor industry. A substantial need, therefore, exists for inexpensive encapsulation technologies which protect the encapsulated material or "active", yet release very slowly with prolonged
0097-6156/95/0590-0143$12.00/0 © 1995 American Chemical Society In Encapsulation and Controlled Release of Food Ingredients; Risch, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
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exposure to heat or water, or which retain the flavor in dry or intermediate moisture food systems. The purpose of this study, therefore, was to evaluate the physicochemical factors associated with the retention and release of flavoring materials from traditional spray-dried carriers in an attempt to better understand how and why diffusion and release of the active occurs. Factors evaluated included maltodextrin or spray-dried corn syrup solids DE, the effects of the glass transition temperature (Tg) and collapse, the ability to allow release of the active over time, the rate at which powders were exhausted of flavor, and changes in the morphology of the spray-dried powders.
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Materials and Methods Powder Preparation. A homologous series of odd-numbered carbon aldehydes ranging from C3 to C l l (Aldrich Co., Milwaukee, WI) was dispersed in fresh vegetable oil and encapsulated in a series of maltodextrin and corn syrup solids including M100, M150, M200, M250 and M365 (Grain Processing Corp., Muscatine, IA). Depending upon the hydration properties of the carbohydrate, approximately 35 to 45% distilled spring water (Glenwood, St. Paul, MN) was added to 1900g of each carrier, and the carriers were allowed to hydrate for 24 hrs while stored at 4.5°C. Four hours prior to spray-drying, the mixtures were allowed to equilibrate to room temperature and then adjusted to a constant viscosity measured as a stirring number of 45 ± 2 at 20°C using a Rapid Visco Analyser (Foss Food Technology, Eden Prairie, M N ) . Immediately prior to spray-drying, a bench-top high shear mixer was used to form an emulsion between the hydrated carrier and 110g of the vegetable oil to which 2% of each aldehyde had been added. For each sample, a constant flavor/oil:solids ratio of 1:17 (equivalent to 0.1% of each aldehyde on a dry-weight basis) was maintained. The emulsions were spray-dried using a Niro Utility Dryer (inside chamber dimensions: 150 cm ht and 120 cm diam.) equipped with a 12 cm diam. radial vane centrifugal atomizer operating at 24,000 rpm. Drying conditions were standardized at an inlet air temperature of 180 +. 5°C and an outlet air temperature of 100 ±_ 5°C using concurrent flow. Under these conditions, the dryer was evaporating approximately 12 kg of water per hr. A l l infeed was introduced into the dryer at room temperature. The resulting powders were allowed to cool and were then stored in sealed glass jars at -20°C until sample analysis. Sample Preparation and Equilibration. To determine the effect of water activity (aj on volatile retention/release and sample collapse, samples were prepared as follows: 4.5g samples of each of the spray-dried powders were weighed into 20 ml standard headspace vials and placed in desiccators containing saturated salt solutions. The desiccators were then sealed under vacuum, placed in a 20°C incubator, and allowed to equilibrate for 15 days. Immediately after equilibration, the vials were sealed with crimp caps and Teflon septa and stored at -20°C until headspace analysis. The salt solutions and the range of water activities evaluated are given in Table I on the following page.
In Encapsulation and Controlled Release of Food Ingredients; Risch, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
13. WHORTON & REINECCIUS
Encapsulated Flavor Materials
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Table I. Water Activities of Saturated Salt Solutions _âw_
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0.00 0.11 0.33 0.44 0.53 0.64 0.75
_SâlL Drierite Lithium Chloride Magnesium Chloride Potassium Carbonate Magnesium Nitrate Sodium Nitrite Sodium Chloride
Gas Chromatographic Headspace Analysis. Headspace samples were analyzed using a Hewlett-Packard static headspace unit (model 19395A, Hewlett-Packard, Avondale, PA) in conjunction with a Hewlett-Packard 5890 gas chromatograph equipped with a hydrogen flame ionization detector. A l l samples were equilibrated at 50°C in the headspace unit prior to pressurization and injection. A bonded phase DB-5 fused silica capillary column (30 m χ 0.32 mm, 1 μτη film thickness) was used in all analyses (J & W Scientific, Rancho Cordoba, CA). Operating parameters were as follows: Carrier gas: helium; Head Pressure: 15 psig; Split: 20:1; Headspace Sample Loop: 2 ml; Initial Temperature: oXFC; Initial Time: 1 min; Rate 1: 15°C/min to 220PC; Rate 2: 20°C/min; Final Temperature: 250 C. Using these basic parameters, two main static headspace analyses of the equilibrated powders were conducted hereon referred to as the equilibration study and the exhaustion study. The objective of the equilibration study was to determine the increase in volatile headspace concentration as a function of equilibration time. Samples of M100, M200, and M365 at each water activity were equilibrated at 50°C for time intervals ranging from 40 min (initial sample) up to 30hrs. Each vial was sampled only once. The amount of each aldehyde (C-3, C-5, C-7, C-9, and C - l l ) was quantitated by an external standard (ESTD) method based upon a standard mix containing 200 to 300 ppm of each of the five aldehydes in the model system. Results were tallied and plotted to evaluate and compare the ability of the different powders to release volatiles into the headspace over time as a function of D E and a*. Most points represent the average of duplicate or triplicate values. The objective of the exhaustion study was to determine the rate at which the concentration of volatiles in the headspace was exhausted with repeated sampling of a given vial over time. Samples of the M100, M150, M200, M250, and M365 at each water activity were equilibrated for 40 min at 50°C prior to each sampling. Once the injection was made, the sample was removed from the headspace unit, vented, and immediately recapped with a new septum prior to the next sampling. As above, each aldehyde was quantitated by ESTD. The process was repeated once per hour for 15hrs or until the sample headspace volatiles were depleted (if depletion occurred before hr 15). Results were tallied and plotted to evaluate and compare the rate at which volatiles were lost from the powders as a function of D E and a*. P
Preparation of Washed Powder Samples. In order to determine i f residual oil or aldehyde standards remaining on the surface of the spray-dried powders had an effect
In Encapsulation and Controlled Release of Food Ingredients; Risch, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
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on experimental results, the exhaustion study was repeated with a control group of washed powders. A 100g sample was taken from each of the M100, M200, and M365 spray-dried flavor powders. Each 100g sample was then washed in a 500 ml Erlenmeyer flask with 150 ml of pentane. The pentane was filtered off and the samples were rinsed again with another 150 ml volume of pentane. The entire process was repeated three times, after which the powders were allowed to dry (approximately lhr) at room temperature under a fume hood. The samples were then weighed (4.5g each) into 20 ml headspace vials and equilibrated to a range of water activities as described above. Absolute Quantitation of Volatiles by Direct Injection. A direct injection method was used to quantitate the volatiles in the powder before and after water activity equilibration and after exhaustion. For each sample, 0.15g of powder was weighed into a 3 dram vial and solubilized with 0.85g of distilled spring water. The carbohydrate carrier was precipitated with 4 ml of acetone containing 0.26 g/L of 2octanone as an internal standard. Approximately 2 ml of the acetone layer was then drawn off the top and transferred to a 0.5 dram auto-sampler vial. Aldehydes in the powders were quantitated by the internal standard (ISTD) method using a HewlettPackard 5890 gas chromatograph equipped with a hydrogen flame ionization detector and a Hewlett-Packard auto sampler (model 7673A). A bonded phase DB-Wax fused silica capillary column (60 m χ 0.53 mm inner diameter, 1 μπι film thickness; J & W Scientific, Rancho Cordoba, CA) was used in all analyses. Operating parameters were as follows: Carrier Gas: helium; Head Pressure: 15 psig; Split 40:1; Injection Volume: 1 uL; Initial Temperature: 45°C; Initial Time: 5 min; Rate: 15°C/min; Final Temperature: 180°C; Final Time: 5 min. Scanning Electron Microscopy (SEM). A Philips 500 S E M (Philips Electronic Instruments, Mahwah, NJ) with a 100 μπι objective lens aperture was used to view characteristics of particle structures and to make comparisons of the variations in morphology observed between the different powders equilibrated to various water activities. The powders (or thinly sliced chips from collapsed sample masses) were mounted on stubs using double stick carbon tape. A thin layer (approximately 20 angstroms) of gold/palladium was then applied to the surface in a vacuum evaporator to make the sample conductive. A l l samples were examined in the secondary electron imaging mode at an acceleration voltage of 12 k V . Photographs were taken at magnifications of 640X and 1250X. Results and Discussion Results of the equilibration study for M100, M200, and M365 are shown in Figure 1 depicting the sum total concentration of aldehydes (C-3, C-5, C-7, C-9, and C - l l ) released from the samples. From the graphs, it was observed that volatile aldehyde release over the 30hr equilibration time varied significantly with water activity. In all cases, release was lowest (
