Formation and characterization of microcapsules by complex coacervation with liquid or solid aroma cores
Department of Food Science and Nutrition, University of Minnesota, 1334 Eckles Avenue, St. Paul, MN 55108, USAFlavour and Fragrance Journal (Impact Factor: 1.97). 01/2009; 24(1):17 - 24. DOI: 10.1002/ffj.1911
The process parameters typically reported in the literature for the encapsulation of aroma compounds via coacervation are reviewed and their effects on capsule formation discussed. We then report on our approach to produce coacervates [liquid (limonene or medium chain triglycerides) or solid core (menthol)] using gum acacia/gelatin as wall materials. Manufacturing parameters were optimized to allow the production of consistent batches of coacervate microcapsules. Capsules were cross-linked with glutaraldehyde and freeze-dried. Coacervates were characterized for their structure and shape, size distribution, flavour load and water uptake rate. In addition, a brief storage study compared the ability of coacervate capsules and spray-dried capsules (using modified starch as carrier material) to protect limonene from oxidation. No detectable increase in limonene oxide could be detected in capsules made by coacervation over 25 days in storage at 45 °C, whereas a significant increase in limonene oxide was detected in spray-dried powder over the same period. Encapsulation by coacervation (as described in this paper) appears to be an effective technique for encapsulating aroma compounds and provides a good barrier against oxidation of sensitive material. Copyright © 2008 John Wiley & Sons, Ltd.
Conference Paper: Compiling and Optimizing for Decoupled Architectures[Show abstract] [Hide abstract]
ABSTRACT: Decoupled architectures provide a key to the problem of sustained supercomputer performance through their ability to hide large memory latencies. When a program executes in a decoupled mode the perceived memory latency at the processor is zero; effectively the entire physical memory has an access time equivalent to the processor's register file, and latency is completely hidden. However, the asynchronous functional units within a decoupled architecture must occasionally synchronize, incurring a high penalty. The goal of compiling and optimizing for decoupled architectures is to partition the program between the asynchronous functional units in such a way that latencies are hidden but synchronization events are executed infrequently. This paper describes a model for decoupled compilation, and explains the effectiveness of compilation for decoupled systems. A number of new compiler optimizations are introduced and evaluated quantitatively using the Perfect Club scientific benchmarks. We show that with a suitable repertiore of optimizations, it is possible to hide large latencies most of the time for most of the programs in the Perfect Club.
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ABSTRACT: Microcapsules were produced by complex coacervation with a gelatin-gum acacia wall and medium-chain-triglyceride core. Dry capsules were partially rehydrated and then loaded with model aroma compounds covering a range of volatility, hydrophobicity, and molecular structure. An experimental design was prepared to evaluate the effects of cross-linking, wall/core ratio, and volatile load level on aroma release from capsules in a hot, aqueous environment. The real-time release on rehydration was measured by monitoring the headspace of a vessel containing the capsules to proton transfer reaction mass spectrometry (PTR-MS). Data collected showed no effects of cross-linking or wall/core ratio on volatile release in hot water for any of the volatiles studied. When comparing real-time release of the prepared coacervates to a spray-dried equivalent, there was no difference in the release from hot water but the release was slower when coacervates were added to ambient-temperature water. We found volatile release to be primarily determined by compound partition coefficients (oil/water and water/air) and temperature.
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ABSTRACT: Microencapsulation is used here as a new technique to immobilize enzymes in a microreactor coupled off-line to capillary electrophoresis (CE), allowing the determination of enzymatic reaction products. The redox enzyme laccase was encapsulated using the method of interfacial cross-linking of poly(ethyleneimine) (PEI). The 50 microm diameter capsules were slurry packed from a suspension into a capillary-sized reactor made easily and quickly from a short length of 530 microm diameter fused-silica tubing. The volume of the bed of laccase microcapsules in the microreactor was in the order of 1.1 microL through which 50 microL of the substrate o-phenylenediamine (OPD) was flowed. The oxidation product 2,3-diaminophenazine (DAP) and the remaining OPD were quantified by CE in a pH 2.5 phosphate buffer. Peak migration time reproducibility was in the order of 0.4% RSD and peak area reproducibility was less than 1.7% RSD within the same day. Using the OPD peak area calibration curve, a conversion efficiency of 48% was achieved for a 2-min oxidation reaction in the microreactor.
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