Development of spray drying technology for microencapsulation of bioactive materials
Type of DegreeDissertation
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Lipophilic bioactive components, such as carotenoids, have received increasing attention in food and pharmaceutical industries because of their potential health benefits. They have been recognized to exhibit physiological activities in metabolic and nutritional studies. However, the utilization of carotenoids as functional ingredients is currently limited due to high susceptibility to adverse environment conditions (such as oxidant, heat, light, pH value and enzyme). To overcome these problems, microencapsulation technology has been proposed in order to make the bioactive component more stable during handling, processing, storage and delivering. In the food industry, the most common procedure for microencapsulation is spray drying. Low cost, easy to scale, wide choices of wall materials and the possibility of producing micro-sized particles with adjustable size and morphology make this means ideal for particle encapsulation. Proper selection of wall materials is of the utmost importance for spray drying so that required functional characteristics are met for the final microcapsules. Gelatin is a natural bitterless, odorless hydrocolloid that has received great attention in food and pharmaceutical industries due to its biocompatible, biodegradable and “generally regarded as safe (GRAS)” characteristics. This study attempts to develop a feasible spray-drying process to prepare gelatin microspheres as viable wall materials to protect bioactive materials from degradation and improve their uptake and bioavailability. The lab-scale spray dryer Buchi B-290 was used to produce particles under various operating conditions and the spray characteristics were visualized by high magnification imaging system for better understanding of the heat and mass transfer and particle formation process during the spray drying. The effect of the processing conditions on dried particle properties (size, morphology, yield, moisture content) was investigated. Data from visualization experiments was collected and used for gelatin shrinkage model development. This study is helpful in the industrial application of gelatin as potential wall material for food and pharmaceutical microencapsulation. A stable oil-in-water (O/W) emulsion system to microencapsulate bioactive materials by spray drying was then developed. Effects of emulsification methods (high-energy and low-energy homogenization methods) on emulsion stability were characterized at various surfactant to oil ratios (SOR) with different types of oil (MCT oil, olive oil) and emulsifiers (gelatin, Tween 80). High-energy method was preferred for safety concerns, as it was able to produce fine stable emulsions at low SOR. O/W emulsions, using MCT oil as core material, gelatin as wall material and Tween 80 as secondary emulsifier, were prepared and spray dried to create micron-size microcapsules. Effects of operating conditions, including inlet temperature, on the resultant microcapsules properties (e.g. size, morphology, moisture content (MC), encapsulation efficiency (EE) and yield (Y)) were investigated. The results demonstrated that spray drying technology could be applied to transform the stable O/W emulsions into powders with desired properties. So it is feasible to use this emulsion-based system to microencapsulate carotenoids in the near future. The residual moisture content (MC) of spray dried powders is of great importance to define the product quality, since it is directly related to drying conditions and it affects particle deposition and yield. Several methods (oven drying, NIR (near infrared spectroscopy)) have been developed to measure MC offline. However, many are not appropriate for spray drying where an online (real-time) assessment of MC is required. The objective of this study was to develop a sensor for measuring moisture content of a moving stream of spray dried powders. A capacitance sensor was built for this purpose using pairs of copper plate electrodes attached to the perimeter of the spray dryer product collection vessel. The plates formed capacitors that were sensitive to changes in dielectric properties of the material within the collection vessel, which in turn were related to MC. Each electrode was connected to a capacitance-to-voltage transducer, the output of which was sampled using a commercial data acquisition system. The amplitude of the sensor output signal was calculated using software LabVIEW and correlated with MC. The self-built system was tested in two modes: a) an offline (non-moving sample) mode in which a mass-based MC prediction model was built to validate the capability of the sensor to measure variation in MC; and b) an online (moving sample) mode to measure MC of sample moving through the sensor enclosure. Tests were made on spray dried gelatin powders ranging in moisture content of 5% to 50% (w.b.). Results indicated a high correlation between sensor output and moisture content (R2>0.9). The capacitance sensor also showed the ability to characterize the distribution of MC (permittivity) within the sensor enclosure, which could reflect spatial variation in deposition of dried powders during spray drying. Overall, the capacitance sensor system was feasible to measure MC for online sampling with acceptable accuracy, and can be applied in quality control applications for continuous spray drying processes. To evaluate the airflow pattern (velocity field) inside a co-current lab scale spray dryer, air velocity magnitudes were measured by a particle image velocimetry (PIV) system at numerous locations in the spray dryer chamber in the absence of spray. Analysis at varied drying air flow rate strongly suggested the flow in the chamber has high turbulence intensity. The PIV analysis also provided information on how drying air flow rate affects fluid flow profiles, which could help to collect data for validation of the CFD simulated results.