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Author Asma Sohail
School, Centre or Institute School of Agriculture and Food Sciences
Institution The University of Queensland
Publication date 2011-08
Thesis type PhD Thesis
Supervisor Prof. Bhesh Bhandari
Dr Mark Turner
A/Prof. Allan Coombes
Total pages 168
Total colour pages 25
Total black and white pages 143
Language eng
Subjects 03 Chemical Sciences
Abstract/Summary Alginate gel encapsulation methods have been proven to be promising for the protection of immobilized biological materials and controlled delivery of drugs. However, existing techniques to produce discrete alginate gel particles have limitations, which can result in the production of macro particles, whose use is restricted by obvious sensory detection during their consumption in food products. Other techniques to produce micron size beads are normally successful only on a laboratory scale or are non-continuous operations. In addition, some of the techniques (such as the emulsion method) require solvent or oil to produce micron size alginate gel particles. To overcome, these limitations a novel impinging aerosols technique was developed at the University of Queensland. This research involved the application of this continuous process for producing micron sized beads without the use of any heat or solvents. This technique possesses high scale up potential and involves aerosols of alginate and CalCl2 solutions, which impinge from opposite directions in a chamber. The atomised alginate solution droplets gel as soon as they come in contact with CaCl2 aerosols and fall to the bottom of the chamber from where the microbeads are collected. Actives may be mixed with the alginate solution prior to atomisation or aerosol formation. This research consisted of five experimental parts to investigate the utility of the micro-gel beads produced by this novel technique for encapsulating biological and pharmaceutical entities. These include evaluating: (1) the survivability of selected probiotics entrapped in the alginate microbeads in simulated gastrointestinal fluids, (2) the survivability of encapsulated probiotics in a food product base such as orange juice, (3) the viability of probiotics encapsulated in microbeads followed by freeze and spray drying and (4) the encapsulation of fluorescein as a model drug in alginate gel microbeads and (5) the encapsulation and release properties of hydrophilic and hydrophobic pharmaceutical actives in microbeads. Alginate microbeads (10-40 µm) containing the probiotics Lactobacillus rhamnosus GG and Lactobacillus acidophilus NCFM were produced and compared with extruded macrobeads (approximately 2 mm diameter) produced by the conventional method. Microbeads produced by the novel aerosols technique offered comparable protection to L. rhamnosus in high acid and bile environments. Chitosan coating of microbeads resulted in a significant increase in survival time of L. rhamnosus from 40 to 120 min in acid condition and the reduction in cell numbers was confined to 0.94 logs over this time. Alginate macrobeads were more effective than microbeads in protecting L. acidophilus against high acid and bile solutions. Chitosan coating of microbeads resulted in similar protection to L. acidophilus in macrobeads in acid and extended the survival time from 90 to at least 120 min. The viability of this organism in microbeads was 3.5 logs CFU after 120 min. The effect of alginate microencapsulation on the survival of L. rhamnosus GG and L. acidophilus NCFM and their acidification in orange juice at 25 oC for nine days and at 4 oC over thirty five days of storage was studied. Unencapsulated L. rhamnosus GG was found to have excellent survivability in orange juice at both temperatures. However, unencapsulated L. acidophilus NCFM showed a significant reduction in viability. Encapsulation of these two bacteria in alginate microbeads did not significantly enhance survivability but did reduce acidification (measured as pH change) at 25 oC and 4 oC. The encapsulated probiotics in microbeads gel-matrix were further stabilized in maltodextrin solids by either spray or freeze drying to form probiotic microcapsule powders. The free cells of L. rhamnosus GG and L. acidophilus NCFM were also spray and freeze dried in maltodextrin without micro-gel encapsulation. Upon rehydration of micro-gel encapsulated powder, gel particles regained their shape. There was no difference in the loss of viability in both probiotics during spray drying or freeze drying. For L. acidophilus NCFM, spray dried bacteria with or without gel encapsulation exhibited higher viability (3.03 and 3.07 log CFU reduction, respectively) than those of freeze dried bacteria (4.36 and 4.89 log CFU reduction, respectively) after six months storage at 4˚C. The same trend was also observed in spray dried L. rhamnosus GG without gel encapsulation, which showed 5.87 log CFU reductions in viability after six months at 4˚C. However, freeze dried L. rhamnosus GG without gel encapsulation exhibited a rapid reduction in viability of 5.91 logs CFU within 2 months. Gel encapsulated L. rhamnosus GG which was freeze dried exhibited higher viability (3.32 log CFU reduction) after six months at 4˚C. Freeze dried gel encapsulated L. rhamnosus GG exhibited major improvements in survivability (5.07 logs CFU/g) over sixth months demonstrating the advantage of double encapsulation (gel matrix + maltodextrin matrix) for certain strains. A challenging small hydrophilic molecule (fluorescein) was directly microencapsulated in alginate gel beads and the release was restricted to around 28-37% in HCl in 2 h. This behaviour indicated that the alginate gel beads were capable of protecting active entities against breakdown in the stomach. Results showed 10% encapsulation efficiency of hydrophilic fluorescein molecules and 0.1% dry weight (w/w) loading. The hydrophilic antibacterial agent (metronidazole, MZ) and a hydrophobic non-steroidal anti-inflammatory drug (ketoprofen, KET) were encapsulated in alginate microbeads, having a mean size of less than 40 µm, using the impinging aerosols method. Maximum loadings of 7% and 0.4% were obtained for MZ and KET respectively with corresponding encapsulation efficiencies of 21 and 4%. Around 75% and 96% of the MZ contents were released from hydrated and dried microbeads respectively in simulated gastric fluid (SGF) within 20 min. Similarly rapid release of 100 % of the drug load occurred in SIF within 20 min for both preparations but anti-bacterial activity of those pharmaceuticals was retained in both media. Alginate microbeads encapsulating KET released less than 60% of the drug in SGF within 2h. Complete extraction of KET was obtained from hydrated microbeads in SIF in 2h but was limited to around 70% from dried samples and the release was sustained for 7h. The above results suggest that the continuous processing capability and scale-up potential of the dual aerosol technique offers great potential for efficient encapsulation of probiotics in very small alginate microbeads while it is still able to confer effective protection in acid and bile environments. The technique also proved capable of reducing acidification and the possible negative sensory effects of probiotics in orange juice. The utility of the impinging aerosols method for direct encapsulation and controlled release of small molecule therapeutics, having a wide range of aqueous solubility in micron- sized alginate microbeads, was also demonstrated. The results presented in this thesis provide evidence of successful applications of the novel alginate encapsulation method and therefore, may be of use for the food and/or pharmaceutical industries.
Keyword Microencapsulation
Lactobacillus rhamnosus GG
Lactobacillus acidophilus NCFM
Orange Juice
Spray drying
Freeze drying
Drug Release
Additional Notes Page numbers that should be printed in colour of the PDF document: 41,46,61,76,78,79,80,82,83,85,86,91,93,102,103,105,106,108,109,114,121,123,124,127,130 Page numbers that should be printed as landscape pages of the PDF document: 35,36

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Created: Tue, 31 Jan 2012, 16:38:29 EST by Ms Asma Sohail on behalf of Library - Information Access Service