Branko Bugarski

Comparison of different technologies for alginate beads production

This paper describes the results of the round robin experiment “Bead production technologies” carried out during the COST 840 action “Bioencapsulation Innovation and Technologies” within the 5th Framework Program of the European Community. In this round robin experiment, calcium alginate hydrogel beads with the diameter of (800 ± 100) μm were produced by the most common bead production technologies using 0.5–4 mass % sodium alginate solutions as starting material. Dynamic viscosity of the alginate solutions ranged from less than 50 mPa s up to more than 10000 mPa s. With the coaxial air-flow and electrostatic enhanced dropping technologies as well as with the JetCutter technology in the soft-landing mode, beads were produced from all alginate solutions, whereas the vibration technology was not capable to process the high-viscosity 3 % and 4 % alginate solutions. Spherical beads were generated by the electrostatic and the JetCutter technologies. Slightly deformed beads were obtained from high-viscosity alginate solutions using the coaxial airflow and from the 0.5 % and 2 % alginate solutions using the vibration technology. The rate of bead production using the JetCutter was about 10 times higher than with the vibration technology and more than 10000 times higher than with the coaxial air-flow and electrostatic technology.

Electrostatic generation of alginate microbeads loaded with brewing yeast

Abstract The substantial concern with the possible use of immobilized yeast cells for beer production is reduction of internal mass transfer resistance during continuous fermentation. One way to minimise this problem is to use small-diameter beads. The effects of bead diameters in the range 0.3–2.0 mm on yeast cell immobilization and growth over a short-term cultivation were investigated. Bead diameters in the range 0.5–0.6 mm were optimal and provided rapid cell growth and the highest final cell concentration (2.33×10 9 cells/ml of beads). Electrostatic droplet generation was investigated as a technique for production of alginate microbeads. The effects of applied potential, internal needle diameter and electrode position on bead diameter were assessed. The results have shown that this method can be used for controlled production of small-size microbeads loaded with yeast. Depending on applied conditions it was possible to produce the beads in the range 250 μm–2.0 mm in diameter.

Alginate-immobilized lipase by electrostatic extrusion for the purpose of palm oil hydrolysis in lecithin/isooctane system

Lipase from Candida rugosa was immobilized in alginate beads for possible application in non-aqueous or microaqueous reaction systems. An electrostatic droplet generation technique was used for production of small diameter (<1 mm) lipase-alginate beads. This technique provided negligible loss of the lipase (immobilization efficiencies were 98.2–99.2%). Under optimal immobilization conditions (applied potential 4.9 kV, needle gauge 21, 2% sodium alginate solution) the lipase-alginate beads, 0.65 mm in diameter, retained enzyme activity equivalent to 75% that of free lipase. The activity of the immobilized lipase was verified in the reaction of palm oil hydrolysis in a lecithin/isooctane system. The reaction rate with alginate-immobilized lipase was lower than with the free enzyme but the final conversions were approximately the same (∼74%). Immobilized lipase could be used for up to three reaction cycles with little loss of activity.

Encapsulation of thyme (Thymus serpyllum L.) aqueous extract in calcium alginate beads

BACKGROUND Encapsulation of Thymus serpyllum L. aqueous extract within calcium alginate beads was studied in order to produce dosage formulations containing polyphenolic compounds. Electrostatic extrusion was applied for encapsulation of thyme aqueous extract in alginate gel beads. In addition to hydrogel beads, heat-dried and freeze-dried forms of beads were examined. METHODS Encapsulation systems were examined and compared in order to choose the optimal one with respect to entrapment efficiency, preservation of antioxidant activity and thermal behaviour under heating conditions simulating the usual food processing. RESULTS The beads obtained with approximately 2 mg g⁻¹ of gallic acid equivalents encapsulated in 0.015 g mL⁻¹ of alginate were spheres of a uniform size of about 730 µm. Encapsulation efficiency varied in the range 50-80% depending on the encapsulation method. Besides, the analysis reveals that the encapsulation process and the material used did not degrade the bioactive compounds, as the total antioxidant content remained unchanged. This was verified by Fourier transform infrared analysis, which proved the absence of chemical interactions between extracted compounds and alginate. Addition of a filler substance, such as sucrose and inulin, in the dried product reduced its collapse and roundness distortion during drying process. CONCLUSION This study demonstrates the potential of using hydrogel material for encapsulation of plant poplyphenols to improve their functionality and stability in food products.

Microencapsulation of Flavors in Carnauba Wax

The subject of this study is the development of flavor wax formulations aimed for food and feed products. The melt dispersion technique was applied for the encapsulation of ethyl vanillin in wax microcapsules. The surface morphology of microparticles was investigated using scanning electron microscope (SEM), while the loading content was determined by HPLC measurements. This study shows that the decomposition process under heating proceeds in several steps: vanilla evaporation occurs at around 200 °C, while matrix degradation starts at 250 °C and progresses with maxima at around 360, 440 and 520 °C. The results indicate that carnauba wax is an attractive material for use as a matrix for encapsulation of flavours in order to improve their functionality and stability in products.

A Parallel plate electrostatic droplet generator: Parameters affecting microbead size

Polymer microbead production by parallel plate electrostatic extrusion is presented. Factors affecting microbead size such as needle gauge, electrostatic potential, distance between needle and collecting solution, and polymer solution concentration and flow rate were evaluated. Smaller microbeads resulted from reduced needle diameter, reduced needle to collecting solution distance, increased electrostatic potential, and reduced polymer solution concentration and flow rate. In terms of process scale-up, it was shown that a multi-needle (20) device could continuously produce relatively uniform beads via electrostatics. The technology was demonstrated to be feasible for cell encapsulation or immobilization as there was no detectable effect of applied potential onSpodoptera frugiperda viability.

Performance of an external loop air-lift bioreactor for the production of monoclonal antibodies by immobilized hybridoma cells

SummaryThe performance of an external loop air-lift bioreactor was investigated by assessing the inter-relationships between various hydrodynamic properties and mass transfer. The feasibility of using this bioreactor for the production of monoclonal antibodies by mouse hybridoma cells immobilized in calcium alginate gel beads and alginate/poly-l-lysine microcapsules was also examined. When the superficial gas velocity, Vg, in the 300 ml reactor was varied from 2 to 36 cm/min, the average liquid velocity increased from 3 to 14 cm/sec, the gas hold-up rose from 0.2 to 3.0%, and the oxygen mass transfer coefficient, kLa, increased from 2.5 to 18.1 h-1. A minimum liquid velocity of 4 cm/s was required to maintain alginate gel beads (1000 μm diameter, occupying 3% of reactor volume) in suspension. Batch culture of hybridoma cells immobilized in alginate beads followed logarithmic growth, reaching a concentration of 4×107 cells/ml beads after 11 days. Significant antibody production did not occur until day 9 into the culture, reaching a value of 100 μg/ml of medium at day 11. On the other hand, bioreactor studies with encapsulated hybridoma cells gave monoclonal antibody concentrations of up to 800 μg/ml capsules (the antibody being retained within the semipermeable capsule) and maximum cell densities of 2×108 cells/ml capsule at day 11. The volumetric productivities of the alginate gel immobilized cell system and the encapsulated cell system were 9 and 3 μg antibody per ml of reactor volume per day, respectively. The main advantage of the bioreactor system is its simple design, since no mechanical input is required to vary the hydrodynamic properties.

Antioxidant edible films based on chitosan and starch containing polyphenols from thyme extracts

The aim of this study was to analyse the antioxidant activity of different polymeric matrices based on chitosan and starch, incorporating a thyme extract (TE) rich in polyphenols. TE provided the films with remarkable antioxidant activity. When mixed with chitosan, the polyphenols interacted with the polymer chains, acting as crosslinkers and enhancing the tensile behaviour of films. The opposite effect was observed when incorporated into the starch matrix. All the films became darker, more reddish and less transparent when TE was incorporated. These colour changes were more marked in starch matrices, which suggests that TE compounds were poorly encapsulated. The use of chitosan-based matrices carrying TE polyphenols is recommended as a means of obtaining antioxidant films, on the basis of their tensile response and greater antioxidant activity, which could be associated with the development of polyphenol-chitosan interactions, contributing to a better protection of the functionality of polyphenols during film formation and conditioning.

Protection of probiotic microorganisms by microencapsulation

Probiotic bacteria are used in the production of fermented dairy foods, pharmaceutical products and health supplements. They play an important role in promoting and maintaining human health. In order, to produce health benefits probiotic strains should be present in a viable form at a suitable level during the products shelf life until consumption and maintain high viability throughout the gastrointestinal tract. Despite the importance of these beneficial microorganisms many investigations have shown their poor viability and stability, especially for bifidobacteria in fermented products. The introduction of microencapsulation techniques for protection of probiotic strains has resulted in greatly enhanced viability of these microorganisms in food products as well as in the gastrointestinal tract. This paper gives an overview of available microencapsulation techniques and materials for probiotic protection and stabilization. Several methods of microencapsulation for probiotic bacteria, including extrusion, emulsification, drying (fluidized bed, spray, freeze) and spray coating techniques, are presented. The commonly used supporting materials like alginate, starch, chitosan, gelatin, waxes, biogums, and some others are also discussed.

Chitosan microbeads for encapsulation of thyme (Thymus serpyllum L.) polyphenols.

In this work chitosan microbeads were prepared by emulsion technique and loaded with thyme polyphenols by diffusion from an external aqueous solution of Thymus serpyllum L. The effects of concentrations of chitosan (1.5-3% (w/v)) and GA (glutaraldehyde) (0.1-0.4% (v/v)), as a crosslinking agent on the main properties of microbeads were assessed. The obtained microgel beads from ∼ 220 to ∼ 790 μm in diameter were exposed to controlled drying process at air (at 37 °C) after which they contracted to irregular shapes (∼ 70-230 μm). The loading of dried microbeads with polyphenols was achieved by swelling in the acidic medium. The swelling rate of microbeads decreased with the increase in GA concentration. Upon this rehydration, thyme polyphenols were effectively encapsulated (active load of 66-114 mg GAE g(beads)(-1)) and the microbeads recovered a spherical shape. Both, the increase in the amount of the crosslinking agent and the presence of polyphenols, contributed to a more pronounced surface roughness of microbeads. The release of encapsulated polyphenols in simulated gastrointestinal fluids was prolonged to 3h.