Enzymatic Stabilization and Formation of Food Nano- and Microstructures

English summary: A biomimetic approach was carried out to stabilize and modify physically assembled food structures based on enzyme technology. Two different enzymes, namely an oxidoreductase (laccase) and an acyltransferase (transglutaminase), were used as ing agents. First, the enzymatic crosslinking of biopolymer layers adsorbed at the interface of oil-in-water emulsions was investigated. A sequential two step process, based on the electrostatic deposition of pectin onto a fish gelatin interfacial membrane was used to prepare emulsions containing oil droplets stabilized by fish gelatin-beet pectin-membranes (structure formation). Laccase was added to the fish gelatin-beet pectin emulsions and emulsions were incubated for 15 min at room temperature (structure modification). The pH- and storage stability of primary, secondary (coated) and secondary, laccase-treated emulsions was determined. Results indicated that crosslinking occurred exclusively in the layers and not between droplets, since no aggregates were formed. Droplet size increased from 350 to 400 nm regardless of oil droplet concentrations within a matter of minutes after addition of laccase suggesting formation of covalent bonds between pectin adsorbed at interfaces and pectin in the aqueous phase in the vicinity of droplets. During storage, size of enzymatically treated emulsions decreased, which was found to be due to enzymatic hydrolysis (Chapter 2). Crosslinked pectin-coated oil droplets had similar or significantly better stability (p < 0.05) than oil droplets of primary or secondary emulsions to NaCl addition (0 - 500 mM), CaCl2 addition (0 - 250 mM), and thermal processing (30 - 90 for 30 min). Freeze-thaw stability and creaming behavior of enzyme-treated, secondary emulsions after two cycles (-8 for 22 h; +25 for 2 h) was significantly improved (p < 0.05) (Chapter 3). Furthermore, the influence of interfacial crosslinking, layer thickness and layer density on the kinetics of Ostwald ripening in multilayered emulsions at different temperatures was investigated. Growth rates of droplets were measured by monitoring changes in the droplet size distributions of 0.5% (w/w) n-octane, n-decane, and n-dodecane oil-in-water emulsions using static light scattering. Lifshitz-Slyozov-Wagner theory was used to calculate Ostwald ripening rates. Ripening rates of single-layered, double-layered and crosslinked emulsions increased as the chain length of the n-alkanes decreased. Emulsions containing crosslinked fish gelatin-beet pectin coated droplets had lower droplet growth rates (3.1 o 0.3 x 10-26 m3/s) than fish gelatin-stabilized droplets (7.3 o 0.2 x 10-26 m3/s), which was attributed to the formation of a protective network (Chapter 4). Multilayering and enzymatic crosslinking of emulsions caused alterations in the release behavior of an encapsulated core material due to changes in thickness, porosity and permeability of the membrane. Release behavior of primary, secondary (coated), and laccase-treated secondary emulsions carrying lutein, an oxygenated carotenoid, were also characterized and studied. Primary WPI-stabilized emulsions showed a five times higher release of lutein after 48 h than secondary emulsions (pH 3.5). Primary DTAB-stabilized emulsions released 7.2% of encapsulated lutein within the observation period, whereas beet pectin-DTAB coated emulsions released only 0.13% of lutein. Crosslinking of adsorbed pectin did not significantly decrease release of lutein in comparison to non-crosslinked secondary emulsions (Chapter 5) (structure properties). Oil droplets of stable emulsions with different interfacial membrane compositions were also subjected to enzymatic crosslinking. The pH-stability of primary emulsions and nanoparticle-coated base emulsions was determined before and after laccase addition. However, results indicated that crosslinking occurred only in deposited monolayers rather than between adsorbed biopolymer nanoparticles (Chapter 6). Moreover, the influence of oil volume fraction of protein-stabilized oil-in-water emulsions on the formation of cold-set particulate gels using microbial transglutaminase was assessed. Texture profile analysis and rheological measurements indicated that a critical oil volume fraction (? > 0.6) was crucial to promote a transglutaminase-induced crosslinking of single oil droplets (Chapter 7). German description: Der Einsatz vernetzungsfahiger Enzyme wurde am Beispiel einer Laccase bzw. Transglutaminase zur Stabilisierung und Modifizierung neuer Verkapselungssysteme untersucht. Ziel der Studien war es insbesondere den Wirkmechanismus der vernetzenden Enzyme in komplexen Lebensmittelmatrizen zu klaren. Im Fokus der Forschung stand die Wirkung der Oxidase Laccase auf eine Fischgelatine-Zuckerrubenpektin-stabilisierte Ol-in-Wasser-Emulsion. Die Ergebnisse belegen, dass ausschliesslich Biopolymere, die an der unmittelbar zur kontinuierlichen Phase hin zuganglichen Grenzflache der Ol-in-Wasser Emulsionen durch die Laccase vernetzt werden konnten. In konzentrierten Emulsionssystemen konnen vernetzende Enzyme neben der Katalyse kovalenter Bindungen innerhalb der Grenzflachenmembran auch Tropfen-Tropfen-Netzwerke induzieren. Die Ausbildung partikularer Emulsionsgele hangt dabei wesentlich vom mittleren Abstand der Emulsionstropfen ab. Diese Dissertation hat gezeigt, dass vernetzende Enzyme wie Laccase oder Transglutaminase in der Lage sind, die Struktur und Eigenschaften von Lebensmitteldispersion zu modifizieren.

• By (author) Benjamin Zeeb