Impact of Heat and Laccase on the pH and Freeze-Thaw Stability of Oil-in-Water Emulsions Stabilized by Adsorbed Biopolymer Nanoparticles |
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Authors: | Benjamin Zeeb Hanna Salminen Lutz Fischer Jochen Weiss |
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Institution: | 1.Department of Food Physics and Meat Science,University of Hohenheim,Stuttgart,Germany;2.Department of Food Biotechnology,University of Hohenheim,Stuttgart,Germany |
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Abstract: | The enzymatic cross-linking of adsorbed biopolymer nanoparticles formed between whey protein isolate (WPI) and sugar beet pectin using the complex coacervation method was investigated. A sequential electrostatic depositioning process was used to prepare emulsions containing oil droplets stabilized by WPI – nanoparticle – membranes. Firstly, a finely dispersed primary emulsion (10 % w/w miglyol oil, 1 % w/w WPI, 10 mM acetate buffer at pH 4) was produced using a high-pressure homogenizer. Secondly, a series of biopolymer particles were formed by mixing WPI (0.5 % w/w) and pectin (0.25 % w/w) solutions with subsequent heating above the thermal denaturation temperature (85 °C, 20 min) to prepare dispersions containing particles in the submicron range. Thirdly, nanoparticle-covered emulsions were formed by diluting the primary emulsion into coacervate solutions (0–0.675 % w/w) to coat the droplets. Oil droplets of stable emulsions with different interfacial membrane compositions were subjected to enzymatic cross-linking. We used cross-linked multilayered emulsions as a comparison. The pH stability of primary emulsions, biopolymer complexes and nanoparticle-coated base emulsions, as well as multilayered emulsions, was determined before and after enzyme addition. Freeze-thaw stability (?9 °C for 22 h, 25 °C for 2 h) of nanoparticle-coated emulsions was not affected by laccase. Results indicated that cross-linking occurred exclusively in the multilamellar layers and not between adsorbed biopolymer nanoparticles. Results suggest that the accessibility of distinct structures may play a key role for biopolymer-cross-linking enzymes. |
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