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## Surface activity of biosurfactant – protein mixtures

### Joanna Lewandowska

#### Abstract

Introduction Biosurfactants are amphiphilic products possessing the hydrophobic and hydrophilic groups, giving a molecule the capacity to mix two immiscible liquid phases. The popularity of saponin from the bark of Quillaja saponaria Molina tree, mainly growing in Chile, is increasing among many commercially available biosurfactants. Currently, saponins are of particular use in the food industry because of their emulsifying properties, foamability and wetting ability as well as the properties of solubilisation antiadhesive and anti-bacterial lubricants. Milk proteins are one of the major groups of proteins found in natural products. β-casein is about 80% of the total protein present in milk. In milk, casein occurs mainly in the form of calcium caseinate, so it is perfectly absorbed during digestion, and is used as an ingredient in dairy products, meat and beverages. The main functions of β-casein are associated with its ability to bind water, emulsification, gelation and foam formation. Proteins and surfactants have quite different mechanisms of stabilization of dispersed systems, and therefore the understanding of effects occurring between the two different components is the key to start reflecting on the stability of colloidal systems containing both components. Results and Discussion Decrease of dynamic surface tension of the mixture QBS/β-casein and solutions of QBS at three interfaces (water/olive oil, water/tetradecane, water/air) was measured by the method of pendant drop in time of 3-3600 s. The surface tension decays were extrapolated to the time converging to infinity to make the surface tension isotherms. For all of the interfaces, an addition of small quantities of QBS didn’t make a significant effect on the surface activity of the solution. Upon increasing the concentration of QBS, the surface activity first increased and then decreased. This is manifested in the isotherms of surface tension on each of the three interfaces as a local maximum, which is the result of changes in the stoichiometry of the QBS/β-casein complex. Dynamic surface tension more rapidly reaches equilibrium in the case of solutions containing a mixture of proteins and biosurfactant than in solutions not containing protein, which suggests that the adsorption barrier of QBS decreases in the presence of β-casein. 73 The size of the olive oil droplets dispersed in a solution containing the mixture of QBS/β-casein was measured by the method of DLS (dynamic light scattering), which allows us to determine the diffusion coefficient, which is the base to calculate the diameter of the dispersed phase droplets. The ability to form a solid-like “skin” at the fluid-fluid interface was studied by visual analysis of the aqueous saponin solution drop’s surface. The "skin" formed only at interfaces between two liquids. The most clearly visible and most stable texture was observed at the water/olive oil interface. The "skin" at the tetradecane/water interface was similar in appearance, but it disappeared after about 2 minutes. In the presence of palmitic acid dissolved in tetradecane (0,5 % w/w), the skin was more stable, and lasted for 4 minutes under similar conditions. As part of this study, the surface activity of two saponins, obtained from two different sources (Supersap, Desert King, Chile and QBS, Fluka) was also compared. Conclusions The surface activity of the QBS/β-casein mixture is higher than the surface activity of pure saponin solution at each of the studied interfaces. When the molar ratio of QBS/β-casein is about 1:1, a complex of higher surface activity than the activity of the individual components is formed. The "skin" formed at the water/olive oil interface may be the result of chemical reactions between the saponin and fatty acids contained in olive oil. Comparison of two saponins from different sources showed that the surface activity of saponin QBS (Fluka) is higher than the surface activity of Supersap (Desert King Chile). The observations on the emulsion formation and stability in the oil-in-water system by DLS analysis did not confirm the conclusions from the studies of the surface tension of the mixture QBS/β-casein.
Record ID
WUTb66c207d8d794b2c9570d9e99c08c045
Diploma type
Master of Science
Author
Joanna Lewandowska (FC/CMB) Joanna Lewandowska,, Chair of Medical Biotechnology (FC/CMB)Faculty of Chemistry (FC)
Title in Polish
Aktywnośd powierzchniowa mieszanin biosurfaktantu z białkiem
Supervisor
Kamil Wojciechowski (FC/CMB) Kamil Wojciechowski,, Chair of Medical Biotechnology (FC/CMB)Faculty of Chemistry (FC)
Certifying unit
Faculty of Chemistry (FC)
Affiliation unit
Department Of Microbioanalytics (FC/CMB)
Study subject / specialization
, Technologia Chemiczna
Language
(pl) Polish
Status
Finished
Defense Date
24-09-2012
Issue date (year)
2012
Keywords in Polish
-
Keywords in English
-
Abstract in Polish
urn:pw-repo:WUTb66c207d8d794b2c9570d9e99c08c045