Chemistry Reference
In-Depth Information
Chapter 30
Adsorption of Macromolecules at
Oil
Water Interfaces during Emulsification
Lars Nilsson,
1
Peter Osmark,
2
Mats Leeman,
3
Ce´ line
Fernandez,
2
Karl-Gustav Wahlund
3
and Bjo¨ rn Bergensta˚ hl
1
1
DIVISION OF FOOD TECHNOLOGY, LUND UNIVERSITY, P.O.
BOX 124, 22100 LUND, SWEDEN
2
DIVISION OF TECHNICAL ANALYTICAL CHEMISTRY, LUND
UNIVERSITY, P.O. BOX 124, 22100 LUND, SWEDEN
3
DEPARTMENT OF EXPERIMENTAL MEDICAL SCIENCE,
MOLECULAR ENDOCRINOLOGY GROUP, LUND UNIVERSITY,
22184 LUND, SWEDEN
30.1 Introduction
Adsorption of macromolecules plays an important role in the formation and
stabilization of food emulsions.
1-3
Macromolecules that adsorb and are able to
form a coherent interfacial layer can provide stability, and thus the adsorption
behaviour is crucial to the understanding of their functionality.
Emulsions are typically made by applying intense mechanical energy to two
immiscible liquids and thereby dispersing one in the other.
4
Adsorption during
emulsification differs from many other adsorption situations as the surface is
being created simultaneously with the adsorption. The adsorption event can
typically be described in three steps: (i) transport of molecules to the newly
formed interface; (ii) sticking of molecules with sufficient affinity for the
interface; and (iii) possible changes in configuration such as unfolding and
spreading of the molecules. During first two steps, which occur during very
short timescales, recoalescence of the newly formed droplets occurs in parallel
with the adsorption, and thus kinetic factors are likely to play a large role and
the adsorption rate can be assumed to be critical. High-pressure homogeniza-
tion is a common way of making an emulsion. In such a device the emulsifi-
cation occurs in turbulent flow and thus convective mass transport dominates
over diffusive transport. To stick at the interface the macromolecule must have
sufficient affinity for it; in the case of oil-in-water emulsions, this implies the
presence of sufficient hydrophobic groups in the macromolecule.
433
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