Effect of lipophilization on the distribution and reactivity of ingredients in emulsions.
OBJECTIVE
The reactivity of small molecules in emulsions is believed to depend on their partitioning between phases, yet this is hard to verify experimentally in situ. In the present work, we use electron paramagnetic resonance (EPR) spectroscopy to simultaneously measure the distribution and reactivity of a homologous series of lipophilized spin probes in an emulsion.


METHODS
4-Hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL) was derivatized with saturated fatty acids to create a series of spin probes with increasing lipophilicity (C4-, C8-, C12-, and C16-TEMPO). The probes were added to a 10 wt.% tetradecane-in water emulsions (d32∼190 nm) stabilized with sodium caseinate (1 wt.% in the aqueous phase, pH 7). The distribution of the probes between phases was measured by electron paramagnetic resonance (EPR) spectroscopy.


RESULTS
TEMPOL partitioned into the aqueous phase, C4-TEMPO distributed between the lipid and aqueous phases (69% and 31% respectively) while the more lipophilic probes dissolved exclusively within the lipid droplets. Interestingly, the more lipophilic probes initially precipitated upon their addition to the emulsion, and only slowly redistributed to the droplets over hours or days, the rate of which was dependent on their carbon chain length. The reactivity of the probes with aqueous an aqueous phase reductant (ascorbate) generally depended on the proportion in the aqueous phase (i.e., TEMPOL>C4-TEMPO>C8-TEMPO∼C12-TEMPO∼C16-TEMPO).
Department of Food Science, College of Agricultural Sciences, The Pennsylvania State University, University Park, PA, USA.
Wai Fun
WF
Leong
Department of Food Science, College of Agricultural Sciences, The Pennsylvania State University, University Park, PA, USA; Food Process Engineering Group, Wageningen University, 6700 AA Wageningen, The Netherlands.
Claire C
CC
Berton-Carabin
Department of Food Science, College of Agricultural Sciences, The Pennsylvania State University, University Park, PA, USA.
Ryan J
RJ
Elias
UMR IATE, CIRAD, 2 place Viala, 34060 Montpellier Cedex 2, France.
Jérôme
J
Lecomte
UMR IATE, CIRAD, 2 place Viala, 34060 Montpellier Cedex 2, France.
Pierre
P
Villeneuve
Department of Food Science, College of Agricultural Sciences, The Pennsylvania State University, University Park, PA, USA.
Yu
Y
Zhao
Department of Food Science, College of Agricultural Sciences, The Pennsylvania State University, University Park, PA, USA. Electronic address: Coupland@psu.edu.
John N
JN
Coupland
D003497:Cyclic N-Oxides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D004655:Emulsions; D013113:Spin Labels
D003497:Cyclic N-Oxides; D004655:Emulsions; D013113:Spin Labels; C001803:tempol; C003959:TEMPO
Electron paramagnetic resonance (EPR); Emulsion; Small molecule partitioning; Spin probe; TEMPOL