Application of ultra high hydrostatic pressure for investigating the binding of flavor compounds to ß-lactoglobulin via headspace solid phase microextraction-gas chromatography
Ultra high hydrostatic pressure (UHP) treatment of BLG at 600 MPa resulted in
an increase in tryptophan intrinsic fluorescence intensity at pH 7.0. A red shift in the
emission wavelength occurred at pH 7.0, indicating a polarity shift from a less polar to a
more polar tryptophan microenvironment and an unfolding of BLG, exposing the
hydrophobic interior. These results provide evidence that UHP treatment induces BLG
into the molten globule state. After come-up time at pH 9.0, BLG exhibited the greatest
surface hydrophobicity, suggesting that UHP treatment increases the flexibility of the
secondary structure concomitant with base-induced denaturation. Following UHP
treatment (32 min) of BLG at pH 3.0, the number of binding sites for the nonpolar
fluorescence probe 6-propionyl-2-(dimethylamino)-naphthalene (PRODAN) decreased
from 2.26 to 1.16. These results indicate that BLG does not require long UHP treatment
times to achieve more binding.
A ten minute extraction time for δ-decalactone, diacetyl, ethyl lactate, and 2-
methylbutyraldehyde is adequate for headspace analysis via solid phase microextraction.
The GC method described is short, requiring 1.7 h for both extraction and detection of
selected flavor compounds.
UHP treatment of BLG does not increase the binding properties of BLG for
diacetyl, 2-methylbutyraldehyde, ethyl lactate and δ-decalactone as observed by intrinsic
fluorescence quenching, suggesting that the fluorescence technique may not be
appropriate for the determination of BLG binding properties. BLG has low binding
affinity for selected flavor compounds with polar groups. On the other hand, as observed
by headspace analysis, UHP treatment of BLG resulted in increases of retention of
selected flavor compounds, indicating that HS-SPME is a dependable method for
quantifying headspace concentrations of flavor compounds.
β-Lactoglobulin has potential as a functional ingredient in the food industry. Fat
replacers are used to provide the physical and sensory properties of fat, and when BLG is
included as a flavor carrier, BLG offers consumers alternative choices of eating healthy,
while maintaining the full flavor experience.