| Fluorescence spectroscopy and headspace-solid phase microextraction (HS-SPME) gas chromatography analysis were used to evaluate the effects of ultra high hydrostatic pressure (UHP) (600 MPa) and pH (3.0--9.0) on beta-lactoglobulin (BLG) surface hydrophobicity and binding of selected flavor compounds. An increase in tryptophan intrinsic fluorescence intensity of BLG was observed after UHP of 16 min, which suggested that the tryptophan residues were exposed during the unfolding of BLG. A 2 nm red-shift in tryptophan emission wavelength was observed after UHP come-up time, indicating changes in the polarity of tryptophan residues from a less polar to a more polar microenvironment. After UHP treatment come-up time of BLG at pH 9.0, there was an increase in BLG surface hydrophobicity, suggesting a flexible molecular structure due to surface denaturation of BLG at alkaline pH. UHP treatment of BLG solutions at pH 3.0, 5.0, and 9.0 resulted in decreases in the number of binding sites for the nonpolar fluorescence probe 6-propionyl-2-(dimethylamino)-naphthalene (PRODAN). UHP treatment did not show significant influences in the apparent dissociation constant of PRODAN.; An extraction time of 10 min was used for HS-SPME of delta-decalactone, 2-methylbutyraldehyde, ethyl lactate, and diacetyl. Although the CAR/PDMS fiber was able to detect diacetyl, ethyl lactate, and 2-methylbutyraldehyde, the PDMS/DVB SPME fiber was selected for the extraction of selected flavor compounds due to reproducible and linear (R2 > 0.954) calibration plots, and its semi-polar nature to extract delta-decalactone.; As observed by fluorescence quenching, there is no linear relationship between UHP treatment of BLG at 600 MPa and the number of binding sites for diacetyl, 2-methylbutyraldehyde, delta-decalactone, and ethyl lactate. BLG has low binding affinity for the selected flavor compounds with polar groups, and UHP treatment of BLG did not influence binding of 2-methylbutyraldehyde as observed by fluorescence quenching experiments. Headspace analysis of UHP-treated BLG resulted in significant increases (p < 0.05) in flavor retention over native BLG. In addition, a short UHP treatment time (come-up time) may be adequate for flavor retention. |
