S. Funtenberger et al., PRESSURE-INDUCED AGGREGATION OF BETA-LACTOGLOBULIN IN PH 7.0 BUFFERS, Lebensmittel-Wissenschaft + Technologie, 28(4), 1995, pp. 410-418
Solutions of a beta-lactoglobulin isolate in water, in potassium phosp
hate buffer (20 or 50 mmoL/L), and in pressure-resistant buffers, at a
protein concentration of 25 g/kg and at pH 7.0, were processed at 150
, 250, 350 or 450 MPa and 25 degrees C, for 15 min, then stored at 4 d
egrees C, usually for 24 h, before analysis. Bis-Tris (20 or 50 mmol/L
) and bis-Tris-propane (10, 20 or 50 mmol/L) were selected as pressure
-resistant buffers, while the pH of water or phosphate buffer is known
to decrease reversibly by 0.2-0.3 pH unit per 100 MPa. After pressuri
zation, nitrogen solubility at pH 4.7 and 7.0, and aggregation pattern
s by polyacrylamide gel electrophoresis were determined. Both indicate
d that aggregation of beta-lactoglobulin was more extensive in pressur
e-resistant buffers than in phosphate buffer or in water. Electrophore
tic patterns also revealed the progressive formation of dimers to hexa
mers and of higher polymers of beta-lactoglobulin as a function of the
type and molarity of buffer and of the pressure level. All high molec
ular weight aggregates and most oligomers disappeared when pressurized
solutions were treated with beta-mercaptoethanol (15 mL/L) prior to e
lectrophoresis. Thus pressure induced the formation of-intermolecular
S-S bonds, especially when the pH was maintained close to neutral. Pre
vious studies with thermally-induced beta-lactoglobulin gels had shown
that SH/S-S interchange reactions were enhanced at or above neutralit
y (C) 1995 Academic Press Limited