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Journal of Spectroscopy
Volume 2015, Article ID 935901, 6 pages
http://dx.doi.org/10.1155/2015/935901
Research Article

Changes of pH in β-Lactoglobulin and β-Casein Solutions during High Pressure Treatment

Food Chemistry, Department of Food Science, Faculty of Science, University of Copenhagen, Rolighedsvej 30, 1958 Frederiksberg, Denmark

Received 29 October 2014; Accepted 9 February 2015

Academic Editor: Guang Zhu

Copyright © 2015 Karsten Olsen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The pH changes in the milk systems, β-lactoglobulin B, β-casein, and mixture of β-lactoglobulin and β-casein (pH 7 and ionic strength 0.08 M) were measured in situ during increasing pressure up to 500 MPa. An initial decrease to pH 6.7 was observed from 0.1 to 150 MPa for β-lactoglobulin, followed by an increase to pH 7.3 at 500 MPa. The initial decrease is suggested to be caused by the deprotonation of histidine, while the increase is suggested to result from an increase of hydroxide ions due to the loss of tertiary structure. The change in pH of the β-casein solution displayed an almost linear increasing pressure dependency up to a pH of 7.7 at 500 MPa. The limited tertiary structure of β-casein could allow exposure of all amino acids; thus the increase of pH can be caused by binding of water protons resulting in an increase of hydroxide ions. Addition of β-casein to β-lactoglobulin (1:1) was found to suppress the initial pH decrease found for the β-lactoglobulin solution. The pH change of the mixture did not suggest any intermolecular interaction, and a simple additive model is proposed to calculate the pH change of the mixture from the corresponding individual samples.