Influence of pH and heat treatment on β-lactolobulin-oleic acid complex

Abstract

One of the major concerns of food technologists is to produce healthier products with specific functionalities. The potential use of β-lactoglobulin as a supplement for new functional products is encouraging due to its nutritional and functional characteristics. The aim of this work was to obtain β-lactoglobulin-oleic acid complexes at different pH values (5.0, 6.0, and 7.0) and to test their stability at different temperatures (25-85°C) such as to allow identifying their potential use in a variety of food products. The complexes were characterized through different fluorescence spectroscopy based techniques: phase diagram, intrinsic and extrinsic fluorescence, along with fluorescence quenching experiments. Results showed the presence of more than two structurally distinct species with intermediates as induced by thermal treatment. The heat treatment at temperatures higher than 70°C caused an increase in both intrinsic and ANS fluorescence intensity.
Acrylamide quenching showed no significant differences between the values of Stern-Volmer constants as function of temperature for pH 5.0, suggesting that no significant changes occurred in the Trp microenvironments. Quenching experiments with KI lead to decreases in Stern-Volmer constants in the temperature range 25-70°C, suggesting protein folding, whereas at higher temperatures a small increase was observed suggesting unfolding and an increased accessibility of the fluorophore to the quencher for all pH values.