Heat Stability of Bovine Lactoferrin at Acidic pH

Abstract

In order to develop a practical method for pasteurization of lactoferrin, the influence of pH on the heat stability of bovine lactoferrin was studied. Solutions (5%; wt/vol) of iron-free lactoferrin (apo-lactoferrin) in distilled water were adjusted to various pH values from 2.0 to 11.O and heated at various temperatures (80 to 120°C) for 5 min. The heated samples were analyzed by HPLC and assayed for iron-binding capacity, antigenic activity, and bacteriostatic effect. The heated solutions of apo-lactoferrin gelled at neutral and alkaline pH. At acidic pH, lactoferrin in the heated samples remained soluble, and solutions were clear. The HPLC pattern of apo-lactoferrin heat-treated at pH 4.0 and 100°C was similar to that of unheated apo-lactoferrin. It resisted heating at pH 4.0 and 90°C for 5 min without any significant losses of iron-binding capacity, antigenic activity, or antibacterial activity. These results indicate that apo-lactoferrin is very stable at pH 4.0 and high temperatures. It was considered that heating conditions of pH 4.0 and temperatures of 90 to 100°C for 5 min were suitable as a practical method for pasteurization of lactoferrin. Moreover, the possibility of using an UHT method for more effective and efficient pasteurization of lactoferrin was demonstrated. Apo-lactoferrin treated at pH 2.0 or 3.0 and 100 or 120°C for 5 min was apparently degraded, but the antibacterial activity was equal to or stronger than that of unheated apo-lactoferrin. This result suggests that some of the lactoferrin fragments produced by heat under acidic conditions have antibacterial activity. © 1991, American Dairy Science Association. All rights reserved.