Characterisation of Egg Albumen Gels as a Function of Dry-Powder Pasteurisation Conditions

Dry-heating temperature and time of egg albumen powder lead to increase in the textural properties stress and strain at fracture of egg albumen gels. Higher WHC and protein binding of gels were obtained under prolonged pasteurisation time. Furthermore, surface pressure in liquid samples correlated with dry-heating time. The surface hydrophobicity increased at short dry-heating periods, after which it stagnated. The molecular changes resulting in higher hydrophobicity and improved gel properties was mainly induced by heating time. INTRODUCTION One way to ensure egg albumen powder a microbiologically long shelf life is through thermal treatment, which at a given temperature has to meet a minimum holding time. The beneficial effects of pasteurisation in the dry state of egg albumen (EA) powder on the technological properties gelation, foaming and emulsification were first reported by Kato et al.1, who applied a 80°C treatment for 10 days. Since then, dryheat pasteurisation has been widely implemented in the egg product industry. However, many various combinations of heating time and temperature find use. In order to optimise the use of storage capacity and energy, it would be beneficial if similar positive effects are obtainable during shorter pasteurisation time. The mechanisms involved in improving the subsequent gel strength have previously been suggested to be intermolecular hydrophobic interactions and disulfide bonding resulting in protein aggregation favouring the gelling properties of EA2. However, the extent and exact role of different interactions during dry-heating is not fully understood. The aim of the present work was to study the effect of dry-heat pasteurisation time and temperature of EA powder on the protein surface activity, surface hydrophobicity and resulting gel texture, colour and water-holding capacity. MATERIALS AND METHODS Materials One batch of spray-dried EA powder (Sanovo Foods A/S, Odense, Denmark) was subjected to dry-heat pasteurisation in an air-heating cabinet. Treatment combinations were temperatures of 80, 85, 90 or 95°C and time periods of 3, 5, 7, 16, 24 or 30 h. A spray-dried non-pasteurised sample was used as control (time = 0 h). pH and conductivity The EA powder was reconstituted in demineralised water to a concentration of 100 g/L. The pH and conductivity of the liquid samples were measured (Radiometer, Copenhagen, Denmark).