ENHANCEMENT OF HEAT-INDUCED GELATION OF FOOD PROTEINS BY MILK a-LACTALBUMIN

Abstract

a-Lactalbutnin is one of the major component of milk whey proteins. This study was conducted to elucidate the contribution and mechanism of a-lactalbumin in heat-induced gelation of the mixed-proteins. At concentration of 8%, a-lactalbumin alone does not form gel, but it mixtures with whey protein isolate, whey protein concentrate, fl-lactoglobulin, bovine serum albumin, egg white protein, lysozyme and ovalbumin resulted in the gel strength of 378.5, 270.6, 380.8, 310.2, 215.6, 0.0 and 400.9 in 104 dyne/cm2, respectively. The mixture of a-lactalbumin and lysozyme did not form a gel, because a-lactalbumin and lysozyme appear to be two very closely related protein both in primary and three-dimensional structures. Determination by electrophoresis, chromatography, immunoassay, surface hydrophobicity and amino acid sequencing indicated that a specific disulfide bond (Cys6-Cys120) in a¬lactalbumin contribute to heat-induced gelation of the mixed proteins. Reducing one, two and three of four disulfide bonds in a-lactalbumin confirmed the enhancement of heat-induced gelation of the mixed proteins. It was postulated that the enhancement mechanisms of a-lactalbumin in heat-induced gelation of the mixed proteins was mainly through disulfide bond and hydrophobicity interactions. INTRODUCTION Proteins are important macro nutrients of foods. The functional properties of proteins are defined as those physicochemical properties that enable proteins to affect the characteristics of food during processing, storage, preparation and consumption (Rupnow, 1992). Gelation is an important functional property of proteins in food systems. Different proteins produce gels which vary in textural characteristics (Aguilera, 1995; Legowo et al., 1996). Milk whey protein consist several proteins such as a-lactalbumin, 13- lactoglobulin, bovine serum albumin (BSA), and some others (Farrell et al., 2004), which contributes to the gelation properties (Aguilera, 1995). The monomeric a