The susceptibility of the individual goat's milk proteins to cross-linking with transglutaminase was investigated. Results from capillary gel electrophoresis showed that a heat treatment of milk before reaction with transglutaminase enhanced the reactivity of milk proteins towards protein cross-linking. The results of this paper suggest that the specificity of transglutaminase varied with the type of milk proteins. kappa-casein was more susceptible to cross-linking than alpha- and beta-casein. However, no significant differences between both caseins were observed. Furthermore, only in heated milk, beta-lactoglobulin was significant cross-linked by transglutaminase, while preheated and unheated alpha-lactalbumin was susceptible to enzymatic cross-linking. Finally, an optimization strategy based on desirability functions together with experimental design was used to optimize the preheating conditions (temperature and time) of goat's milk that maximized the cross-linking reactions catalyzed by transglutaminase. (c) 2005 Elsevier Ltd. All rights reserved.