Renneting properties of transglutaminase-treated milk

The paper describes the renneting properties of transglutaminase-treated mi lk. The studies have shown that the renneting ability of milk decreases wit h an increasing degree of cross-linking. The increase in cross-linking is a result of increased heat impact and incubation time with transglutaminase, respectively. A high-heating of milk (e.g. 92 degrees C, 5 min) followed b y an enzyme treatment leads to a complete loss of the renneting ability. Th e contents of sialic acid decrease linearly when high-heated milk is mixed with an increasing amount of high-heated as well as transglutaminase-treate d (40 degrees C, 120 min) milk. Model examinations using calcium caseinate and whey protein isolate as substrates were performed to analyse the mechan ism of the decreased renneting ability. From the results of these model inv estigations it is assumed that the loss of the renneting ability of transgl utaminase-treated milk is induced by "surface sealing" of casein micelles w ith cross-linked whey proteins, especially beta-lactoglobulin. Additionally , the model investigations have shown that rennet gels from transglutaminas e-treated calcium caseinate dispersions have a different structure and cons istency as well as appearance than rennet gels from the untreated caseinate .