Age Gelation of UHT Milk: Changes that Occur During Storage, Their Effect on Shelflife and the Mechanism By Which Age Gelation Occurs

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Heat Treatments and Alternative Methods


International Dairy Federation, Brussels, Belgium

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A theory describing the age-gelation of UHT milk was developed based on changes in storage stability and microstructure of concentrated milk after UHT processing. This included studies on extent of whey protein denaturation during UHT processing and changes in casein micelle size, influence of lactose on protein crosslinking, influence of milk pH on casein micelle surface potential, influence of phosphates on shelf life, influence of UHT heating conditions on shelf life, and movement of milk proteins during storage of UHT milk. It is proposed that age-gelation of UHT milk involves release of the beta-lactoglobulin/kappa-casein complex (beta kappa-complex) that is formed during heating from the casein micelles followed by subsequent aggregation of the beta kappa-complexes and formation of a three-dimensional network of crosslinked proteins. Release of the beta kappa-complex is observed as protuberances and tendrils on the micelle surface. Involvement of the casein micelles in age-gelation occurs through attached beta kappa-complex appendages and not via direct contact between micelle surfaces. The numerous observed phenomena related to age-gelation of UHT milk can be explained based upon this theory.

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