[39] Continuous treatment of ultrahigh-temperature sterilized milk using immobilized sulfhydryl oxidase

This chapter describes the treatment of ultrahigh-temperature sterilized milk using immobilized sulfhydryl oxidase. Sulfhydryl oxidase (SOX) is an iron-containing, glycomembrane enzyme existing primarily in the membrane vesicle fraction of skim milk. Unlike other enzymes that have been developed for use in immobilized forms, SOX is a membrane enzyme, and consequently, certain considerations are important to the choice of immobilization conditions. Sulfhydryl oxidase may be purified by the solubilization of the membrane vesicles with nonionic detergent and isolation of this enzyme by transient covalent affinity chromatography on cysteinylsuccinamidopropyl-glass. At present, however, the quantities obtainable by this procedure prevent its commercial application. Several methods have been developed for the preparation of active isolates directly from whey that are, therefore, commercially attractive. Whey is obtained from the skim milk upon removal of the caseins by clotting with chymosin (rennin). This reaction occurs at the pH of milk and results from the hydrolysis of a specific peptide bond in K-casein; thus, other proteins are not proteolyzed in this treatment.