Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8979222 | International Dairy Journal | 2005 | 9 Pages |
Abstract
This study examined the effect of hydrolysis of casein by added plasmin (6 mg Lâ1) on the heat stability of raw, pre-heated, serum protein-free or concentrated skim milk. Plasmin activity markedly affected the heat stability-pH profile of skim milk and serum protein-free milk, apparently by altering the properties of the casein micelles. It is probable that changes in the surface charge of the micelles, as a result of the hydrolysis of caseins, contributed to this effect. Hydrolysis by plasmin reduced the zeta-potential of the casein micelles from â¼â19 to â¼â16 mV. The effect of hydrolysis of casein by plasmin on the heat stability of pre-heated milk was less pronounced, shifting the heat stability-pH profile to more alkaline values; the heat stability of concentrated milk was unaffected by plasmin. A very high (50 mg Lâ1) level of added plasmin resulted in clearing of the skim milk; the L* value decreased from â¼75 to â¼35 after 24 h incubation at 37 °C. Clearing was correlated with a change in casein micelle diameter from an initial value of â¼175 to â¼250 nm. It is suggested that plasmin-induced changes in zeta-potential may promote micellar aggregation or changes in micelle stucture.
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Authors
Anthony Crudden, Damien Afoufa-Bastien, Patrick F. Fox, Guillaume Brisson, Alan L. Kelly,