Effects of succinylation on the renneting properties of raw milk

Succinylation (0-100 mM succinic anhydride) of milk proteins in their natur al environment and related effects on the rennet coagulation were studied b y rheological and biochemical methods. The rheological properties of succin ylated milk during rennet coagulation was followed by using of an oscillati on rheometer analyzing rennet gelation time and gel firming as a function o f time. Effects of succinylation of milk on the primary phase of renneting were estimated indirectly by analyzing the glycosylated and non-glycosylate d caseinomacropeptide fractions. SDS-PAGE was carried out on whey to visual ise the non-clottable N-content. Rheological results revealed that both the rennet gelation time and the rel ative rate of gel firming were affected by succinylation of milk proteins. This chemical modification affected first the Ca-status of milk. The change s involved were reversible mostly up to 7 mM succinic anhydride if the trap ped Ca ions were replaced. Modification of milk protein in the presence of 20-100 mM succinic anhydride were caused to irreversible changes in the pro tein and thus to impaired rennet clotting properties of milk. The alteratio n of the rheological properties was found to result from changes affecting the primary stage of enzymatic coagulation of milk, which involves the lysi s of the glycosylated and non-glycosylated caseinomacropeptides. Analysis o f the release of these peptides revealed that the enzymatic release of the non-glycosylated peptide was hindered proportionally with the degree of irr eversible milk succinylation. SDS-PAGE-analysis showed that the amounts of individual caseins in the serum increased with the extent of succinylation of the milk.