Heat-induced changes in the proportion of types I and III collagen in bovine Longissimus dorsi.

Intramuscular collagen (IMC) was isolated from the Longissimus dorsi of six Simmental bulls, 17 months of age, to evaluate the effect of heating on the proportion of types I and III collagen. Cyanogen bromide (CNBr) peptides were prepared from unheated IMC and the soluble and insoluble fractions of IMC heated to 70°C for 70 min or 90°C for 140 min. Percentage of type III collagen was determined by densitometric scans of the CNBr peptides, αl(I)CB8 and αl(III)CB8, as resolved by SDS-PAGE. Percentage of collagen solubilized was greater (P < 0·05) at 90°C than at 70°C. The 70°C and 90°C insoluble IMCs were similar (P > 0·05) for percentage of type III, but both had a greater (P < 0·05) percentage of type III than unheated IMC, indicating that type I is more heat labile than type III. Heat-soluble IMC contained both α and β components and the CNBr peptides of 70°C soluble IMC were mostly type I. These results indicated that heating intramuscular collagen from bulls mainly solubilized type I collagen. Improved tenderness associated with increased heat solubility of collagen may be more closely related to heat-induced solubilization of type I than of type III collagen.