Quality Changes and Protein Degradation in Edam Yak Cheese during Ripening

Abstract

In order to study the ripening mechanism of Edam yak cheese, the sensory, physicochemical and textural properties, and proteolysis and lipolysis indexes of Edam yak cheese were determined after 0, 20, 40, 60 and 80 days of ripening. The degradation of casein was investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier transform infrared (FTIR) spectroscopy, and the correlation between maturation time and quality indices was analyzed by Pearson’s correlation analysis. The results showed that the sensory score decreased at first and then increased with increasing ripening time; the water content and pH decreased; the brightness value (L*) decreased, while the redness value (a*) and yellowness value (b*) increased; the hardness, elasticity and adhesiveness all increased, while the cohesiveness gradually decreased. The storage and loss moduli increased, and the tangent of the loss angle was always less than 1. The ripening time was positively correlated with the total nitrogen content, and the nitrogen content of soluble fractions at pH 4.6 and in 12% trichloracetic acid (TCA) (P < 0.01). The fat content increased firstly and then decreased, and the free fatty acid content and thiobarbituric acid-reactive substances (TBARS) value increased gradually. The results of casein (CN) degradation showed that αs1-CN, αs2-CN, β-CN and κ-CN were degraded continuously during cheese ripening, macromolecular proteins were degraded obviously after 80 days of maturation, and β-sheet and α-helix were gradually transformed to random coil during maturation. The ripening time was positively correlated with the carbonyl content and surface hydrophobicity (P < 0.01), but negatively correlated with the total sulfhydryl content (P < 0.05).

Keywords

• yak cheese; edam cheese; mature; quality changes; protein degradation