Abstract: The effects of fat content on the texture, rheology and microstructure of yak milk hard cheese were clarified by measuring the functional properties of yak milk cheeses containing different proportions of fat. Full-fat, semi-skimmed and low-fat hard cheeses were made from defatted and whole yak milk mixtures at ratios of 0:1, 1:1 and 2:1, respectively, and their physicochemical indicators were tested and texture characteristics were analyzed using texture profile analysis (TPA). Moreover, the correlation between fat content and each of the measured texture parameter was analyzed. The microstructure of cheese was observed by confocal laser scanning microscopy, and rheological properties were measured in the temperature range of 25–80 ℃. Furthermore, a regression equation between elastic modulus and viscoelasticity and temperature was set up. The cheese yield increased with increasing fat content. There were significantly negative correlations between fat content and water content, hardness, elasticity or chewiness with correlation coefficients of ?0.909, ?0.851, ?0.795 and ?0.768, respectively, while it was significantly positively correlated with cohesiveness with a correlation coefficient of 0.898. The areas of fat granules in full-fat, semi-skimmed and low-fat cheese were 1 800.20, 1 317.59 and 792.02 μm2, respectively, accounting for 10.0%, 7.3% and 4.4% of the total area, respectively. The lower the fat content, the greater the elastic modulus; conversely, the higher the fat content, the greater the viscoelasticity. The fat content was closely related to the physicochemical properties, texture, microstructure and rheological properties of cheese. This experiment provides a basis for the study of the mechanism of the effect of fat content on yak milk cheese.

Key words: fat content; yak milk hard cheese; texture; correlation analysis; rheological properties