PHYSICOCHEMICAL INDEXES AND PHYSICAL CHARACTERISTICS OF SIX KINDS OF MARKET TIBET BUTTERS

Tibet butter which is extracted from yak milk grease products,is not only the major food source in the Tibet region,but also is an essential raw material for making butter sculpture and butter lamps in religious activities.The production process of Tibet butter is complicated and the butter products are not easy to store.Therefore,the main components,physical and chemical indexes of six kinds of commercial Tibet butters products were determined in the present study.The fatty acid compositions,solid fat contents,rheological properties,thermodynamic properties and crystal type were analyzed using GC,NMR,rheological,DSC and XRD methods,respectively.The results showed that the mainly fatty acid compositions of Tibet butters were palmitic acid (28%-34%),oleic acid (21%-37%) and stearic acid (9%-19%).The higher content of saturated fatty acids was the reason that Tibet butter existed in solid status.Moreover,the six kinds of Tibet butters all contained a small amount of trans-oleic acid.The results of solid fat contents and thermodynamic properties showed that the melting temperature ranges of six Tibet butter products were large,indicating their strong plasticity.The analysis of rheological properties indicated that the elastic modulus (G') of six kinds of Tibet butter products was greater than the viscous modulus (G″),implying they all belonged to the shear thinning fluid and showed solid-like properties.The results of XRD showed that all the 6 kinds of products had soft texture and mainly contained β'-crystal.In conclusion,the Tibet butter has the function of crisp,beating and plasticity,which can be used as the raw material of food and butter sculpture.