Effect Of Refrigeration And Homogenization On FFA Related Flavour Of Yak Milk

In this paper,Yak milk in Tianzhu Tibetan areas will be used as materials.Investigate the fat content,fat globule size,Lipoprotein lipase activity in cream phase and skim milk and the free fatty acids.And comparing this with Sannen Goat,Holstein and Donkey milk achieve the main effect and the main effect flavour component in yak milk.In addition,fresh milk and after storage for up to 4 h at a cooling temperature(4 °C)from Yak,or after storage for up to24 h at a cooling temperature(4 °C)or at the room temperature(25 °C)will be used as materials.Analysed the acid value and Lipoprotein lipase activity in cream phase and skim milk.Yak milk will be used as materials at two homogenization speeds(4000 and 15000r/min)and three temperatures(30?,40?C and 50?C).And analysed the fat globule size,Lipoprotein lipase activity,acid value.Accuratly investigate the content and variety of free fatty as measured GC-MS choosing the highest acid value after refrigeration and homogenization.Achieving the effect of refrigeration and homogenization on FFA related flavour of yak milk.1.The main effect and main componens of flavour in Yak milk achieve follow result:(1)The fat content of Yak milk,Saanen Goat milk,Holstein milk and Donkey milk were6.65,4.04,3.55,1.03 g/100 m L respectively,the mean fat globule size were 4.04,3.46,3.16,1.18 ?m respectively,the linear and positive relationship was found in the milks between fat globule size and fat content.(2)The Lipoprotein Lipase activity in Yak milk,Saanen Goat milk,Holstein milk and Donkey milk were 238.12,229.62,366.81,163.43 U/L,the distribution of Lipoprotein Lipase of Saanen milk and Holstein milk in the cream phase were 51.38%,51.35%,27.09%,23.81%,in skim milk were 48.65%,48.62%,72.91%,83.04%.(3)The total free fatty acids from Yak,Saanen Goat,Holstein Cattle,and Donkey milk were 803.03,200.78,686.40 and 33.24 mg/kg,the short chain free fatty acids were 76.49,183.90,21.44,1.75 mg/kg.The data were analyzed by principal component analysis.The free fatty acids of C4:0,C6:0,C8:0,C10:0,C12:0,C14:0,C16:0 from lipolysis were related to off-favor of yak milk.2.The effect of refrigeration and homogenization on flavour of Yak milk.The result is follow:(1)The Lipoprotein Lipase in milk cream is significant increase after stored at 4 °C 4h and 24 h(P<0.05).The Lipoprotein Lipase in milk cream and skim milk is significant decrease after stored at 25°C 24h(P<0.05).But the Acid Value is highest in this sample.(2)The mean fat globule size decrease significantly after the homogenization(P<0.05).Homogenization temperature have the significant effect for the lipoprotein lipase activity(P<0.05),Homogenization speed have not the significant effect for the lipoprotein lipase activity(P>0.05).Homogenization temperature and speeds have the significant effect for the acid value(P<0.05).(3)The free fatty acid levels have large change through the homogenization in30 ?,40 ?C and 50 ?C at 15000 r/min.C8:0?C10:0 in short chain free fatty acids and C16:0,C18:0,C18:1in medium and long chain free fatty have largely increase in 30 ?,40 ?C and 50 ?C at 15000r/min.These results suggest that C8:0?C10:0 is the main component relate to flavour of Yak milk.Homogenization have the effect for the content of free fatty acids.This is because that Homogenization erupt the milk fat globule and a lot of Lipoprotein Lipase contact the milk fat.In addition,the Homogenization temperature have the significant effect for Lipoprotein lipase activity.We can control the Homogenization temperature and Homogenization rate to control the content of free fatty acids in yak milk when Milk enterprise process.