The Research on the Plant Fat Adulteration in Raw Milk by Determination of β-sitosterol

WEI Xue-dong;JIANG Yu-jun;SHI Xin;LIU Bo;YU Li-tao;WANG Xiang-xin;SHAN Yi;The National Dairy Testing Center,Northeast Agricultural University;

dairy fat adulteration;;β-sitosterol;;GC-MS

A gas chromatography-mass spectrometric(GC-MS)method was established for the determination ofβ-sitosterol in raw milk.Theoretical studies had shown that the fat in raw milk belonged to animal fat,fresh milk should not contain plant oils or rarely contain phytosterols,especiallyβ-sitosterol.Based on the analysis of the content ofβ-sitosterol in raw milk from different area,the identical method of mixing plant oil in raw milk had been given.Using the mass ratio of KOH aqueous solution of 1.25of the 25mL saponificate sample,100mL vitamin C ethanol solution as stabilizer,liquid saponification with petroleum ether and diethyl ether,turn solvent to toluene,centrifugal inlet mass spectrometry.Selecting 60mDB-5capillary column with high column efficiency,the injection volume was 1μL,programmed raising temperature to achieve a good separation ofβ-sitosterol and other alcohols and impurities within 35minutes.Selected ion 414quantitative,the detection limit was 0.10mg/L.The linear correlation coefficient r was 0.9991.Using this method to detectβ-sitosterol content in fresh milk from 6different regions,the highest content was 0.86mg/L,the content ofβ-sitosterol common plant oil were 1to 3g/L.In conclusion,using plant fat replace dairy fat,and each one percent of plant fat would produceβ-sitosterol as 12times as the milk without plant fat at least.Thus,mixing plant fat could be identified in raw milk.