Study Of Infrared Model On Rapid Detection Of Five Fatty Acids In Milkfat

Objective:To establish and optimize a system of infrared model spectroscopy of detecting the fat in milk rapid qualitatively and quantificationally in the base of detection of stearic acid, linoleic acid, oleic acid, myristic acid and palmitic acid in the cream, olive oil, peanut oil and palm oil, as well as the changes of fatty acid content after the cream and exogenous fat was homogenized.Methods:The relative content of five fatty acids, including stearic acid, linoleic acid, oleic acid, myristic acid and palmitic acid, in milk fat, peanut oil, olive oil, and palm oil was analyzed with gas chromatography (GC), which provided the reference for near infrared model of milk fat. Based on the standard spectrogram of five fatty acids, fourier infrared spectrometer was used to detect qualitatively the difference of spectrogram in milk fat, peanut oil, olive oil and palm oil in mid-infrared spectra. In addition, the changes of content were analyzed after the cream and exogenous fat was homogenized. According to the milk fat models of fourier transfrom near-infrared, the content of five fatty acids in milk were analyzed accurately.Results:1. The results of GC showed that the retention time of standard methyl myristate, methyl palmitate, methyl linolate, methyl oleate, and methyl stearate by GC was 9.188 min, 11.388 min,13.883 min,13.979 min,14.390 min, respectively. The detection limits of five fatty acids methyl ester were 0.8 mg/mL,0.4 mg/mL,0.6 mg/mL,0.6 mg/mL, and 0.8 mg/mL. There were significant differences on fatty acids composition among milk, peanut oil, olive oil and palm oil. However, myristic acid was not detected in the peanut oil and olive oil, and oleic acid was not detected in the palm oil. Furthermore, the content of the fatty acids in the samples was also different. The oleic acid content in olive oil was 88%, while the oleic acid content was only about 41% and that of linoleic acid was 39% in the peanut oil. The palm oil mainly contains palmitic acid and oleic acid.2. The results of qualitative detection with the technique of Fourier mid-infrared showed that there were significant difference in the 1100-1070 cm-1 range in the standards of oleic acid and linoleic acid. There were two peaks (1119 cm-1 and 1091 cm-1) in the oleic acid, but there were three peaks (1048 cm-1,1102 cm-1 and 1121 cm-1) in the linoleic. The fat could be well dissolved with carbon tetrachloride or n-hexane as the extraction agent, and the peaks of cream could be detected when the volume ratio of the sample and organic was 5:10(g:v). The main difference between peanut oil and cream was at 3007 cm-1 and 1114 cm-1, and the main difference between palm oil and milk fat in the peak was at 3005 cm-1. Compared with cream, olive oil had two obvious peaks, which are 3005 cm-1 and 1238 cm-1.3. The near infrared model could be used to quickly detect the content of fatty acids and exogenous fat in milk, and the pre-treatment of sample was simple and fast.Conclusion:1. Gas chromatography (GC) can be used to detect the difference between the type and content of fatty acids in milk, olive oil, peanut oil and palm oil, which has a good repeability for the detection of fat in the plant and animal.2. Carbon tetrachloride and hexane extraction are good solvent extraction agent, and the preparation time can be shortened in the qualitative detection of milk fat with Fourier transform infrared spectroscopy.3. Fourier transform infrared spectroscopy can be used to detect the difference between a variety of vegetable oils, and the method is fast. The near infrared model can be used to accurately analyze the exogenous fat content in the milk, and the standard deviation is small. The milk samples need not be pretreated and the method is rapid, simple, and environmentally friendly, which is very suitable for the field tests to the fat adulteration of in milk.