Simultaneous Determination of C18 Fatty Acids in Milk by GC-MS

Abstract

The determination of C18 fatty acids (FAs) is a key and difficult aspect in FA profiling, and a qualified method with good chromatographic separation and high sensitivity, as well as easy methylation, is required. A GC-MS method was established to simultaneously determine C18 FAs in milk. To simplify the methylation protocol for milk samples, besides a base-catalyzation methylation (50 °C for 20 min), the necessity of an additional acid-catalyzation was also studied using different temperatures (60 °C, 70 °C, 80 °C, and 90 °C) and durations (90 min and 150 min). The results showed that the chromatographic resolution was improved, although three co-eluted peaks existed. The base-catalyzation was sufficient, and an additional acid-catalyzation was not necessary. The proposed method was validated with good sensitivity, linearity, accuracy, and precision, and then applied in determining C18 FAs in 20 raw milk and 30 commercial milk samples. UHT milk presented a different profile of C18 FAs from raw milk and PAS milk samples, which indicated that excessive heating could change the profile. Overall, the proposed method is a high-throughput and competent approach for the determination of C18 FAs in milk, and which presents an improvement in chromatographic resolution and sensitivity, as well as a simplification of methylation.

Biohydrogenation Pathway of α-Linolenic Acid in Rumen of Dairy Cow In Vitro

“…Previous studies reported that t 9, c 12, c 15-C18:3 has been found in the processing of food [ 5 ]. Recent studies have found that there are t 9, c 12, c 15-C18:3 in milk [ 6 ], but the concentration was low.…”

“…The extraction of fatty acids and fatty acid methyl esters (FAMEs) from ruminal fluid was according to a previous protocol [ 6 ]. A 2 mL aliquot of each sample was transferred to a 15 mL tube and 4 mL of n-hexane/isopropanol ( v / v = 3/2) solution was used to extract the fat.…”

“…The FAME peaks were identified using known FAME standards, including linoleic acid methyl ester mix CRM 47791 ( t 9, t 12-C18:2, c 9, t 12-C18:2, t 9, c 12-C18:2 and c 9, c 12-C18:2), α-linolenic acid methyl ester mix CRM 47792 including ( t 9, t 12, t 15-C18:3, t 9, t 12, c 15-C18:3, t 9, c 12, t 15-C18:3, c 6, c 9, c 12-C18:3, c 9, t 12, t 15-C18:3, c 9, c 12, t 15-C18:3, c 9, t 12, c 15-C18:3, and t 9, c 12, c 15-C18:3), CLA methyl ester mix Nu-Check prep including c 9, t 11-C18:2, t 10, c 12-C18:2 (Elysian, MN, USA), c 6, c 9, c 12-C18:3, t 6-C18:1, t 9-C18:1, t 11-C18:1, c 6-C18:1, c 9-C18:1, c 11-C18:1, and C18:0 FAME standards individually from Nu-Check Prep (Elysian, MN, USA), c 8-C18:1 and c 12-C18:1 FAME individual standards from Cayman (Ann Arbor, MI, USA), c 9-C18:1, c 9, c 12-C18:2 and c 9, c 12, c 15-C18:3 triacylglycerols (TAGs) individual standards from Nu-Check Prep (Elysian, MN, USA), and c 6, c 9, c 12-C18:3 TAGs from BePure (Beijing, China). The method of Chen et al [ 6 ] was used to calculate fatty acids from FAME data.…”

“…A previous study reported that ALA could isomerize to t 9, c 12, c 15-C18:3 through frying [ 5 ]. Recent studies have found that t 9, c 12, c 15-C18:3 was present in milk [ 6 ]. Therefore, it can be hypothesized that ALA may also convert to t 9, c 12, c 15-C18:3 through biohydrogenation in rumen.…”

Simultaneous determination of 22 fatty acids in total parenteral nutrition (TPN) components by gas chromatography-mass spectrometry (GC-MS)

“…Optimization of the sodium methoxide FAME derivatization technique. See DOI: https://doi.org/10.1039/d3ay00407d ionization detector (GC-FID) methods [3][4][5][6][7][8][9] to gas chromatography-mass spectrometry (GC-MS) methods [10][11][12][13][14][15][16][17][18][19] due to the higher sensitivity of the MS detectors, 20,21 giving a better estimate of FAs present in the analyte of interest.…”