Technical note: Common analytical errors yielding inaccurate results during analysis of fatty acids in feed and digesta samples

Abstract

The basic rules governing the proper fatty acid analysis of feed and digesta samples are sometimes overlooked, leading to potential errors in reporting the fatty acid content or composition of feed and digesta samples. The direct transesterification procedure of Sukhija and Palmquist (1988, J. Agric. Food Chem. 36:1202-1206) has become popular in analyzing fatty acids in feed and digesta samples obtained from animal feeding trials. One shortcoming of the Sukhija and Palmquist transesterification procedure is inaccurate analysis of fatty acids with conjugated double bonds. Digesta and milk samples from ruminant species typically contain a multitude of conjugated linoleic acid (CLA) isomers that easily undergo isomerization and epimerization following prolonged exposure to methanolic HCl. Modifications to the Sukhija and Palmquist procedure are given in this paper that allow successful determination of CLA isomers. Errors in fatty acid analysis also occur from misuse of internal standards; use of an internal standard is recommended in the Sukhija and Palmquist procedure as the preferred method to quantify total fatty acid content. The choice of internal standard may sometimes be important for obtaining accurate results. As an example, applying the direct transesterification procedure to a fat supplement high in saturated fatty acids yielded 613 mg/g of total fatty acids when C17 was used as the internal standard compared with 930 mg/g total fatty acids when C19 was used as the internal standard. Fatty acid content further increased to 952 mg/g when a unique unsaturated fatty acid (C13:1) was used as the internal standard.

Effects of sex and dietary lysine on performances and serum and meat traits in finisher pigs

“…The AA composition was analysed in an external laboratory (Office, Barcelona, Spain) by HPLC-Fluorescence (PNT-M-109), with the exception of tryptophan and cystine that were determined by HPLC-UV and gas chromatography, respectively. The fatty acids of diet were extracted and quantified as described by Jenkins (2010). Laboratory equipment used will be described in the meat analyses section.…”

Replacement of grass and maize silages with lucerne silage: effects on performance, milk fatty acid profile and digestibility in Holstein-Friesian dairy cows

“…Hemicellulose was calculated as the difference between NDF and ADF. Fatty acid methyl esters (FAME) in hexane were prepared from milk fat by the method of Feng et al (2004) and from feeds by the method of Jenkins (2010). Individual FAME were determined by GLC (Hewlett Packard 6890, Wokingham, UK) fitted with a CP-Sil 88 column (100 m × 0.25 mm i.d.…”

Long-Chain Polyunsaturated Fatty Acids in Breast-Milk and Erythrocytes and Neurodevelopmental Outcomes in Danish Late-Preterm Infants

“…A few previous studies have found that LC-PUFA composition of breast-milk/formula, maternal RBC and umbilical cord blood was associated with the early QoM in term infants [18][19][20] as well as in preterm infants (born in gestational week [24][25][26][27][28][29][30][31][32][33][34][35][36] [17,35], but the investigated LC-PUFA indices and ratios vary and the results are not very consistent. None of these studies have tested the infants as shortly after delivery as in the present study.…”

“…The freeze-dried material was mixed with 1 mL of heptane containing 0.4 mg/mL of internal standard (C12:1 cis11 triacylglycerol from NuChekPrep Inc, Elysian MN, USA). Methylation was carried out as a two-step procedure based on Jenkins [29] with modifications. Base-catalysed methylation carried out by addition of 0.2 mL 25% sodium methoxide, followed by incubation at 50°C for 10 min.…”