Omega-3 fatty acids are polyunsaturated fatty acids found in foods and when consumed at optimal levels are reported to have health benefitting properties including promoting cardiovascular health and playing an essential role in cell structures and the inflammatory response. Rich sources of n-3 PUFA include oily fish, seeds, nuts, and brassica vegetables. There are two main avenues, which are responsible for altering the lipid profiles and fat content of meat products 1) genetics, and 2) diet of the animal. Grass is known to be rich in alpha-linolenic acid (C18:3 n-3), which is a known precursor for longer chain fatty acids, however, undergoes significant hydrogenation in the rumen, limiting its deposition in muscle. Increasing n-3 PUFA using feed supplements has limitations due to LC-PUFAs such as C20:5, C22:5 and C22:6 n-3 PUFA being toxic to rumen microbiomes. Microalgae is reported to have protective properties which allows the LC n-3 PUFA to bypass without being exposed and damages by rumen processes.
This study investigate how animal diet impact fatty acid composition, specifically omega-3 PUFA, and the concentration and distribution of lipid species across classes. The aim of this study was to investigate the effect of lamb diet on production performance, muscle lipid profiles and effect on rumen microbiome. At the start of the study, all the ruminal volatile fatty acids (VFA) were similar between the control and the microalgae treatment. At time of the slaughter propionic acid was the only VFA with significant difference between both treatments and the microalgae treatment lowered the propionic acid concentrations from 24 to 15 mmol/L. A methane reduction of 23% was estimated by microalgae treatment compared to control. The number of bacteria and archaea genera present in gastrointestinal samples during the study decreased similarly across the different treatments.
Dried lipid extracts of Longissimus and Leg muscle samples (n=26) from the grass, concentrate and high microalgae as well as grass and concentrate treatments, respectively were reconstituted in 900 µL 20% of mobile phase B (mobile phase B was 90% isopropanol, 10 mM ammonium formate and 0.1% HCOOH in ultrapure water) and 100 µL chloroform and centrifuged. 3 µL was injected into the UHPLC/MS system. Lipids were then directly analyzed using a Vanquish UPLC-System (Thermo Scientific, Waltham, MA, USA) with a heated electrospray ionization (HESI) QExactive plus Orbitrap mass spectrometer (Thermo Scientific, Waltham, MA, USA) in positive ion mode. Chromatographic separation took place on a reversed-phase column (Accucore Polar Premium 100×2.1 mm (2.6 µ) with guard column: Accucore Polar Premium 10×2.1 mm (2.6 µ)) from Thermo Scientific (Waltham, MA, USA). Identification and quantification of individual lipid species were performed by LipidSearch Software 5.1 from Thermo Scientific (Waltham, MA, USA) on product level (MS/MS fragmentation).
Results of LC-MS analysis have shown that several C18:3 n-3 lipid species increases two to tenfold only in Longissimus and Leg muscle of grass treatment and not in algae treatment in comparison to concentrate treatments. Main lipid class of C18:3 n-3 in which the increase occur is alkenyl-PE. An increase of C18:3 n-3 in the TG class could be detected only in Leg muscle samples of grass treatment compared to concentrate treatment and not in Longissimus muscle. The main lipid classes with C22:5 and C22:6 n-3 increase are alkyl and alkenyl-PE and alkyl-PC. The highest increase (by 3 to 10) is seen for algae treatment. Furthermore a tenfold increase of PI 18:0_22:6 and AcCa 22:6 is detected in Longissimus muscle after microalgae treatment in comparison to concentrate treatment. In microalgae treatment of Longissimus muscle further incorporation of C22:6 n-3 occurs in specific C22:6 n-3 TG species with medium-chain fatty acids with less or equal than 10 carbons.
This detailed lipidomics study of lamb muscle diet treatments shows that C18:3 n-3 lipid species are mainly incorporated into phospholipids of Longissimus and Leg muscle after grass diet treatment but also into TGs of exclusively Leg muscle. The algae diet treatment lead to a considerable increase of C22:5 and C22:6 n-3 in specific phospholipids and TGs that is not seen in the grass diet treatment.