Analysis of phytosterols by gas chromatography with mass spectrometry in Atlantic salmon (Salmo salar) fed novel lipid sources

Abstract

Fishmeal and fish oil have been considered the most digestible and nutritious ingredients for farmed fish, but there is a shift towards more sustainable alternatives. In this study, fish oil was replaced with four alternative oil sources, oil from Camelina sativa seeds, oil from rapeseed, oil from Pavlova sp., and a microbial oil produced from Schizochytrium sp.. Atlantic salmon (Salmo salar) were fed experimental diets, including either microbial oil or camelina oil at low and high levels of inclusion, as well as a control diet containing traditional fish oil. Sterol content was investigated to determine if added phytosterols were incorporated by the salmon, and subsequently transferred to the fish tissue for human consumption. Sterols were identified, and quantified where possible, in the alternative oil sources and then in salmon muscle tissue after feeding trials. Gas chromatography/mass spectrometry (GC-MS) and gas chromatography/flame ionization detection (GC-FID) were used in the analysis. Five sterols were identified in camelina oil: cholesterol, brassicasterol, campesterol, stigmasterol, and β-sitosterol. In the experimental diets from the 16-week feeding trial containing various inclusion levels of camelina oil, brassicasterol, campesterol, stigmasterol, and β-sitosterol were also identified, however in the muscle tissue from salmon fed these diets, only campesterol and β-sitosterol were detected. In the microbial oil experiment, cholesterol, lathosterol, brassicasterol, 24-methylenecholesterol, 24-methylenelophenol, stigmasterol, and spinasterol were the sterols identified. In the experimental diets containing 5% or 10% microbial oil, cholesterol, brassicasterol, lathosterol and stigmasterol were found, with the addition of campesterol, and two other sterols (23,24-dimethylcholest-5-en-3β-ol and 24-ethyl-5α-cholest-7-en-3β-ol). In the muscle tissue from salmon fed the diets containing microbial oil, cholesterol, cholestanol, campesterol, stigmasterol, and dinosterol were detected. Campesterol and β-sitosterol from the camelina oil were transferred from the diet to the tissue, and with the microbial oil, stigmasterol was also detected in both the diets and the salmon tissues. This indicates that sterols in microbial oil can be transferred to the fish by consumption, but not all sterols were found to do so. Also, phytosterols can be metabolized to other sterols by the fish, as was seen with cholesterol and cholestanol.