Rapid quantitation of feed rotifer ( Brachionus plicatilis ) fatty acids by Raman spectroscopy

Abstract

Improving the lipid composition of feed-rotifers enhances the survival and growth rates of juvenile fish in aquaculture, but monitoring enrichment profiles using gas chromatography (GC) is slow, labour-intensive and requires expensive instrumentation. Here, we describe the potential of Raman spectroscopy as an alternative, more rapid tool for quantitation of rotifer fatty acid composition in an aquaculture setting. A compositionally diverse sample set was prepared by periodically subsampling rotifers undergoing enrichment using three different feeding regimens. Sampled rotifers were freeze-dried and their fatty acid content and composition was measured by GC–MS (mass spectrometry). Raman spectra (1064 nm excitation) were acquired with two instruments: a state-of-the-art Fourier transform (FT)-Raman spectrometer equipped with a liquid nitrogen-cooled Germanium detector; and a smaller, portable spectrometer equipped with an InGaAs detector. Fatty acid reference data acquired by GC–MS were related to structured variance in each Raman spectral data set using partial least squares regression. The resultant models could accurately quantitate total fatty acids (TFA) and total polyunsaturated fatty acids (PUFA) using both FT-Raman spectra (Root Mean Square Error [RMSEV] = 5.0 mg g−1 TFA and 6.1 mg g−1 PUFA) and spectra generated using the portable instrument (RMSEV = 4.2 mg g−1 TFA and 5.3 mg g−1 PUFA). Analysis times with the portable instrument were approximately 3 min, compared to 16 min with the FT-Raman system. Portable Raman spectroscopy may be a useful tool for high throughput screening of rotifer lipid composition when testing and optimizing enrichment protocols and developing microdiets for aquaculture species.