Screening for low molecular weight compounds in fish meal solubles by hydrophilic interaction liquid chromatography coupled to mass spectrometry

There is increasing evidence that low molecular weight water soluble compounds of marine protein are important for fish performance, thus identifying and quantifying them to incorporate in feeds are needed. A simple analytical method using hydrophilic interaction liquid chromatography coupled with mass spectrometry was developed to screen for low molecular weight water soluble compounds in enzyme treated and untreated Alaskan pollock (Theragra chalcogramma) stickwater (SW) generated from processing fish meal with pollock byproduct. Sample preparation was quick and involved centrifugation with ultrafiltration membrane (cut off <3000 g/mol) of reconstituted freeze dried samples for direct analysis on mass spectrum (MS). Full MS scan (50–2000 g/mol) in dual ion mode (atmospheric pressure chemical and electrospray ionisation) resulted in the identification of 5 abundant compounds (creatine, creatinine, inosine, trimethylamine and trimethylamine oxide (TMAO)); quantification was performed with selective ion monitoring based on calibration standards. The major low molecular weight compound detected in untreated SW was TMAO at 25.2 ± 2.08 mg/g dry weight (dw) and in enzyme-treated SW was creatine at 10.5 ± 0.47 mg/g dw.