Recent advances in the development of innovative chemical methods for determining the nutritional value of fish meals and aquafeeds

Abstract

Aspartic acid racemization and oxysterol content have been evaluated as indicators of fish meal and aquafeed nutritional value in a series of studies reviewed in the present paper. Kinetic studies and assessment of the d‐aspartic acid content of commercial fish meals and fish feeds supported the use of the extent of racemization of this amino acid as a reliable indicator of the thermal history of fish meal. Preliminary results suggest that d‐aspartic acid could be a useful indicator of the protein nutritional value for fish, expressed by nitrogen retention or in vivo digestibility. However, species‐related differences seem to occur. Therefore, further studies are needed to evaluate the reliability of d‐aspartic acid content as an indicator of protein nutritional value affected by processing conditions. With regard to lipid quality, two major oxysterols, namely 7β‐hydroxycholesterol and 7‐ketocholesterol, have been identified and quantified in commercial fish meals. The measured levels were very low compared with the values reported in the literature for fish products, probably because of antioxidant addition during fish meal processing. An effect of storage time on cholesterol oxidation was also demonstrated in a laboratory‐scale experiment. Research needs for the future include a deeper understanding of the chemical reactions affecting the nutritional quality of aquafeeds, development of innovative and reliable chemical methods for raw material and feed quality assessment, and identification of critical control points in the manufacturing process to try to maintain the original nutritional value of raw materials.