Recent
advances in the development of innovative chemical methods for determining
the nutritional value of fish meals and aquafeeds
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.
(Universita degli Studi di Milano, Facolta di
Medicina Veterinaria, Instituto di Zootecnica via Trentacoste 2, I-20134
Milan, Italy)