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Effect of processing technology on the quality of aquaculture feeds


The main objective of the project is to verify the reliability of several innovative chemical methods (aspartic acid racemisation, proportion of SH to S-S bonds and Near Infrared Reflectance (NIR) techniques) to predict the protein digestibility of protein fed to farmed fish. The prediction of the true nutritive value of the protein ingredients used in aquafeed preparation has a central role in allowing a correct use of food resources, reducing wastes and thereby contributing to establish a real sustainable aquaculture, both from an economic and ecological point of view. The kinetics of aspartic acid racemisation and S-S bonds formation will be studied to elucidate the role of different processing parameters (pH and moisture content of the raw material, oxygen pressure, temperature and duration of the thermal treatment) on the protein quality of fish meal, soya meal and extruded diets, aiming at defining indicative guidelines for the production of feeds ingredients and fish feeds characterized by higher protein quality. The availability of reliable and rapid predictive chemical methods to evaluate the quality of the protein ingredients of fish feeds would in fact allow the European fish feed manufacturing industry to produce a dietary protein of high quality which is expected to be well utilized by fish, to allow reduction in the protein content of the feed and to reduce the environmental impact of fish farming.
Suitable analytical methods are now available for the determination of the chemical parameters under study. A preliminary calibration of NIR equipment in order to get predictive estimates of fishmeal digestibility has been achieved. Laboratory equipment for the controlled heat treatment of raw material for fishmeal manufacture has been constructed and is now working satisfactorily. This apparatus has been used for the production of the material, which will be analysed by the developed methods to determine the kinetics of formation of D-aspartic acid and of conversion of SH groups to S-S bonds. Significant progress has been achieved in planning the subsequent steps of the project, in particular with regards to the production of feeds and the conduct of feeding trials with fish.

The above reported objectives will be reached through the following steps:
2.1Method development for chemical analysis of D-aspartic acid, SH groups and S-S bonds and for the application of NIR techniques to the feed and feed ingredients such as fishmeal and soya meal.
2.2 Elucidation of the basic physical/chemical reactions involved in modifying the quality of the protein through the production on a laboratory scale of feed materials (using whole herring Clupea harengus as raw material) treated under defined physical and chemical conditions: the kinetics of aspartic acid racemization and S-S bonds formation will be studied in relation to the major processing variables such as time and temperature of treatment, oxygen pressure, pH and moisture content or the raw material.
2.3 Production on a pilot plant scale of samples of fishmeal and extruded fish feed treated under different processing conditions and evaluation of the chemical parameters under study (i.e. D-aspartic acid content and SH/S-S ratio). Two different samples of fish meal (high and low temperature) will be produced and each one will be subjected to three different extrusion conditions (gentle, medium and tough extruder conditions) to produce the experimental fish feeds.
2.4 Digestion studies (both in vitro using fish enzymes and in vivo with rats, chicks, mink and fish) to determine the protein digestibility in the various species and to evaluate the reliability of the above-reported chemical parameters to predict the digestibility of the protein.
2.5 Production of extruded feeds in commercial conditions (extruder conditions based on the results of the pilot plant-scale study) and quantifications of the chemical parameters under study (i.e. D-aspartic acid content and SH/S-S ratio), to evaluate possible differences with the pilot plant-produced feeds, therefore allowing a correct evaluation of the effects of the treatments occurring in a real commercial production plant.
2.6 In vivo utilization study of the experimental feeds on tank scale (pilot plant-produced feeds) and on farm scale (commercial plant-produced feeds), to evaluate the effects on the growth performances and capacity for protein synthesis in the muscle of farmed fish using both North European (such as Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss, this latter under Northern Italian farming conditions) and Mediterranean (European seabass Dicentrarchus labrax) species. During the farm scale trials, possible effects of using different feeds on the water quality parameters of the effluents from the fish farms will also be recorded.
2.7Determine regression relationships between chemical determinations of D-aspartic acid, SH and S-S content in fish meals and fish feeds and ileal digestibility in rats or chicks, and digestibility determined in mink, Atlantic salmon, rainbow trout and European seabass. Determine regression relationships between chemical determinations of D-aspartic acid, SH and S-S in fish meals and fish feeds and growth of Atlantic salmon, rainbow trout and European seabass. Determine regression relationships between ileal digestibility of protein in rats, chicks and faecal digestibility in mink and fish. Determine regression relationships between the various estimates of protein digestibility and growth of Atlantic salmon, rainbow trout and European seabass. To fully validate the proposed chemical methods the chemical methods will also be applied to commercial samples of fish meal on which in vivo digestibility has been determined.


The major benefit expected for the European aquafeed manufacturing industry from the project will be the availability of rapid and cheap chemical, physical or biological methods for the evaluation of protein quality in aquaculture feeds. As a consequence it will be possible to use feed ingredients with a better, controlled, protein value, therefore allowing a reduction of the protein content in the feed and a reduction of the percentage of non-utilized nitrogen excreted by farmed fish.


The main product of the project is expected to be, as cited above, the availability of new chemical, physical or biological quality parameters for the rapid evaluation of the protein quality of the proteins in the feed ingredients. These, in turn, will allow us to identify appropriate guidelines for the production of feed ingredients and extruded diets with a higher quality of the protein.


Via Celoria 10
20133 Milano

Participants (7)

I. Kk. 10.
5540 Szarvas
Viale Del Lavoro 45
37036 San Martino Buon Albergo (Vr)

5392 Storeboe
United Kingdom
2 College Yard Lower Dagnall Street
St. Albans, Hertfordshire
Norwegian Herring Oil and Meal Industry Research Institute
Kjerreidviken 16
5033 Fyllingsdalen, Bergen
Universitetet i Bergen
19,Aarstadveien 19
5009 Bergen
University of Cambridge
United Kingdom
Madingley Road
CB3 0ES Cambridge