From grain to feed – process development concerning production of high protein fractions from grain and legum products to be used in extruded fish feed pellets

Abstract

The Danish project “Organic Aquaculture” the link between sustainable production and superior products” is examining the availability of relevant organically produced crops with a high protein content to be used as raw materials for fish feed. Fish meal is the main source of protein for fish feed. On a global scale the production of fish meal will not increase. There is a demand for developing sustainable protein sources as a substitution for fish meal. Protein from crops and legumes is an obvious solution, however, the crops and legumes need to be processed into fractions with a higher protein content in order to compete with fish meal. The process development was carried out at The Danish Technological Institute’s pilot plant located in Sdr. Stenderup, Denmark. Sweet lupine seeds were processed among other grains and legumes. A dehulling process was developed based on three process steps: knife mill grinding, vibration sifting and zig zag air classifying. The protein content was concentrated from 34 % to 43 % protein on dry matter and fat free basis. 90,5 % of the hull was removed. The dehulled lupines were grinded so that 84 % of the fraction was below 250 µm. The grinding was carried out using a hammer mill with a 2.0 mm and a 1.0 mm sieve at 2950 rpm and finally using an Alpine 160 Z pine mill at 18.900 rpm. The grinded product was air classified by using a MP 400 Alpine Air Classifier. A protein fraction of 62 % protein on dry matter and fat free basis was reached. The relation between the particle size of the protein product and the protein content in the fraction was investigated. A linear relation was found and demonstrated; when the protein content in the product was increased the amount of particles in the fraction below 70 µm also increased linearly. The lupine protein was incorporated into a recipe for fish feed and extruded into pellets on a Werner Pfleider Continua 37 Twin Screwed Extruder