Introduction
The pressing need to identify appropriate alternative resources to support aquafeed sustainability demands alternatives for resources that cannot directly be used for human food. Clover, a legume grown frequently as catch crop, was chosen as a novel non-food protein feed ingredient for the yellowtail amberjack (Seriola lalandi). The cultivation of clover grass can enhance soil quality, farm profits and the product is harvested in appropriate amounts to serve as a reliably available, sustainable, alternative protein ingredient for aquafeeds.
Its applicability in aquafeeds was tested
Material and Methods
Digestibility trials were conducted in a recirculating aquaculture system as described by Glencross et al. (2007). The reference diet was formulated to meet nutritional requirements of S. lalandi (Table 1) (IAFFD and pers. comm. Infinite Sea GmbH). The test diet was prepared by adding 3 parts clover gras protein concentrate to 7 parts of the reference diet mash on weight basis. Additionally, one test feed contained amylase to test its efficiency to support starch digestion in S. lalandi and one contained psyllium to test its effect on faeces properties. Each diet was fed to tank triplicates containing 20 fish.
Results presented will include digestibility of Clover grass, details of S. lalandi growth and health as well as rheological parameters of faeces.
Pellet Production
A twin-screw extruder (ZK 20/40 P, Collin Lab & Pilot Solutions) was used to produce all experimental diets. The pellets were produced at a constant mass flow rate of 5 kg/h and with a 2 mm die. The screw speed (200, 400 rpm ) and the temperature profile (Table 2) was varied during production.
The pellets were cut with a pelletizer (ELG 10, Econ GmbH) and dried continuously using an infra-red drum dryer (B.IRD Machinery Stricker GmbH). During measurement, the specific mechanical energy [SME] (Wh /kg), the pressure (bar) and the melt temperature (°C) we re determined and documented using Fecon software.
Pasting properties of pellets
The gelatinisation was determined using a Global Rheological Solution Viscosimeter (Australia) according to the ICC 169 method. The sample was mixed with water to form a 6 % starch suspension (dry substance) and placed in a sample beaker. Defined heating and cooling cycles were carried out for analysis. The measurement was carried out applying a heating cycle from 30 °C to 93 °C. A temperature of 90 °C was maintained for 20 minutes. The sample was then cooled to 50 °C and held again for 20 minutes. The stirrer speed wa s 75 rpm. The heating rate wa s 1.5 °C per minute. Global Rheological Solution software was used to determine gelatinisation temperature, highest observed viscosity, breakthrough viscosity, final viscosity and restoring viscosity.