28 MARCH 2025 • WORLD AQUACULTURE • WWW.WAS.ORG yield a needed elevation in bulk density towards the target. Simply put, the ability of AFX to effectively apply a wider range of process moisture levels is what enabled it to achieve target densities across all runs. It is also worth taking note that the AFX runs in average utilized 2% less water inclusion across all runs than SX and 1% less than the TX runs. This yields improved resource efficiency and sustainability, from reduced energy costs associated with drying. When looking at the durability across all the different runs, both of the twin screw technologies stand out as slightly better than the SX runs (Figure 3). However, this effect was not statistically significant due to the amount of data and number of runs carried out. It can be observed though, that the run ‘3’ on the SX, which utilized lower water gave 15-20% lower durability than in the twin screw runs. All products were tested for gelatinization levels of starch, and numbers generally fell between 86-93% across all runs — with no pattern. Hence, it is not ‘inadequate cooking’ of starches that gave the SX run ‘3’ with lower water a poor durability value. More likely this could be from protein alignment, porosity, pellet shape and mechanical properties of the pellets. In aquafeed manufacturing, particularly for high-energy feeds, coating dried feed pellets with oil is crucial to achieving the desired digestible energy levels. This is essential not only for salmon feed but also for most other cold-water finfish, as their dietary requirements include high energy density for optimal growth and performance. Figure 4 shows how the different runs perform for oil uptake amount when vacuum coated with a rapeseed oil. All pellets were allowed to settle and excess oil removed prior to being weighed and assessed for oil uptake. While pellet density surely influences the amount of oil uptake, the cell structure also plays a crucial role in retaining the oil through adsorption and capillary forces. Feed pellets produced on the AFX platform exhibit a uniform and high level of oil uptake across all run conditions. This high level is significantly different than the TX runs (p=0.02) which shows a uniform behavior across runs. For the SX runs, the oil uptake varies substantially across the different runs. Part of this is due to the differences obtained in density, e.g. runs SX4 and SX5. Pellet uniformity is also a crucial quality aspect of aquatic feeds, primarily due to its impact on downstream processing. Pellets of varying sizes do not dry or cool at the same rate, potentially leading to differences in physicochemical properties such as water activity and lipid crystallization strength within the pellet. The most immediate PHOTO 3. A schematic of the Tumbling Box used to measure pellet durability. PHOTO 4. A flowchart of the experimental approach in the benchmark trial of the three extruders, AFX, TX and SX. LEFT, FIGURE 1. The ability to reach density target of 400 g/L for each run conditions across the extrusion platforms (1: High SME/STE, 2: Low SME/STE, 3: Low water, 4: Low oil, 5: High oil). MIDDLE, FIGURE 2. Water inclusion for AFX and TX was in average 2 % less than on SX and 1 % less than on TX. Also, it appears the ability to achieve target density is countered by successful alteration of processing water. RIGHT, FIGURE 3. Durability of pellets produced on AFX and TX compared to those for SX was seemingly higher, though data insufficiency does not evaluate this as statistically significant, at p=0.11.
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