Developing soft texture and water stable fish feed

Authors: Liu, Keshun; Woolman, Michael - Mike; BARROWS, FREDERIC - Retired ARS Employee; Frost, Jason; Welker, Thomas; Overturf, Kenneth - Ken

Submitted to: Annual Meeting World Aquaculture Society
Publication Type: Abstract Only
Publication Acceptance Date: 12/10/2018
Publication Date: 3/9/2019
Citation: Liu, K., Woolman, M.J., Barrows, F., Frost, J.B., Welker, T.L., Overturf, K.E. 2019. Developing soft texture and water stable fish feed. Annual Meeting World Aquaculture Society. 352-77.

Interpretive Summary:

Technical Abstract: Over the past 40 years, extrusion processing has become the primary technique for producing fish feed. A common extrusion process takes place at low moisture (15-40%) levels. Upon exiting from the extruder, the feed undergoes a sudden drop in pressure, causing rapid moisture loss and volume expansion. The porous extrudate is cut into pellets and then dried. In water, these pellets disintegrate easily and quickly. Addition of starch as a binder improves feed stability, but the increased starch content can reduce performance in some fish species. To address the issues associated with the conventional extrusion process, we have developed a new extrusion method. It features using a twin-screw extruder and a tempering unit under high moisture (50-80%) levels. Unlike conventional extrusion methods, high moisture extrusion (HME) prevents product expansion and moisture loss at die outlets due to the cooling effect of the tempering unit. The addition of a binding agent also becomes unnecessary. HME aquafeed has a texture like natural aquatic foods. The product can also be cut into pellets and dried. In this study, trout feed formulations were processed with a twin-screw extruder by two methods: conventional extrusion and HME. Under each method, five different extrusion temperatures were used, ranging from 240 to 315°F. Fresh extrudates (like large noodles) were divided into two portions, one was refrigerated (as fresh feed) and the other was dried under a forced air oven (as dried feed). All feed samples were measured for moisture content, strength of rupture after soaking for different times, and solid loss after shaking in water for 6 hr. The objective was to compare the effect of the two extrusion methods on physical properties of the trout feed. Results show that, when freshly made, conventional feed had higher strength of rupture than HME feed, but when dried, HME feed had harder texture. Yet, upon contacting with water, conventional feed (fresh or dried) quickly lost its resistance to rupture, while dried HME feed slowly returned to the soft texture of freshly made feed, and both fresh and dried HME feed showed some resistance to rupture even after 24 hr of soaking. Upon shaking in water for six hr, dry matter loss from conventional feed was significantly higher than HME feed. Extrusion temperatures had some effect, but it was much less than the effect of method itself. It is concluded that, unlike conventional feed, HME feed (fresh or dried) retained its structural cohesion for an extended amount of time upon submersion of water. The technology provides a promising strategy to produce aquafeed that is soft texture and water stable and to mitigate water pollution issues associated with aquaculture.