Extrusion, essential oils and fish feed optimisation Advanced microencapsulation improves delivery of phytogenic feed additives by Rui Gonçalves and Gonçalo A. Santos, Biomin Holding GmbH, Austria
anufactured feeds are an essential part of modern commercial aquaculture, providing the balanced nutrition needed by farmed species. Much of aquaculture’s recent growth can be attributed to improved formulations, resulting in superior physical and nutritional feed properties. As more intensified culture systems are developed, greater emphasis has been placed on critical optimisation of the properties of aquaculture feeds, all of which contribute to a more economically sound feed conversion ratio.
is microencapsulation. Microencapsulation is a technology that coats tiny particles of various substances in a sealed capsule. A benefit of microencapsulation of essential oils is that can considerably limit any strong odors or flavors, therefore avoiding potential palatability issues for some sensitive species such as shrimp. Traditional microencapsulation consists of a filled core surrounded by a wax or fat shell that, once it bursts, discharges its contents. In contrast to mononuclear, or single core, capsules, matrix encap-
Phytogenic feed additives
In farmed aquatic species, the benefits of phytogenic feed additives, or botanicals, have been reported in several scientific studies. Their plant-derived active ingredients (e.g. phenols and flavonoids) can exert multiple effects in animals, including improvement of feeding conversion ratio (FCR), digestibility, growth rate, reduction of nitrogen and phosphorous excretion, improvement of the gut microbiota and health status.
The extrusion process
During extrusion, ground, blended ingredients are processed at high temperatures, moisture and pressure levels compared to conventional steam pelleting. Normally, the process begins by steam treating ingredients, raising the moisture by 20 percent to 30 percent and reaching temperatures of 65˚ to 95˚C. The mixture is then conveyed into a pressurised extrusion barrel (extruder) where it is cooked to a temperature of 130˚ to 180˚C for anywhere from 10 seconds to one minute. In these conditions, starch present in the mixture readily gelatinizes. The cooked mixture is then extruded through a die plate. When the mixture emerges from the pressurised chamber, some of the superheated water mixture vaporises, causing a rapid expansion in the volume of the pellets, which are then cooled and dried. Extrusion has proven key to producing fish feeds with desired characteristics in terms of floatability, durability, and water stability. While most fish feeds rely on extrusion, the heat, moisture and pressure that this introduces can render essential oils, which are volatile substances contained in phytogenic feed additives, less effective.
Encapsulation of phytogenics
One of the most frequent conventional encapsulation techniques
Figure 1: Conventional coating (Micro-encapsulation) vs. matrixencapsulation (Digestarom® P.E.P. MGE) of essential oils
Figure 2: Improved recovery rates for of Digestarom® P.E.P. MGE compared to non-encapsulated essential oils
16 | INTERNATIONAL AQUAFEED | November-December 2015