Understanding the nutritional and functional variability of grain protein resources to optimise their application in aquaculture feeds

The increasing use of grain protein resources in aquaculture feeds has highlighted the importance of ingredient quality. Assessment of ingredient quality for aquaculture feeds is also becoming more stringent as requirements for specific feed products also become more refined. Key quality criteria include nutrient and energy digestibility, palatability, absence or presence of metabolic modifiers, effects on fish quality and ingredient functionality. Like all biological products, grain protein meals have a level of compositional variability intrinsic to each product. Understanding the nature and extent of this variability is critical to maXimiSing the value that can be obtained from these products. Assessment of chemical composition is the first step to understanding this issue, but further steps such as digestibility and palatability assessment are often also warranted. Most grain protein resources also contain some level of anti-nutritional factors (ANF) Essentially these are chemical defence mechanisms by plants to avoid being eaten, but their variety, content and effects can be variable among the different grain protein resources. Understanding the extent of the influence of ANF from particular grain protein resources can be the difference between a successful feed and a nutritional failure. Grain protein meals are often co-products or by-products of other processing activities such as oil extraction. However, such processing of grain can also Influence the nutritional value of the prodUCt. Usually such processing methods involve heat and/or chemical processes that can modify the quality of the grain protein meal. Because of some of the inherent nutritional limitations with some grain protein resources, the development of protein concentrates has also taken place. Such processing while conferring many nutritional benefits on the final product also comes at a high economic cost. Further efforts to reduce the cost of such products will be the key to commercialising such technology for widespread adoption in the aquaculture feed industry. Functionality is a relatively new issue that recognises the importance of an ingredient in its use In processing of an aquaculture feed, particularly through extrusion processing. It is recognised that some ingredients can confer specific functional as well as nutritional properties to a diet in which it is included. The potential application of grain protein resources in aquaculture feeds is enormous provided these key considerations can be managed Case examples of each of these considerations will be presented.