LIPID OXIDATION AND ITS IMPACT ON AQUAFEED QUALITY

Feed quality can be described as the combination of physical and chemical properties that have a direct impact on both feed mill economics and fish farm zootechnical performance. The aim of this review is to examine the impact of lipid oxidation on feed quality. Due to their specific formulation and production processes, aquafeeds are very susceptible to oxidation. This is primarily due to the high inclusion level of fats and oils with a fatty acid profile rich in long chain polyunsaturated fatty acids (PUFAs). These are highly prone to oxidation, with DHA (C22:6) being five time more sensitive than linoleic acid (C18:2). Additionally, fish meals, the main sources of protein for aquafeeds, are especially vulnerable to oxidation due to their production process (use of high temperature) and composition. The use of other protein sources will also not reduce the risk of oxidation, as the most used alternatives are represented by rendered meals and blood meal. Rendered meals are prone to oxidation due to their production process, and blood meal contains high levels of reactive metal ions that act as a pro-oxidative compound for fats, vitamins and pigments.

Lipid oxidation has a direct effect on the nutritional properties of aquafeed. In a scientific trial, it was registered a reduction of final body weight and SGR, as well as an increase of FCR in juvenile carps fed diets containing oxidized oil (Table 1.). This could be due to a reduction in metabolizable energy (ME) of oxidized feedstuffs. In literature is reported a reduction between 5 to 20% in ME in not stabilised fish meal compared to the one treated with an antioxidant (AOX). Another possible explanation is the change in the lipid profile of oxidized oils, especially the reduction of essential fatty acids (i.e low Omega-3 in oxidised fish oils).  

Good oxidative quality of aquafeeds can be achieved by using high quality and stable raw materials and by preventing the oxidation process during feed production and storage. Both targets can be achieved by including an effective AOX at the correct dose. The first criterion to select an AOX is to follow legal and market requests. The second criterion is the AOX's specific activity linked to their main features. An effective AOX needs to be easily and uniformly distributed to the substrate. Therefore, solubility of liquid formulas or particle size and distribution of active ingredients in dry formulas, represent the main features of a potential AOX. Moreover, it is recommended to prefer specific blends of active AOX with synergistic activity (BHA and Propyl Gallates heterodimers), including a chelator and with different composition depending on substrate to treat, over single ingredient AOX (Table 2).