| dc.description.abstract | Selenium (Se) is essential for human and animal health and crucial for selenoprotein synthesis with diverse biological roles. It's mainly sourced from animal feed, particularly fish feed, with fishmeal and marine by-products ensuring adequate Se levels. However, recent shifts from marine to plant-based feed ingredients have decreased Se levels in fish feed and whole-body fish, highlighting the need for Se supplementation. It can be added as inorganic (selenite) or organic (SeMet) forms. In Europe, the maximum limit is 0.5 mg/kg feed for total Se in animal feeds. The European Food Safety Authority (EFSA) approved organic feed additives like selenized yeast (organic Se), limited to 0.2 mg/kg feed due to its higher bioavailability than inorganic Se. Thus, the difference in the legislative limit between supplemented total Se and organic Se emphasizes the need for precise analytical methods for Se speciation. In this thesis, the main aim was to validate an in-house method of Se speciation for animal feed and fish tissue samples. In addition, one aim was to study total Se content in different feeds, including fish feed, land animal feed, feed ingredients and fish tissues using ICP-MS. The application of the validated method for the determination of organic Se (SeMet) in rainbow trout feeds and whole-body samples using HPLC ICP-MS. This study examined total Se concentrations in salmonid commercial feeds (n = 27), salmonid experimental feeds (n = 6), zebrafish feed (n = 3), rainbow trout feed (n = 12), land animal feeds for ruminants (n = 10), swine (n = 2), and chicken (n = 3), feed materials (n = 9), and rainbow trout whole-body samples (n = 39). The results showed that fish feed has more total Se than land animal feeds. Several animal feed exceeded the legal limit of 0.5 mg/kg total Se. Pig and poultry feeds lower total Se contents. Tuna meal-based rainbow trout feed has more total Se than plant meal-based feeds. Tuna and fish meals have much more total Se than plant and insect meals. In rainbow trout whole-body samples, tuna meal-fed trout showed greater total Se concentrations than plant meal-fed trout. The validation procedure for the Se speciation (SeMet) was performed by analyzing feed and tissue samples over six days using Eurachem and NMKL guidelines. The validation procedure revealed good selectivity for SeMet in several sample types, where SeMet was baseline separated from other Se peaks. Zebrafish, land-animal, and blue mussel meal samples exhibited unknown Se species peaks. Linearity (r = 0.99) between concentration and response indicated a linear fit model. Method LOD and LOQ were estimated at 0.02 and 0.06 mg/kg, respectively. Method trueness indicated 53% to 80% recovery for wheat-based CRM (ERM BC210a) and 72% to 83% for selenized yeast-based CRM (SELM-1). CRM recovery, especially ERM BC210a, was low and not in acceptable range. Method precision was good, notably for SELM-1. Fish tissue and land-animal feed samples showed the lowest and highest within-day variance. Fish feed, tuna tissue, salmon tissue, and SELM-1 exhibited better precision. The analytical method's precision was acceptable because the Horwitz ratio was within the required range of 0.5–2. Salmon tissue had the lowest MU (13%), while land-animal feed had the greatest (64%). Fish feed, zebrafish feed, tuna tissue, blue mussel, and SELM-1 had acceptable MU (%). Application of method on rainbow trout experimental feeds demonstrated that plant meal-based diets recovered more SeMet than tuna meal-based diets. Tuna based-meal feed had a greater total Se concentration than vegetal based-meal feed. These data may suggest that this study's enzymatic extraction method works better with vegetal meal-based feed than tuna meal-based feed. SeMet recovery from rainbow trout raised on vegetable and tuna meal-based diets was 18% and 14%, respectively, for whole-body samples. The group that fed on vegetal meal-based diet with organic Se and Hg had the greatest SeMet concentration (0.44 mg/kg) and recovery (25%). A rainbow fish sample fed a tuna meal-based diet with organic Se had a SeMet level of 0.43 mg/kg and a recovery of 17%. The present study presented an overview of total Se content in commercial and experimental feeds of marine and land animals. Higher Se concentrations in commercial feeds raised concerns for compliance to current legislative requirements and animal and public health risks. Moreover, the method validation parameters showed good potential of this in-house developed method for Se speciation in feed and tissue samples. The application of the method also proved its potential applicability on diverse sample matrices. However, further improvements will be needed, particularly for its application on land animal and fish meal-based feeds. | |
