Natural Antioxidants in Salmon Aquaculture: Processing Fate, Tissue Deposition, and Oxidative Protection

The use of natural antioxidants (NAOXs) to prevent feed oxidation and reduce oxidative stress in fish is gaining momentum in the aquafeed industry. As sustainable alternatives to synthetic antioxidants like ethoxyquin (banned) and butylated hydroxytoluene (BHT)/butylated hydroxyanisole (BHA) (under scrutiny), NAOX (particularly polyphenols) require assessment for their stability during feed production and their biological effects on fish. This study followed four natural polyphenols (NPs) in a plant-based ingredient, which was then incorporated into a standard feed. The polyphenols were tracked through various processing stages (ingredients, diet mix, extrusion, drying, and storage) and in fish tissues (liver and muscle) using liquid chromatography mass spectrometry. Post-smolt Atlantic salmon were fed diets containing 0.00%, 0.01%, or 0.05% of the polyphenol-rich ingredient for 100 days. NAOX supplementation led to increased levels of astaxanthin, α-tocopherol, and γ-tocopherol, and reduced thiobarituric acid reactive substance (TBARS) in the feed, indicating improved oxidative stability. In the fish, NAOX had no effect on growth, organ indices, cataracts, or fillet color. However, it significantly reduced malondialdehyde (MDA) levels in liver and muscle and lowered hepatic glutathione (GSH), suggesting improved antioxidant protection. Among the four NPs, only three were consistently detected in fish tissues, especially in the liver. Although extrusion caused substantial losses, the polyphenol profiles in feed and tissue reflected those of the original ingredient. This is the first study to trace NAOXs throughout the entire production chain in salmon aquaculture. The findings support the use of NAOX to enhance feed stability and fish oxidative resilience in a sustainable and effective manner.