Trub, a Brewing Byproduct, Is an Innovative and Valuable Source of Nutrients and Natural Antioxidants Viable for Fish Dietary Supplementation

The present study investigated the nutritional composition, phenolic profile, and antioxidant activity of trub, a byproduct of the brewing industry, for its use in the formulation of aquatic feeds. High performance liquid chromatograph-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS) was used to determine the phenolic compound profile, and 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid)/2,2-diphenyl-1-picrylhydrazyl (ABTS/DPPH) assays were used to determine the antioxidant activity. Two samples of trub (approximately 500 g) were characterized: sample A, composed of malts Pilsen, Pale Ale, and Caramunich II and hops Herkules and Fuggle, and sample B, composed of malts Pilsen, Pale Ale, and Melanoidin and hops Cascade, Chinook, and Amarillo. The trub B contained carbohydrates and proteins, and its extracts had high total phenolic (754.74 ± 0,08 mg 100 g⁻¹) and total flavonoid (894.71 ± 0.16 mg 100 g⁻¹) contents. In the trub extracts, 21 (trub A) and 19 (trub B) polyphenols were identified, of which 17 and 14 were quantified in trub A and B, respectively. Ferulic and protocatechuic acids were found in greater concentrations, followed by isoquercitrin and p-coumaric acid. With respect to antioxidant activity, trub A showed greater activity in the DPPH assay (2.13 ± 0.01 mg mL⁻¹), whereas trub B showed greater activity in the ABTS assay (29.07 ± 0.15 mg mL⁻¹), which could be related to the content and variety of phenolic compounds in the samples. These results indicate that both trub extracts can be sources of natural antioxidants with significant potential for fish dietary supplementation.