Antioxidant and antihypertensive properties from muscle hydrolysates of farm rainbow trout

Aquaculture is an economic activity with worldwide production of 82.1 million tons. A high potential of bioactive peptides from fish sources has been demonstrated but rainbow trout research is scarce and focused mainly on by-products. Thus, the present work aimed to obtain bioactive protein fractions through the enzymatic hydrolysis from the protein muscle of farm rainbow trout. Muscle fillets of trout at the commercial stage (250-300 g) from a local farm were homogenized in a food processor to obtain a uniform paste, which was used for protein content determination by Kjeldahl method. Afterward, trout paste was ultra-frozen at -70°C and freeze-dried at -43°C and 286X10^-3 mbar. A lyophilized sample was used to perform suspensions at 5% (p/v) in Tris-HCl buffer (pH= 9), which were hydrolyzed with alcalase, having a mass ratio of 100:10 (soluble protein: enzyme). Enzymatic hydrolysis was carried out at 55°C and sampled at 0, 1, and 2 h, ending it through a boiling water bath for 10 min to inactivate the enzyme. Then, samples were centrifugated and supernatants were used for in vitro determinations of hydrolysis degree, antioxidant capacity, and antihypertensive bioactivity. All last tests were realized by spectrophotometric methodologies, measuring the amine-TNBS complex at 340 nm, DPPH remanent at 515 nm, TPTZ-Fe²⁺ complex at 595 nm, and hippuric acid presence to determine ACE inhibition at 228 nm. Trout muscle paste exhibited 17.87±0.31% of protein content. The maximum hydrolysis degree was equivalent to 32.64±0.37 mM of glycine. The best time for scavenging and ferric reducing power was at 2 h with 3.69±0.09 µM and 33.98±0.75 mM of Trolox and Fe²⁺ equivalent, respectively. At the same time, ACE inhibition was only 2.14±0.04%, having the best inhibition (56.43±2.05%) at 1 h. Results showed that antioxidant properties increased with higher hydrolysis time, but antihypertensive bioactivity could be lost.