Antioxidant Properties of Bioactive Peptides from Rainbow Trout Viscera Using Different Ultrafiltration

Abstract
Introduction: The fishing industry is one of the most important factors affecting the economy of many countries in the world. By-products of aquaculture processing constitute a large part of fish (He et al., 2013). The use of waste from aquatic processing will not only increase the economic value of aquatic harvesting, but also by reducing the amount of aquatic processing waste, it will reduce pollution and economic costs related to the treatment of produced waste (Fang et al., 2017). The main of by-products of aquatic processing industries including skin, intestines and viscera and blood, which contain a good amount of protein that can be used as a source for bioactive peptides (Chalamaiah et al., 2012). Hydrolyzed protein usually contains small fragments of bioactive peptides that contain 2-20 amino acids (Ryan et al., 2011). The most important functions of these bioactive compounds, can mention the anti-oxidation, anti-microbial, anti-cancer and immune system boosting activities (Vioque et al., 2001). Fiches viscera are one of their most important wastes and are rich in unsaturated fatty acids and protein (Bhaskar et al., 2008). Since the production of bioactive peptides from fish waste and their bioactive properties including antioxidant properties have been done in other studies, in this research we are looking for the effect of the molecular weight of peptides on their antioxidant properties using ultrafiltration membranes.
Material and method: The viscera of rainbow trout (Oncorhynchus mykiss) were prepared from fresh rainbow trout from the salmon breeding farm in Mashhad and were transported to the laboratory with sufficient amounts of ice in the shortest time and it was kept at -20°C until use. Approximate analysis of the samples was determined according to the standard method of AOAC (2005). Production of hydrolyzed protein from viscera was done by the method of Ovissipour et al (2012). The amount of protein in the solution phase was measured by the method of Lowry et al (1951) and the degree of hydrolysis was estimated by the equation of Kristinsson and Rasco (2000). The antioxidant property of the hydrolyzed protein of treatments 1 and 2 was measured by examining of DPPH free radical inhibition and ABTS+ radical scavenging power indices. and according to the results, it was determined that treatment 2 (2% concentration of alkalase) has a higher antioxidant effect, therefore this treatment were divided by ultrafiltration membranes with molecular weights (<30KDa, <10KDa and <3KDa) and treatment 1 was removed at this stage. After this step, the antioxidant property of peptide fractions in molecular weights (<30KDa, <10KDa and <3KDa) in the treatment of 2% alkalase was measured again by examining the DPPH and ABTS+ indices. Then, the antioxidant properties of peptide fractions in different molecular weights from treatment of 2% alkalase were again measured by the DPPH and ABTS+ indices. Results and discussion: The results of approximate compositions showed that the highest compositions of viscera were moisture (60.817%), and fat (21.91%) and protein content (13.57%), followed by was the low amount of ash content (1.12%) and carbohydrates ( 2.17%). The chemical compounds of food play an important role in the body's health by providing essential nutrients. The ratio between waste compounds is varied according to the age and sex of fish. The amount of moisture from this evaluation was similar to the waste of rainbow trout 64.52% (Mirsadeghi 2015) and the amount of protein is similar to the waste of Zalon fish 13.00 (Nemati e al., 2019). The ash similar to common Kilka 1.46% (Soleymani et al., 2016) and the fat was 22.83% similar to Anchoy Kilka (Mehdabi et al., 2021). The degree of hydrolysis estimates the change of peptide content in a hydrolytic reaction. The degree of hydrolysis increased by increase of enzyme concentration in hydrolysis, so treatment 2 showed a significant increase (68.15±0.02%) compared to treatment 1 (53.60±0.22%) (p<0.05). The results of antioxidant property using DPPH and ABTS+ indicators on research treatments showed that treatment 2 (2% concentration of alkalase) had a higher antioxidant property than treatment 1. The results of the antioxidant property of the peptide components again using DPPH and ABTS+ indicators on the treatment of 2% alkalase enzyme concentration showed that the hydrolyzed protein and all peptide components (<30KDa, <10KDa and <3KDa) have the ability to DPPH and ABTS+ free radicals inhibition but in the comparison of peptide components with the same concentration (1.25 mg/ml), the peptide component <3KDa had a higher inhibitory property than other fractions, that the value in DPPH free radical inhibition was 76.55±0.01 and ABTS+ free radical inhibition was 88.25±0.05 and the difference between the peptide components was significant (p<0.05). It should be noted that free radical scavenging of DPPH and ABTS+ had icreased by use of the ultrafiltration process. Also, short-chain peptides have higher antioxidant properties than long-chain peptides (Bordbar et al., 2018), the reason of this case is the number of hydrophobic amino acids in peptide components that affect the intensity of antioxidant activity (Guillén et al., 2010). The results of this study about the DPPH radical inhibition were similar to the results of Wang et al (2013), Jang et al. (2017) and Xi et al (2008). Also, the results of the antioxidant properties of ABTS+ were consistent of the results of Ma et al (2010) and Martysiak-Zurowska and Venta (2012). Conclusion: The results of this study showed that, firstly, the used of concentration of the enzyme and the degree of hydrolysis has an effect on antioxidant property of the hydrolyzed protein and secondly, the ultrafiltracin process had a different effect on the antioxidant properties of peptides, so that all peptide components had antioxidant properties but also the molecular weight has an effect on the bioactivity, so that peptides with low molecular weight has an stronger bioactivity properties.