Evaluation of oil fatty acid profile, functional properties and antioxidants activity of hydrolyzate produced from rainbow trout (Oncorhynchus mykiss) viscera by application of protamex and neutrase enzymes

With the growing population and following the efforts of food production industries, more waste is produced which can be recovered by adding value and brought them back into the cycle of production and consumption. The reason behind is firstly the reduction of waste and secondly the economic importance of value added resultant products. Aquaculture sector produces large volume of wastes including the head, tail, fins, spine, and most importantly their viscera. If the waste managed properly, valuable materials such as hydrolyzed protein powder (the resulting waste hydrolysis using proteases enzymes) and fish oil (byproduct of enzymatic hydrolysis) can be produced. In this study rainbow trout waste was chosen, due to its large volume production in the country. The functional properties and antioxidant activity of hydrolysates as well as the oil fatty acid profile are the main factors to be considered. This study was aimed to investigate the hydrolysis of rainbow trout viscera (oncorhynchus mykiss) by protamex and neutrase enzymes individually and compare the functional properties and antioxidants activity of protein hydrolysate as well as analyze the fatty acid profile of fish oil obtained as by-product of enzymatic hydrolysis process.
Rainbow trout viscera (Oncorhynchus mykiss) were obtained from the fish market in Sari and transported in ice containers to the laboratory. Protamex and neutrase enzymes were purchased from Novozymes Company and protein hydrolysates prepared enzymatically according to the method of Guerard et al. (2002). Proximate analysis was carried out according to the procedures outlined by the AOAC (1995). Degree of hydrolysis determined as described by Hoyle and Merritt (1994). Peptide chain length (PCL) was measured using the method of Adler-Nissen and Olsen (1979). Protein recovery (PR) determined using the method used by Ovissipour et al (2009). Protein solubility for hydrolysates was determined using the method of Robinson and Hodgen (1940). Foam stability index was measured according to the method described by Sathe and Salunkhe (1981). Water holding capacity (WHC) was determined using the method of Rodriguez-Ambriz et al. (2005). DPPH radical-scavenging activity was measured using the method of Yen and Wu (1999). Reducing power was determined by the method of Oyaiza (1986).The chelating activity on Fe2 was determined, using the method of Decker and Welch (1990).
Protamex leads to the production of protein powder with higher degree of hydrolysis (34.76 ± 2.92%) and protein recovery (68/16 ± 1.98%) compared to neutrase (p0.05) despite the difference in L* value. The viscera oil contains 34% monounsaturated, 34.49% polyunsaturated and 31.4% saturated fatty acid. Apart from pH 4 (isoelectric point), the solubility of both protein powders in water was remarkable (more than 90%). The foam activity and stability index of hydrolyzate produced by protamex were more desirable than hydrolyzate produced by neutrase, whereas at pH 6, these indices reached to their maximum values of 200.13± 9.31% and 135.6 ± 5.64 %, respectively. Furthermore, water holding capacity of both hydrolyzates was measured as approximately 4.5 ml/g protein (p>0.05). Protamex leads to the production of protein powder with the higher DPPH radical scavenging activity compared to hydrolyzate produced by neutrase. Conversely, the reducing power of hydrolyzate produced by neutrase was higher than that of protamex (p0.05).