Value Addition to Dagaa “omena” (Rastrineobola Argentea) Through Recovery of Fish Protein Hydrolysate With Potential Bioactive Properties

Abstract

Food insecurity is increasingly becoming an issue of national concern. The fish industry has been identified as one of the sectors that if improved would effectively contribute towards alleviation of food insecurity as a food resource and also through income and employment generation. Production of fish protein hydrolysate (FPH) has been a great improvement to the fish industry. This is due to the array of potential bioactive properties associated with these compounds. This study aimed at production of protein hydrolysate with antioxidative activity from Dagaa (Rastrineobola argentea); locally known as “Omena” using exogenous food grade enzyme (Alcalase 2.4L ®). This was guided by the nutritional content of the Dagaa which was informed by proximate composition analysis of the fresh Dagaa. The functional properties of the Alcalase hydrolysate (AH) were also studied and compared to Dagaa endogenous enzymes hydrolysate (EH) and commercial synthetic antioxidant Butylhydroxytoluene (BHT). The antioxidative properties were investigated using spectrophotometric methods; 2, 2, Diphenyl-1-picrylhydrazyl (DPPH) % radical scavenging ability (%RSA), Ferric ion reducing inhibition and % lipid peroxidation inhibition. The proximate composition of fresh Dagaa on wet weight basis (wwb) was found to be: For protein 19.11% Usari, 21.07% Nduru, 19.53% Dunga, 21.78% Paga and 20.31% Rota. The lipid content in Dagaa was found to be 4.35% Usari, 7.32% Nduru, 3.87% Dunga, 7.78% Paga, and 5.47% Rota. Dagaa ash content was established at 1.88% Usari, 2.08% Nduru, 4.38% Dunga, 2.36% Paga and 3.08% Rota indicative of high mineral content. The Dry matter content was 23.65% Usari, 25.95% Nduru, 27.17% Dunga, 25.63% Paga, and 23.1% Rota. Dagaa hydrolysis by Alcalase 2.4L® was optimized at solvent ratio of 0.5% (v/w), pH7, 56°C, Enzyme /substrate ratio of 2% (v/w) and 6 hours at minimum stirring speed. At these optimized conditions, hydrolysis of upto 83% was achieved with 71% nitrogen recovery. Autolysis assisted hydrolysate (EH) showed 45% hydrolysis with 67% recovery. The antioxidant potential was established as: Oleic acid peroxidation inhibition at 31.5%, 49.5% and 29% for AH, EH and BHT respectively. DPPH %RSA IC were 4.07mg/ml, 24.74mg/ml and 2.47mg/ml for AH, EH and BHT respectively. Ferric ion reducing inhibition test followed this order AH >EH >BHT. AH showed significantly higher (p<0.05) Ferric ion reducing inhibition power in comparison to EH. Consequently, it can be concluded that AH is a better antioxidant in polar systems (DPPH and Ferric ion reduction inhibition) whereas the EH was a better antioxidant in non-polar systems (Lipid peroxidation inhibition). This study findings show potent antioxidative and functional activity of Alcalase Dagaa protein hydrolysate. Consequently, the hydrolysate is a promising candidate for inclusion in food systems as well as in pharmaceutical and nutraceutical industry. In addition, the study revealed differences in bioactive properties between Alcalase and Dagaa endogenous enzyme hydrolysates. These are indicative of composition (structure) differences between the hydrolysates despite a common protein substrate (Dagaa) that can be attributed to enzyme specificity differences between Alcalase and Dagaa endogenous enzymes. As well as the varying degree of hydrolysis reported for the two hydrolysates. Further studies are therefore needed to determine the peptide structure of the hydrolysates. Moreover, other enzymes may be utilized to produce Dagaa protein hydrolysate with other bioactive properties.