In Vitro Antioxidant Properties of Cod (Gadus morhua) Head Hydrolysates and Ultrafiltration Fractions
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An increasing world population calls for the development of sustainable primary processing of renewable biological resources. In Norway, there is a potential for increased utilization of white-fish. Hydrolysed cod heads may serve as a source of high-quality proteins that can be used for human consumption and create added-value to the Norwegian fish industry. In the HEADS UP project, the goal has been to develop technology for producing cod head protein hydrolysates (CPH) for human consumption. Studies have shown that hydrolysates produced from fish rest-raw materials exhibit desirable bioactivities, including antioxidant activity. Proteins with antioxidant activity can be applied in foods to prevent lipid peroxidation or as dietary additives to reduce the damage of oxidative stress in the human body. The aim of this study was to investigate in vitro antioxidant properties of CPH samples derived from the HEADS UP project. The hydrolysates were fractioned through a 4 kDa UF (ultrafiltration) membrane. The permeate and retentate were collected. The molecular weight distributions of the peptides, and the total and free amino acid content and compositions of the CPH, permeates, and retentates were determined. The in vitro antioxidant properties were evaluated using four different methods. These assays included the ABTS (2,-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) radical scavenging activity, FC (Folin-Ciocalteu) reducing capacity, and iron chelating activity. Moreover, the reduction of lipid oxidation in a liposome system induced with the pro-oxidant iron was investigated in the original CPH. Overall, the results from this study suggest that the CPH and UF fractions exhibited in vitro antioxidant properties. Both the CPH and fractionated hydrolysates demonstrated strong iron chelating activity. The crude CPH was found to exhibit the highest ABTS radical scavenging activity and showed promising effects in the reduction of OUR (oxygen uptake rate) in an iron-induced liposome system. The FC antioxidant activity in the permeate were found to be significantly higher than in the retentate, suggesting a higher content of phenolic compounds in this fraction. The fractionation of hydrolysates based on molecular weights did not significantly change in vitro antioxidant activities compared to crude CPH. Gel filtration of permeate and retentate showed that the hydrolysate samples were not completely separated by UF. The degree of hydrolysis was found to be negatively correlated with the amount of water used for hydrolysis, suggesting that decreasing the amount of water added, increased the activity of hydrolysis. Based on analysis of the amino acid content, the hydrolysates were found to be of high nutritional value, as all samples contained sufficient amounts of essential amino acids.