Abstract
Fish roe produced in New Zealand is considered as a co-product by many companies. Physical damage due to rough handling causes a substantial portion of harvested roes to fail to reach a desirable grade and is not profitable to process. Numerous studies have demonstrated that roe contains high protein levels, and hydrolysed proteins from roe exhibit substantial bioactivity, such as antioxidant activity, enzyme inhibition, anti-cancer effects, and immune modulation. This highlights the potential for utilization of high-grade and low-grade fish roe in various ways, which promotes sustainable practices within New Zealand's seafood industry. Enzymatic hydrolysis is recognized as one of the best methods for producing bioactive peptides due to the hydrolytic specificity of proteases, which cleave protein peptide bonds at specific sites, and the possibility to customise hydrolytic activity of enzymes under different hydrolysis conditions. Hence, there is a potential to control the production of bioactive compounds through hydrolysis. The objective of this study was to investigate the bioactivity of New Zealand commercial fish (Gemfish and Hoki) roe to upgrade the value of low-grade fish roe and to investigate the effects of delipidation and freeze-dry process on roe proteolysis and bioactivities.
Proximate composition, fatty acid content, and phospholipid content of Gemfish roe and Hoki roe were analysed by determining the proximate analysis, fatty acids composition using Gas Chromatography Flame Ionization Detector (GC-FID), and phospholipids using Phosphorus-31 nuclear magnetic resonance (31P NMR). The results reveal that both Hoki and Gemfish roe are rich in protein and lipids. Specifically, Gemfish roe has a higher total crude protein content of 23.8%, and 17.9% in Hoki roe, whereas Hoki roe demonstrates a higher fat content at 10.10%, compared to 7.6% in Gemfish roe. Moreover, Gemfish roe oil has a higher (p<0.05) polyunsaturated fatty acid (PUFA) content, including elevated levels of DHA, DPA, and EPA, than Hoki roe oil. These results suggest that Gemfish roe offers nutritional value on par with Hoki roe, highlighting the potential of both roe types in the development of premium roe products.
Three antioxidant assay methods (ABTS, DPPH, and FRAP) were optimized prior to the start of the experiments to make them more suitable for fish roe materials. Protein hydrolysates were prepared from Hoki roe using three different proteases, namely, the bacterial proteases Alcalase and HT, and a fungal protease FP-II. The study was conducted in two parts. The first study investigated the effects of enzyme type (Alcalase, HT and FPII), enzyme concentration (1, 2 and 4%, w/w) and total protein concentrations (2.5 mg/ml, 5 mg/ml, and 10 mg/ml) on the antioxidant activity of the Hoki roe protein hydrolysates. The optimised in vitro antioxidant 2 assays (DPPH, ABTS, and FRAP) were used for the evaluation of the antioxidant activities. In the second part of the chapter 4, the same proteases were used at 10% (w/w or v/w) protease concentration and under the same experiment conditions mentioned in part one was used to hydrolyse fresh or freeze-dried Hoki roe and Gemfish roe after a delipidation step. This aimed to provide information in relation to delipidation before hydrolysis versus delipidation after hydrolysis for Hoki and Gemfish roe. It was found that the incubation time for the DPPH, ABTS, and FRAP assays needed for this study was 8h, 2.5h, and 6h, respectively. It was found that the Alcalase hydrolysate had a higher antioxidant activity than that of HT and FP-II (p<0.05). A 10 mg/ml sample concentration based on protein exhibited the highest antioxidant activity compared to 5 mg/ml and 2.5 mg/ml (P<0.05) in the antioxidant activity. The results from the second part of this study show that delipidation after hydrolysis decreases the antioxidant activity of the fish roe hydrolysate. This is likely due to the solvent removing some fatty acid, phospholipid, and peptides that have antioxidant activity.
Previous research has indicated that the defatting process affects the antioxidant activity of Hoki and Gemfish hydrolysates. Further, the present study assessed the effects of defatting and freeze-drying processes on the enzymatic hydrolysis of Hoki and Gemfish roe homogenates using three protease preparations: namely Alcalase, HT, and FP-II However, both defatting and freeze-drying treatments were observed to reduce the degree of hydrolysis and antioxidant capacities (DPPH and ABTS radical scavenging activities and Ferric Reducing Antioxidant Power), indicating that pre-processing treatments of delipidation and freeze-drying could negatively impact the effectiveness of enzymatic hydrolysis in extracting valuable compounds from roe. These results suggest that both Hoki roe and Gemfish roe protein hydrolysates have the potential to be functional food and can add value to low-grade roe. Maximum antioxidant activities of Hoki and Gemfish roe hydrolysates can be achieved by controlling the processing factors.