Bioactive compounds from the roe of New Zealand fish

The identification of bioactive compounds in fish processing by-products may add value to what is regarded as waste or products of low value. The present study was performed to screen the roes of five commercial New Zealand fish - hoki (Macruronus novaezelandiae), southern blue whiting (Micromesistius australis), hake (Merluccius australis), ling (Genypterus blacodes) and chinook salmon (Oncorhynchus tshawytscha) for bioactive compounds. The aim was to explore the possibilities to exploit these fish by-products as a new source of bioactive compounds and to potentially add value to them. The compounds of interest included lectins and protease inhibitors. Results demonstrated that hoki, southern blue whiting, hake and ling roe extracts did not have any agglutination activity towards the tested erythrocytes (rabbit, sheep, chicken, bovine and human O positive), indicating the lack of lectin presence. Hoki roe extract possessed protease inhibitory activity towards papain while southern blue whiting, ling and hake possessed protease inhibitory activity towards trypsin. Hoki roe extract was not cytotoxic towards MDCK cells and did not have any antifungal activity towards the microorganisms tested (Valsa mali, Mycosphaerella arachidicola, Helminthosporium maydis, Setosphaeria turcica, Bipolaris maydis and Rhizoctonia solani). Hoki and southern blue whiting roe had no ribonuclease activity but demonstrated a weak anti-proliferative effect towards human breast cancer cells MCF-7. Chinook salmon roe extract was the only one out of the five fish species tested in the present study which possessed agglutination activity towards rabbit and bovine erythrocytes, indicating the presence of lectin in the roe. The chinook salmon roe lectin had specificity towards L-rhamnose, D-galactose, L-arabinose, D-fucose, melibiose and raffinose. The lectin was purified using ion exchange chromatography on CM-Sepharose and SP-Sepharose and further ion exchange chromatography by fast protein liquid chromatography (FPLC) on Mono S. Chinook salmon roe lectin had a molecular mass of 30 kDa and the hemagglutination activity of the lectin was stable up to 70 °C and between pH 4 and pH 11. The hemagglutination activity started to disappear after heating at 90 °C for 5 minutes and at pH 1. The hemagglutination activity of chinook salmon roe lectin was not affected by the metal ions tested in this study (Ca2+, Mn2+, Mg2+, Zn2+ and Fe2+). Chinook salmon roe lectin did not exert antifungal activity toward the tested microorganisms (Valsa mali, Mycosphaerella arachidicola, Helminthosporium maydis, Setosphaeria turcica, Bipolaris maydis and Rhizoctonia solani). It also did not exhibit any mitogenic response towards mouse splenocytes up to a concentration of 5 mg/ml. Interestingly, chinook salmon roe lectin had selective antiproliferative activity towards human tumour cells, but had no effect on normal cells. It also induced the production of nitric oxide from mouse peritoneal macrophages. This is the first report that demonstrates these activities in chinook salmon roe lectin. The effect of processing on chinook salmon roe lectin was also studied. Salting increased the hemagglutination activity and the specific activity of the lectin, indicating the potential modification of the lectin during the processing. Salted fermentation initially caused an increase in agglutination activity for a period of 50 days, after which there was a gradual decrease in hemagglutination activity. Finally, it was found that the activity of chinook salmon roe lectin was inhibited by salted marinated fermentation possibly due to proteolysis caused by proteases excreted by microorganisms. As lectins play an important role in many biological systems and are used increasingly in human disease therapy, the knowledge gathered in this study about chinook salmon roe lectin as a bioactive compound with activity towards human tumour cells, and potentially modifying lectin activity through processing increases the prospect of using chinook salmon roe lectin in biotechnological applications, thus adding value to what is normally a by-product