The bioactive potential of New Zealand farmed abalone (Haliotis iris)
The pharmaceutical, nutraceutical and cosmeceutical industries are always in search for new bioactive molecules. Though synthetic compounds can be constructed by just studying their intended targets, natural sources can provide an abundance of unique chemical structures that are hard to replicate. These industries utilise the vast biodiversity offered by the ocean, by screening various plants, animals and microbes for bioactive compounds. Marine molluscs, especially those of commercial value, have consistently been shown to contain bioactives.
A plethora of bioactives have been isolated from the meat, blood and shell, of commercially viable abalone species. These compounds typically demonstrate antioxidant, antiaging, antihypertensive, antimicrobial or anticancer activities. However, there is a lack of biochemical or pharmacological data on New Zealand endemic black-footed abalone (Haliotis iris) or ‘paua’. So the present study was prompted to primarily determine the bioactive potential of farmed paua.
Solvent extraction with either methanol, ethanol, acetone, n-butanol, ethyl acetate, hexane or hot water, was used on grounded paua meat or shell powder. The gravimetrically measured dry yield of these extracts, indicated that a 90 % yield could be achieved for the meat using acetone. For the shell extracts, methanol achieved a yield of 4.5 %. However, neither hot water extracted (HWE)-meat or -shell extracts surpassed 1 %. Fermentation and enzyme hydrolysis processes improved HWE-meat by a factor of 160 or more. FT-IR analysis indicated the presence of uronic acid and the absence of sulphate groups for meat and shell extracts, which were also respectively supported by the carbazole and barium chloride-gelatin methods. The Bradford assay revealed that HWE-meat contained approximately 17.07 mg/ml uncharacterized protein. Fermentation or enzyme hydrolysis broke this down to less than 1 mg/ml. The blood contained only 0.28 mg/ml haemocyanin protein.
The DPPH, cupric reducing antioxidant capacity (CUPRAC) and ferrozine assays respectively revealed the free radical scavenging, reducing and metal chelating activities of paua. The solvent-derived meat extracts had weak scavenging activities, but showed low to moderate reducing and metal activities. The measured antioxidant activities of HWE-meat were increased via fermentation or enzyme hydrolysis. The supernatant and pellet of the waste blood, as well as the solventderived shell extracts, demonstrated chelation activity as strong as EDTA (positive control). The blood pellet and supernatant also showed antiaging properties by inhibiting collagenase activity by 59.7 and 61.58 % respectively. HWE-meat and methanol-derived meat extracts were stronger, measuring 71.27 and 68.22 % respectively.
Lastly, disc and well-diffusion assays were used to determine the potential antibacterial properties of paua. However, none of the meat, shell or blood extracts had any antibacterial affect against Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, Salmonella typhimurium, Staphylococcus aureus, Streptococcus pneumonia and Streptococcus pyogenes.
In conclusion, New Zealand farmed paua has antioxidant and anti-collagenase properties which could be utilised in antiaging creams. Additionally, the meat extracts could also be utilised in health supplements. Future studies on these extracts is required to determine if pH adjustments influence activity. Purification and structural elucidation of the bioactive compounds in paua is also required.