Nutritional composition and heavy metal profiling of Australian kelps cultured in proximity to salmon and mussel farms

Abstract

Global demand for seaweed is increasing alongside the interest for sustainable aquaculture, stimulating industry investment in the production of seaweeds, particularly through integrated multitrophic aquaculture systems. We report the first results of the nutritional value (proximate composition, fatty acids, and dietary minerals) and heavy metal profiling of two Australian kelps, Macrocystis pyrifera and Lessonia corrugata, cultivated in proximity to Atlantic salmon and blue mussels in south-eastern Australia, and compare the effects of freeze- and air-drying on biochemical composition. There were no consistent effects of drying method on the nutritional composition and concentration of contaminants amongst sites and species. Overall, significant variation in protein content was reported amongst sites, lipids were generally low (<2%), while ash and nitrogen-free extract (NFE) were high. Contaminants were low in concentration in all samples, with mercury (Hg) below the detection limit. Results reported here suggest that M. pyrifera and L. corrugata have an overall nutritional composition conducive to human and animal consumption, except for the iodine content which was above the maximum tolerable level in dried seaweed established by Food Standards Australia New Zealand, and support species selection and sites for the development of seaweed aquaculture systems in south-eastern Australia. However, we found that the more expensive freeze-drying of samples did not consistently yield higher nutritional quality than air-dried samples. These findings will inform commercial applications of seaweeds in multiple sectors (e.g. food, feed/agriculture, and nutraceutical) for the development of the Australian seaweed industry, projected to reach a value of $1.5 billion by 2040.