Research
Protein diversification: exploring the potential of seaweed for food Authors: Stephen Haines, Alastair Ross, Ancy Thomas, Linda Samuelsson, Santanu Deb-Choudhury Affiliation: AgResearch Limited, Lincoln Research Centre, 1365 Springs Road, Lincoln 7674, New Zealand
Introduction Undaria spp., a nutritious food All-year-round availability and relatively easy collection makes seaweed a potentially inexpensive food source [1]. Undaria pinnatifida is directly used in culinary applications in several Asian countries [2]. Seaweed in general is, however, also used exclusively for the extraction of food hydrocolloids such as agar, alginates and carrageenan. Marine algae are a viable protein source with an essential amino acid composition often on par with other food protein sources [3]. They are a rich source of nutrients including those that are insufficient in some Western diets, including fibre, micronutrient minerals, omega-3 fatty acids and other lipids, and proteins. In general seaweed proteins are rich in glycine, alanine, glutamic acid and arginine and, although limited in lysine and cysteine, contain all the essential amino acids. The amino acid score in Undaria species is determined to be 100, similar to that in animal-derived foods [4]. Red seaweed has the highest protein content, comparable to legumes at 30-40% on a dry weight basis, whereas brown seaweed such as Undaria has a protein content of 16% [5]. Amino acids such as aspartic and glutamic acid which impart flavour are present in higher quantities in brown compared to red seaweed [1]. Undaria pinnatifida or ‘Wakame’ is a kelp that has been studied extensively in New Zealand as an invasive species but the best approach for its management is yet to be reached and the ecological impact of Undaria has not been conclusively proven [6]. Undaria pinnatifida has a broad ecological niche and is highly productive at forming habitats. It inhabits rocky substrates up to a depth of 18 m and is widespread at depths of 1-3 m [7]. It is an important species for seaweed mariculture in China, Japan and Korea and therefore has significant economic value. Although Undaria pinnatifida may have an ecological impact it is not considered major as it does not appear to cause ecosystem change in most invaded regions. This is mainly due to its low natural dispersal ability and comparatively low rate of nutrient uptake and nitrate storage compared to other invasive brown macroalgae species [8]. The Ministry of Primary Industries (New Zealand) has a revised policy for the commercial use of Undaria and for its wild harvest from artificial substrates or when cast shore, in selected regions [6].
Nutrient availability Blanched and salted Undaria pinnatifida is a major wakame product. For blanching, fresh wakame is plunged in water at 80°C for one minute and then cooled quickly using cold water. For the salted product, 1:3 ratio of salt to seaweed is used and the seaweed is treated for 24 hours 30
after which it is stored at -10°C [9, 10]. Wakame is usually cooked before consumption. Although seaweed have poor protein digestibility in their raw and unprocessed form and therefore require adequate processing to improve their bioavailability in food, in vitro studies suggest that Undaria pinnatifida has 87% bioaccessibility expressed as a percentage of casein bioaccessiblity (100%) [3]. One of the major reasons for reduced algal protein digestibility is due to the fibre content of the algal cell wall [11]. Other contributing factors are a high level of cell wall anionic polysaccharides, which may vary according to species, the time of harvest [12] and the presence of phenolic compounds that react with amino acids, rendering them inaccessible [12]. Previous studies have shown different modes of cooking wakame and their effects on nutrient availability of potential bioactives such as carotenoids, polyphenols and polysaccharides and physical characteristics such as colour and texture [13]. There is little evidence of the effect of cooking on the protein profiles and their subsequent modifications. However, to understand cooking effects, robust procedures need to be established to first extract and then to analyse the proteins present in wakame. Proteins in marine algae are also affected by seasonal changes such as seawater temperature and nutritive salt concentration, which greatly affect the growth and maturation of seaweed. Proteomic and metabolomic studies can provide valuable information at a molecular level both on the seasonal changes in seaweed composition and on the effect of processing such as cooking on protein bioaccessibility in seaweed derived food.
Research project Joint research between AgResearch, University of Otago and A*STAR (Singapore) funded through the MBIE Catalyst Strategic fund will be looking at the digestive and nutritional attributes of seaweed, as relevant to humans, using Undaria pinnatifida as an exemplar. The research will create new knowledge about flavour, digestibility, and health benefits of Undaria seaweed from New Zealand and Singapore, as a whole food. The project’s aim is exploring how these attributes can be modulated through cooking technologies, to create an alternative whole food protein source. As well as characterising the protein fraction of Undaria and how it is affected by cooking, we will also be investigating the small molecules (metabolites) present in the seaweed to determine the impact of cooking beyond proteins and get a wider understanding of potential functionality of seaweed constituents. This short paper reports some early results obtained during development of proteomic and metabolomic methods that will be applied to the detailed analysis of the Undaria.
