1
Algae: A Functional Food with a Rich History and Future Superfood

Gaurav Rajauria1 and Yvonne V. Yuan2

1School of Agriculture and Food Science, University College Dublin, Lyons Research Farm, Celbridge, Ireland

2School of Nutrition, Ryerson University, Toronto, Ontario, Canada

1.1 Introduction

With increased consumer interest in simple, clean, minimally processed, and additive- or preservative-free food products and ingredients, it is only natural that interest in macro- and microalgae as foodstuffs has grown exponentially in recent years. This consumer interest in macro- and microalgae-based foods is supported by lay press sources including fashion and beauty industry magazines such as Elle Magazine (Davidson 2019); television and media personality websites such as that of Dr. Mehmet Oz (Ni 2018); daily newspapers (Liu 2020); as well as food and beverage industry trade publications (Hein 2016). Specific examples of this burgeoning consumer demand and interest include seaweed salads appearing on menus of mainstream seafood (non-Asian) restaurants; roasted seaweed snacks being sold in many mainstream supermarkets (Sloan 2018); dried seaweed flakes being offered as condiments in restaurants; dehydrated seaweeds and seaweed salad kits being sold in mainstream and specialty grocery stores; and nutritional supplement products such as GREENS+T, which include microalgae such as Spirulina sp., Chlorella sp., Dunaliella salina, the macroalga dulse (Palmaria palmata) (https://www.greensplus.com/superfood-powders), and numerous microalgae powders containing Spirulina sp. and Chlorella sp.

Moreover, there is a steadily increasing body of knowledge in the scientific literature about the potential nutritional, functional food, and nutraceutical benefits of whole micro- and macroalgae consumption as well as the potential biological activities of micro- and macroalgal extracts and extractable constituents in vitro, in situ, and in vivo from animal model studies, case-control, and epidemiological studies in reducing chronic disease risk factors, as well as inflammation. Key areas of investigation continue to be the chemical characterization of unique micro- and macroalgal specimens collected and isolated from terrestrial as well as fresh-, brackish, and marine environments due to the influence of oxidative stress on these algae from exposure to varying nutrient levels, temperatures, tides and/or desiccation, and UV irradiation. Oxidative stress experienced by these photosynthetic organisms can ultimately influence growth rates, metabolism, and synthesis of secondary metabolites, with many of the latter compounds of interest as potential nutraceuticals, cosmeceuticals, or in pharmacognosis. While bench-top and in vitro cell culture studies are key to understanding the mechanisms of action of extracts and/or their constituent purified compounds, the in vivo bioaccessibility and ultimately bioavailability and metabolism of these molecules are key to determining their potential to influence and protect human health. A particularly intriguing avenue of investigation is evaluating the efficacy of UV-absorbing compounds from micro- and macroalgae as potential nutraceuticals, antioxidants, and sunscreen molecules in cosmeceuticals.

1.2 History of Macro- and Microalgae Consumption

Edible marine macroalgae, often referred to as seaweeds or sea vegetables, as well as marine and freshwater microalgae have a long history in the diets of ancient cultures and increasingly in modern, health-conscious, and environmentally sustainable cuisines as recently reviewed (Pérez-Lloréns et al. 2020; Tou et al. 2020; Gomez-Zavaglia et al. 2019; Mac Monagail et al. 2017; Talero et al. 2015; Athukorala and Yuan 2013; Yuan and Athukorala 2012; Christaki et al. 2011; Lordan et al. 2011). For example, the importance of edible seaweeds in East and Southeast Asian (e.g. China, Japan, Korea, Vietnam, Indonesia, Philippines) cultures is commonly known, as well as in Pacific (e.g. Hawai'i, Maori of New Zealand), Caribbean (e.g. Jamaica, Saint Lucia, Grenadines), Central (e.g. Belize, Honduras, Panama) and South American cultures (e.g. Chile, Argentina, Brazil, Peru, Venezuela) (Figure 1.1). Conversely, seaweeds are not as common in Northern American or European cultures with some local exceptions such as Atlantic Canada and the USA, Mexico as well as Iceland, Ireland, Norway, Wales, Spain, and more recently France. Many of these cultures have incorporated macro- and microalgae as well as seaweed extracts throughout the diet in salads, soups, stews, sushi wraps, condiments, gelled desserts, and beverages (Tou et al. 2020; Yuan 2008; Robledo and Freile Pelegrín 1997).

The edible marine macroalgae comprise the Ochrophyta (containing those of the Phaeophyceae class [brown (B)]), Chlorophyta (the Chlorophyceae class [green (G)]), and Rhodophyta (the Rhodophyceae class [red (R)]) phyla or divisions, with species valued, and therefore, wild-harvested or cultivated as sources of hydrocolloids (e.g. agar agar, alginates, carrageenans), other soluble (e.g. Floridean starch, fucoidans) and insoluble dietary fibers (e.g. cellulose, mannans, xylans), proteins, minerals, vitamins, small amounts of long-chain n-3 polyunsaturated fatty acids (PUFAs), as well as a host of nutraceutical compounds including mycosporine-like amino acids, fucoidans, carotenoids, tocols, polyphenols, phenolic acids, phlorotannins, and lignans with potential biological activities (Tou et al. 2020; Athukorala and Yuan 2013; Plaza et al. 2008; Yuan 2008). It is noteworthy that the medicinal or functional food properties of edible macroalgae in the treatment or prevention of chronic disease risks such as breast cancer were noted as far back as approx. 1534 BCE in the Egyptian "Ebers Papyrus." Moreover, nine species of marine algae were recovered from the hearths of homes in the archeological site of Monte Verde II in southern Chile dating from approx. 14 000 years ago, indicating the use of seaweeds from coastal and estuarine environments for food and medicine by these peoples.

Figure 1.1 "Seaweed Gatherers" (a) Loading trailers on the shore; (b) Beach collection of Gracilaria after wash up, Bahia Bustamante, Argentina, (1960). Source: Adopted from (with permission) Mac Monagail et al. (2017).

Unicellular microalgae are similarly diverse including Dinoflagellata (eukaryotic, photosynthetic, marine and freshwater dinoflagellates or plankton), Cryptophyta (eukaryotic, freshwater algae, but also in marine and brackish waters), Raphidophyta (eukaryotic, marine and freshwater algae), and Cyanophyta (prokaryotic, photosynthetic blue-green algae, e.g. Cyanophyceae) phyla or divisions (Tou et al. 2020; Garcia et al. 2017). Microalgae, wild-harvested worldwide or even grown in culture, have been valued as part of macrobiotic diets and dietary supplements for nutritional (e.g. protein, PUFAs, carotenoids, carbohydrates) or nutraceutical benefits in modern times (Garcia et al. 2017), but also have an ancient history, such as with the Aztecs harvesting Spirulina platensis (or Arthrospira platensis) (Cyanophyceae) from Lake Texcoco as tecuitlatl, which was eaten with roasted corn or tortillas; or the consumption of S. platensis in Chad from Lake Kossorom, where it is known as dihé; or the consumption of Nostoc commune (Cyanophyceae) in China, where it is known as fah-tsai or dacai; or Spirogyra varians (eukaryotic, Charophyta division, Zygnematophyceae class) known as Tao or water silk, pond silk or mermaid's tree in Thailand (Tou et al. 2020; Garcia et al. 2017).

1.3 Economic Relevance of Macro- and Microalgae

With 71% of the Earth's surface covered by oceans, comprising 97% of the Earth's water, and with less than 1% of the Earth's water as freshwater with the remaining 2-3% contained in glaciers and ice caps, it is no surprise that wild harvesting of macroalgae for food, animal feed, fertilizer, and even fuel has been instrumental in the establishment of coastal communities across the globe. Countries including Chile, Norway, France, Ireland, Iceland, the Russian Federation, Spain, Italy, Denmark, Portugal, Indonesia, Korea, South Africa, Japan, China, the UK, Canada, and the USA are among those playing a role in wild-harvesting of macroalgae historically and today. Statistics from 2014 indicate that global macroalgal harvests have increased approx. 5.7% annually with Europe, Asia, Africa, North and South America, and Oceania accounting for 1.3, 1.9, 0.10, 2.4, and 0.015 million t, respectively (Mac Monagail et al. 2017). Approximately 20 countries are harvesters of brown macroalgae, including Norway, Chile, and Ireland, with 0.6 million t of kelps harvested for alginates annually. On the other hand, 32 countries are harvesters of Rhodophyceae with 0.22 million t harvested annually, dominated by Chile and Indonesia representing 76% of the harvest, while 11 countries harvest Chlorophyceae with 1661 t collected annually, mostly by Korea (Mac Monagail et al. 2017). Interestingly, while there are more than 10 000 species of macroalgae that have been reported to exist, of these, only approx. 200 species are consumed across the globe as discussed above. However, today,...