Botanica Marina 53 (2010): 387–408  2010 by Walter de Gruyter • Berlin • New York. DOI 10.1515/BOT.2010.044 2010/009 Article in press - uncorrected proof Review A review of antihypertensive and antioxidant activities in macroalgae Michelle S. Tierney 1 , Anna K. Croft 2 and Maria Hayes 1, * 1 Teagasc, Food Research Centre, Ashtown, Dublin 15, Ireland, e-mail: maria.hayes@teagasc.ie 2 School of Chemistry, University of Wales Bangor, Bangor, Gwynedd LL57 2UW, UK * Corresponding author Abstract There has been a significant increase in the occurrence of chronic diseases caused by oxidative stress and hypertension in recent decades. Hypertension is a sustained increase in blood pressure and is a controllable risk factor in the devel- opment of a number of cardiovascular diseases such as stroke and coronary infarction. As a result, the number of investi- gations aimed at identification of dietary compounds from natural sources that can be effective in preventing such dis- eases has increased. Macroalgae, also known as seaweeds or sea vegetables, have been traditionally incorporated into Pacific and Asian foods for hundreds of years and have recently become a popular addition to some Western diets. Macroalgae are classified into three higher taxa according to their pigmentation: brown (Class Phaeophyceae), green (Phylum Chlorophyta) and red (Phylum Rhodophyta). Owing to the harsh environments in which many macroalgae exist, they have developed effective defence mechanisms and, as a result, are a rich source of bioactive compounds, including polysaccharides, polyphenols, fatty acids and pep- tides, with different structures and activities from those found in terrestrial plants. This review explores the potential use of macroalgal species as bioactive ingredients that could be incorporated into functional foods for use in the prevention and/or treatment of hypertension and oxidative stress-related diseases. Keywords: angiotensin-I-converting enzyme (ACE-I) inhibitors; antioxidant; functional food; macroalgae. Introduction Macroalgae are classified into three higher taxa, brown (Class Phaeophyceae), red (Phylum Rhodophyta) and green (Phylum Chlorophyta), based on their pigmentation (FAO 2004). Brown macroalgae can be large, ranging from kelps, such as Laminaria species and Macrocystis pyrifera (Lin- naeus) C. Agardh that can often be as long as 20 m, to thick, leathery seaweeds from 2 to 4 m long, to smaller species 1–60 cm long. Red macroalgae, such as Mastocarpus stel- latus (Stackhouse) Guiry and Chondrus crispus Stackhouse, are typically smaller, ranging from a few centimetres to approximately a metre in length. Green macroalgae, such as Ulva and Codium species, are also smaller, with a similar size range to that of the red macroalgae (FAO 2004). Macroalgae are harvested and used globally for many dif- ferent applications, such as emulsifying agents in foods (Dhargalkar and Pereira 2005) and as ingredients in cosmetic formulations (Dhargalkar and Verlecar 2009), and have con- siderable ecological and economic importance. The ecolog- ical significance of macroalgae is highlighted by the fact that they assist in supplying oxygen to the sea, acting as one of the primary producers in the marine food chain (Chan et al. 2006). Coastal marine environments of developed countries often experience metal contamination as a result of the pres- ence of industrial waste products (Morrison et al. 2008), and some macroalgae are used efficiently in the cleanup of these waste products, acting as biosorbents due to their ability to bind heavy metals (Davis et al. 2003). The brown algal orders Laminariales and Fucales are the most highly regarded groups in relation to biosorption capability due to the abun- dance of matrix polysaccharides and extracellular polymers in their cell walls (Davis et al. 2003). Macroalgal species, such as ‘‘nori’’ (Porphyra sp.) (Kita- mura et al. 2002) used in sushi preparation, ‘‘haba-nori’’ w Petalonia binghamiae (J. Agardh) K.L. Vinogradovax which is eaten dried and roasted lightly (Kuda et al. 2006), ‘‘hijiki’’ w Hizikia fusiforme (Harvey) Okamurax consumed in soups, salads and vegetable dishes (Wondimu et al. 2007), ‘‘kom- bu’’ (Laminaria sp.) used in ‘‘dashi’’ soup, and ‘‘wakame’’ w Undaria pinnatifida (Harvey) Suringarx which is also added to salads and soups (Dawczynski et al. 2007), are tradition- ally used in the diets of certain cultures and additionally are found in modern commercial food products, such as tea, mustard, chutney and tagliatelle (BienManger  2010). Cer- tain macroalgae, such as Gracilaria species, Saccharina japonica (J.E. Areschoug) C.E. Lane, C. Mayes, Druehl et G.W. Saunders and Chondrus crispus, have commercial applications, owing primarily to their phycocolloids or non- fibrillar wall carbohydrates, which include agar-agar, algi- nates and carrageenan, respectively (Dhargalkar and Pereira 2005). The commercial value of phycocolloids extends to many industries, including the textile industry, where alginate is utilised for thread making, the pharmaceutical industry, where alginate and carrageenan are used for tablet encap- sulation (Dhargalkar and Pereira 2005), in the food industry