University:
Amherst College
Course:
BIOL 104 | Food, Fiber, and Pharmaceuticals
Academic year:

2024
Views:

71

Pages:

24
Author:

Rocco Calhoun

What are algae? Are they a monophyletic group? How did chloroplasts arise? 1. Cyanobacteria: photosynthetic bacteria 2. Endosymbiosis: engulfing of cyanobacterium by early eukaryotic cell (primary endosymbiosis) 3. Primary endosymbiosis: red and green algae 4. Secondary endosymbiosis: engulfing eukaryotic cell that contains photosynthetic plastid; capturing a red or green alga 5. Brown algae such as kelp got their chloroplasts via secondary endosymbiosis Primary endosymbiosis Cyanobacterium Green & Red algae Secondary endosymbiosis Brown algae Primary endosymbiosis Green algae Secondary endosymbiosis Consumption/use of cyanobacteria • Spirulina (Arthrospira sp.) • Occurs naturally in tropical/subtropical lakes • Food source for Aztecs: cultivation of bacterial mats • Chad—dried cakes called Dihé • High amount of protein, essential fatty acids, vitamins & minerals • Suggestion of medicinal/health benefits including anti-HIV • Source of blue dye for new (2008) naturally-dyed Smarties in UK • Used as animal feed additive Artificial dye Spirulina dye Spirulina clip 100 species of marine algae consumed, especially in Asia • Domestication of macroalgae recent compared to terrestrial plants • <20 species domesticated in last 200 years, seven within last 10 years • Important to understand and control reproduction and propagation • Seaweed aquaculture in Asia, Chile for food and colloid production • High protein content, vitamins and minerals • Main farmed species: brown kelps Laminaria sp. (Kombu) and Undaria pinnatifida (Wakame); red algae Porphyra sp. (Nori) and Gracilaria sp. Brown algae Laminaria sp. (Kombu) • Used for centuries in Japan, with majority cultivated in Hokkaido (cultivated since 1730) • Often boiled with aniline dye malachite green • Main ingredient for soup stock dashi, also source of glutamic acid (umami taste); brewed with tea (kombucha) Brown algae Undaria pinnatifida (Wakame) • Often cultivated with Laminaria • Cultivated in Japan and Korea, invasive in New Zealand • Eaten as “wakame chips”, coated with sugar, or mixed with rice • Used in soups (Miso) & salads, side dishes Primary endosymbiosis What is the most commonly consumed red alga? Red algae Nori (Porphyra sp.) • Consumed by many cultures; long history of use (533 A.D.) • Cultivation began ca. 1625 in Japan (Porphyra yezoensis), bamboo twigs were placed in intertidal zones and algae grew on bamboo • In mid-1900’s, with understanding of life-cycle, commercial cultivation possible • Cultivated in shallow bays with nets seeded with propagules • Washed, chopped, poured onto frames (similar to paper making), dried, toasted Porphyra used wherever in grows: laver in England and US, slack in Scotland, sloke in Ireland, karengo by the Maori in New Zealand, luche in Chile Green algae • Sea lettuce (Ulva lactuca) consumed in various places including the UK, Scandinavia, China and Japan • Eaten raw in salads or cooked in soup • Various microalgae used/investigated as biofuels, health food supplements (e.g., beta-carotene, omega-3 fatty acids), aquaculture feeds Colloid Compounds • Phycocolloids/Hydrocolloids in cell walls; polysaccharides that are used as emulsifiers, stabilizers, gelling agents • Also referred to as “gums”, polysaccharide compounds composed of sugars other than glucose (often galactose, xylose…) that are soluble in water or absorb water • Mixing these compounds with water forms a gel; colloid = substances suspended but not dissolved in water • Common gels not from algae include gum arabic (exuded from wounded trees of Acacia senegal; Fabaceae)—sticky substance licked on a stamp or envelope; also two other legumes: locust bean gum (seeds of carob, Ceratonia siliqua) and guar gum (ground endosperm of Cyamopsis tetragonolobus) Phycocolloids from red algae Carrageenan: a sulfated polysaccharide composed of galactose derivatives • Whole plants of Irish moss (Chondrus crispus) used for centuries in jellies and puddings • Added for creamy texture, thickening, gelling • Component of de-icing fluid for airplanes • May have some anti-viral properties, anti-coagulant • First extracted from Irish moss (in North Atlantic), now also extracted from Euchema and Kappaphycus (Phillipines and Indonesia) • Irish moss usually collected from wild by hand along beaches, Eucheuma cultivated on lines attached to poles. Phycocolloids from red algae Agar: mixture of agaropectin and agarose Agarose is a polysaccharide like carrageenan but no sulfates; agaropectin is also composed of galactose, but with sulfates and other side groups • Ingredient in Japanese desserts • Use as laxative, vegetarian gelatin, thickener, clarifier (aggregate with proteins that “cloud” products such as juices, vinegar), binder for medicines • Agar as culture medium in laboratory (ease of transition between liquid and gel states through heating and cooling) Agarose • Agarose does not bind to proteins, DNA; very useful for gel separation of these large molecules • Gracilaria, Gelidium are the main genera used for these products Phycocolloids from brown algae Alginic acid: gummy substance in cell walls; used as glue to stick holdfast to substrate • Polymer with sugar acids, mannuronic and guluronic acids • Alginates very important for colloidal properties--stabilize emulsions. Used in pharmaceuticals, foods (emulsifier in ice cream), cosmetics, treatment of latex during manufacture, dental impressions • Absorbs water quickly (gelatinous substance can absorb 200-300 times its weight in water)—used as appetite suppressant • Active ingredient in heartburn/acid-reflux medication Gaviscon: works with bicarbonate to create a barrier preventing stomach acid from going up esophagus • Extracted commercially from giant kelp (Macrocystis pyrifera), Ascophyllum nodosum, Laminaria sp. Laminaria Giant kelp Algae and medicine: Red algae • Anti-viral activity of polysaccharides from red algae • Digenea simplex used for internal parasites (properties suggested by dugong, which eats both sea grasses and Digenea); kainic acid is active compound that acts as vermifuge, also found to be central nervous system stimulant Algae and medicine: Brown algae • Fibers from alginate to make calcium alginate fabrics that can be used as absorbent wound dressings • Chelating agents for treatment of heavy metal or radioactive poisoning • Laminaria prescribed for goiter (insufficient iodine) • Laminaria stipes used for dilation in obstetrics/gynecology Algae and medicine: Brown algae • Fucoidan is a sulfated polysaccharide (galactose, xylose and fucose sugars) from various brown algae including kombu • Medicinal uses under investigation: anti-coagulant and anti-tumor properties

What are Algae

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