**1. Introduction**

Macroalgae or called seaweeds are multicellular, marine species and are considered as non-vascular plants. Although term seaweed is widely used but these species are characteristically far from "weeds" but the fact is, seaweeds are the main productive species in the oceans and food chain basis. Seaweeds are used directly or indirectly in food and household products without being tasted or smelled. They are vastly used in food industry due to their valuable elements, vitamin, and proteins [1]. Sea or brackish water is the main habitat for seaweeds (macroalgae), and are referred as benthic marine algae or sea vegetables due their choice of habitat in the sea [2–4]. These simple unique organisms are one of the major productions of Asian industries, and main goal for these industries is to use the production to the maximum extent [2, 5]. Since seaweeds are main part of the diet in east Asia and to some extent being used as snacks and delicacies in other countries. Although seaweeds are as part of food in Far East countries, western countries use them as sources of phycocolloids, thickening and gelling agents for various industrial applications including food. Different applications are due to various chemical composition of seaweeds with habitats, maturity, salinity, environmental habitat, and temperature [2, 6].

Seaweeds are produced more than million tons per year, while microalgae are being produced almost 20,000 tons annually. This has to be mentioned the macroalgae have higher biomass sells in comparison with seaweeds. Seaweeds are mostly cultivated in near shores in China, Philippines and Japan [7, 8]. The total aquatic production in 2004 passed 15.36 million tons while 93% of the contribution belonged to seaweeds. Among this, 6000 species of seaweeds are harvested which fall into three categories as, green (Chlorophytes), brown (Phaeophytes) and red (Rhodophytes). Regarding the abundancy, the human consumption is mainly on brown algae (66.5%), red algae (33%), and green algae (5%) in Asia [2, 9]. The main producers in Asia are focusing on specific algae such as, in China, Japan and Korea are Nori (Porphyra, red algae), Konbu (Laminaria, brown algae) and Wakame (Undaria, brown algae). Among 6000 species discovered about 150 species are known as food source and 100 for phycocolloid production. The total revenue for edible algae passed 1 billion US dollars only in Japan and this estimation is the value of 1.4 kg seaweed per person consumption.

Marine algae, in addition of being used in food, dairy, pharmaceutical, cosmetic and medicine industries, they can also be used in biodiesel, bioethanol, and hydrogen gases preparation. They can also be applied as antioxidant, antibiotics, and virostatic agents [10, 11] application of algae in food industry either for human or animal consumption has brought some negative perspectives due to some toxic elements such as cadmium or fucotoxins. The amount of toxin in algae is related to the contents of fiber and bioactive compounds present. This has direct impact on digestibility and application in food industry. Digestibility has connections mainly with the nitrogen consumption before and after digestion by using specific enzymes called pepsin [10, 12].
