Active substances of seaweeds are a kind of biomass components extracted from seaweed organisms that can have an effect on life phenomena through chemical, physical and biological mechanisms, including the extracellular matrix, cell wall, components of protoplasmic bodies of seaweeds as well as primary and secondary metabolites in cellular organisms.
Primary metabolites are amino acids, nucleotides, polysaccharides, lipids, vitamins and other substances necessary for maintaining life activities through catabolism and anabolism after absorbing nutrients from the outside world, while secondary metabolites are organic compounds synthesized by seaweeds in a certain growth period with primary metabolites as precursors that are not necessary for biological life activities, also known as natural products, including bioinformation, medicinal substances, biotoxins and other substances. Secondary metabolites are organic compounds synthesized by seaweed during a certain growth period using primary metabolites as precursors, which are not essential for biological life activities, and are also called natural products, including bioinformatics, medicinal substances, biotoxins, functional materials and other algal compounds.
Food Value of Bioactive Substances in Seaweeds
Seaweed organisms are rich in bioactive substances. Alginate, carrageenan, agar, mannitol, fucoidan, fucoidan, fucoidan and other components in seaweeds have important application values in the field of functional foods. Table 1 shows the biological roles of major algal active substances in seaweed organisms and their application values in functional foods.
Table 1 Role of seaweed active substances in seaweed organisms and their application value in functional foods
Polysaccharides are structural components of seaweed plants and are also used for energy storage. more than 100 years ago, humans possessed enzymes that could degrade seaweed starch, but there were no corresponding enzymes for polysaccharides with more complex structures. these degradation-resistant polysaccharides are dietary fibers.
Unlike the cellulose contained in land plants, the polysaccharides contained in the cell walls of seaweeds may be methylated, acetylated, acetonated or sulfated.
Alginate, carrageenan, agar, and other seaweed polysaccharides extracted from seaweeds are important food ingredients of seaweed origin, and are widely used in beverages, meat products, and dairy products.
Edible seaweeds generally contain a large amount of dietary fiber, with dry basis contents ranging from 23.5% to 64.0%, exceeding the dietary fiber content of wheat bran.
In green and red algae, water-soluble fiber accounts for 52% to 56% of the total fiber, while in brown algae it is 67% to 85%. Most of these dietary fibers can be converted into short-chain fatty acids, such as acetic acid, propionic acid, and butyric acid, through fermentation, which can nourish the epithelial cells of the large intestine and provide other benefits for the host, e.g., acetic and propionic acids are transported through the bloodstream into many organs of the human body, providing energy through oxidation and play specific physiological roles.
Short-chain fatty acids produced by the fermentation process also nourish the flora of the colon and act as prebiotics. Much has been written about the health effects of seaweed polysaccharides on the intestinal flora, resulting in health benefits such as reduced risk of diabetes, high blood pressure and heart disease.
Application of seaweed actives in functional foods
There are 2 main ways of applying seaweed active substances in the food field, i.e., seaweeds are consumed as marine food, and active substances extracted from seaweeds are directly or derivatively applied in food processing.
1. Seaweeds are consumed as marine food
Ancient Chinese ancestors had already recognized the health concept of homology of medicine and food, and the health value of seaweeds has been recorded in many medical writings, for example, “Shennong Ben Cao Jing”, “Famous Doctors of Medicine”, “Oceanic Materia Medica”, “Compendium of Materia Medica” and other writings have discussions on seaweeds.
In the modern food industry, seaweed is a delicious and nutritious marine vegetable. Seaweeds can be compounded with other ingredients for consumption. For example, the seaweed noodles made by mixing crushed seaweeds with flour have the taste and nutritional value of both noodles and seaweeds; the seaweed butter made by mixing seaweeds with butter is also popular with consumers in the UK.
2. Application of Seaweed Active Substances and Their Derivatives in Foods
2.1 Application of Seaweed Gum in Foods
Alginate, carrageenan, agar and other seaweed gum extracted from seaweeds are a kind of functional food ingredients of marine origin with excellent performance, which have wide applications and broad prospects for development in the food industry.
Seaweed gum is a class of hydrophilic polymer. Alginate, carrageenan, and agar are the same alginate gums with important applications in the food industry, which can be applied to the production of functional foods in many different ways to produce a series of unique efficacy of use. Table 2 summarizes the main functions and applications of alginate gum food ingredients.
2.1.1 Application of Alginate Gum in Gelatinous Foods
Gelatin is a traditional food in China, and there are many kinds of products on the market, including pea gelatin, bract gelatin, mung bean gelatin, rice gelatin, wheat gelatin, and other gelatin made from starch as raw material, and gelatin made from seaweed such as rockweed, and gelatin made from gelatin as raw material.
The production process of these cold noodles is basically similar, i.e., dissolving the raw materials with hot water and cooling them to obtain cold noodles. Utilizing the property of forming gel after combining sodium alginate and calcium ions to make cold noodles, its functional properties include heat irreversibility, low calorie, can be cold, fried, steamed, shabu-shabu hotpot, soup, etc., and it plays a role in satiety, weight loss, calcium replenishment and other health effects after consumption.
Table 2 Main functions and applications of alginate gum
2.1.2 Application of alginate in bionic foods
Using the property of sodium alginate to form a gel under the action of calcium ions, the meat-mimicking fiber with heat-resistant performance can be prepared by using sodium alginate as a gel-forming agent and separated soy protein as a filler, and molding under stirring.
This kind of meat imitation fiber can be dried or fried after seasoning, and with reference to the cooking method of meat products, a variety of soy protein meat imitation products with excellent color, aroma and taste can be produced, such as five-spice imitation dried meat, delicious imitation shrimp strips, sweet and sour imitation meatballs, spicy imitation shredded meat and so on.
2.1.3 Application of seaweed gum in meat products
As a natural polymer, alginate has excellent film-forming properties and can be used to prepare sausage casings. In the production process, the meat mixture is extruded and first covered with a layer of aqueous sodium alginate on its surface, and then formed into a film after contacting with aqueous calcium chloride, so that the calcium alginate sausage casings formed can protect the sausage and reduce the loss of water and oil.
Fat substitutes are fat substitutes for meat products with high strength, high elasticity and high toughness similar to solid fat prepared by high-speed mixing and static molding, utilizing the characteristics of sodium alginate and calcium to form thermally irreversible gel and its good compatibility with other polymer polysaccharides, combining with animal fats or vegetable fats, and can be applied to salami products such as salami, which can significantly improve the hardness and elasticity of the intestinal body, reduce the fat content of the products, give the products a good appearance, meet the requirements of the sausages and so on. It can significantly improve the hardness and elasticity of the sausage body, reduce the fat content of the product, give the product a good appearance, and satisfy the consumers’ demand for low-fat and nutritious meals.
2.1.4 Application of seaweed gum in dairy products and beverages
Adding alginate and other seaweed gum in fermented yogurt can play the role of thickening and emulsifying, stabilize protein, emulsify fat, improve taste and protect aroma. In neutral beverages it can improve the stability of the system by thickening and prevent the product from delamination. The application of alginate and other seaweed gums in ice cream can improve the stability of the product against freezing and thawing, so that the ice cream paste is delicate and has a good taste.
2.1.5 Application of alginate in noodle products
Adding alginate in noodle products can make the products stronger, not mixing soup, anti-freezing and thawing, anti-aging, resistant to cooking, smooth, and reduce the rate of broken strips.
2.1.6 Application of alginate in baked products
Adding alginate and other seaweed gum in baked products can play the role of water retention, thickening, shaping, and make the product organization delicate.
2.2 Application of alginate derivatives in food products
Alginate, carrageenan, agar and other seaweed gum can be prepared through the application of chemical, physical, biological and other modification technologies to prepare derivative products.
For example, propylene glycol alginate (PGA) is a nonionic derivative obtained by reacting alginate with propylene oxide.
As the carboxylic acid group in alginate is esterified by propylene glycol, the viscous colloid formed by PGA dissolved in water is highly resistant to salts, and it is very stable to metal ions such as calcium, sodium, etc., and does not salt precipitate even in concentrated electrolyte solution.
Due to the propylene glycol ester group in the molecular structure, PGA has strong lipophilicity and good emulsification stability, and can be effectively used in foods and beverages with low pH such as lactic acid beverages and fruit juice beverages.
Figure 2 shows some of the derivatives made from alginate. In the field of marine functional foods, propylene glycol alginate and fucoidan oligosaccharides are two important types of alginate derivatives, and their unique structures and properties give the two types of products excellent efficacy for use.
As an esterified derivative of alginate, propylene glycol alginate has unique emulsifying, thickening and stabilizing properties, and has unique application value in dairy products, functional beverages, beer, bakery products and other fields.
Figure 2 Derivatives made from alginate as raw material
Oligosaccharides made from alginate are generally oligosaccharides with a degree of polymerization of 2 to 10. Alginate oligosaccharides have low molecular weight, are easily soluble in water, and have a lot of unique physicochemical properties and biological activities, such as antitumor, antioxidant, antibacterial, anti-inflammatory, immunomodulation, etc. They are more and more favored by scholars at home and abroad in the fields of food, health care, cosmetic, biomedicine, agriculture, forestry, animal husbandry, fishery and so on, and they have a broad prospect for development and huge application value. It has a broad development prospect and great application value.
2.3 Application of fucoidan in functional food and health care products
Fucoidan, also known as fucoidan, fucoidan sulfate, fucoidan, fucoidan sulfate, etc., is a kind of water-soluble heteropolysaccharide with sulfuric acid, which is rich in L-fucose and organic sulfate, and it is a unique natural functional polysaccharide in the ocean.
Fucoidan is mainly found in the mucus on the surface of brown algae, such as kelp, sea cucumber and wakame, and is a unique bioactive substance of brown algae. The content of fucoidan in brown algae is very small, about 0.1% in fresh kelp and 1% in dried kelp, which is a very valuable active substance of seaweeds, and its content in brown algae is higher in Murraya and Kelp.
As a biomass component, fucoidan exists in the cell wall matrix, cell interstitial space and mucus of the surface layer of brown algae, and plays an important role in the algal body, such as moisturizing, antibacterial, and anti-ultraviolet damage.
Fucoidan has a variety of physiological activities such as anticoagulant, antioxidant, protection of nerve cells, immune regulation, lowering blood glucose and blood lipids, protection of kidneys, anti-tumor, anti-virus and so on, and its research and development is one of the hotspots in the field of marine drugs and health care products at present. The most important property of fucoidan for human body is its unique anti-tumor efficacy by inhibiting the proliferation of human cancer cells.
Conclusion
The earth inhabited by human beings is a blue planet, and the sea is the cradle of life, containing the mystery of health. With the booming development of blue economy, the health industry using marine resources as raw materials is emerging.
As a treasure trove of human food resources, seaweeds in the ocean can provide human society with a wealth of functional food ingredients. A large number of scientific studies have proved that seaweed active substances such as alginate, carrageenan, agar, fucoidan and other seaweed active substances have unique properties and efficacy, and have high application value in the field of functional food.