1. Composition and nutritional value of red algae protein
The amount of protein in red algae depends on species and environmental factors such as season, temperature and light. The protein content of red algae ranges from 2.7% to 47.0% (dry weight). The total amino acid quantification method is the most accurate method so far. Most red algae proteins are considered good sources of protein because they provide high levels of essential amino acids and contain high levels of sulfur-containing amino acids (methionine and cysteine). Secondly, acidic amino acids (glutamic acid and aspartic acid) contribute significantly to the unique umami taste of seaweed.
Besides amino acid composition, protein digestibility is an important parameter to evaluate protein quality, and it can reflect the bioavailability of protein. Compared with other terrestrial plant proteins, the in vitro digestibility of red algal proteins in The genus Laporphyra ranged from 69.4 to 78.5%. In order to minimize the impact of non-protein components, pretreatment can improve protein digestibility.
2. Physicochemical properties of red algae protein
Most of the red algae proteins were observed with different bands near 15, 20, 40, and 56kDa by electrophoresis. The isoelectric points of different red algae species ranged from 2.0 to 4.5. The algal proteins showed a high proportion of β -folded structure in the secondary structure, and the α -helix structure was the most sensitive to temperature. FTIR was used to determine the secondary structure of seaweed protein, and its main characteristic peaks were in the Amide I (1700 and 1600 cm-1) and Amide II (1580 and 1510 cm-1) regions.
3. Extraction of red algae protein
Post-harvest pretreatment is critical to maximize extraction and reduce biomass degradation. Existing pretreatment methods include drying, freezing and silage. Among these methods, drying is the most common and effective pretreatment method before extracting seaweed protein. Drying technology and temperature have significant effects on the physicochemical and functional properties of seaweed protein. Due to the high solubility of proteins at alkaline pH, NaOH solution is usually used for extraction, and extraction temperature is the main parameter to control the yield. The results showed that the extraction rate at 4°C was higher than that at ambient temperature. The use of polysaccharide enzymes under mild conditions also contributes to the degradation of algae cell walls, thereby improving the bioavailability of proteins. However, its high cost and strict extraction conditions hinder its application in large-scale production. In addition, shear, ball milling and ultrasonic treatment can also destroy the cell wall of seaweed, thus improving the recovery of protein extract.
4. Functional characteristics of red algae protein
Most of the red alga protein extracts are alkali-soluble proteins. The emulsifying activity and stability of k. avruarezII protein were measured. Excellent emulsification was observed after mixing with oil for 15 min. Foaming properties of proteins include foaming ability (FC) and foaming stability (FS). The FS and FC of the protein concentrate from P. Dioica were 204 ± 4 s and 1.00 ± 0.02 mL/s, the high FC was related to good expansion rheology, and the poor FS was due to weak interfacial shear forces. However, structural modification may improve the foaming ability of red algae protein. There is still little information on the functional properties of red algae proteins, so more research is needed in this area.
5. Application of red algae protein
The protein and hydrolysate of red algae have antioxidant properties and antihypertensive activity, and the protein hydrolysate of red algae has high ACE inhibition. In addition to these activities, peptides from red algae have shown antithrombotic properties in vitro in human platelet plasma and whole blood. Taurine is also found in high concentrations in red algae and is added to functional foods to boost energy and muscle endurance. C-phycocyanin (C-PC) from spirulina is permitted to be added to foods as a food colorant. As for the industrial production of seaweed protein, food safety has attracted much attention, especially the heavy metal content in seaweed. In order to study the application of algal protein in functional food and confirm its health benefits, more research in different fields can be carried out to fill the gap of algae in the food industry.
● Conclusions and prospects
Macroalgae is a new alternative source of dietary protein, and red algae has a broad application prospect in this field. Pretreatment and extraction are the key to regulate protein digestibility and function. Enzyme extraction method can improve the nutritional value and food function. The research on red algae protein as a functional food component is on the rise, and more research is needed to enhance the value of seaweed protein in food and health care products.
