# An Overview of the Alternative Use of Seaweeds to Produce Safe and Sustainable Bio-Packaging
## 3 Physicochemical Characteristics of Seaweeds Phyccolloids
### Common Extraction Processes for Commercial Seaweed Hydrocolloids  
Before extraction, it is important to clean the seaweed to remove epiphytes, impurities, sand, debris, salts, and contaminants. Agar and carrageenanan are submitted to alkali pre-treatment to improve gelling properties through the conversion of unstable sulfate molecules into 3,6-anhydro-L-galactopyranose (3,6-AG) [56]. Alginate undergoes formaldehyde pre-treatment to eliminate the color pigments in the seaweed tissue and increase the alginate yield, and hydrochloric acid (HCI) pre-treatment to \"clarify\" the phenolic compounds and formaldehyde residue while promoting the conversion of insoluble alginate salts (calcium, magnesium, etc.,) into soluble salts [99, 100, 101, 102, 103]. Hot water extraction is performed for agar and carrageenanan, and is followed by alkali extraction to obtain compounds with desirable properties and functionalities through the manipulation of various parameters, such as temperature, time, pH, solvent concentration, etc. For alginate, only alkali extraction is performed. All three compounds are further neutralized by removing excess chemicals and solvents; subsequently, through precipitation and filtration, the residuals are eliminated, and the pure compound is obtained; in the last steps, drying and milling are performed to obtain dry and purified final products ready for commercial purpose (Figure 4) [56]. Some of the limitations of common hydrocolloid extraction include the high consumption of time, energy, and water. Moreover, to obtain an optimum yield, a huge quantity of chemical solvents are used, some of which are health hazards; because of the lack of control throughout the whole production process and discharge, these chemicals can be a serious threat to human health and the environment [104; 105]. Another downside of traditional extraction process is the expensive cost of ethanol used during precipitation of carrageenan to obtain refined carrageenan [104]. To overcome these disadvantages, new industrial processes of extraction that are cheaper and eco-friendly have been researched. The \"green\" extraction and processing methods are reported by [PERSON] et al. [56], which are as follows: microwave-assisted extraction (MAE), enzyme-assisted extraction (EAE), ultrasound-assisted extraction (UAE) [106], supercritical fluid extraction (SPE), pressurized solvent extraction (PSE), reactive extrusion and photobleaching processes. Some of these methods are already used to extract bioactive compounds from plants [107; 108]. Nevertheless, all these techniques possess pros and cons in terms of cost, yield of production, and time consumption [56]. To prove the effectiveness of dry and purified phycooloids for producing bioplastics, it is necessary to perform tests to evaluate the physical, optical, mechanical, thermal, antioxidant, and antibacterial properties, and biodegradability. Physical properties include thickness, solubility, water vapor permeability, water vapor transmission rate, and moisture content of the films. Optical properties include transparency, opacity, and light transmittance values. Mechanical properties include strength and elongation at break. Antioxidant properties can be measured via total phenolic content and the DPPH radical scavenging activity test. Antimicrobial properties are analyzed by inhibitory effects of the purified phycooloids against bacteria, such as _Escherichia coli_, _Listeria monocytogenes_, and _Salmonella Typhimuriumium_, while biodegradability is usually tested via a soil burial test [109]. Seaweed bioplastics biodegradable in the soil over a short time period, and no plastics residuals are dispersed into the environment [110], which is useful in those applications related to human health, such as foods or drugs packaging [111]. Figure 4: Common extraction process for commercial seaweed hydrocolloids: carrageenan and agar (**a**) and alginate (**b**).