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Among the natural polymers, polyhydroxyalkanoates (PHAs) comprise a family of biodegradable polyesters (figure 1) that are produced under unbalanced growth conditions as intracellular carbon and energy reserves by a wide variety of microorganisms. As with the characteristics of biodegradability, biocompatibility and environmental friendliness, the polyhydroxyalkanoates are considered as future polymers to replace petrochemicals-based plastics which can be widely used in agricultural, medical and pharmaceutical industries.
Fig. 1 General molecular formula of polyhydroxyalkanoates. Typically, x=1-8, and n ranges from 100 to 1000
Polyhydroxyalkanoates are grouped into three discrete classes according to the chain length, i) short chain length (scl) polyhydroxyalkanoates (containing maximum five carbon atoms chain), ii) medium chain length (mcl) polyhydroxyalkanoates (containing 6 to 14 carbon atoms in the chain), iii) long chain length (lcl) polyhydroxyalkanoates (containing more than 14 carbon atoms in the chain, less studies are reported to focus on lcl-polyhydroxyalkanoates). Common polyhydroxyalkanoates are showed in figure 2.
Fig. 2 Common chemical structures of polyhydroxyalkanoates. a) scl-polyhydroxyalkanoate, b) mcl-polyhydroxyalkanoate
Polyhydroxybutyrate (PHB), as the most well-studied scl-polyhydroxyalkanoate, is produced by remote type bacteria as linear, crystalline and amorphous forms. Polyhydroxyvalerate (PHV) is most commonly synthesized with PHB to form the copolymer poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) which is a mcl-polyhydroxyalkanoates. Compared to scl-polyhydroxyalkanoate, mcl-polyhydroxyalkanoate has improved mechanical properties such as decreased brittleness, decreased crystallinity, low glass transition temperature, high melting temperatures and poor tensile strength characteristics.
According to the carbon source and genomic structure of the bacterial strain, polyhydroxyalkanoate biosynthesis can be performed by three pathways (figure 3) [1]. Pathway I is the most common way for polyhydroxyalkanoate synthesis. The presence of coenzyme A from the tricarboxylic acid cycle influences the metabolic flux of this pathway. Pathway II is predominantly reported in bacteria that can utilize fatty acids as a primary carbon feedstock. However, pathway III can be used alternatively for mcl-polyhydroxyalkanoate synthesis from several carbon feedstocks such as sugars, oils and fatty acids.
Fig. 3 Three pathways of polyhydroxyalkanoate synthesis
Polyhydroxyalkanoates are applied in the biomedical field mainly for tissue engineering, as drug delivery carriers, and in many single use applications such as disposable tableware, food packaging, plant pots, and they are suitable materials for applications such as the slow release of chemicals. The table [2] below represents the potential industrial applications of the different bioproducts synthesized concomitantly with polyhydroxyalkanoate.
| Type | Co-product | Applications |
|---|---|---|
| Exopolysaccharides | Alginate | Food industry (ice cream, frozen custards, creams, cake mixtures), beer production, suspension of fruit pulp, thickener and gel forming agents in pharmaceutical industries, drug delivery and wound dressing |
| Succinoglycan | Thickening and stabilizing hydrocolloid, cosmetic additive, gravel packing, industrial crosslinker, emulsifier, drug delivery, anti-inflammatory agent in medical applications | |
| Enzymes | α-amylase | Starch industry (hydrolysis of starch), textile industry, brewing, detergent industry, paper industry, fuel production, candy production |
| Lipase | Dairy industry, fat and oil industry, cosmetics and personal care products, bioremediation, leather degreasing, pulp-paper industry, detergents manufacturing | |
| Amino acids | Ɛ-polylysine | Food preservatives, edible films, cosmetic and personal care products, drug delivery agent, gene delivery applications, biological adhesives, biofibers |
| Biosurfactants | Rhamnolipids | Bioremediation, soil washing, enhancing phytoremediation, removal of metal contaminants, antimicrobial agents, immune modulators, antitumor agents in medicines |
| Osmolytes | Ectoines | Cosmetic ingredients, health care products, nasal sprays, eye drops, dermatological creams, cough-cold medicines, therapeutic agents against diseases |
| Organic acids | Succinate | Packaging materials, vegetation nets, compost bags, mulching films |
| Carotenoids | Astaxanthin | Nutraceutical, food additives, animal feed, cosmetics, medicinal applications |
Our polyhydroxyalkanoate pellets are bio-polyesters produced naturally from plant-based bacteria and other living organisms.
Alfa Chemistry is a professional supplier of polyhydroxyalkanoates. For high quality products, professional technical service, use suggestion and latest industry news, please feel free to contact us.
References
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