Packaging Applications of Polyhydroxyalkanoates (PHAs) - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 213

- Growth biomass process under aerobic conditions without nutrients
and carbon source limitation;
- Biopolymer (PHA) production process can be anaerobic or limited-
oxygen aerobic (low KLa ), with limited essential nutrients (one or more,
such as Mg, N, P, S etc.) and an excess of the carbon sources (carbo-
hydrates and carboxylic acids);
- Separation of biomass containing intracellular PHA;
- Cell disruption (solvents, hydrocyclone, ball mill etc.);
- Biopolymer separation, purification, concentration and drying;

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Many gram-positive and gram-negative microorganisms, found in the soil,
sea and euent, are able to accumulate PHAs. The production costs of these
plastics are directly related to microorganism type and substrates employed.
It is desirable that producing strains have a high specific growth rate and are
able to utilize low cost substrates with a good yield and are able to utilize
euents from food industries. The conversion factor substrate-PHA should
be high and the ratio (PHA accumulated mass) -(total dry biomass) should
be as high as possible.
Typically, P(3HB) production on an industrial scale uses gram-negative
bacteria, such as Cupriavidus necator, Alcaligenes latus and recombinant
Escherichia coli, because these microorganisms present a very good yield and
easy growth using low cost substrates. However, P(3HB) isolated from gram-
negative bacteria incurs additional costs during the purification steps, once
the biopolymer granules are involved in lipopolysaccharide membranes,
they may contain endotoxins, resulting in severe immunological reactions
in the body, which would prevent this material's use for biomedical reasons.
The additional costs relating to the separation and purification steps of
P(3HB) can be avoided by working with gram-positive microorganisms.
The selection of mixed cultures with a high capacity for PHA accumulation
occurs naturally because of reactor operation conditions and, consequently,
there is no need to sterilize the system. On the other hand, having mixed
cultures facilitates the use of complex substrates made from organic resi-
dues, such as food industry euent, and the microbial population con-
tinuously adapts to substrate changes. Therefore, it is possible to minimize
costs by using mixed cultures and selected substrates. The cost of PHAs
produced by mixed cultures may decrease to around half of the cost of those
produced by pure cultures, due to lower substrate and investment costs.
The following bacteria: recombinant Ralstonia eutropha, Ralstonia eutro-
pha, recombinant Escherichia coli, Burkholderia sacchari, Burkholderia cepa-
cia, Azotobacter vinelanddi, Pseudomonas olevorans, Methylobacterium
organophilum and Bacillus cereus have more favorable characteristics for
industrial scale production.
Among these microorganisms, Cupriavidus necator (Ralstonia eutropha),
Azotobacter vinelandii and recombinant Escherichia coli are the most popular
due to their yield and high biopolymer formation rate. Ralstonia eutropha
is now called Cupriavidus necator. Most biodegradable polymers show

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