Valorisation of local agro-industrial processing waters as growth media for polyhydroxyalkanoates (PHA) production

• Bacterial polyesters as polyhydroxyalkanoates (PHA) produced using two processing waters rich in vegetable proteins and reducing sugars.
• Growth kinetics of a unique marine bacterium using leguminous processing water and fruit processing water as growth media for batch fermentation.
• Detection of PHA inside the biomass using the Nile Red staining.
• PHA characterization indicating that the two substrates lead to the biosynthesis of polymers with different chain length, distribution and crystallinity.
• Production of cost-effective bio-sourced and biodegradable polymers by valuing non-food residues derived from local agri-food industry.

Polyhydroxyalkanoates (PHA) are bacterial polyesters usually produced from costly sugars or volatile fatty acids (VFAs). In this work, two processing waters rich in vegetable proteins and reducing sugars, i.e., a mixture of saccharose and stachyose in Leguminous Processing Water (LPW) and a mixture of glucose and fructose in Fruit Processing Water (FPW), were tested as growth medium for PHA production in a two-stage fermentation with a unique marine bacterial species: Halomonas i4786. In preliminary shake flask experiments, it was shown that the two media can effectively support the bacterial growth and the accumulation of PHA (evaluated using Nile Red staining). In batch cultivation mode in a 5-L fermentor, PHA productivities of 1.6 g L−1 and 1.8 g L−1 were further achieved within 72 h, in LPW and FPW respectively. Polymer characterization by Differential Scanning Calorimetry and Steric Exclusion Chromatography indicated that the two substrates led to the biosynthesis of polymers with different chain length, distribution and crystallinity. To summarize, these results show that by-products derived from local agri-food industry can be used as a user-adapted and cost-effective source to produce bio-sourced and biodegradable plastic materials.