Food wastes for bioproduct production and potential strategies for high feedstock variability.

Unavoidable food wastes could be an important feedstock for industrial biotechnology, while their valorization could provide added value for the food processor. However, despite their abundance and low costs, the heterogeneous/mixed nature of these food wastes produced by food processors and consumers leads to a high degree of variability in carbon and nitrogen content, as well as specific substrates, in food waste hydrolysate. This has limited their use for bioproduct synthesis. These wastes are often instead used in anaerobic digestion and mixed microbial culture, creating a significant knowledge gap in their use for higher value biochemical production via pure and single microbial culture. To directly investigate this knowledge gap, various waste streams produced by a single food processor were enzymatically hydrolyzed and characterized, and the degree of variability with regard to substrates, carbon, and nitrogen was quantified. The impact of hydrolysate variability on the viability and performance of polyhydroxyalkanoates biopolymers production using bacteria (Cupriavidus necator) and archaea (Haloferax mediterranei) as well as sophorolipids biosurfactants production with the yeast (Starmerella bombicola) was then elucidated at laboratory-scale. After which, strategies implemented during this experimental proof-of-concept study, and beyond, for improved industrial-scale valorization which addresses the high variability of food waste hydrolysate were discussed in-depth, including media standardization and high non-selective microbial organisms growth-associated product synthesis. The insights provided would be beneficial for future endeavors aiming to utilize food wastes as feedstocks for industrial biotechnology.

Continuous bioreactor production of polyhydroxyalkanoates in Haloferax mediterranei.

In this work, the viability of continuous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) production with controlled composition in Haloferax mediterranei when fed volatile fatty acids is demonstrated. Continuous fermentations showed to greatly outperform batch fermentations with continuous feeding. Operating the bioreactor continuously allowed for PHBV productivity normalised by cell density to increase from 0.29 to 0.38 mg L-1 h-1, in previous continuously fed-fed batch fermentations, to 0.87 and 1.43 mg L-1 h-1 in a continuous mode of operation for 0.1 and 0.25 M carbon concentrations in the media respectively. Continuous bioreactor experiments were carried out for 100 h, maintaining control over the copolymer composition at around 30 mol% 3-hydroxyvalerate 3HV. This work presents the first continuous production of PHBV in Haloferax mediterranei which continuously delivers polymer at a higher productivity, compared to fed-batch modes of operation. Operating bioreactors continuously whilst maintaining control over copolymer composition brings new processing opportunities for increasing biopolymer production capacity, a crucial step towards the wider industrialisation of polyhydroxyalkanoates (PHAs).