High production of poly(hydroxybutyrate-co-hydroxyvalerate) with controllable 3-hydroxyvalerate content by Paracoccus sp. KKU01 using cassava processing wastes and propionic acid as feedstocks: Optimizing propionic acid feeding and kinetic analysis

Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) has been recognized as a viable substitute to petroleum-based plastics, and 3-hydroxyvalerate (3HV) content is known to influence its mechanical and thermal properties. Being able to control 3HV content in PHBV, therefore, enables the production of PHBV to serve various purposes. This study investigated the production of PHBV from cassava processing wastes (cassava pulp and cassava processing wastewater) and propionic acid (HPr) using Paracoccus sp. KKU01. The aims were to develop a process for high PHBV production and control the production of 3HV during PHBV synthesis. Two HPr feeding strategies, i.e., pulse and continuous constant-rate feedings, were tested. The results were further used to develop an approach for controlling 3HV content during the fermentation. With pulse feeding of hydrolysate derived from cassava processing wastes, and continuous feeding of HPr at 0.6–1.2 g/h, biomass production of as high as 55.5 ± 0.3 to 84.8 ± 2.2 g/L, and PHBV production of 11.4 ± 0.2 to 33.9 ± 0.5 g/L, were attained. Increasing the feeding rate of HPr from 0.6 to 1.2 g/h also enhanced the 3HV content in PHBV from 12.0 ± 1.6 % to 45.0 ± 1.8 % (w/w), equivalent to 10.7 ± 1.4 to 41.9 ± 1.8 mol%, respectively. Based on these results, an approach to control 3HV content during PHBV production was proposed, under which, aiming at achieving 30 % (w/w) 3HV content, PHBV with 27.1 ± 7.2 % (w/w) 3HV content, equivalent to 24.7 ± 6.8 mol%, was successfully produced.