Résumé:
This study was aimed at the mixotrophic cultivation of Cyanobacteria (Arthrospira plantesis)
using molasses as organic substrates for the production of cell biomass and
polyhydroxyalcanoate (PHA) accumulation destined for food packaging applications. Test
cultivations with different molasses sugar concentrations (g/L) supplemented in Zarrouk medium
were performed and a 2,5g/L sugar concentration proved to be the most optimum concentration
for efficient cultivation and cellular biomass accumulation. A 2,5g/L sugar concentration was
thus supplemented to Zarrouk cultivation medium for the targeted mixotrophic cultivation and
polyhydroxyalcanoate accumulation in cells.
The molasses used as the substrate had a total sugar content of 75,3± 0,6 %, water content of
15,56 ± 0,02 %, ash content of 13,88 ± 0,13 % and organic matter content of 84,73 ± 0,38 %.
The molasses were subjected to acid hydrolysis to hydrolyse the sucrose sugars into
monosaccharides before being supplemented to the cultivation medium. The mixotrophic
cultivation was done in 3 phases; Cell adaptation to heterotrophic metabolism, the growth phase
involving biomass accumulation and lastly, the PHA accumulation phase. The cultivation
parameters, cell growth and PHA accumulation were periodically analysed throughout the
experiment.
The highest specific growth rate (μmax, j−1) in this 2,5g/L mixotrophic cultivation was (0,125±
0,0045/jour) and the highest biomass Productivity (Pmax, gL−1 j−1) was observed in in the first
days of cultivation (0,46 ± 0,036g/L/jour). The highest biomass concentration (Xmax, gL−1) was
determined after cell harvest (2,178 ± 0.0017 gL−1) and the total PHA content was obtained after
solvent extraction using Soxhlet apparatus expressed as a percentage of the cell dry weight
30,9384 ± 0,0482 % (p/p) of cell dry weight. The results obtained in this study show that
Arthrospira plantesis cells can be successfully cultivated mixotrophically using molasses as
organic substrates in an objective of valorizing the sugar product by-product (molasses) to
produce cellular biomass and produce biodegradable and less toxic bioplastics
(Polyhydroxyalcanoates).
