Culture mixotrophique de cyanobactéries (Arthrospira plantesis) utilisant de la mélasse comme substrat organique pour la production de biomasse cellulaire et de bioplastiques (Polyhydroxyalcanoates) pour des applications d'emballage alimentaire.

Abstract

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).