The effects of medium composition and cultivation conditions on the growth and protein production of Physarum polycephalum microplasmodial

Abstract

Previous study found that Physarum polycephalum (P.polycephalum) microplasmodial would be an ideal species for functional food development of which the biomass obtained from glucose or sugarcane powder-based medium displayed a high nutritional value. Since fresh sugarcane juice is a more affordable substrate compared to glucose, thus, the main objective of this study was to evaluate the effects of the composition and cultivation condition on P. polycephalum growth and the nutritional value of the biomass including protein and amino acid profiles in fresh sugarcane juice based medium. Optimization of the sugarcane-based media components by Response Surface Methodology (RSM) showed that sugarcane concentration had a significant effect on both biomass production and protein content. The optimal medium consisted of 50 ml fresh sugarcane juice (equivalent to 37.5 g/L reducing sugars), 15 g/L tryptone, and 1.0 g/L yeast extract. This medium yielded 22.682 g/L dry cell weight with 16.84% protein after five days of cultivation. These are significantly higher than the amount of biomass (13.86 g/L) and protein content (14.88%) obtained from the previously reported optimal sugarcane powder medium. Quantification of amino acid profiles by HPLC-UV showed that the total amount of amino acids in the optimal sugarcane juice medium was higher than that of sugarcane powder medium. Remarkably, some essential amino acids are also significantly increased, such as isoleucine (8.45 mg/g), leucine (11.78 mg/g), lysine (10.45 mg/g), tryptophan (6.74 mg/g). Aspartate was found to be the most predominant amino acid with 17.05 mg/g. This study found that sugarcane juice is an ideal replacement for glucose and/or sugarcane powder. Biomass production from this substrate is not only cheaper, but also better in term of yielding higher contents of the essential amino acids.