Valorisation of buttermilk in mixotrophic and heterotrophic conditions by using the acidophilic strain Galdieria sulphuraria

Abstract

Abstract The growth of the polyextremophile red microalga Galdieria sulphuararia ACUF064 under mixotrophy and heterotrophy was evaluated in a lab-scale stirred photobioreactor, using buttermilk as carbon source. Beforehand, G. sulphuraria growth on glucose, galactose and lactose, was evaluated. The final biomass concentration of G. sulphuraria was about 2 and 1.5 times lower in mixotrophy and heterotrophy, respectively, when G. sulphuraria ACUF064 was grown on lactose rather than in glucose or galactose. No significant difference was observed in mixotrophy between growth in glucose and galactose. C-phycocyanin content was about 1.6 and 1.37 times higher in mixotrophy on lactose than on galactose and on glucose. In heterotrophy, C-phycocyanin content, on lactose was 1.57 and 1.56 times higher than values detected in glucose and galactose, respectively. The preliminary mixotrophic flask experiment with different buttermilk dilutions showed that the highest biomass production was obtained at 1:2.5 dilution rate, corresponding to 40% v/v of butter milk and to 2.5 gC L− 1. On buttermilk, the highest biomass production was obtained in mixotrophy, at 1:2.5 dilution rate, in a 13 L photobioreactor where the algal productivity was 0.55 g L− 1 d− 1, and no contamination occurred at pH 1.6.