Optimization of the inoculum concentration and pH of the culture medium, for the increase of the production of Chlorella vulgaris in ricotta cheese whey

Abstract

The aim of this study was to determine the optimum conditions of both inoculum concentration (IC) and pH, regarding their effect on the increase of cellular concentration of the microalga Chlorella vulgaris, cultivated in microfiltered ricotta cheese whey.
A central composite design with 2 independent variables in 3 levels was carried out. The independent variables were IC and the pH. The response was measured through the cell’s concentration with an improved Neubauer Chamber and a microscope. Moreover, final pH of each system was measured.
Systems were prepared with the addition of 5 mL of inoculum in 45 mL of microfiltered ricotta cheese whey in Erlenmeyers of 250 mL. The pH of each system was adjusted post inoculation by the addition of sterilized solutions of NaOH 1M and HCl 1M. Systems were grown during 96h at 26 ± 2 °C with a 12/12h light/dark photoperiod. The source of light was a blue LED light with an intensity of 46.46 μmol.m^-2s^-1. Furthermore, orbital shaking was applied at a constant speed of 100 rpm.
Results were analyzed by means of a response surface methodology using the statistics software Statgraphics Centurion XV (02/15/06 V, 2007). The optimum initial pH value was 8.28. Systems showed a trend to the selfregulation of pH, as at the end of the essay all of them were found inside the range 7.90-9.11. The optimum nominal IC was determined at a DO₆₈₀ value of 0.1. Further essays should be carried out to confirm the IC value, as the optimum determined by this study was found to be at the edge of the response surface.