Impact of nutrient starvation on intracellular biochemicals and calorific value of mixed microalgae

Abstract

A two-stage cultivation strategy was applied to mixed microalgae, which were first cultured in complete nutrient medium then switched to different nutrient-free mediums in order to assess the impact of nutrient starvation on intracellular biochemical components of mixed microalgae. The effects of nitrogen, sulfur and phosphorus starvation on cell counts, chlorophyll, carotenoid, protein, starch and lipid content of the mixed microalgae are compared in this study. The obtained results revealed that starch, as a dominant storage compound, was the highest in the nitrogen-free medium up to 49% of dry weight (DW). Protein and chlorophyll content declined slightly from 512 to 472.96mgL−1 and 29.43 to 26.58mg.L−1 only in the case of nitrogen starvation. Nitrogen starvation showed the best result as it ceased cell division immediately whereby in the case of sulfur and phosphorus starvation, cell division was not interrupted as microalgae are a pool of phosphorus and store sulfur. Calculation of starch and lipid energy content on the basis of electron equivalent and J/mg dry weight showed the higher energy content of lipid in compare with that of starch for all nutrients starvation. Nitrogen deprivation condition represents the superlative energy value of storage compounds content with the value of 17.61J/mg dry weight. The finding proves the potential of attractive and economically feasible mixed microalgae cultivation for high percentages of storage compounds production under nitrogen starvation