Assessment of the shelf-life of Nannochloropsis oculata flocculates stored at different temperatures

Abstract

The cell and culture viability of concentrates of the microalga Nannochloropsis oculata were assessed after storage for a period of 16 weeks at -18, 0 and 5ºC. The concentrates were obtained from the crop of N. oculata, which was harvested at the start of the seasonal growth period using a process of flocculation. Flocotac Plus was used as the flocculation agent, achieving flocculation of 90% of the suspended microalgae. It was observed that the chemical process did not affect the number of live cells. The concentrate stored at -18ºC presented slow freezing, which deteriorated the cells and therefore reduced cell viability after five weeks (75%). The concentrates stored at 0 and 5ºC showed cell viability over 97% after the 16 weeks. Culture viability was only seen in the concentrates stored at 0 and 5ºC, which showed specific growth rates similar to those of the control culture. It may be concluded that it is possible to use flocculates stored at 0 and 5ºC after 16 weeks as inoculum for mass crops of N. oculata for food, green water and other uses.