Enhancement of Biomass and Protein Production of <i>Chlorella protothecoides</i> in Heterotrophic Cultivation Using Expired Juices as Alternative Source of Nutrients for an Added-Value Biorefinery Scheme

Abstract

Microalgae are among the most suitable sources of new protein ingredients and bioactive compounds, although their cost-effective production still remains a developmental bottleneck. Heterotrophic growth has advantages, such as higher productivity and non-dependence on light and CO2, but it has not yet been fully implemented. The aim of this study was to increase the biomass and protein of Chlorella protothecoides in heterotrophic conditions using expired fruit and vegetable juices (FVJ) and to compare the results to those obtained using a modified Bristol (MB) medium. The initial amounts of sugars (15 g L-1) and yeast extract (8 g L-1) led to the highest protein production (43\%) and protein yield (5.2 g L-1) in trials using 1 L bottles. Bioreactor trials using FVJ resulted in a similar biomass productivity (2.94 g L-1 d(-1)) compared to MB (3.04 g L-1 d(-1)) and in enhanced polyunsaturated fatty acid content; nonetheless, a lower amount of essential amino acids (EAA) was obtained. Biomass was further processed by ultra-high-pressure homogenisation for protein concentration and residual pellet production. The protein extracts showed significant increases in EAA (11.8\% and 26\% increase in MB and FVJ, respectively). Residual biomass showed potential as a source of lutein and antimicrobial compounds. The results indicate that FVJ is a promising source of nutrients for the heterotrophic production of C. protothecoides, and that the extracts obtained present nutritional profiles and bioactivities of potential interest.