Abstract
The unicellular green alga Chlorella is an ideal protein source. However, the high production cost and low production capability of the current main photoautotrophic culture mode limit its application especially as an alternative protein source for food and feed, which might be overcome through high-cell-density cultivation in fermenters. In this study, a Chlorella sorokiniana strain CMBB276 with high protein content was selected from five Chlorella strains by comprehensive evaluation of their growth rates, protein contents, and yields. The optimal cultural temperature, pH, and mole ratio of carbon and nitrogen (C/N) for C. sorokiniana CMBB276 growth were found to be 30°C, 6.5, and 18, respectively. Ammonium chloride was proved to be the best nitrogen (N) source for C. sorokiniana CMBB276 growth, whereas growth inhibition caused by the accumulation of salts was observed under fed-batch cultivation when maintaining a constant C/N ratio of 18 by controlling pH with sodium hydroxide solution. By simultaneously reducing the concentration of ammonium chloride in the feeding medium and controlling pH with ammonium hydroxide, we finally achieved the ultrahigh-cell-density cultivation of C. sorokiniana CMBB276. The highest biomass concentration and protein yield reached 232 and 86.55 g l−1, respectively, showing the great potential of culturing C. sorokiniana CMBB276 in fermenters for economic and large-scale protein source production.
Highlights
A growing global population and a higher demand for more and better quality food will place increased pressure on the world’s natural resources (Henchion et al, 2017)
Commercial production of Chlorella biomass used in healthy foods and feeds of animals is provided mostly in open raceway ponds and this commonly used way of algal cultivation is characterized by rather low production rates and high production cost, limiting the widespread application of Chlorella as a food or feed commodity (Liu and Hu, 2013)
To obtain the optimal Chlorella stain suitable for protein production, a comprehensive evaluation of both the cellular growth and protein production performances of five Chlorella strains were conducted through primary flask cultivation
Summary
A growing global population and a higher demand for more and better quality food will place increased pressure on the world’s natural resources (Henchion et al, 2017). Ultrahigh-Cell-Density Cultivation of a High Protein-Yielding Chlorella content of most microalgae is equal to or even higher than conventional plant protein sources (Madeira et al, 2017). The unicellular green alga Chlorella is one of the few microalgae largely employed for human consumption, which has high protein content with a balanced amino acid composition (Becker, 2007; Liu and Hu, 2013). A large number of nutritional and toxicological evaluations have demonstrated the suitability of Chlorella biomass as a valuable feed supplement or substitute for conventional protein sources (e.g., soybean meal, fish meal, and rice bran) (Madeira et al, 2017). Commercial production of Chlorella biomass used in healthy foods and feeds of animals is provided mostly in open raceway ponds and this commonly used way of algal cultivation is characterized by rather low production rates and high production cost, limiting the widespread application of Chlorella as a food or feed commodity (Liu and Hu, 2013)
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