Meat byproduct hydrolysates are an abundant and problematic process stream of the growing rendering industry. Current technology for extracting valuable amino acids from these hydrolysates relies on expensive evaporation. This work supports growth of nutraceutical Chlorella sorokiniana algae on these heat-sterilized hydrolysates, valorizing this waste as microbial media. Dissolved air flotation solids, a challenging high-moisture meat byproduct, were used as feedstock. When C. sorokiniana was grown on rendered hydrolysate, it accumulated 1.8x more protein and nearly double the essential amino acids and chlorophyll, compared to growth on mineral medium. Due to these intriguing results, proteomics and mechanistic experimentation were performed to elucidate the causes of this substantial protein upregulation. Proteomics confirmed significant (p < 0.05) increases in many photosynthetic proteins. During algal growth, the hydrolysate medium shifted to a dark color and led to a new hypothesis that light blocking effects drove the increases in chlorophyll and photosynthetic proteins. An experiment was conducted in which mineral medium was artificially darkened with graphite powder, increasing protein content from 48% to 61%. Combining media darkening with addition of free amino acids to match levels in the hydrolysate further increased protein content to 68%, approximately equal to the hydrolysate-grown algae (66%), without growth suppression. These are among the highest protein contents ever recorded for Chlorella . This work advances understanding protein upregulation in nutraceutical algae and demonstrates the potential of dark shifting the media as a novel technique for algal biotechnology.
Drabold et al. (Sun,) studied this question.