In view of the growing global need for sustainable protein sources, this study explores the utilization of short-chain fatty acids into single-cell protein using the non-conventional yeast Cyberlindnera jadinii. Short-chain fatty acids can be sustainably produced via anaerobic digestion of organic waste, presenting a promising fermentation substrate for a circular bioeconomy. Cyberlindnera jadinii is demonstrated to be capable of growing on acetate, propionate and butyrate as both a carbon and energy source without strong inhibition. Bioprocess development was conducted in stirred tank bioreactors, where a fed-batch pH-stat bioprocess led to improved efficiency without substrate inhibition. The highest titer of 31.3 ± 1.0 g/L, rate of 0.67 ± 0.02 g/L/h and yield of 0.36 ± 0.01 g/g was achieved with propionate. The resulting biomass contained 41.3% crude protein, and 17.3% crude lipids with 81% unsaturated fatty acids. In contrast to acetate and butyrate, propionate as a substrate led to accumulation of 37% odd-chain fatty acids with titer, rate and yield of 1.74 ± 0.06 g/L, 0.037 ± 0.001 g/L/h and 0.020 ± 0.001 g/g. These findings confirm that short-chain fatty acids are viable fermentation substrates not only for single-cell protein, but also unsaturated and odd-chain fatty acid production with Cyberlindnera jadinii.

A novel approach for converting non-edible plant biomass into single-cell protein and oil (SCPO) via consolidated bioprocessing has been established, leveraging aerotolerant thermophilic cellulolytic consortia consisting mainly of Thermoanaerobacterium thermosaccharolyticum, Sporolactobacillus spp. and Clostridium sensu stricto to achieve the rapid and complete conversion of crystalline cellulose into a consistent cocktail of lactate, acetate and ethanol. This cocktail is an excellent substrate for cultivating organisms for SCPO production and food and feed applications, including Cyberlindnera jadinii, Yarrowia lipolytica and Corynebacterium glutamicum. Cultivation on this cocktail resulted in yields (Y_X/S) of up to 0.43 ± 0.012 g/g, indicating a yield from cellulose (Y_X/Cellulose) of up to 0.27 ± 0.007 g/g (dwb). The resulting SCPO was rich in protein (42.5% to 57.9%), essential amino acids (27.8% to 43.2%) and lipids (7.9% to 8.4%), with unsaturated fatty acid fractions of up to 89%. Unlike fermentation feedstocks derived from easily digested feedstocks (i.e., food waste), this approach has been applied to cellulosic biomass, and this mixed-culture bioconversion can be carried out without adding expensive enzymes. This two-stage cellulosic bioconversion can unlock non-edible plant biomass as an untapped feedstock for food and feed production, with the potential to strengthen resiliency and circularity in food systems.