The type of microorganism and substrate determines the odor fingerprint of dried bacteria targeting microbial protein production.

The rapidly increasing demand for protein has led to the pursuit of new protein sources, among which microbial protein (MP) is one of the most promising. Although the nutritional properties of MP are important and often well-studied, the sensory properties of the microbial cells will in part determine the commercial success of the product and are much less investigated. Here we assessed the odor fingerprint of dried bacteria originating from pure cultures and enriched mixed microbial communities using an electronic nose (e-nose). The e-nose discriminated between the different MP sources, while the choice of culture and substrate substantially affected their volatile organic compound (VOC) profile. The most dominant odor descriptors (>20% of VOC peak area) were sweet, fruity and fishy, while the mixed cultures presented higher peak areas indicating potentially more intense aromas than the pure cultures. The e-nose can detect the suitability of new MP sources and determine their best end-use.

Impact of substrate and growth conditions on microbial protein production and composition.

Production of microbial protein (MP) from recovered resources - e.g. CO2-sourced formate and acetate - could provide protein while enabling CO2 capture. To assess the protein quality obtained from this process, pure cultures and enriched communities were selected and characterized kinetically, stoichiometrically and nutritionally. Growth on acetate resulted in up to 5.3 times higher maximum specific growth rate (µmax) than formate (i.e. 0.15-0.41 h-1 for acetate compared to 0.061-0.29 h-1 for formate at pH = 7). The protein content was a function of the growth phase, with the highest values during stationary phase, ranging between 18 and 82%CDW protein depending on the organism and substrate. The negative correlation between biomass productivity and protein content indicated a trade-off between production rate and product quality. The final product (i.e. dried MP) quality was in most cases superior to soybean and all cultures were rich in threonine, phenylalanine and tyrosine, regardless of the carbon source.