From cheese whey to single-cell protein production: By-product valorization through acidogenic fermentation and purple phototrophic bacteria

Purple phototrophic bacteria (PPB) offer a sustainable solution for valorizing agri-food by-products, particularly through single-cell protein (SCP) production as high-grade feed ingredients. This study investigates the valorization of deproteinated cheese whey (DCW) using a two-stage process through acidogenic fermentation (AF) in anaerobic sequencing batch reactors (AnSBRs) of 1 and 9 L under different conditions to produce volatile fatty acids (VFAs), which are then used as carbon-rich substrates by PPB mixed cultures for SCP production. Both AnSBRs resulted in effective DCW acidification, producing desirable VFA mixtures during AF that PPB subsequently assimilated in batch tests. VFA mixtures from the 9-L AnSBR emerged as a promising substrate for high SCP production up to 64 % (g⋅g_TSS^-1) and amino acid production by PPB mixed cultures. Additionally, PPB grown on this substrate also exhibited significantly higher digestibility than soybean meal. This integrated approach paves the way towards cost-effective and sustainable SCP production from DCW.