Using pre-fermented sugar beet pulp as a growth medium to produce Pleurotus ostreatus mycelium for meat alternatives

This study aimed to determine the compatibility of pre-fermented sugar beet pulp to support the growth of Pleurotus ostreatus mycelium in submerged fermentation. The goal was to create a meat alternative based on mycelial-fermented pulp. It was further explored whether pre-fermentation with lactic acid bacteria (LAB) on the pulp increased meat-like properties, such as aroma, springiness, and hardness, in the final product. Three strains were selected from a high throughput screening of 105 plant-derived LAB based on their acidification and metabolite production in the pulp. Two homofermentative strains (Lactococcus lactis) and one heterofermentative strain (Levilactobacillus brevis) were selected based on their low ethanol production, high lactic acid production, and overall acidification of the pulp. Mycelium of P. ostreatus was grown in submerged fermentations on the pre-fermented pulp, and the biomass was removed by centrifugation. The fungal strain consumed all available sugars and acids and released arabinose to the media. Volatiles were detected using GC-MS, and a large increase in concentrations of hexanal, 1-octen-3-ol, and 2-octenal was measured. Concentration of 1-octen-3-ol was lower in the pre-fermented samples vs. the non-pre-fermented. LC-MS amino acid analysis showed the presence of all essential amino acids on day 0 and 7 of fermentation. The highest concentration of amino acids was for glutamic acid/glutamine and aspartic acid/asparagine. A decrease in all amino acids after 7 days of fungal fermentation was measured for all fermentations. The decrease was more significant for pre-fermented samples. This was also confirmed through a total protein determination, except for samples pre-fermented with Lactococcus lactis strain NFICC142 which increased in total protein content after fungal fermentation. The protein digestibility increased after fungal fermentation, and the highest increase was seen for non-pre-fermented samples. The springiness of the fermented product indicated similarities to meat alternatives, while the hardness was much lower than other meat alternatives. The results indicate that dried sugar beet pulp can be used for submerged cultivation of P. ostreatus, but that pre-fermentation does not improve the physical or nutritional properties of the end product significantly, except for an increased protein content for NFICC142 pre-fermented media. This is the first known attempt to use LAB and P. ostreatus in mixed fermentation to produce fungal mycelium, as well as the first attempt at using SBP in a liquid fermentation for mycelial production of P. ostreatus.