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.

Utilization of plant derived lactic acid bacteria for efficient bioconversion of brewers' spent grain into acetoin.

Brewers' spent grain (BSG) is a major side-stream from the beer industry, with an annual estimated production of 39 million tons worldwide. Due to its high nutritional value, high abundance and low price, it has been proposed as an ingredient in human food. Here we investigated the ability of different lactic acid bacteria to produce the flavor molecule acetoin in liquid BSG extract, in order to broaden the possibilities of utilization of BSG in human food. All the investigated lactic acid bacteria (LAB) covering the Leuconostoc, Lactobacillus and Lactoccocus species were able to convert the fermentable sugars in liquid BSG into acetoin. Production levels varied significantly between the different LAB species, with Leuconostoc pseudomesenteroides species reaching the highest titers of acetoin with only acetate as the main byproduct, while also being the fastest consumer of the fermentable sugars present in liquid BSG. Surprisingly, the currently best investigated LAB for acetoin production, L. lactis, was unable to consume the maltose fraction of liquid BSG and was therefore deemed unfit for full conversion of the sugars in BSG into acetoin. The production of acetoin in Leu. pseudomesenteroides was pH dependent as previously observed in other LAB, and the conversion of BSG into acetoin was scalable from shake flasks to 1 L bioreactors. While all investigated LAB species produced acetoin under aerobic conditions, Leu. pseudomesenteroides was found to be an efficient and scalable organism for bioconversion of liquid BSG into a safe acetoin rich food additive.