Some of the products of fermentation include not just simple glycans but short-chain fatty acids (SCFAs), molecules which can be absorbed by the host and have direct links to different health effects. SCFAs come in a few forms, but in the gut predominately acetate butyrate and propionate, all of which have unique benefits including modulating the inflammatory response, influencing cholesterol production and interacting with the immune system. However, imbalances in SCFAs such as overproduction of acetate can lead to disease. For example, high concentrations of acetate can lead to overproduction of the mucosal layer in the gut, making it harder for beneficial bacteria to establish themselves; this is mitigated by the processing of acetate into butyrate by secondary fermenter species, so it is essential diversity is maintained in the HGM so that imbalances can be mediated by bacteria sequestering and converting over-abundant SCFAs. Mycoprotein Continuous air-lift fermentation of the fungal species Fusarium venenatum produces a broth which is heat-shocked to induce natural nucleases which degrade the RNA content in the broth making the F. venenatum non-viable and non- pathogenic to the consumer. The broth is then centrifuged into a paste of 75% water and 25% mycelium known as mycoprotein. Mycoprotein is then processed to form a meat- like structure, primarily through the addition of calcium to form cross-linkages between hyphae to form a fibrous texture. Quorn products are marketed as healthy meat alternatives due to the nutritional content of mycoprotein, which is high in protein (45%) high in fibre (25%) and low in fat (13%); the fibre portion comes from the cell wall of F. venenatum , made up of three complex dietary glycans. Mannoprotein Mannoproteins are mannan-based glycoproteins that form the outermost layer of the fungal cell wall and mycoprotein as a whole, so are heavily responsible for extracellular interactions and, importantly, the interactions between the mycoprotein and other ingredients during processing. The structure of mycoprotein is non-filamentous and consists of an α -mannan backbone with varying branches that differ between species (typically consisting of glucose and phosphate groups), along with an N -acetylglucosamine (GlcNAc) terminus which the functionally specific proteins bind to. The exact structure of
mannoproteins in F. venenatum has not yet been determined, although it is of particular interest in Quorn as the processing of mycoprotein into a meat-like fibrous structure is likely to be heavily reliant on the networks formed between mycoprotein. Little work has been done to describe the degradation pathway of mannoprotein; however, possible similarities can be drawn between it and fungal-derived α -mannan due to structural similarities. Bacteroidota species, such as Bacteroides thetaiotaomicron , have been described as α -mannan primary fermenters, but through a selfish mechanism in which no products of degradation are released extracellularly, this provides no simple sugars or SCFA for secondary fermenters to utilise. For this reason, mannoprotein is likely to be an excellent prebiotic for specifically promoting the growth of Bacteroides spp., which are known for having the ability to act as generalist glycan degraders and sustain other beneficial bacteria through cross-feeding.
The health of the gut has many links to different aspects of the host’s overall health including cholesterol level, immune system and even neurological disorders such as autism and Alzheimer’s disease via the gut-brain axis.
β -Glucan and chitin Forming the structural layer of the cell wall, β -glucan maintains cell shape and rigidity. The polysaccharide comprises β -d-glucose linked by β -1,3 and β -1,6 glycosidic bonds; the long filamentous structure along with the binding to some chitin in its fraction of the cell wall provides it with stability. The innermost layer of the cell wall is entirely chitin, formed of exclusively β -1,4-linked GlcNAc.
Mannoprotein
β -Glucan
Chitin
Cell membrane
β -Glucan synthase
Chitin synthase
GlcNac
Glc
Structure of F. venenatum cell wall. Jose Munoz and Jonathon Woods
25 Microbiology Today May 2023 | microbiologysociety.org
Made with FlippingBook - Online magazine maker