Shiitake Extract

Shiitake extract is made from the fruiting body of Lentinula edodes (Berk.) Pegler, family Omphalotaceae. Older literature, most ingredient specifications and the Harmonised System itself still use the synonym Lentinus edodes (Berk.) Singer, so both names will be seen on documents for the same organism. The mushroom is cultivated on oak and other hardwood logs or, more usually at industrial scale, on supplemented hardwood sawdust blocks; the caps and stipes are dried, milled and extracted with hot water, then vacuum concentrated and dried. Thovek supplies the fruiting-body extract, carrier-free by default. The polysaccharide that defines the ingredient is lentinan (CAS 37339-90-5), a beta-(1 to 3)-glucan whose backbone carries two beta-(1 to 6)-linked glucose branches for every five backbone residues, with a reported molecular weight around 500,000 Da. Purified lentinan used as a parenteral pharmaceutical in Japan is a different article entirely from a food-grade extract, and the two must never be quoted against each other; a 30% polysaccharide food ingredient is not a purified lentinan preparation and should not be described as one. Commercial food grades are specified at 30% polysaccharide, with higher figures available, and Thovek additionally reports beta-glucan enzymatically as total glucan minus alpha-glucan on the Megazyme K-YBGL principle, because a polysaccharide number obtained by alcohol precipitation counts any residual substrate starch as though it were fungal glucan. Shiitake also carries constituents that are characteristic of the species rather than of mushrooms generally: L-ergothioneine (CAS 497-30-3), of which shiitake is one of the richer dietary sources; D-eritadenine (CAS 23918-98-1), a shiitake-characteristic purine; and ergosterol, reported in shiitake powder at roughly 2.4 to 6.2 mg/g dry weight. Two further properties are worth putting in front of a formulator. First, ergosterol is the biosynthetic precursor of vitamin D2, and controlled UV-B exposure converts it: irradiation has been shown to raise vitamin D2 in dried shiitake powder from undetectable to around 40 micrograms per gram dry weight, so UV-treated grades can be supplied and sold as a declared vitamin D2 source with the assayed content stated on the certificate. Second, dried shiitake is the material in which 5'-guanylate was originally identified as the umami principle, which is why shiitake extract does double duty as a savoury flavour base in broths, seasonings and meat analogues and not only as a supplement actives ingredient. On labelling: the material is vegan and vegetarian, and the hardwood substrate involves no animal input, but wheat bran is a common block supplement so gluten cross-contact is controlled and tested rather than assumed. Shiitake is itself a recognised cause of allergic reaction in a minority of consumers, so it should be named plainly in the finished-product ingredient list wherever local labelling rules require the source to be identified.