Abstract
Fermented persimmon juice, Kakishibu, has traditionally been used for wood and paper protection. This protective effect stems at least partially from inhibition of microbial cellulose degrading enzymes. The inhibitory effect of Kakishibu on lytic polysaccharide monooxygenases (LPMOs) and on a cocktail of cellulose hydrolases was studied, using three different cellulosic substrates. Dose dependent inhibition of LPMO activity by a commercial Kakishibu product was assessed for the well-characterized LPMO from Thermoascus aurantiacus TaAA9A, and the inhibitory effect was confirmed on five additional microbial LPMOs. The model tannin compound, tannic acid exhibited a similar inhibitory effect on TaAA9A as Kakishibu. It was further shown that both polyethylene glycol and tannase can alleviate the inhibitory effect of Kakishibu and tannic acid, indicating a likely mechanism of inhibition caused by unspecific tannin–protein interactions.
Highlights
Persimmon, or kaki, from the tree species Diospyros kaki and Diospyros virginiana, is a fruit with large significance to Asian culture, cuisine, and folk medicine
Non-impregnated and Kakishibuimpregnated filter paper discs were subjected to hydrolysis by the commercial enzyme cocktail, Celluclast, in the absence and presence of Thermoascus aurantiacus lytic polysaccharide monooxygenases (LPMOs), TaAA9A
Substrate breakdown was further boosted by the addition of the LPMO and ascorbate as its reductant, reaching a 7.6% conversion
Summary
Kaki, from the tree species Diospyros kaki and Diospyros virginiana, is a fruit with large significance to Asian culture, cuisine, and folk medicine. Phytochemicals, such as proanthocyanidins, flavonoids, tannins, and other polyphenols, are among the important bioactive constituents of persimmon [1,2]. The use of Kakishibu in Asian folk medicine stemmed from its high polyphenolic content, with applications such as a neutralizing agent against proteinaceous snake toxins [4]. It is known that fruit astringency stems from the presence of tannins, which are able to interfere with and precipitate salivary enzymes, creating a bitter taste and a dry sensation [5]. Polyphenols from astringent persimmon have been reported to inhibit various enzymes, among which are cellulase [6], amylase and glucosidase [4], and tyrosinase [7]
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