Rhamnogalacturonan <scp>I</scp>‐rich polysaccharide isolated from fermented persimmon fruit increases macrophage‐stimulatory activity by activating <scp>MAPK</scp> and <scp>NF‐κB</scp> signaling

Abstract

BACKGROUND: Persimmon (Diospyros kaki) is a familiar and widespread fruit, cultivated worldwide. To date, physiological and chemical changes in fermented persimmon fruit and its active compounds have been rarely investigated. Moreover, comparative studies on the pharmacological activities of fermented persimmon fruit-derived compounds have not been reported. RESULTS: To investigate the effect of traditional fermented foods on immunostimulatory activity, non-fermented persimmon fruit (D. kaki, DK) and fermented persimmon fruit (fermented D. kaki, FDK) were prepared and further fractionated into low- and high-molecular weight fractions. FDK exhibited significantly higher activity toward the production of macrophage-stimulatory mediators compared with that of DK, and the high-molecular weight fraction (FDK-H) isolated from FDK was shown to have more potent activity than FDK. FDK-H not only increased the expression of immunostimulatory genes (TNF-α, IL-6, IL-12, and iNOS), but also stimulated the phosphorylation of both MAPK (ERK, JNK, and p38) and NF-κB (p65 and IκB) signaling molecules underlying macrophage activation. The putative chemical characteristic of FDK-H was identified as a pectic rhamnogalacturonan (RG) I-rich polysaccharide with a high molecular weight of 304 kDa containing galacturonic acid, arabinose, rhamnose, and galactose as the major monosaccharide units. CONCLUSION: The present study reveals that traditional fermentation is a useful method for increasing the macrophage-immunostimulatory activity of persimmon fruit, and the increased activity may be associated with structural modification of persimmon polysaccharides. This study may serve to identify a functional ingredient as an immunostimulatory agent, and our results may be applied to develop a new immunostimulatory product using FDK-H. © 2021 Society of Chemical Industry.