Industrial Applications of Different Parts of Flatland Polygonum cuspidatum by Combining Microwave-Assisted Extraction and Fermentation Process

<i>Polygonum cuspidatum</i> is a well-known and versatile medicinal plant. In Taiwan, <i>P. cuspidatum</i> is typically found in central mountainous regions. Once acclimated, it can also thrive in flat areas, where it is known as flatland <i>P. cuspidatum</i>. Flatland <i>P. cuspidatum</i> has several advantages over alpine <i>P. cuspidatum</i>; for example, flatland <i>P. cuspidatum</i> grows faster and has larger leaves. This study enhanced the functionality of different parts of flatland <i>P. cuspidatum</i> (flowers, leaves, and rhizomes) by using microwave-assisted extraction (MAE) technology and Box-Behnken response surface methodology. Experiments revealed that the combination of MAE parameters that yielded optimal results was influenced by which plant part was used as input material. Regarding whitening activity, the extracts were ranked as follows: leaf > rhizome > flower. Leaf extracts had higher total flavonoid content, and rhizome extracts had higher total phenolic content. Regarding antiaging activity, the extracts were ranked as follows: rhizome > leaf > flower. The rankings for antimicrobial activity were as follows: leaf > rhizome > flower. Regarding anti-inflammatory activity, the extracts were ranked as follows: flower > rhizome > leaf. The rhizome extract exhibited slight cytotoxicity. UHPLC-UV-Q-TOF-HRMS/MS analysis identified 27, 34, and 37 bioactive compounds in the leaf, rhizome, and flower extracts, respectively. Given the relatively low pharmacological activity observed in the MAE-optimized flower extract, fermentation with <i>Aspergillus oryzae</i> was employed to enhance its efficacy. This process significantly enhanced the extract's pharmacological properties, including its whitening, antiaging, and antimicrobial properties. Increased levels of 3-<i>O</i>-caffeoylquinic acid, decursin, quercetin, quercitrin, kaempferol, resveratrol, epicatechin gallate, resveratrol-3-<i>O</i>-D-(2-galloyl)-glucopyranoside, resveratrol-4'-<i>O</i>-β-D-glucoside, apigenin, emodin-8-<i>O</i>-(6'-<i>O</i>-malonyl)-glucoside, physcion, emodin, and torachrysone in the fermented flower extract likely contributed to its enhanced pharmacological activities. The results of this study indicate that the newly developed flatland <i>P. cuspidatum</i> extracts can be considered viable substitutes for alpine <i>P. cuspidatum</i> extracts.