## 1 Introduction
Aligned with green biotechnology and the objectives of the United Nations Sustainable Development Goals, the fermentative release of EA presents itself as a favorable alternative to chemical liberation [8; 9; 12; 14]. In addition to serving as an antioxidant, EA provides numerous health advantages, such as antimutagenic, antitumor, anti-inflammatory, and antimicrobial properties [15; 16; 17]. These effects are attributed not only to EA, but they are also linked to EA metabolites known as urolithins. Urolithins are microbial cleavage products of ellagic acid, which are produced by colonic microbiota in anaerobic conditions [18; 19]. Urolithin A seems to be the most promising urothel with significant health benefits, making it a key focus from a health perspective. Obviously, the formation of urolithins depends on the composition of the microbiota. [PERSON] observed both producers and nonproducers of specific urolithins, leading him to introduce the concept of metabotypes. A metabotype is a metabolic phenotype capable of producing selected urolithins [20]. And obviously, these metabotypes are closely linked to a particular gut microbiota composition. In essence, three metabotypes have been identified so far: the metabotypes A, B, and 0. Metabotype A individuals exclusively produce urolith A as the final urolithin, while metabotype B individuals generate, besides urolithin A, also isourolithic A and urolith B. On the other hand, metabotype 0 individuals are unable to produce any of the aforementioned urolithins. Therefore, urolithin A, which has been demonstrated to have associations with the most beneficial health effects, remains elusive for metabotype 0 persons. There are currently efforts to form urolithin A from EA in the human body. Only a few microorganisms have been described that transform EA to urolithin A. [PERSON] et al. used in their study _Gordonibacter urolithfaciens_[21]. They used laborious techniques to form microorganism-loaded alginate hydrogels, or to encapsulate the microorganisms in alginate coated beds, to protect _Gordonibacter_ from gastrointestinal digestion. The so-protected microorganisms have been simultaneously applied with EA in mice. The authors observed, in fact, an enhanced formation, systemic circulation, and tissue accumulation of various urolithins, including urolith A. Another approach to provide urolithin A to nonproducers would be to form urolithin A directly in the food during fermentation. The aim to create a functional food based on urolithin A in one-step fermentation becomes intriguing. For the liberation of ellagic acid from filamentous fungi using SSF, the organisms need to be able to cleave ester and depside bonds to liberate ellagic acid from ellagitannins. Many microorganisms produce tannin acyl hydrolases (EC 3.1.1.20). Commercial enzymes could also be used, but this approach has not been considered commercially viable in previous studies [22]. _Aspergillus oryzae_, producing a higher level of ellagitannin acyl hydrolase, has been shown to yield a cost-effective approach to ellagic acid production from forestry by-products, yielding 17.7% ellagic acid in 84 h of fermentation. Results from that research suggested that the physiological parameters influence ellagitannin acyl hydrolase activity during fermentation, and subsequently altered the ellagic acid yield. Specifically, it was determined that optimal yields were obtained using a 3% substrate concentration, an incubation time of 72 h, and an initial pH of 5.5 [22]. Similar results were observed in SSF of pomergnate husk using _Aspergillus niger_[23]. Here, however, the optimal pH for the best enzyme activity in the fermentation was determined to be pH 5.0, with no activity detected at pH 6-7. A recent study explored the application of SSF on WPC using the fungi _A. oryzae_ and _R. oligosaccharidesorus_, with a particular focus on the liberation of ellagitannins to EA, but showed limited success in the transformation of free EA to urolithins [24].