## 2 Results and Discussions
### Bioactive Properties  
The fermentation process increased the number of soluble phenolic compounds in HOC by 3.5 times and the total number of soluble peptides by 14.3 times (Table 7). The highest amounts of phenolic compounds were determined in aqueous extracts of HOC and FHOC, followed by 80% methanolic extract and methanolic extract. The fermentation process increased the amount of phenolics dissolved in methanol, which corresponds to a 48-fold increase. The process also increased the phenolic contents in 80% methanolic extract and aqueous extract but the increments were more limited as 7-fold and 3.5-fold, respectively. Similar increments in phenolic content during fermentation have been reported in the literature. The amounts of water-soluble and methanol-soluble phenolic compounds in rice samples fermented by _Aspergillus oryzae_ increased 8% and 244%, respectively, compared to the non-fermented rice [97]. Similarly, the phenolic compound contents of fermented wheat, brown rice, maize, and oats increased significantly [98]. There are many studies showings that the fermentation process converts conjugated phenolic compounds into free phenolic compounds by microbial-derived enzymatic activities [99]. It is thought that the enzyme \(\beta\)-glucosidase (beta-D-glucose glucohydrolase, (E.C. 3.2.1.21) is particularly effective in the increase of phenolic compounds. This enzyme hydrolyzes phenolic glycosides to form free aglycones with high antioxidant activity [100]. Extracellular enzymes produced by _Aspergillus oryzae_ include \(\alpha\)-amylase, glucoamylase, \(\alpha\)-glucosidase, cellulase, \(\beta\)-galactosidaseinase, polygalacturonase, pectin lyase, and xylanase [49; 101]. These enzymes are especially effective in the release of phenolic compounds in hazelnut meal, which are bound to carbohydrates, into the environment in free form. Ligneocellular enzymes also break down polysaccharides in the cell wall, hydrolyze insoluble cellular components and release bioactive components such as phenolic acids bound to the cell wall. In addition, the activities of \(\beta\)-glucosidase, which hydrolyze phenolic glycosides, and phenolic esterases, which can liberate phenolic compounds upon disruption of cell integrity, may also have contributed to the increase in total phenolics in fermented hazelnut meal [102]. At the end of the fermentation process, changes in the bioactive properties of hazelnut meal were expected as a result of various hydrolysis reactions occurring with the activities of microbial enzymes in the medium. The emergence of free amino acids and bioactive peptides as a result of protein hydrolysis due to the high extracellular enzymatic activities of _Aspergillus oryzae_, the increase in free phenolic compounds and water-soluble carbohydrate content as a result of alpha amylase, and other glucosidase enzyme activities may be the main factors that cause significant changes in the bioactivity of fermented hazelnut meal [82; 103]. The bioactive properties of food products, such as antioxidant, antimicrobial, antihypertensive, antidiabetic, etc., are generally associated with their phenolic components and bioactive peptides. On the other hand, there was a limited increase in the amount of total soluble protein content, from 256.8 \(\pm\) 3.3 to 279.5 \(\pm\) 4.0 mg BSA/g. [PERSON] et al. (2012) reported an increase in the soluble protein content of soybean meal fermented with _Aspergillus oryzae_, but the increase was limited, close to 20% [82]. However, the results showed that there was a high increase in the number of primary amino groups in the medium during the fermentation process which was expressed as a total peptide content (TPC). The method used to determine the TPC is based on the determination of the compound formed as a result of the reaction between primary -NH\({}_{2}\) groups and OPA (ortho-phthalaldehyde) in the presence of reduced sulfhydryl groups by spectrophotometric methods.