## 2 Results and Discussions
### Functional Properties of HOC and FHOC  
The WAC and OAC of HOC were measured as 5.31 \(\pm\) 0.06 and 2.14 \(\pm\) 0.06 (g/g), respectively (Table 8). These values are slightly different than the values [PERSON] et al. (2015) reported in the literature [121]. They measured the WAC of HOC as 4.10 \(\pm\) 073 g/g, which is slightly lower, whereas the OAC (3.38 \(\pm\) 0.11 g/g) was slightly higher than our results. These slight differences might be caused by the different de-oiling process of hazelnut flours or type of the hazelnuts used in the studies. In general, the WAC seems higher than the OAC of hazelnut cakes or flours. The higher WAC of de-oiled hazelnut cake might be attributed to its protein and dietary fiber content, which have many functional groups tending to interact with water molecules [61; 121]. It has been reported that the WACs of cake/meal such as soybean, sunflower, canola, flaxseed, hemp, milk thistle, poppy, pumpkin, rapeseed, and safflower are lower than the WAC of the HOC [59; 62; 122; 123]. On the other hand, the WAC of flaxseed cake was found to be higher than HOC by [PERSON] and [PERSON] (2009) [62]. Similar to these results, the OAC of HOC was measured higher than those of soybean, sunflower, flaxseed, hemp, milk thistle, poppy, pumpkin, rapeseed, and safflower cake in the literature [59; 122; 123]. In addition to this, [PERSON] and [PERSON] (2021) reported that the OACs of soybean, canola, and flaxseed meals used in their study were similar to the OHC of HOC used in our study [62]. The fermentation process led to remarkable changes in the functional properties of HOC. While WAC decreased after fermentation, significant increases in OAC were measured. After the fermentation process, the WAC of HOC decreased by 52.3%. [PERSON] et al. (2016) reported for moringa flour that while there was a steady increase in the WHC \begin{table}
\begin{tabular}{c c c} \hline \hline
**Functional Property** & **HOC** & **FHOC** \\ \hline Oil absorption capacity (g/g flour) & 2.14 \(\pm\) 0.06 & 3.31 \(\pm\) 0.06 \\ Water absorption capacity (g/g flour) & 5.31 \(\pm\) 0.06 & 2.53 \(\pm\) 0.07 \\ Emulsion activity index (m\({}^{2}\)/g) & 42.32 \(\pm\) 2.18 & 36.74 \(\pm\) 1.42 \\ Emulsion stability index (min) at 60 min & 175 \(\pm\) 10 & 763 \(\pm\) 32 \\ Foaming activity (mL) & 10.96 \(\pm\) 1.41 & 13.00 \(\pm\) 0.88 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Functional properties of HOC and FHOC. of the flour during the first 48 h of fermentation, a statistical decrease in the WHC value started at 72 h of fermentation [124]. This can be explained by the fact that in the first stages of fermentation, the water absorption ability of some polymeric carbohydrates increases due to the release of more functional groups with partial hydrolysis, and as a result of progressive fermentation, partially hydrolyzed polymeric structures are further hydrolyzed into monomers or oligomers and lose their water absorption ability by dissolving in water [124]. The fermentation time applied in our study may have caused FHOC to have a lower WAC value for this reason. On the other hand, the OAC value of FHOC was 55% higher than that of HOC by fermentation. A similar result was observed in the OAC values of soybean cakes fermented using _L. plantarum, L. brevis,_ and _L. acidophilus._ Significant increases in the OAC of the sample were detected depending on the type of microorganism used after fermentation [125]. [PERSON] et al. (2016) similarly reported that the OAC of moringa flour increased with fermentation time [124]. The higher OAC of FHOC can be attributed to the fact that more hydrophobic protein groups are exposed after hydrolysis and absorb oil molecules and the OAC increases with the help of more hydrophobic interactions as a result of decreased protein solubility by decreasing medium pH [62; 125]. As the medium pH approaches the isoelectric point of proteins in FHOC, the surface charge and solubility of proteins begin to decrease.