# Optimization of Valorization of Chicken MDCM to Produce Soluble Protein and Collagen Peptides
## 3 Results and Discussion
### Properties of Extracted Protein Hydrolysates  
Enzymatic hydrolysis treatments in the optimal process conditions produced protein fragments with a broad molecular weight range. The smallest fragments were observed at a molecular weight of 50 Da, and the largest proteins were observed at 45 kDa. The majority (approximately 70%) of the proteins were around 10 kDa, indicating that the hydrolysis treatments were rather mild.  
The nitrogen solubility index (NSI%), which describes the proportion of nitrogen that is water-soluble compared with total nitrogen content, is relevant to the evaluation of protein quality. The NSI values of the hydrolyzed chicken MDCM protein fractions were determined at pH 5-8 and are shown in Figure 2.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Enzyme** & **Time of Hydrolysis** & **Ash (\% DW)** & **Dry Matter** & **Protein (\% DW)** & **Fat (\% DW)** \\ \hline Ermitase 1 & 4 h & 9.90 & 93.31 & 87.01 & 0.74 \\ \hline Ermitase 1 + 2 & 4 h & 11.58 & 95.16 & 86.17 & 2.44 \\ \hline \end{tabular}
\end{table}
Table 3: The ash, dry matter, protein, and fat content of the soluble protein fraction after treatment with ERM 1 and ERM 1 + 2 for 4 h.  
The measurements indicated that a large proportion of the samples had a high solubility of up to 90%, and no clear trend in the pH change was observed. Using ERM 1 and 2 enzymes increased solubility at pH 6. The protein fraction from MDCM seemed to have much lower solubility at pH 6 after four hydrolys when the hydrolysis was carried out only using ERM 1, but the solubility increased remarkably when both ERM 1 and ERM 2 were used.  
The gelling property and gel hardness were evaluated at concentrations of 5%, 10%, and 15% and at pH values of pH 6.0 and pH 6.5. Furthermore, gelatin gels made by adjusting the protein content to 6.67% were used as a reference. Gel hardness was measured with a Lloyd's instrument (Lloyd LR 10K, Geleen UK). The results showed that gels from MDCM fractions were remarkably weaker than the reference gelatin. It was also revealed that there was no major difference in gel hardness whether ERM 1 or ERM 1 + 2 enzymes were used in the hydrolysis. At pH 6.0 and 5% protein content, the ERM 1 gel hardness was 0.0145 \(\pm\) 0.01 N, and the ERM 1 + 2 showed a hardness of 0.01 \(\pm\) 0.0061 N. The effect of the pH on gel hardness was somewhat more visible in the results. The gel with 10% protein content treated in ERM 1 treatment showed a gel hardness of 0.014 \(\pm\) 0.0022 N at pH 5.5. At pH 6, the value was 0.036 \(\pm\) 0.016 N. To this end, a considerable difference in hardness was observed at the same 10% protein content but different pH in ERM 1 treatment; at pH 6, the gel had 20 times higher hardness compared to pH 5.5.  
The gel hardness of protein fraction is an important factor to determine its applicability in foods. In many meat-related products, the gelling property is important to obtain the proper structure and functionality. If the protein derived from the mechanically deboned meat through enzymatic hydrolyses has no good gelling property, the amount added to the product should be carefully calculated to avoid having a negative impact on the final hardness, chewiness, and taste of the product. For example, [PERSON] et al. [26] observed that up to 10% of chicken meat could be replaced with MDCM hydrolyses with an effect on the organoleptic and physicochemical properties of Mortadella-type sausage.  
It is also important to mention that this study's aim was not to produce a protein isolate but to develop a simple and affordable technology for the better valorization of mechanically deboned meat.  
Figure 2: Nitrogen solubility index of chicken MDCM protein fractions obtained with ERM1 or ERM1 + 2 after 4 h hydrolysis.