## 3 Results and Discussion
### Volatiles
The differences in total volatile peak areas (Figure 1) are also visible in the correlation loadings. The Neutrase-treated samples show a negative correlation with most volatiles, and these samples had the smallest volatile peak areas compared to the samples with other enzymes. The 70-min extractions using Alcalase and Protamex, on the other hand, correlate with most of the volatiles, indicating increased oxidation. \begin{table}
\begin{tabular}{c c c c c} \hline
**Compound Number** & **Compound** & **Identification Method** & **RT (min)** & **RI 1** \\ \hline
1 & Acetaldehyde & STD & 6.51 & \\
2 & 2-Propenal & MS & 9.79 & \\
3 & Propanal & STD & 9.97 & \\
4 & Butanal & STD & 14.55 & 638 \\
5 & 2,3-Butanedione & MS & 14.64 & 640 \\
6 & Unknown 1 & - & 14.84 & 644 \\
7 & Formic acid & MS & 15.96 & 667 \\
8 & 1,3-Butanediol & MS & 14.64 & 676 \\
9 & Acetic acid & STD & 17.44 & 696 \\
10 & 3-Methylbutanal & MS & 17.67 & 700 \\
11 & Heptane & STD & 17.84 & 704 \\
12 & 2-Methylbutanal & MS & 18.05 & 709 \\
13 & (Z)-2-Butenal & MS & 18.13 & 711 \\
14 & 2-Ethylfuran & STD & 18.85 & 727 \\
15 & 1-Penten-3-one & MS & 19.31 & 738 \\
16 & 1-Penten-3-ol & STD & 19.44 & 741 \\
17 & 2,3-Pentanedione & MS & 19.68 & 746 \\
18 & Cyclopentanol & MS & 19.73 & 747 \\
19 & Propanoic acid & MS & 21.67 & 787 \\
20 & (_E_)-2-Pentenal & STD & 22.41 & 801 \\
21 & Hexanal & STD & 24.44 & 851 \\
22 & 2-Methyl-4-pentenal & MS & 24.48 & 852 \\
23 & 3-Hexanol & MS & 25.71 & 880 \\
24 & 2,4-Hexadien-1-ol & MS & 26.84 & 905 \\
25 & (_E_)-2-Hexrenal & STD & 27.37 & 920 \\
26 & Heptanal & STD & 28.69 & 954 \\
27 & (_E_,_E_)-2,4-Hexadienal & STD & 30.05 & 988 \\
28 & Unknown 2 & - & 30.58 & 1002 \\
29 & 2-Pentylfuran & STD & 31.23 & 1020 \\
30 & (_Z_)-2-Heptenal & MS & 31.48 & 1027 \\
31 & (_E_)-2-(2-Penteny1)furan & MS & 31.72 & 1034 \\
32 & Octanal & STD & 32.55 & 1058 \\
33 & Hexanoic acid & MS & 32.62 & 1060 \\
34 & (_E_,_Z_)-2,4-Heptdenal & MS & 33.22 & 1076 \\
35 & (_E_,_E_)-2,4-Heptdenal & MS & 33.81 & 1091 \\
36 & (_E_,_E_)-3,5-Octadien-2-one & MS & 35.57 & 1146 \\
37 & 2-Nonanone & MS & 35.73 & 1151 \\
38 & Nonanal & STD & 36.08 & 1161 \\
39 & 5-Ethyl-2(5H)-furanone & MS & 36.45 & 1173 \\
40 & (_E_,_E_)-3,5-Octadien-2-one & MS & 36.52 & 1175 \\
41 & Nonanoic acid & MS & 41.94 & 1334 \\ \hline \end{tabular}  
* The retention indices are calculated in regard to a series of \(n\)-alkanes.  
\end{table} 
Table 5: All identified volatile compounds of enzymatically extracted Baltic herring oil. The compounds were identified based on the literature, NIST library and external standards (STD). Retention indices for HS-SPME-GC-MS of some volatile compounds are also presented. The column was SPB®-624 Fused Silica Capillary Column 60 m \(\times\) 0.25 mm \(\times\) 1.4 \(\mu\)m.  
The scores plot for PC1 and PC2 from oils extracted from by-products (Figure A2a) show that Alcalase samples separate well from Neutrase and Protamex samples. PC1 and PC2 explain 87% of the variance in the dataset. PC1 seems to relate to the differences between the enzymes, whereas PC2 show no clear trend in treatment time or other known factors. The correlation loadings (Figure A2b) show that most volatiles group on the negative side of the Y-axis, whereas 2-methylbutanal is the only volatile with a significant effect on the positive side. 2-Methylbutanal has a negative correlation with heptane and 2,3-butanedione. Butanal is also located on the positive side of the Y-axis, but it does  
Figure 1: Total peak areas in HS-SPME-GC-MS chromatogram of all identified volatile compounds (N = 41) from different enzymatically extracted oils from whole fish (blue bars) and by-products (orange bars) of Baltic herring. Figure 2: The correlation between \(p\)-anisidine value (AV) and total area of all identified aldehydes from the volatile analysis of enzymatically extracted oils from whole fish (blue) and by-products (orange) of Baltic herring. not have a significant effect in the model with PC1 and PC2.