## 3 Results and Discussion
### Final Extraction and Re-Extraction of Mixed Tissues  
Using the optimized methods, type A and type B gelatins were finally extracted and re-extracted using the mixed tissues from the head of Kalamtra sturgeon. The final yields and band patterns of gelatin in SDS-PAGE are presented in Table 4 and Figure 5. The yield of type B extracted gelatin was higher than that reported in the previous type B gelatin extracted from tiger tooth croaker head (1.67%), whereas that of type A extracted gelatin was similar to that of the type A gelatin extracted from mackerel had (3.3-3.7%) [23; 24]. Type B extracted gelatin had the highest yield, while type A extracted gelatin had the significantly strongest \(\alpha\)- and \(\beta\)-bands than the others. The low molecular-weight bands were significantly higher in type B extracted gelatin. These results again indicate that type A extracted gelatin is of the best quality. In other words, type B gelatin may contain more non-gelatinous substances (like non-gelatinous proteins, lipids, sugar, and ash) and result in a higher yield. As the head is a mixture of collagenous and non-collagenous tissues, alkali pretreatment might allow more gelatinous and non-gelatinous materials to be extracted than in the acid pretreatment. This phenomenon might arise because the alkali-pretreatment lowers the isoelectric point and destroys the amide groups of proteins, resulting in a weaker collagen matrix [25] than the acid-pretreatment. However, acid- and  
Figure 4: An overview of protocols used for the extraction and re-extraction of type A and type B gelatins from the head of Kalamtra sturgeon. alkali-pretreatments affect the physicochemical characteristics and purity of gelatin is now under investigation. The quality of type A extracted gelatin, indicated from the low molecular-weight bands in SDS-PAGE, was better than that of type A gelatin extracted from mackerel had [24]. The yields of type A and type B re-extracted gelatins were lower than those of the extracted gelatins but were similar to those of perch bone (1.3-2.4%) [26]. The intensity of gelatin bands of re-extracted gelatins was lower than that of type A extracted gelatin (Figure 5); thus, the quality of re-extracted gelatins was likely to be lower than extracted gelatins. The total yields (extraction + re-extraction) of type A (5.01%) and type B (7.25%) gelatins from the sturgeon head in the current study were higher than those previously reported for fish head gelatins; examples include 1.67% type B gelatin in tiger tooth croaker head [23] and 3.3-3.7% type A gelatin in mackerel head [24]. In contrast, the present yields were close to those of fish skin type A gelatins of pink perch and croaker (5.57-7.56%) [27] but lower than that of the leatherjacket fish (5.23-11.54%) [15] and sturgeon (5.04-24.11%) [4; 5; 6]. As the skin is the most dominant collagenous tissue, it is logical that the sturgeon head had lower gelatin yields than sturgeon skin. However, the head is the major by-product of commercial sturgeon, as its weight is about three times greater than that of skin. Thus, the sturgeon head is a suitable raw material for extracting both high-quality type A and high-yield type B gelatins at an industrial scale. Consequently, this novel extraction method from the head could open new opportunities for by-product utilization and enhance the economic benefits of aquaculture farming of sturgeon. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Gelatins**} & \multicolumn{3}{c}{**Yields (\%)**} \\ \cline{2-4}  & **Extraction** & **Re-Extraction** & **Total** \\ \hline Type A & 3.42 \(\pm\) 0.11 & 1.59 \(\pm\) 0.11 & 5.01 \(\pm\) 0.02 \\ Type B & 5.71 \(\pm\) 0.06 * & 1.54 \(\pm\) 0.06 & 7.25 \(\pm\) 0.11 * \\ \hline \hline \end{tabular} All values are the mean \(\pm\) standard error of three replicates. * Significantly different from the value of type A gelatin (\(p<0.05\)).  
\end{table} 
Table 4: Yields (%, Dry weight gelatin/wet weight sample) of gelatins extracted from the head of Kalamtra sturgeon.