Effect of the ratio of SPOMFs to solvent (w/v)
Subsequently, the effects of the ratio of SPOMFs to solvent (w/v) on purity (% palmitoleic acid relative to total fatty acid) and yield of palmitoleic acid were investigated, and the results are shown in Figure 2b. When crystallization was carried out at -20 °C, our preliminary study showed that SPOMFs: methanol ratios from 1:3 to 1:6 were inappropriate, because the solution froze too quickly to allow monitoring. Therefore, the SPOMF to methanol ratios were set at 1:9, 1:12, 1:15 and 1:18 (w/v), and the methanolic SPOMF solutions were stored at -20 °C for 12 h.
At shown in Figure 2b, when the ratio of SPOMFs to methanol (w/v) was changed from 1:9 to 1:15, the purity of the palmitoleic acid solution increased from 36.32% to 40.43%. This is due to the effective crystallization of the saturated fatty acid at high volume use of the methanol (Shahidi, 2016). However, as the SPOMFs to methanol ratio changed beyond 1:15, the proportion of palmitoleic acid in solution decreased, indicating solubilization of the saturated fatty acids due to the high solvent volume.
In terms of yield, no significant difference was found between SPOMFs to methanol ratios of 1:12 and 1:15. Considering both purity and yield of palmitoleic acid, an SPOMFs to methanol ratio of 1:15 (w/v) gave the best result. Hence, an SPOMF to methanol ratio of 1:15 (w/v) was used for further crystallization studies. Under these conditions, a solution with 40.43% palmitoleic acid was obtained, that translates to an 88.47% palmitoleic acid yield.