triacylglycerol with oleic acid at the sn-2 position (Table \ref{tab:table_2}). When triacylglycerol containing oleic acid at the sn-2 position is acidolysed with oleic acid using a specific lipase of sn-1,3 will produce triolein \cite{Wang_2020}, which is not a sn-2 palmitate product. Table \ref{tab:table_3} shows that palm stearin has palmitic acid content at the sn-2 position ranging from 23.0\%-70.1\%. Thus, the palmitic acid content at the sn-2 position in palm stearin needs to be increased to produce a good substrate for HMFS synthesis \cite{Hasibuann_2021b}.

Technologies for improving the positioning of palmitic acid at the sn-2 position of palm stearin are solvent fractionation \cite{Ghosh_2016, Lee_2010, Wang_2019, Zou_2012a}, enzymatic interesterification \cite{Jimenez_2010a, Jimenez_2010b} or chemical interesterification \cite{Zou_2011, Zou_2012b}. Palm stearin is fractionated using acetone as a solvent to produce a tripalmitin-rich triacylglycerol (92.0\%) \cite{Lee_2010} and palmitic acid (88.57\%-92.30\%) \cite{Ghosh_2016, Wang_2019, Zou_2012a}. In general, the palm stearin solvent fractionation process condition is carried out at an acetone ratio of 5-9 and a fractionation temperature of 20$^{\circ}$C-40$^{\circ}$C for 3-24 hr.

Enzymatic interesterification between palm stearin (60.0\% palmitic acid and 23.0\% palmitic acid at the sn-2 position) with palmitic acid using Novozym 435 produces a product with 68.0\%-75.0\% palmitic acid at the sn-2 position \cite{Jimenez_2010a, Jimenez_2010b}. Meanwhile, chemical interesterification of palm stearin (41.7\% palmitic acid at the sn-2 position) resulted in a product with 58.0\% palmitic acid at the sn-2 position \cite{Zou_2011}.

\begin{table}[h]
\centering
\caption{Triacylglycerols composition of palm oil fractions}
\label{tab:table_2}
\begin{tabular}{lcccccc}
Triacylglycerols (\%) & Palm oil* & Palm olein* & Palm stearin* & Soft palm stearin** & Hard palm stearin** & Palm kernel oil* \\
CCLa &  &  &  &  &  & 6.8 \\
CLaLa &  &  &  &  &  & 9.9 \\
LaLaLa &  &  &  &  &  & 21.2 \\
LaLaM &  &  &  &  &  & 17.0 \\
LaLaO &  &  &  &  &  & 5.3 \\
LaMM &  &  &  &  &  & 8.8 \\
PLL &  &  & 1.0 & ND &  &  \\
MMM & 0.4 & 0.6 & 0.2 & ND & ND &  \\
LaLaP &  &  &  &  &  & 1.2 \\
LaMO &  &  &  &  &  & 4.6 \\
MPL & 2.4 & 3.7 & 1.0 & 0.1 & ND &  \\
LaMP &  &  &  &  &  & 4.6 \\
LaOO &  &  &  &  &  & 3.8 \\
LaPO &  &  &  &  &  & 4.3 \\
LaPP+MMO &  &  &  &  &  &  \\
OOL & 0.7 & 0.8 & 0.1 & 0.8 & ND &  \\
MMP & 1.8 & 2.6 & 0.8 & ND & ND & 0.7 \\
MOO &  &  &  &  &  & 2.0 \\
POL & 10.1 & 15.8 & 5.3 & 6.9 & 0.9 &  \\
PPL & 9.8 & 11.2 & 7.8 & 8.1 & 3.8 & 0.6 \\
MPP & 0.6 & ND & 2.3 & ND & ND &  \\
OOO & 4.1 & 5.6 & 1.8 & 4.1 & 4.5 & 1.4 \\
POO & 24.2 & 36.3 & 12.0 & 18.0 & 3.0 & 1.9 \\
PPO & 31.1 & 17.1 & 29.8 & 32.0 & 26.4 & 1.1 \\
PPP & 5.9 & 0.1 & 29.2 & 20.6 & 51.0 & 0.1 \\
SOO & 2.3 & 3.6 & 0.8 & ND & ND & 0.4 \\
PSO & 5.1 & 2.5 & 3.8 & 4.9 & 2.9 & 0.4 \\
PPS & 0.9 & ND & 5.2 & 3.5 & 7.4 &  \\
SSO & 0.5 & ND & ND & ND & ND &  \\
\end{tabular}

Note: ND - not detected; L - lauric acid; M - myristic acid; O - oleic acid; P - palmitic acid; S - stearic acid. Source: *Tan and Man (2002); **Ibrahim et al. (2006).
\end{table}