## 3 Results
### MEL Production  
To develop a suitable cultivation process for MEL production using acid oil, batch fermentation was performed using _P. antarctica_. Batch experiments with different initial  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Properties** & **AOCS Method of Analysis** & **Acid Oil** \\ \hline Acid value (mg KOH g\({}^{-1}\)) & Te-la-64 & 114.7 \(\pm\) 0.5 \\ Saponification value (mg KOH g\({}^{-1}\)) & Tl-la-64 & 119.8 \(\pm\) 0.6 \\ Iodine value (mg lag\({}^{-1}\)) & Tg-la-64 & 91.1 \(\pm\) 0.4 \\ Peroxide value & Cd 8b-90 & 7.09 \(\pm\) 0.23 \\ Anisidine value & Cd 18-90 & 15.69 \(\pm\) 0.22 \\ Viscosity (cP) at 28 \({}^{\circ}\)C & Ja-10-87 & 45.2 \(\pm\) 0.4 \\ Specific gravity (28 \({}^{\circ}\)C) (g cm\({}^{-3}\)) & & 0.93 \(\pm\) 0.07 \\ Color (Gardner scale) & Cc 13e-92 & 14 \\ Fatty acid composition (wt\%) & & 8.1 \\ C8 & & 14.8 \\ C10 & & 0.4 \\ C12 & & 0.2 \\ C14 & Ce-1-62 & 1.5 \\ Polarite C16:0 & & 3.1 \\ Oleic C18:1 & & 48.22 \\ Linoleic C18:2 & & 19.5 \\ Others & & 2.5 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Physicochemical properties of acid oil.  
substrate concentrations (80, 120, 160, 200, 240 g L\({}^{-1}\)) were implemented on shake flask mode for the production of MEL. The cultivation data were as shown in Figure 2.  
It should be noted that the biomass and MEL titer were increased with an increase in the initial substrate concentration. After 7 days of incubation, the maximum biomass and MEL titer were observed with 160 and 200 g L\({}^{-1}\) of initial acid oil concentration. As the results suggested, the acid oil was utilized by microbes for both purposes: specifically, both for cell growth as well as for MEL synthesis. However, the biomass and MEL titer were not affected by further increases in the initial acid oil concentration above 200 g L\({}^{-1}\). [PERSON] et al. [20] had also reported a similar trend for MEL production using soybean oil. Thus, the present study elucidated efficient cell growth and MEL production with acid oil with a maximum titer of 3.89 g L\({}^{-1}\). Here, the major fatty acid components of acid oil were C8, C10, C18:1, and C18:2, which had beneficial effects on microbial growth during the synthesis of MEL biosurfactants. According to the literature, all vegetable oils, except for coconut oil, produce significant amounts of MEL by fermentation, and there is no compelling difference in MEL productivity between safflower, corn, olive, and soybean oils [17]. As this observation suggests, the growth of microbes and titer of MEL are satisfactory in the case of acid oil, and so the main component fatty acids of acid oil are different from those of coconut oil, and hence, acid oil is a suitable carbon source for MEL production.  
The literature suggests the use of different carbon sources for the production of MEL, such as honey with 5.61 g L\({}^{-1}\) titer [13], olive oil with 37 g L\({}^{-1}\) titer [21], safflower oil with 19 g L\({}^{-1}\) titer [22], and castor oil with 22 g L\({}^{-1}\) titer [23]. [PERSON] et al. [24] reported MEL production from cassava wastewater with 1.26 g L\({}^{-1}\) titer, supporting the present study on the use of industrial waste as a carbon source for biosurfactant production. [PERSON] et al. [25] reported that 12.7 g L\({}^{-1}\) MEL-B produced from sugarcane containing sucrose in a high concentration was considered the most economical resource for a microbial process. However, the use of vegetable oil and sugar as carbon substrates detracts from the sustainability of MEL production due to the prominence of conserving dedicated crops for human nutritional consumption. Several sources of residual vegetable oils and/or sugars present in byproducts are inadequate for human or animal consumption.