Presentation Information
[P02-180]Upcycling waste frying oil and its effect on sophorolipid productivity
○Ryu Ishizaki1, Michiaki Araki1, Glen Lelyn Quan1, Yoshihiko Hirata1 (1. Saraya Research Institute, Saraya Co., Ltd. (Japan))
Keywords:
biosurfactant,sophorolipid,fermentation,waste frying oil,upcycling
Waste frying oil (WFO) is produced in large amounts worldwide and is often discarded improperly, causing environmental burden. Sophorolipids (SLs) are biodegradable, low-toxicity glycolipid biosurfactants produced by Starmerella bombicola, but their broader use is limited by high production cost. Using WFO as a cheap hydrophobic substrate could reduce costs; however, WFO quality varies and degradation products may affect SL production. Understanding the impact of WFO is essential for optimizing the fermentation process. In this context, this study evaluated how oil deterioration indices—acid value (AV), peroxide value (PV), and carbonyl value (CV)—influence SL productivity. To this end, it was necessary to prepare oils with various degrees of deterioration. Therefore, fresh palm olein was artificially degraded by heating at 150°C, and was collected periodically to obtain oils with different deterioration levels.
Subsequently, one-liter jar fermentations were performed using dual lipophilic substrates (oleic acid and untreated palm olein/treated palm olein). Yeast growth (OD660), residual oil, hydrous SL concentration, and final SL titer were monitored.
During heating, PV rose early and then decreased, consistent with peroxides being unstable intermediates, whereas AV and CV increased with heating time. Fermentation results showed SL production was feasible for all degraded oils. Final SL titers were similar to those obtained with untreated palm olein (106.7–117.3 g/L), indicating that degradation did not substantially reduce final yield. In contrast, degradation affected cultivation time: oils with high CV (>100 μmol/g) required longer cultivation to reach comparable SL levels, extending culture duration from 6 to 9 days and lowering SL productivity (g/day). Early growth profiles were nearly identical across conditions, suggesting degradation mainly slowed oil utilization and SL synthesis rather than initial biomass formation.
Palm olein with a high AV contains a large amount of free fatty acids. However, since free fatty acids are substrates for SL production, this alone does not explain the extended cultivation period.
To further examine PV, old palm olein stored for several years was tested; it had high PV (43–53 meq/kg) but low AV and CV. These high-PV palm olein did not prolong cultivation and produced SL titers close to the control, supporting the conclusion that peroxides alone have limited impact.
Overall, CV was the most informative indicator for predicting slower SL production when using degraded oils, likely because aldehydes and ketones can stress cells and require detoxification before efficient secondary metabolite formation. Measuring CV in incoming WFO could help estimate fermentation duration and support industrial planning. The study supports WFO upcycling for SL production, while highlighting carbonyl compounds as the key factor controlling productivity.
Subsequently, one-liter jar fermentations were performed using dual lipophilic substrates (oleic acid and untreated palm olein/treated palm olein). Yeast growth (OD660), residual oil, hydrous SL concentration, and final SL titer were monitored.
During heating, PV rose early and then decreased, consistent with peroxides being unstable intermediates, whereas AV and CV increased with heating time. Fermentation results showed SL production was feasible for all degraded oils. Final SL titers were similar to those obtained with untreated palm olein (106.7–117.3 g/L), indicating that degradation did not substantially reduce final yield. In contrast, degradation affected cultivation time: oils with high CV (>100 μmol/g) required longer cultivation to reach comparable SL levels, extending culture duration from 6 to 9 days and lowering SL productivity (g/day). Early growth profiles were nearly identical across conditions, suggesting degradation mainly slowed oil utilization and SL synthesis rather than initial biomass formation.
Palm olein with a high AV contains a large amount of free fatty acids. However, since free fatty acids are substrates for SL production, this alone does not explain the extended cultivation period.
To further examine PV, old palm olein stored for several years was tested; it had high PV (43–53 meq/kg) but low AV and CV. These high-PV palm olein did not prolong cultivation and produced SL titers close to the control, supporting the conclusion that peroxides alone have limited impact.
Overall, CV was the most informative indicator for predicting slower SL production when using degraded oils, likely because aldehydes and ketones can stress cells and require detoxification before efficient secondary metabolite formation. Measuring CV in incoming WFO could help estimate fermentation duration and support industrial planning. The study supports WFO upcycling for SL production, while highlighting carbonyl compounds as the key factor controlling productivity.
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