Exploration on the effect of phospholipids on free lipase-mediated biodiesel production

• Free lipase NS81006 was used for biodiesel production from oil with phospholipids.
• More than 5% phospholipids had negative influence on NS81006-mediated biodiesel production.
• Either phospholipids or methanol alone did not have adverse effect on free lipase.
• It showed that the coexistence of phospholipids and methanol resulted in inhibitory effect on lipase's catalytic performance during methanolysis for biodiesel production.

Free lipase-mediated biodiesel production has been drawing great attention for its lower cost and faster reaction rate compared to immobilized lipase. Since biodiesel derived from vegetable oils may cause competition with food supply, the exploration of crude vegetable oils as well as microbial oils as the feedstock has aroused great interest worldwide. It is reported that those crude oils usually contain some amount of phospholipids, typically with content varying from 2% to 10%. Our previous study showed that phospholipids content within 2% in the oil feedstock was even beneficial to free lipase NS81006-catalyzed biodiesel production. However, there was no research about the influence of much higher phospholipids content on free lipase-mediated methanolysis for biodiesel production. In this paper, the effect of varied content of phospholipids on free lipase NS81006-mediated biodiesel production as well as the related mechanism was investigated for the first time. It was found that both the catalytic performance and reuse stability of free lipase NS81006 were inhibited with more than 5% phospholipids contained in the oil feedstock. Exploration on the related influence mechanism revealed that either phospholipids or methanol (with appropriate addition strategy) alone did not have negative effect on the catalytic performance of the lipase, while the coexistence of phospholipids and methanol in the system led to significant inhibitory effect on the lipase. The further exploration indicated that with the increase of phospholipids content, the amount of solubilized methanol gradually increased in the micelle, which may subsequently result in negative effect on the enzyme's catalytic performance.

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