A study on the mechanism of subcritical water treatment to maximize extractable cellular lipids

• Subcritical water treatment of microbial biomass enhances extractable lipid.
• Neutral lipid extracted was increased by 2–4 times after SCW treatment.
• Size reduction is not required prior to extraction.
• Mechanism of lipid increase in SCW treatment of biomass was investigated.
• The use of toxic solvents for extraction could be avoided after pretreatment.

Lipids of microbial origin have gained much attention due to its wide applicability and high productivity. Widely studied microbial lipids are those coming from single cell oils such as microalgae, yeast and other fungi. Many researches have focused on enhancing lipid accumulation as well as biomass productivity with hope to utilize the accumulated lipids as an alternative source for biodiesel production. Unfortunately these biological lipids have often been under utilized due to inefficient extraction technologies. In addition, in order to maximize lipid extraction toxic solvents such as chloroform are often employed. In this study subcritical water (SCW) was employed for the treatment of samples from microbial origin to enhance their extractable intracellular lipids. Optimum temperature and time for SCW treatment of wet microbial cells such as activated sludge and yeast cells was found to be 448 K and 900 s, respectively. After SCW treatment, a 2–4 folds increase in the extractable neutral lipid was observed without the need of using toxic solvent such as chloroform and cyclohexane. An investigation on the possible mechanism on how SCW treatment was able to improve lipid extractability was also carried out in this study.