Lipase-catalyzed synthesis and characterization of medium-long-medium (MLM) type structured triacylglycerols from peony seed oil

Structured triacylglycerols (STAGs) with medium-chain fatty acids (FAs) at sn-1,3 positions and long-chain FAs at the sn-2 position are known as medium-long-medium (MLM) type STAGs. They can not only provide energy immediately and control weight effectively, but may also provide essential or beneficial FAs to meet the human needs. In this study, MLM type STAGs were synthesized from lipase-catalyzed acidolysis of peony seed oil (PSO) with octanoic acid (OcA) and decanoic acid (DA) as medium-chain FAs in solvent-free systems. Optimal reaction conditions were 1:8 (PSO to OcA/DA), 40 °C and 24 h. The OcA content and DA content at sn-1,3 of two STAGs were 81.1% and 82.5%. The total essential FA (α-linolenic acid and linoleic acid) contents at sn-2 reached 61.5% and 57.2%, and long-chain unsaturated FA contents reached 93.3% and 87.4%. Infrared absorptions of two STAGs were weaker than those of PSO at 723 cm−1 [-(CH2)n-rocking] and 3011 cm−1 [ = CH (cis) stretching]. The end melting temperature and maximum weight loss temperature of STAG rich in DA were higher than those of STAG rich in OcA. This study is conducive to the deep processing of PSO and provides a new and promising substrate for MLM type STAG synthesis.