Liquid smoke characterisation and production from empty fruit bunches via consecutive pascalisation and microwave-assisted pyrolysis

Empty fruit bunches (EFBs) were pascalised at 200–400 MPa, then pyrolysed with microwave oven at 350 and 450 °C. Physical and thermal properties of EFBs were characterised. Yields, chemical compositions, and functional properties including total phenolic content, antioxidant capacity, acidity, antimicrobial activity, and colour of the liquid smoke were also evaluated. Results showed that pascalisation at 300 MPa produced the maximum surface area of 6.385 m² g⁻¹ and pore volume of 0.5511 cm³ g⁻¹, whilst pascalisation at 400 MPa caused pore collapse. Liquid smoke yield showed irregular trends: at 350 °C, 400 MPa achieved the highest yield of 21.2 ± 2.3% despite collapsed pores, whilst 200 MPa yielded the lowest at 5.2 ± 1.4%; at 450 °C, the trend reversed, with 200 MPa reaching the highest yield of 11.9 ± 1.7% whilst 400 MPa fell sharply to 5.4 ± 2.0% due to rapid heating rate. GC–MS analysis identified phenolic compounds and ketones, showing compositional shifts related to pore structure modifications. The irregular trend of most functional properties suggests that densified EFB structures concentrated phenolic compounds whilst more open structures produced dilute liquid smoke. These findings demonstrate that pascalisation modifies EFB structure and influences liquid smoke yields and composition through structural mechanisms.