The mesocarp is the primary oil storage tissue in oil-bearing fruits such as oil palm, olive, and avocado. Among these, the palm fruit mesocarp represents the leading global source of edible oil, accumulating high levels of triacylglycerols and a diverse spectrum of bioactive components. Mechanical pressing is the primary method for extracting palm oil and generating mesocarp fiber as a lignocellulosic residue. However, due to extraction limitations, 5–11 % of residual oil remains entrapped within the fibrous matrix. Oil palm mesocarp fiber, a lignocellulosic by-product of the crude palm oil extraction process, contains residual oil within its fibrous matrix. While mesocarp fiber from oil-bearing fruits has gained attention as a carbon source in solid-state fermentation, the role of residual oil in microbial adaptation and enzyme secretion remains unclear. This study examines the effect of residual oil on enzyme production by comparing oily mesocarp fiber (OMF) and deoiled mesocarp fiber (DeMF) as solid matrices for solid-state fermentation using Trichoderma reesei RUT-C30. Lipase and (hemi)cellulolytic enzyme activities were assessed under varying moisture content and pH conditions alongside fungal biomass morphology. OMF promoted higher lipase production, reaching 24.79 IU per gram dry solid (GDS) at a 1:3.5 solid-to-liquid ratio (SLR). In comparison, DeMF enhanced (hemi)cellulolytic enzyme activity, with CMCase peaking at a 1:1.5 SLR, while xylanase and β-glucosidase activity peaking at pH 7.5 under buffered conditions. Furthermore, residual oil exhibited an antifungal effect at pH 7.5, reducing fungal biomass and extracellular enzyme yields. These findings provide valuable insights into the role of residual oil in solid-state fermentation, highlighting its dual function as a lipase inducer and a potential inhibitor under certain conditions.   Keywords: Oil palm mesocarp fiber, Residual oil, Lipase, (Hemi) cellulolytic enzymes, Solid-state fermentation

Fig 1: Schematic diagram of experimental design

Fig 2: Macroscopic visualization of fungal biomass across different SLR and pH levels. A1-3: Fungal biomass variation across different SLRs using DeMF hydrated with distilled water. B1-3: Fungal biomass variation across different SLRs using OMF hydrated with distilled water. C1-3: Fungal biomass variation across different initial pH levels using DeMF hydrated with McIlvaine buffer. D1-3: Fungal biomass variation across different initial pH levels using OMF hydrated with McIlvaine buffer.

Fig 3. Activities of (hemi)cellulolytic enzymes across varying SLRs and pH levels using DeMF and OMF as solid matrices. A: CMCase activity at different SLRs using distilled water as a hydration medium. B: CMCase activity at different pH levels using McIlvaine buffer as a hydration medium. C: Xylanase activity at different SLRs using distilled water as a hydration medium. D: Xylanase activity at different pH levels using McIlvaine buffer as a hydration medium. E: β-Glucosidase activity at different SLRs using distilled water as a hydration medium. F: β-Glucosidase activity at different pH levels using McIlvaine buffer as a hydration medium   Source: Ali Abdulkareem Al-Qassaba, Robiah Yunus, Mohamad Amran Mohd Salleh, Mohd Noriznan Mokhtara, Mohd Rafein Zakaria. Influence of residual palm oil in pressed mesocarp fiber on extracellular enzyme secretion and morphological characteristics of fungal biomass during solid-state fermentation. Biomass and Bioenergy 205: 108548   Link: https://doi.org/

Date of Input: 27/02/2026 | Updated: 27/02/2026 | ainzubaidah