Pinecones valorization: process intensification and eco-friendly extraction of antioxidant compounds

Considering the circular economy, this research addresses concerns about Tunisian pinecone valorization within the cosmetic industry. This study aims to optimize the extraction of antioxidant compounds from P. halepensis petals through maceration in water by analyzing rheological behavior and decantation phenomena to intensify the extraction process. Granulometry of samples raw, Cl1, Cl2 and Cl3, with a mean diameter in volume-weighted (D [4,3]) values of 1200, 1400, 1100 and 120 mu m respectively, and concentrations of suspensions from 0 to 170 ghm/Lsus were analyzed on rheological behavior, settling kinetics, extraction yields, and antioxidant activity. The result showed that the viscosity increases with concentration and granulometry but decreases with increasing shear rate (ranging between 0.5 and 500 s-1), indicating shear-thinning behavior. Increasing concentration from 0 to 170 ghm/Lsus also raised the consistency factor (k), a measure of the fluid's resistance to flow or its internal friction (higher values indicate a more viscous or thicker suspension), from 0.003 to 8.525 Pa/sn and decreased the power-law index (n), quantifying the degree of shear-thinning (a lower n indicates a more intense shear-thinning behavior), from 1 to 0.11. Quemada equation, commonly used to describe the viscosity of suspensions, effectively modeled the behavior of dilute and semi-dilute regimes and identified two critical concentrations: CCrit1<10 ghm/Lsus (dilute) and CCrit2 > 34 ghm/Lsus (concentrated). The apparent viscosity suspension depends on particle concentration and physical properties (granulometry, morphology, density), as well as decantation kinetics impacted by particle-particle interactions. Suspension with coarser granulometry (Cl1) exhibited the highest viscosity (100 Pa.s) at = 1 s-1 and settling velocity (84.3 mm/h), necessitating a minimal pumping flow rate to balance superficial and settling velocities to select impeller and maintain suspension homogeneity. High value of sediment porosity (0.84) suggests a sediment water retention capacity of 80%, indicating the need for sediment filtration after extraction. Extraction yields are correlated with granulometry ranging from 50 (Cl1) to 215 (Cl3) mgES/gdm and plateaued after 5 h. Statistical analysis confirms the good fit of the order 1 model for all experimental data. Cl3 exhibited interesting antioxidant activity with IC50 of 8.89 mu g/mL against DPPH. Intensification (concentration, granulometry and time) of maceration (water as green solvent) by optimizing the extraction of bioactive compounds, stands as a new way to valorize forestry byproduct (petal pinecones).