Valorization of Teak Leaf Agricultural Waste: Impact of Drying Technique and Production Scale on Extract Quality

This study investigates how drying technique and production scale govern the quality, structure, and functionality of teak leaf extracts derived from an abundant agricultural byproduct. Freeze-drying (FD) and spray-drying (SD) were applied at laboratory and pilot scales, and the resulting extracts were evaluated for physicochemical properties, bioactive composition, antioxidant activity, powder flowability, and thermal behavior. Across both leaf maturities, FD preserved higher total phenolic and flavonoid contents and yielded extracts with higher antioxidant activity (DPPH IC₅₀: 20-25 μg/mL) than SD-derived extracts (DPPH IC₅₀: 30-43 μg/mL), while all samples exhibited strong radical-scavenging capacity overall (DPPH IC₅₀: 19.93-42.61 μg/mL), underscoring the high intrinsic antioxidant potential of teak leaf extracts. Thermal analysis revealed that FD extracts formed more crystalline and energetically stable matrices, whereas SD produced predominantly amorphous structures with improved thermal dryness. At the laboratory scale, SD powders exhibited low moisture content, good flowability, and uniform spherical morphology, while FD powders showed porous, irregular structures associated with reduced flow. Importantly, pilot-scale processing altered both thermal stability and phenolic retention, particularly in young leaf extracts, indicating that laboratory-scale drying behavior cannot be directly extrapolated to larger-scale production. These results demonstrate that drying technique and production scale jointly influence the structure-property relationships of teak leaf extracts. The findings support tailored use of FD and SD extracts according to formulation requirements and highlight the potential of teak leaves as a sustainable source of natural antioxidants and colorants for food, cosmetic, and pharmaceutical applications.