Research Articles

Spent coffee grounds (SCG) are an abundant lignocellulosic biomass rich in galactomannan and cellulose, rendering them a promising feedstock for biorefinery, especially for the production of manno-oligosaccharides (MOS) as high-value prebiotics. This study investigated the role of α-galactosidase (α-G) in the enzymatic hydrolysis of ammonia-pretreated SCG, with particular emphasis on MOS production and cellulose hydrolysis. Enzymatic hydrolysis was conducted at 50 °C and pH 5.0, and the resulting sugars and MOS were quantified by HPLC. Supplementation with α-G effectively removed α-1,6-linked galactose side groups from galactomannan and increased MOS yield. Notably, the addition of α-G enabled a 50% reduction in mannanase dosage without compromising MOS production, indicating its potential to improve galactomannan conversion efficiency. However, α-G treatment altered the properties of the resulting MOS and was associated with stronger inhibition in MOS-containing cellulase systems. Under the tested conditions, α-G supplementation in MOS-containing systems was associated with additional numerical reductions in glucose yield of 15.8% for CBHI and 8.1% for EGII, whereas little numerical change was observed in the βG system. These results reveal a trade-off associated with α-G supplementation: although it promotes MOS generation, stronger inhibition was observed in MOS-containing cellulase systems, which may impair downstream cellulose hydrolysis.

Plant-derived materials offer sustainable platforms for functional nanomaterial development; however, Leptadenia arborea remains poorly explored for silver nanoparticle (AgNP) synthesis, and quantitative approaches linking phytochemistry, antimicrobial efficacy, and cellular damage are limited. This study investigated L. arborea leaf extract as a reducing and stabilizing system for AgNP synthesis. HPLC identified chlorogenic acid (53.8 µg mL⁻¹) and gallic acid (53.3 µg mL⁻¹) as major phytochemicals. Replicated optimization experiments identified 1:50 extract dilution, 5 mM AgNO₃, 70 °C, and 2 mL extract as optimal conditions, producing a surface plasmon resonance peak at 435 nm. TEM revealed predominantly spherical AgNPs (12 to 24 nm), while XRD showed (111), (200), (220), and (311) reflections characteristic of crystalline face-centered cubic silver. AgNPs produced inhibition zones of 15 ± 0.7 mm against Escherichia coli and 30 ± 1.0 mm against Candida albicans, with an MIC of 0.117 µg mL⁻¹ against E. coli. As a key novelty, AEF enables normalized comparison with reference antimicrobials, while NBIP converts SEM-observed cellular damage into a quantitative index. This framework extends conventional inhibition-based assessment by integrating antimicrobial potency with cellular damage and provides a transferable approach for evaluating plant-derived antimicrobial nanomaterials.