Journal of Mathematical and Fundamental Sciences

Localized Green Fabrication of Hydroxyapatite/ZnO Nanocomposite: Toward A Sustainable Antibacterial Biomaterial

Fri, 31 Jul 2026 00:00:00 +0700

Using a plant-assisted sol–gel strategy, a hydroxyapatite–zinc oxide (HAp/ZnO) composite was produced from Padalarang calcite and lemon (Citrus limon L.) extract. The calcite supplied the calcium component, while constituents of the lemon extract promoted metal-ion complexation and helped control precursor stabilization. This environmentally friendly approach reduces the use of hazardous chemicals while facilitating the formation and stabilization of the composite precursor during the sol–gel process. The synthesized HAp/ZnO nanocomposite exhibited crystalline HAp and ZnO phases and the mean crystallite dimension calculated from the diffraction data was 45.52 nm. XRF analysis confirmed the elemental composition and Ca/P ratio, while FTIR spectroscopy identified the characteristic functional groups of HAp and ZnO. Further, SEM observations revealed the particle morphology of the nanocomposite. In disk-diffusion testing against Escherichia coli, the inhibition diameter increased from 5 mm at 5 mg/mL to 15 mm at 20 mg/mL. The antibacterial response was interpreted mainly in terms of ZnO-derived reactive oxygen species and the action of released Zn²⁺ ions. The findings of this study indicate that the synthesized HAp/ZnO nanocomposite is a promising candidate material for further investigation in the development of sustainable antibacterial biomaterials.

Engineering Coffee Cherry Pulp-derived Activated Carbon for Cellulase Immobilization and its Role in Regulating Non-Sterile Coffee Fermentation

Thu, 10 Sep 2026 00:00:00 +0700

During non-sterile coffee fermentation, microbial activity and substrate availability change as the mucilage is degraded. Activated carbon prepared from Arabica coffee cherry pulp by carbonization and ZnCl₂ activation was used as a support for cellulase immobilization. Cellulase produced by Cytobacillus sp. isolated from civet (Paradoxurus hermaphroditus) feces was immobilized by adsorption and used as part of the fermentation starter system. The immobilization efficiency was 80% and the immobilized cellulase had a specific activity of 613.22 U/mg. During fermentation, cellulase activity decreased from 2.45 U/mL at 0 h to 1.71 U/mL at 72 h, with approximately 70% of the initial activity remaining. At 48 h, the reducing sugar concentration was 10.7 mg/mL in the fermentation with immobilized cellulase, compared with 6.1 mg/mL in the control. The microbial growth rate was 0.132 h⁻¹ with immobilized cellulase and 0.084 h⁻¹ in the control. Pearson correlation coefficients were 0.93 between cellulase activity and reducing sugar concentration, 0.91 between reducing sugar concentration and microbial growth, and 0.88 between cellulase activity and microbial growth rate. Immobilized cellulase was associated with changes in sugar availability and microbial growth during non-sterile coffee fermentation.