Enhancing milk quality assessment with watermelon (Citrullus lanatus) urease immobilized on VS2-chitosan nanocomposite beads using response surface methodology

Abstract

An eco-friendly hydrothermal method synthesized VS2 nanosheets. Several spectroscopic and microscopic approaches (TEM) were used to characterize the produced VS2 nanosheet microstructure. VS2, Chitosan, and nanocomposite were used to immobilize watermelon (Citrullus lanatus) urease. Optimization using the Response Surface Methodology and the Box-Behnken design yielded immobilization efficiencies of 65.23 %, 72.52 %, and 87.68 % for chitosan, VS2, and nanocomposite, respectively. The analysis of variance confirmed the mathematical model's validity, enabling additional research. AFM, SEM, FTIR, Fluorescence microscopy, and Cary Eclipse Fluorescence Spectrometer showed urease conjugation to the matrix. During and after immobilization, FTIR spectra showed a dynamic connectivity of chemical processes and bonding. The nanocomposite outperformed VS2 and chitosan in pH and temperature. Chitosan and VS2-immobilized urease were more thermally stable than soluble urease, but the nanocomposite-urease system was even more resilient. The nanocomposite retained 60 % of its residual activity after three months of storage. It retains 91.8 % of its initial activity after 12 reuse cycles. Nanocomposite-immobilized urease measured milk urea at 23.62 mg/dl. This result was compared favorably to the gold standard p-dimethylaminobenzaldehyde spectrophotometric result of 20 mg/dl. The linear range is 5 to 70 mg/dl, with a LOD of 1.07 (±0.05) mg/dl and SD of less than 5 %. The nanocomposite's ksel coefficient for interferents was exceptionally low (ksel < 0.07), indicating urea detection sensitivity. Watermelon urease is suitable for dairy sector applications due to its availability, immobilization on nanocomposite, and reuse. © 2024 Elsevier Ltd