Integrated SERS and Chemometric Characterization of Ultrasound-Induced Quality Changes in Stevia-Sweetened Aguaymanto (Physalis peruviana L.) Nectar.

This study evaluated the molecular, physicochemical, antioxidant, color, and colloidal characteristics of stevia-sweetened aguaymanto (Physalis peruviana L.) nectar under 10 processing-formulation conditions combining ultrasound power (0-600 W), treatment time (0-15 min), and stevia concentration (0%-0.4%). Surface-enhanced Raman spectroscopy (SERS) coupled with principal component analysis (PCA) was integrated with conventional physicochemical, antioxidant, CIELAB color, and particle-characterization analyses. The citrate-reduced AgNP substrate exhibited a surface-plasmon-resonance maximum at approximately 408 nm, a Z-average diameter of 42.6 ± 6.3 nm, and a zeta potential of -37.8 ± 3.6 mV. Significant differences were observed among treatment combinations (p < 0.05), with T9 (600 W, 15 min, 0.4% stevia) exhibiting the most favorable overall instrumental profile. Particle size decreased from 980 nm in the untreated control to 270 nm in T9, whereas the absolute zeta potential increased from -18.2 to -37.8 mV and the PDI decreased from 0.49 to 0.21. T9 also showed the highest antioxidant, phenolic, flavonoid, and DCPIP-reactive vitamin C responses. SERS revealed treatment-dependent changes in characteristic bands at approximately 495, 1007, 1388, and 1613 cm-1, whereas PCA differentiated the treatment combinations according to their integrated molecular and biochemical profiles. Because ultrasound power, treatment duration, and stevia concentration were varied concurrently, the observed responses cannot be attributed independently to individual factors; therefore, T9 is considered the best performing combined condition rather than a statistically optimized formulation. Overall, integrating SERS and chemometrics with conventional quality measurements provides a promising analytical framework for evaluating processing-induced changes in functional fruit beverages. Further factorial optimization, chromatographic validation, microbial and storage assessment, and sensory evaluation are required before industrial application.