Sidaguri (Sida rhombifolia) is one of the herbal components used in traditional medicine. The application of chemometrics in the standardization of herbal medicine is common. The objective of this study was to classify Sidaguri from different regions based on FTIR spectra with chemometrics of principal component analysis (PCA) and to correlate the antioxidant activities with FTIR spectra using the multivariate calibration of partial least square regression (PLSR). The extraction of Sidaguri powder was performed using ultrasound-assisted extraction (UAE) at optimum conditions. The obtained extracts were subjected to antiradical scavenging activities using DPPH (2,2’-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid) radicals. The PCA result shows that Sidaguri from different regions could be separated using 14 wavenumbers of FTIR spectra based on the PCA's loading plot. PLSR regression using the second derivative FTIR spectra at wavenumbers of 3662–659 cm–1 could predict radical scavenging activities (RSA) of Sidaguri with R2 values of 0.9636 and 0.9024 for calibration and validation models, with RMSEC and RMSEP values of 1.45% and 2.65%, respectively. It can be concluded that FTIR spectra treated by PCA were reliable for classifying Sidaguri from different regions. At the same time, PLSR was accurate and precise enough to predict the RSA of Sidaguri.

Sidaguri (Sida rhombifolia) is widely distributed in tropical and subtropical regions and has been reported to possess many bioactive compounds that are beneficial for human health, including polyphenolics having antioxidant activities. The objective of this study was (1) to optimize ultrasound-assisted extraction (UAE) of Sidaguri and (2) to evaluate antioxidant activities of extracts resulting from the optimized condition using radical scavenging assay of 2,2′-diphenil-1-picrylhydrazyl (DPPH) and 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid. The optimum UAE conditions obtained were solvent to solid ratio of 26:1, temperature of extraction of 45.45°C, methanol concentration of 42%, power of sonication of 86%, and time of extraction of 5 minutes. Sidaguri obtained from locations of Kretek and Ngemplak had the highest radical scavenging activity accounting for 83.69% ± 0.30% and 82.95% ± 0.49%, respectively.