Antioxidant activity and metabolite changes in Centella asiatica with different drying methods using FTIR- and quantitative HPLC-based metabolomics

Centella asiatica, known as Indian or Asiatic pennywort, is consumed raw as salad or used as a brain tonic, treatment of Alzheimer’s disease, and memory improvement. Differences in the drying method will lead to different levels of phytochemical profile and biological activity. Therefore, the present work aimed to investigate the Fourier transforms infrared (FTIR) spectra fingerprint profiles, HPLC analysis of four bioactive compounds, and antioxidant activity of C. asiatica samples exposed to various drying methods, including air-, oven-, and sun-drying. Results showed that all samples had identical FTIR spectra patterns, but there were differences in the absorbance intensities at 1692 and 1634 cm-1, showing the effect of drying methods on the content of extracts’ bioactive compounds. These differences were analysed by chemometrics namely principal components analysis (PCA), and groupings were shown for the three samples. Based on the IC50 values, oven-drying (OD) had the highest antioxidant activity, followed by sun-drying (SD) and air-drying (AD), with IC50 values of 52.25, 94.18, and 99.29 μg/mL, respectively. HPLC analysis showed that OD had a higher percentage for madecassoside and asiaticoside with values of 0.86 and 0.96%, respectively, compared to SD and AD. Meanwhile, AD had the highest content of madecassic and asiatic acids, with values of 0.50 and 0.48%. The absorbance and antioxidant activity data for the three C. asiatica extracts were analysed for the correlation using an orthogonal partial least square. Results showed that at 1006 - 989 cm-1, it positively correlated with antioxidant activity, and could be identified as the C–O functional group of alcohol and phenol.