Accelerated stability study of Orthosiphon stamineus standardised ethanolic extract and its solid dispersion

Abstract

The objective of the present study is to develop accelerated stability of Orthosiphon stamineus standardised ethanolic extract (SEE) and its solid dispersion (ESD). The stability study of SEE and ESD has been performed using high-performance liquid chromatography (HPLC) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) analyses. The spectroscopic datasets of ESD were applied to the principal component analysis (PCA) to extract the maximum information of the ATR-FTIR spectra. SEE and ESD were stored at three different temperatures with two different humidity conditions (30 °C/75% RH, 40 °C/75% RH and 60 °C/85% RH) for six months. Overall, the degradation of marker compounds; rosmarinic acid (RA), 3'-hydroxy-5, 6, 7, 4’-tetramethoxyflavone (TMF), sinensetin (SIN) and eupatorin (EUP) at high temperature (60 °C/85% RH) was higher compared to low temperature (30 °C/75% RH) for both samples. Moreover, the degradation of RA, TMF, SIN and EUP in ESD was slower compared to SEE. The deterioration of marker compounds for both samples followed the first-order reaction kinetics. The shelf life of SEE and ESD is based on the estimated shelf life RA, TMF, SIN, and EUP present in the samples. The shelf life of RA, TMF, SIN, and EUP in ESD were significantly enhanced (p < 0.001) compared to the same markers in SEE with EUP was showing the highest shelf life (15 months), while RA showed the lowest shelf life (7 months) when stored at the temperature below 30 °C. The shelf life of all marker compounds in SEE was less than two months when stored at the same temperature (below 30 °C). Based on ATR-FTIR fingerprinting datasets analysed with PCA, ESD kept at 30 °C/75% RH were still preserved of its chemical properties, which indicates that low temperature is better to keep the formulation.