Hibiscus sabdariffa Linn. (roselle) extract nanoemulsion for controlled-release consumption and its physicochemical properties

Abstract

Hibiscus sabdariffa Linn. (Roselle) is well-known worldwide as a medicinal plant, which recently attracted the attention of scientists for its therapeutic characteristics. However, delivering the maximal anti-diabetic bioactive ingredients through the stomach lining is challenging. This is due to poor solubility and low bioavailability of bioactive substances. Therefore, a water-in-oil nanoemulsion was chosen as a carrier for the anthocyanidin glycosides' control-release (cyanidin-3-sambubioside, delphinidin-3-sambubioside, and delphinidin-3-glucoside-rich roselle extract. In this work, the nanoemulsion containing the roselle extract was prepared using a low-energy phase inversion- and high-energy technique using an ultrahomogenizer. Screening for suitable compositions of components of the W/O nanoemulsion containing the roselle extract, done by the ratio of surfactants Tween 80 to PGPR (11.2:15.7% – 13.3:17.8% w/w), the composition of canola oil:water (10%:58.7% - 10% :60.8% w/w), the effects of xanthan gum (0.1% - 0.3%w/w), and the concentration of roselle extract (0.1% -2% w/w). This work's ultimate goal is to formulate nanoemulsion containing concentrated roselle extract with minimum average droplet size (< 150 nm). The best compositions of the w/o nanoemulsion containing the roselle extract were Tween80: PGPR (12.5%:16.5% w/w), canola oil to water (10%:60.6% w/w), xanthan gum (0.2% w/w), and roselle extract (0.2% w/w) with a hydrophilic-lipophilic balance of 7.3. The transmission electron micrograph of the optimized w/o nanoemulsion containing the roselle extract exhibited the smallest particle size (133.6 nm) with a polydispersity index of 0.165. The optimized w/o nanoemulsion was an initial pH 3.4 with a low conductivity of 0.5 µScm-1, affirmed it is a w/o system. The nanoemulsion remained stable without any phase separation under an accelerated stability study (centrifugal force and freeze-thaw cycles) and temperatures 4, 25, or 40°C for up to 71 days of storage. In vitro release study at different pHs showed 0.17% (w/w) of the bioactive ingredients released at pH 6.8 (2 hours) compared to 0.12% (w/w) at pH 2.5 (2 hours) from the loaded 0.2% (w/w) drug amount at a maximal release of 3 hours. The release kinetics of w/o nanoemulsion containing the roselle extract showed linear relationships to all kinetic models for pH 6.8 and followed the first-order kinetic with the highest R² at 0.9986. Hence, the release of the w/o nanoemulsion containing the roselle extract followed the first-order kinetics at pH 6.8 under a simulated gut condition. Thus, the results conclude that the formulation exhibited possible application as a natural food supplement to treat diabetics.