Solubility Study of Flexirubin Pigment Isolated from Chryseobacterium artocarpi CECT 8497 in Bio-Based Solvents

Abstract

Flexirubin is a natural pigment having yellowish-orange color and pharmacological properties. However, its solubility is limited to a few organic and inorganic solvents such as acetone, sodium carbonate, and sodium hydroxide. Therefore, further research works to improve the solubility of flexirubin in solvents are highly required to enhance its applications and properties. In this study, bio-based solvents which are D-limonene, ethyl acetate, ethanol, propanol, butanol were applied in the solubility study of flexirubin pigment and were compared with acetone as the positive control. These solvents were chosen due to their non-toxic and biodegradable properties. The crude flexirubin pigment was obtained from the cultivation of Chryseobacterium artocarpi CECT 8497 and extracted using acetone solvent. It was observed that the production of flexirubin pigment was 0.095 mg/L. The presence of flexirubin pigment was confirmed using attenuated total reflectance - Fourier transform infrared (ATR-FTIR) spectrophotometer and ultraviolet-visible (UV-Vis) spectrophotometer. Meanwhile, the appearance color of flexirubin was assessed using ColorFlex colorimeter. It was demonstrated that the polarity of a solvent affects the solvent efficiency to solubilize the flexirubin pigment. Hence, it is vital to understand the solvent properties, especially the solvent polarity, in order to explain the solute-solvent interaction and solvatochromism phenomenon. The molar absorptivity coefficient obtained from UV-Vis absorption was calculated using Beer-Lambert law. The results demonstrated that the molar absorptivity coefficient of flexirubin increased from acetone, ethyl acetate, propanol, ethanol, D-limonene, and butanol with a range of 19 to 84 L mol-1 cm-1. The hydrophobic structure of crude flexirubin pigment has caused it to deliver better solubility in non-polar solvents, D-limonene, and butanol. Hence, both solvents gave slightly similar absorption with less polar acetone. In conclusion, this study confirmed the feasibility of applying bio-based solvents as alternative solvents to expand the solubility potential of flexirubin pigment. This finding is expected to provide its usefulness as the potential bio-based solvent, especially in the pharmaceutical and food industries.