Fluorescence quantum yields and lifetimes of annatto aqueous solutions dependent on hydrogen potential: Applications in adulterated milk

This work reports the thermo-optical and photophysical properties of annatto extracted from the seeds of the tropical shrub Bixa Orellana L. Aqueous natural dyes were extracted using different amounts of NH4OH solution (4 M) and separated into two groups of annatto samples extracted using ambient temperature (G1Amb) and heated (98 °C, G2Heat) alkaline solutions. Thermal lens (TL) and time-resolved fluorescence lifetime (TRFL) techniques were applied to determine the fluorescence quantum yield (η) and lifetime (τ) for G1Amb and G2Heat colorant solutions with different hydrogen potentials (pHs) ranging from 5.4 to 11.5. Fluorescence spectra corroborate the η results for natural dye extracted at different pH values. Additionally, the annatto dyes were tested as possible colorimetric and/or fluorimetric pH-biosensor probes in adulterated milk at different pHs.