A sustainable methodology employing the extract of red dragon fruit peel as a fluorescence probe for detection of indigo carmine (E132) in food samples: evaluation of the method's greenness, whiteness, and blueness

Abstract

Indigo carmine dye is one of the most widely used dyes in various fields. In this study, the ethanolic extract of red dragon fruit peel (Ex-RDFP) was employed as a green fluorescence probe for measuring the synthetic dye indigo carmine. At a fluorescence excitation of 290.5 nm, the Ex-RDFP exhibits a fluorescence emission band at 341.5 nm. Meanwhile, the indigo carmine dye possesses an absorption spectrum at a maximum peak of 290 nm. Consequently, the fluorescence intensity of the Ex-RDFP was reduced upon the addition of indigo carmine solution due to the inner filter effect mechanism. This quenching in the fluorescence intensity of Ex-RDFP was substantially associated with the indigo carmine concentration at a linear scale of 1.0–7.0 μg mL⁻¹ (r² = 0.9993). Furthermore, the limit of detection and the limit of quantitation of the method were found to be 0.209 μg mL⁻¹ and 0.635 μg mL⁻¹, respectively. The optimal analytical conditions, such as solvent used for dilution, pH, reaction time, volume of the reagent, and temperature, were examined and carefully studied. In addition, the proposed method was successfully applied to detect indigo carmine dye in various natural syrup samples, including lemon syrup, apple syrup, cantaloupe syrup, pineapple syrup, and guava syrup, with acceptable recovery values. The method's beneficial sustainability footprint was found by using an extensive greenness analysis that incorporated the modified National Environmental Methods Index (NEMI), the complex Green Analytical Procedure Index (GAPI), and the Analytical Greenness Calculator (AGREE) prep algorithms. In addition, “whiteness” and “blueness” were also assessed with the newly released (Red Green Blue 12) RGB12 and Blue Applicability Grade Index (BAGI) computational methods, emphasizing the benefit of the proposed method in terms of analytical efficiency, sustainability, and economy. The suggested technique is the answer to the worldwide popularity of ecologically conscious solutions by providing a green-and-white substitute for traditional techniques and advancing towards creating more sustainable quality control procedures in the future.