Mediated electrochemical method for the determination of indigo carmine levels in food products

Indigo Carmine: Between Necessity and Concern

Dyes, such as indigo carmine, have become indispensable to modern life, being widely used in the food, textile, pharmaceutical, medicine, and cosmetic industry. Although indigo carmine is considered toxic and has many adverse effects, it is found in many foods, and the maximum permitted level is 500 mg/kg. Indigo carmine is one of the most used dyes in the textile industry, especially for dyeing denim, and it is also used in medicine due to its impressive applicability in diagnostic methods and surgical procedures, such as in gynecological and urological surgeries and microsurgery. It is reported that indigo carmine is toxic for humans and can cause various pathologies, such as hypertension, hypotension, skin irritations, or gastrointestinal disorders. In this review, we discuss the structure and properties of indigo carmine; its use in various industries and medicine; the adverse effects of its ingestion, injection, or skin contact; the effects on environmental pollution; and its toxicity testing. For this review, 147 studies were considered relevant. Most of the cited articles were those about environmental pollution with indigo carmine (51), uses of indigo carmine in medicine (45), and indigo carmine as a food additive (17).

Dual emission N-doped carbon dots as a ratiometric fluorescent and colorimetric dual-signal probe for indigo carmine detection

Novel dual-emission fluorescent nitrogen-doped carbon dots (N-CDs) were synthesized by a facile one-pot hydrothermal method using ascorbic acid and rhodamine B as precursors and melamine as nitrogen source. The obtained N-CDs exhibited dual-emitting peaks at 435 nm and 578 nm under the single excitation of 350 nm. The fluorescence at 578 nm was more effectively quenched by indigo carmine (IC) based on the internal filtration effect and aggregation-induced emission quenching. Meanwhile, the apparent color change of N-CDs from pink to blue-purple after adding various concentrations of IC could be clearly observed with the naked eye. Therefore, a ratiometric fluorescent and colorimetric dual-signal probe based on N-CDs was developed for IC detection with high selectivity and sensitivity. The addition of IC caused the ratiometric fluorescent value (F₄₃₅/F₅₇₈) to increase linearly within the range from 0 to100 µM with a detection limit (LOD) of 0.18 µM and the colorimetric signal presented a linear response in the range of 0-133 µM with a LOD of 57.4 nM. Furthermore, the IC in juice drink, candy, and water was successfully detected. Besides, the N-CDs were also designed as a ratiometric temperature probe, and the ratiometric fluorescence signal (F₄₃₅/F₅₇₈) was linearly and reversibly responsive to temperature in the range of 20-75 °C.

Indigo Carmine in a Food Dye: Spectroscopic Characterization and Determining Its Micro-Concentration through the Clock Reaction

Indigo carmine is a commonly used industrial blue dye. To determine its concentration in a commercially available food dye composed of a mixture of indigo carmine and D-glucose, this paper characterizes it through (ATR, KBr) FTIR micro-Raman as well as UV/Vis and clock: Briggs–Rauscher (BR) oscillatory reaction methods. The indigo carmine was detected in the bulk food dye only by applying micro-Raman spectroscopy, indicating a low percentage of the indigo carmine present. This research provides an improvement in the deviations from the experimental Raman spectrum as calculated by the B97D/cc-pVTZ level of theory one, resulting in a better geometrical optimization of the indigo carmine molecule compared to data within the literature. The analytical curves used to determine indigo carmine concentrations (and quantities) in an aqueous solution of food dye were applied by means of UV/Vis and BR methods. BR yielded significantly better analytical parameters: 100 times lower LOD and LOQ compared to commonly used UV/Vis. The remarkable sensitivity of the BR reaction towards indigo carmine suggests that not only does indigo carmine react in an oscillatory reaction but also its decomposition products, meaning that the multiple oxidation reactions have an important role in the BR’s indigo carmine mechanism. The novelty of this research is the investigation of indigo carmine using a clock BR reaction, opening new possibilities to determine indigo carmine in other complex samples (pharmaceutical, food, etc.).

Voltammetric Sensor Based on SeO2 Nanoparticles and Surfactants for Indigo Carmine Determination

Indigo carmine is a widely used colorant in the food and pharmaceutical industry a high concentration of which can lead to a wide range of negative effects on human health. Therefore, colorant contents have to be strictly controlled. SeO₂-nanoparticle-modified glassy carbon electrodes (GCE) have been developed as a voltammetric sensor for indigo carmine. Various types and concentrations of surfactants have been used as reagents for the stabilization of SeO₂ nanoparticle dispersions and as electrode surface co-modifiers. An amount of 1.0 mM cationic cetylpyridinium bromide (CPB) provides the best response of the indigo carmine on the modified electrode. The electrodes were characterized by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS). SeO₂ nanoparticle–CPB-modified electrodes show 4.2-fold higher electroactive area vs. GCE as well as a dramatic 5043-fold decrease in the electron transfer resistance indicating effectivity of the modifier developed. The surface-controlled electrooxidation of indigo carmine proceeds irreversibly (α_a = 0.46) with the participation of two electrons and two protons. A linear dynamic range of 0.025–1.0 and 1.0–10 µM of indigo carmine were obtained with the detection and quantification limits of 4.3 and 14.3 nM, respectively. The practical applicability of the sensor was successfully shown on the pharmaceutical dosage forms.

Efficient Bioproduction of Indigo and Indirubin by Optimizing a Novel Terpenoid Cyclase XiaI in Escherichia coli

Blue indigo dye, an important natural colorant, is used for textiles and food additives worldwide, while another red isomer, indirubin, is the major active ingredient of a traditional Chinese medicine named "Danggui Longhui Wan" for treating various diseases including granulocytic leukemia, cancer, and Alzheimer's disease. In this work, we constructed a new and highly efficient indigoid production system by optimizing a novel terpenoid cyclase, XiaI, from the xiamycin biosynthetic pathway. Through introducing the flavin-reducing enzyme Fre, tryptophan-lysing and -importing enzymes TnaA and TnaB, and H₂O₂-degrading enzyme KatE and optimizing the fermentation parameters including temperature, the concentration of isopropyl-β-d-thiogalactopyranoside, and feeding of the l-tryptophan precursor, the final maximum productivity of indigoids by the recombinant strain Escherichia coli BL21(DE3) (XiaI-Fre-TnaAB-KatE) was apparently improved to 101.9 mg/L, an approximately 60-fold improvement to that of the starting strain E. coli BL21(DE3) (XiaI) (1.7 mg/L). In addition, when the fermentation system was enlarged to 1 L in the flask (feeding with 5 mM tryptophan and 10 mM 2-hydroxyindole), the indigoid productivity further increased to 276.7 mg/L at 48 h, including an indigo productivity of 26.0 mg/L and an indirubin productivity of 250.7 mg/L, which has been the highest productivity of indirubin so far. This work provided a basis for the commercial production of bio-indigo and the clinical drug indirubin in the future.

An optimization approach for fast, simple and accurate determination of indigo-carmine in food samples

This study report optimization of vortex-assisted natural deep eutectic solvent based liquid-phase microextraction (VA-NADES-LPME) for determination of indigo-carmine in some food samples by UV-Visible spectrophotometer. To ensure efficient extraction, nine different NADES were prepared and tested for the extraction of indigo-carmine. In order to increase extraction efficiency of indigo-carmine, the effects of VA-NADES-LPME variables and their interactions were optimized with central composite design. The optimized method exhibited a linear range between 10 and 900 ng mL^-1. Limit of detection, limit of quantification and enrichment factor were determined as 3.3 ng mL^-1, 10 ng mL^-1 and 135-fold, respectively. The applicability of the optimized method was investigated in selected food samples using the matrix-matching calibration curve. Using optimised experimental conditions (pH of 3.2, 75 µL of NADES-4, 285 µL of THF, and 4 min vortexing), satisfactory recovery results were found in the range of 95.9-104.2% with 1.4-3.7% of relative standard deviation. Finally, the optimized method was economical, simple, green, requires less laborious sampling, and provides superior accuracy and precision in trace-level analysis.

Colorimetric and fluorometric nanoprobe for selective and sensitive recognition of hazardous colorant indigo carmine in beverages based on ion pairing with nitrogen doped carbon dots

Indigo carmine (IC) dye is hazardous and allergenic for humans even though it has been excessively used in a wide range of industries. Therefore, the quantitative determination of IC is still challenging. Herein, for the first time, we have developed fluorometric and colorimetric dual-mode nanoprobe derived from the ion-pair association complex between the negatively charged IC and positively charged N@C-dots in pH = 3.0. Consequently, the binding between N@C-dots and IC resulted in cyan blue and quenching of N@C-dots fluorescence. The dependence of the fluorescence response on IC concentrations was linear over the range of 0.73-10.0 µM (R² = 0.9989) with LOD of 0.24 µM. On the other hand, the linearity of the colorimetric method ranged from 9.97 to 80.0 µM (R² = 0.9986) with LOD of 3.3 µM. The sensor was applied for estimation of IC in fruit juice and soft drink without the need for exhaustive extraction steps.

Synthetic Food Dyes – Some Aspects Of Use And Methods Of Determination

Color is one of the key ingredients for increasing the appetizing of food, so food dyes have become firmly established in food production technologies. However, with the acquisition of toxicity data of synthetic food dyes (SFD), there were restrictions and standards for their content in food have emerged. Numerous papers published in recent years demonstrate the importance of the problem of the use and definition of SFD. The review contains over 180 literary references in the field of usage and methods of determination of synthetic food dyes, among them regulatory documents (regulations), official internet resources of international and Ukrainian organizations, review articles and original works. Varieties of chromatography, enzyme-linked immunoassay, optical and electrochemical methods are used to identify and determine SFD. Special attention was paid to voltammetry (VA) as a method that is cheaper than chromatography and completely satisfies selectivity, sensitivity, reliability requirements and is compatible with the concept of green analytical chemistry, as it doesn't need organic solvents. Moreover, single sweep voltammetry can be considered as a screening method with low limits of determination and rapid respons

Novel sensor platform for rapid detection and quantification of coliforms on food contact surfaces

In this paper, a novel sensor platform based on screen printed carbon electrode coated by graphene modified polyacrylamide gel (GR/PAAGC) was developed and implemented for sampling, detection and enumeration of coliform bacteria (coliforms) on food contact surfaces. The optimized formula of polyacrylamide (PAA) and agar-agar increased the adhesive properties of the gel, being crucial for the coliforms recovery, attached to food contact surfaces. The 6-Chloro-3-indoxyl-β-D-galactopyranoside (6-CIGP) was used as a new electrochemical reporter for β-D-galactosidase activity. The released 6,6'-Dichloro-Indigo (6-DI) was directly detected by GR/PAAGC sensor. The presence of Isopropyl-β-D-thiogalactopyranoside (IPTG) and n-Octyl-β-D-thiogalactopyranoside (OBDG) in the gel contributed to reduction of the detection time. The addition of graphene enhanced the voltammetric signal and increased the conductivity of PAA gel. The anodic and cathodic peaks of the released product were directly proportional to the concentration of coliforms. Bacterial cell concentrations ranging from 1.6log₁₀CFU/mL to 6.6log₁₀CFU/mL were detected. Well-shaped, sharp voltammetric curves were generated within 3 h. Redox peaks exhibited good sensitivity with detection limits (LOD) < 0.6log₁₀CFU/mL. After series of optimization experiments, coliforms ranging from 0.6log₁₀CFU/cm² to 6.6₁₀CFU/cm² on stainless steel surfaces have been detected within 30 min with a LOD of 0.1log₁₀CFU/cm². The developed rapid, sensitive, reproducible and specific sensor successfully applied for single detection as well as for real-time monitoring of growth of coliform bacteria on stainless steel surfaces during food processing.