An Indirect Competitive Immunoassay for Analysis of Carminic Acid in Meat Products

A rapid colorimetric method for the detection of carminic acid in samples based on visible color change

Carminic Acid (CA), an insect-derived red color, is widely used as a colorant and additive in food and non-food items. The detection of CA is of great concern since it is unacceptable for vegetarians and vegans consumers. Therefore, it is important for food authorities to have a rapid detection method for CA. We describe here a simple and rapid method for the qualitative detection of CA, using Pb2+ for complex formation. As a result, the sample solution shows a visible change from pink to purple (bathochromic shift) which could also be analyzed through a spectrophotometer at λmax = 605 nm. The structure of the CA-Pb2+ complex was also studied through advanced spectroscopic techniques. Moreover, the presence of iron results in the formation of a stable CA-Fe2+ complex without any significant color change, as Fe2+ has a stronger binding affinity with CA. Thus, sodium fluoride (NaF) was used to prevent CA-Fe2+ complex formation. Therefore, two methods were developed based on the absence (method I) and presence (method II) of NaF. The LOD and LOQ for the method I was 0.0025 and 0.0076 mg mL-1, and for method II, values were 0.0136 and 0.0415 mg mL-1, respectively. The methods were also validated by intra and inter-day analyses. A total of 45 commercials, including food and non-food samples, were screened for the detection of CA. The developed methods are applicable for the effective and rapid surveillance of CA in various samples without the use of high-tech instruments.

Sensitive voltammetric quantification of carminic acid in candies using selenium dioxide nanoparticles based electrode

Carminic acid is a food colorant which concentration has to be controlled due to the possible negative health effects. Sensitive voltammetric method is developed for carminic acid determination using electrode modified with SeO₂ nanoparticles (SeO₂ NPs) and hexadecyltriphenylphosphonium bromide (HDTPPB) acting as dispersive agent for nanoparticles and electrode surface co-modifier. SeO₂ NPs of 37-45 nm are uniformly distributed at the electrode increasing its electroactive area (41 ± 2 vs. 8.9 ± 0.2 mm² for bare glassy carbon electrode (GCE)). Electrochemical impedance spectroscopy data confirm an 18.3-fold decrease of charge transfer resistance compared to GCE (12.7 ± 0.3 vs. 232 ± 7 kΩ, respectively). In differential pulse mode, the linear dynamic ranges of carminic acid are 0.010-2.5 and 2.5-10 μmol L^-1 with a detection limit of 3.4 nmol L^-1. The method is successfully employed in candies and lozenges for sore throat treatment. The approach is simple, reliable, and can be used as an alternative to chromatography in routine analysis.

Sensitive and Selective Carmine Acid Detection Based on Chemiluminescence Quenching of Layer Doubled Hydroxide-Luminol-H2O2 System

Carminic acid (CA) extracted from cochineal is widely used in food additives as a natural colorant, and its potential risk to human health makes its detection important. In this work, a layered doubled hydroxide (LDH)-luminol-H₂O₂ system-based chemiluminescence (CL) platform has been successfully applied for CA sensing. The principle detection consists of two steps: first, LDH adsorbs CA onto the surface via electrostatic attraction; second, CA quenches the CL of the LDH-luminol-H₂O₂ system via the synergistic effect of CL resonance energy transfer, reduction of reactive oxygen species, and occupation of positively charged centers of brucite-like layers. With this CL approach, 0.5 μM CA is detectable using a CL spectrometer, and the limit of detection is 0.03 μM. This CL system exhibited a linear response to CA in the concentration range from 0.5 to 10 μM. In addition, the practical application of the designed CL sensing system is evaluated with dried pork slice samples.