Simultaneous analysis of natural pigments and E-141i in olive oils by liquid chromatography–tandem mass spectrometry

Synthetic dyes: A mass spectrometry approach and applications

Synthetic dyes are found in a wide variety of applications today, including but not limited to textiles, foods, and medicine. The analysis of these molecules is pertinent to several fields such as forensics, environmental monitoring, and quality control, all of which require the sensitivity and selectivity of analysis provided by mass spectrometry (MS). Recently, there has been an increase in the implementation of MS evaluation of synthetic dyes by various methods, with the majority of research thus far falling under electrospray ionization and moving toward direct ionization methods. This review covers an overview of the chemistry of synthetic dyes needed for the understanding of MS sample preparation and spectral results, current fields of application, ionization methods, and fragmentation trends and works that have been reported in recent years.

Pigment Identification and Gene Expression Analysis during Erythrophore Development in Spotted Scat (Scatophagus argus) Larvae

Red coloration is considered an economically important trait in some fish species, including spotted scat, a marine aquaculture fish. Erythrophores are gradually covered by melanophores from the embryonic stage. Despite studies of black spot formation and melanophore coloration in the species, little is known about erythrophore development, which is responsible for red coloration. 1-phenyl 2-thiourea (PTU) is a tyrosinase inhibitor commonly used to inhibit melanogenesis and contribute to the visualization of embryonic development. In this study, spotted scat embryos were treated with 0.003% PTU from 0 to 72 h post fertilization (hpf) to inhibit melanin. Erythrophores were clearly observed during the embryonic stage from 14 to 72 hpf, showing an initial increase (14 to 36 hpf), followed by a gradual decrease (36 to 72 hpf). The number and size of erythrophores at 36 hpf were larger than those at 24 and 72 hpf. At 36 hpf, LC-MS and absorbance spectrophotometry revealed that the carotenoid content was eight times higher than the pteridine content, and β-carotene and lutein were the main pigments related to red coloration in spotted scat larvae. Compared with their expression in the normal hatching group, rlbp1b, rbp1.1, and rpe65a related to retinol metabolism and soat2 and apoa1 related to steroid hormone biosynthesis and steroid biosynthesis were significantly up-regulated in the PTU group, and rh2 associated with phototransduction was significantly down-regulated. By qRT-PCR, the expression levels of genes involved in carotenoid metabolism (scarb1, plin6, plin2, apoda, bco1, and rep65a), pteridine synthesis (gch2), and chromatophore differentiation (slc2a15b and csf1ra) were significantly higher at 36 hpf than at 24 hpf and 72 hpf, except for bco1. These gene expression profiles were consistent with the developmental changes of erythrophores. These findings provide insights into pigment cell differentiation and gene function in the regulation of red coloration and contribute to selective breeding programs for ornamental aquatic animals.

POSS-based fluorescence sensor for rapid analysis of β-carotene in health products

Recent years, fluorescent organic-inorganic hybrid nanomaterials have received a lot of interest as potential fluorescent sensor materials. In this study, fluorescent organic-inorganic hybrid nanomaterials (POSS@ANT) were created utilizing polyhedral oligomeric silsesquioxane as the precursor and 9,10-bromoanthracene as the monomer. The morphology and composition of POSS@ANT, as well as its pore characteristics and fluorescence properties were studied. And POSS@ANT displayed steady fluorescence emission at an excitation wavelength of 374 nm. Then a β-carotene fluorescence sensor was developed using the capacity of β-carotene to quench the fluorescence of POSS@ANT. The quenching process is linked to acceptor electron transfer and energy transfer, and the sensor has a high selectivity for β-carotene. This β-carotene fluorescence analysis method we established has a linear range of 0.2-4.3 mg/L and a detection limit of 0.081 mg/L. Finally, it was used to quantify β-carotene in health products, the recovery rate was 91.1% - 109.9%, the RSD was 2.2% - 4.3%, and the results were compatible with the results of high-performance liquid chromatography. The approach is reliable and can be used to determine β-carotene in health products.

Atmospheric pressure photoionization versus electrospray for the dereplication of highly conjugated natural products using molecular networks

Natural products are sources of inspiration and reservoir of high valuable molecules. Recently, analytical tools based on liquid chromatography coupled to tandem mass spectrometry to generate molecular network became widely employed for dereplication. This strategy greatly accelerates the identification of known and structural hypothesis of unknown. Despite the availability of different ionization sources, alternatives to classical electrospray ionization (ESI), such as atmospheric pressure chemical ionization (APCI) or photoionization (APPI), have been neglected. In particular, APPI has been described for its ionization efficiency on non-polar molecules bearing no acid or basic groups. For that reason, we investigated APPI potential to generate molecular network and compare it to ESI on several criteria that are generation of ion species, sensitivity and signal-to-noise ratio (SNR) for different extracts rich in highly conjugated natural products. We first optimized APPI experimental conditions on crude extract from a fungus, Penicillium sclerotiorum, producing polyketones belonging to the azaphilone family. Then we compared APPI and ESI on different fractions of the fungus and on two plant extracts, French Guyanese Swartzia panacoco (Aubl.) R.S. Cowan (arial parts) and Indian Cassia auriculata L. (leaves) containing phenolic compounds, such as flavonoids. While ESI generated more ion species and displayed a better sensitivity, APPI generated only protonated adduct and better SNR. Comparing ESI and APPI generated species on molecular network reveal that both strategies overlap for the majority of protonated ions.

Development of an accurate and direct method for the green food colorants detection

Color impression represents between 60 and 90% of the final acceptance/rejection choice made by consumers. Consequently, color additives are attribute standards for our daily life in any market and any culture. Currently, authorized natural green food colorants comprise several copper-chelated chlorophyll derivatives. Both the raw materials and the manufacturing processes for the acquisition of these green food colorants are numerous and diverse. Hence, each producer applies its own know-how to obtain 'signature' green colorant products. Indeed, the chlorophyll profile of these products is partially known and may substantially differ among batches, while their identification just by HPLC-UV-Vis is not complete. Native chlorophylls do not chelate copper. Therefore, we propose a fast and specific method for copper chlorophyll detection, as indicative (except in a few fermented foods) of probable green food colorant addition or "re-greening" with copper salts. The new method is based on the characteristic isotopic pattern of the copper chlorophyll derivatives and does not require the precise characterization of the corresponding chlorophyll structure. This accurate methodology, based on a specific HPLC-ESI/APCI-HRMS method assisted with powerful post-processing software, is versatile as it can be used for other metallo-chlorophyll complexes also applied to improve the green coloration of food products.

Pigment profiles of Spanish extra virgin olive oils by ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry

This work studies the natural pigment profiles (chlorophylls and carotenoids) of Spanish Extra Virgin Olive Oils (EVOO) produced in different Spanish regions. The simultaneous qualitative and quantitative analysis of EVOO natural pigments has been performed by ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS) using atmospheric pressure chemical ionisation (APCI). The results showed a similar natural pigment pattern for all the analysed EVOOs, although the total pigments content differed significantly. Moreover, the chlorophyll/carotenoid ratio was close to 1, while the lutein/β-carotene ratio was higher than 1, showing that lutein is the most abundant carotenoid in the studied Spanish EVOOs. Data from multivariate statistical approach demonstrated that the olive variety does not discriminate between EVOO samples. However, they were classified based on their origin allowing good differentiation of samples from the Basque Country and Canary Islands from the rest of regions. The results of this study show the differences of the nature and pigments concentration of Spanish EVOO samples, parameters that are of significance for reliable characterisation.

HPLC-hrTOF-MS study of copper chlorophylls: Composition of food colorants and biochemistry after ingestion

Despite the daily consumption of copper chlorophylls (E-141i), the green food colorants in foods high in fats, there is a general need for knowledge regarding their exact composition. Consequently, we have analyzed by HPLC-ESI(+)/APCI(+)-hrTOF-MS² the accurate composition of different commercial copper chlorophyll colorants for the first time. Data showed a favored yield of copper pheophytins from a series, while pheophytins from b series are preferentially no complexed with copper. The copper pheophytins present in the food colorants consisted mainly of three structural rearrangements. New fragmentation patterns and structural assignments have been described for several copper pheophytins. During the ingestion of copper chlorophylls, no chlorophyll derivative was present in serum nor urine except a new copper-pyroporphyrin a accumulated in a few livers. In any case, this green additive could represent the ideal food colorant, as most of the copper pheophytins are excreted in the feces showing almost no absorption of copper-chlorophylls compounds.