Applications of Chromatographic Techniques in Food and Environmental Analysis

1. Introduction

Throughout history, analytical chemistry has been a key area for many other scientific fields. The tools provided by analytical chemistry are essential to solving separation, determination, or remediation problems, which are of great interest to the general society. In this sense, there are numerous publications which have demonstrated the potential of various developments achieved in this field to afford different issues associated with food and environmental analysis, among other areas of application [1,2].

Considering the importance of the use of analytical approaches in those fields and the increasing requirements, not only in terms of legislation, but also due to societal concerns surrounding the quality of food and the protection of the environment, the increasingly integral need to develop the most reliable and effective analytical methodologies can be clearly understood. This aspect is even more critical for toxicological evaluations, food safety, and food fraud studies, since it has been reported that many contaminants and hazardous substances could cause enormous harm in human population when exposed to these substances, even when they are present at very low concentration levels [3]. Such aspects can also be transferred to the analysis of micronutrients present in food or natural environmental matrices with relevant bioactivity, which can provide important benefits, even though they are present at very low levels.

In this context, various requirements in terms of sensitivity and selectivity are sharply increasing within the analytical field in order to provide reliable and suitable information to important sectors, such as food and environmental analysis, with direct influence on the food industry and the general society. Over the last fifty years, the advances in chromatographic techniques (liquid chromatography (LC) and gas chromatography (GC), and, most recently, supercritical fluid chromatography (SFC)) have made these techniques and their different modes of operation essential tools to comply with above-mentioned demands. Besides, the development of powerful detection systems, such as mass spectrometry (MS), and their combination with chromatographic techniques have constituted the most relevant advances in the area of analytical determination [4].

Additionally, the current trends in analytical chemistry, based on the principles of green chemistry and sustainability, demand novel procedures, which not only provide reliability, sensitivity, and selectivity, but also safety, cost reduction, low time and energetic requirements, and the generation of less residues that could endanger the environment or animal and human health. In this context, the development of miniaturized and automated equipment, the application of novel and versatile materials and green solvents, as well as improvements in the efficiency of instruments have constituted important challenges for the scientific community. Some of them have already been solved, although the majority are issues which scientists are still currently working on in order to provide suitable alternatives to conventional analytical techniques [5].

That explains why the development of efficient, fast, economical, and green methodologies based on the application of LC, GCor SFC systems combined with novel sample preparation procedures is continuously rising and improving in order to offer adequate solutions with higher effectiveness and rapidity to the problems posed above.

This Special Issue aims to compile and present the most recent applications of chromatographic techniques in the analysis and evaluation of food and environmental samples, as well as to provide an accurate overview of the recent advances and future trends in this field.

2. Special Issue Summary

Six different experimental works and one revision article were published in the present Special Issue, highlighting the relevance of chromatographic techniques in food and environmental analysis. Among them, GC coupled to conventional and MS detection systems, as well as LC in different modes, including ultra-high-performance liquid chromatography (UHPLC), high-performance liquid chromatography (HPLC), and high-performance thin-layer chromatography (HPTLC), combined with both kinds of detectors for the analysis of food and environmental samples, were applied with varied objectives.

Different techniques were applied for the characterization of food and plants with nutritional or pharmaceutical interest. In this sense, it is worth mentioning the work of Antonysamy Johnson et al. [6], who used HPTLC combined with UV detection for the phytochemical characterization of Asplenium aethiopicum in order to evaluate the potential therapeutic character of this plant. The results helped to identify phenolics, tannins, alkaloids, and flavonoid profiles that confirmed the antioxidant and cytotoxicity potential of this plant and, additionally, provided a powerful tool for their identification and differentiation from other adulterants, which could be used with the same aim. This study demonstrates the potential of simple and low-cost chromatographic techniques, but with high effectiveness for the identification of relevant compounds in samples of interest.

With the same aim, Nuñez et al. [7] used an untargeted approach by applying UHPLC high-resolution mass spectrometry (HRMS) to obtain the fingerprint of turmeric and curry samples in order to develop an efficient strategy to characterize, authenticate, and classify these two species. This strategy not only allowed an efficient metabolite profile to distinguish both species, but also to distinguish between the different varieties of each one. The authors have stated the advantage of achieving a very reliable potential approach using HRMS identification without the necessity of using standards, which decreases the cost and requirement of materials in concordance with the objectives of green analytical chemistry.

Nevertheless, the application of HPLC with conventional detectors has also demonstrated good results for the unmasking of fraud in the food industry. An interesting application was included in this Special Issue, in which Debola et al. [8] used a combination of HPLC with UV detection to evaluate the activity of the most important thermolabile enzyme present in milk, α-1-fucoside, in Fiore Sardo cheese. The main purpose of monitoring this compound was to check the influence of using raw or heat-treated milk during the production of the final product, which involves a fraud in the production since this process is not allowed in the preparation of Fiore Sardo cheese with protected designation origin. The strategy allows both p-nitrophenyl-l-fucopyranoside and its degradation product, p-nitrophenol, to be monitored. These results showed the good performance of the developed methodology to monitor enzymatic activity, providing a good tool to identify real Fiore Sardo cheese submitted to the legislated production procedures. Indeed, the authors were able to demonstrate that the introduction of a chromatographic separation technique intended to determine and monitor α-1-fucoside, provided a lower limit of detection, greater operative simplicity, and a better automatization level than the previous works reported with the same aim. This fact highlights the relevance of the chromatographic techniques and underlines HPLC as a suitable and powerful separation technique for the analysis of very complex samples, such as cheese, with a very complex composition.

The potential of the combination of target and untargeted analysis using UHPLC-MS with a Q-orbitrap as the analyzer was described and demonstrated by Musatadi et al. [9] for the analysis of xenobiotics in very complex matrices, such as commercial and breast milk. The authors have discussed the importance of developing efficient analytical methodologies that enable reliable evaluation centered around exposing the population, particularly infants, to hazardous substances through commercial milk intake or lactation. This information could help to clarify and assess the possible adverse effect that those substances can have in human organisms. The chromatographic separation of milk extract obtained after a simple deproteinization and clean-up procedure through filtration was successfully performed, allowing the adequate validation of the methodology for 200 different compounds in the target approach and more than 170,000 compounds after applying the untargeted strategy. The analysis of the selected samples showed the presence of food additives, phytoestrogens, and stimulants in commercial milk; and plasticizers, UV filter, or pharmaceuticals in breast milk, which proved their presence in commercial food and biological fluids, and therefore, the exposition of humans to such hazardous substances. In this sense, the UHPLC-MS approach has shown to be a suitable tool in conducting this kind of analysis in an effective, versatile, and reliable way.

Regarding the application of GC, Costa et al. [10] proposed an interesting combination of GC-MS (for reliable identification purposes) and GC flame ionization detection (FID) (for quantification purposes) to determine chemical constituents of Calyptranthes concinna essential oil to evaluate its antibacterial activity. This identification was carried out through two different strategies, using a spectra database and a comparison of linear retention indices, calculated from the injection of a homologous hydrocarbon series, as well as a comparison of data with the literature previously published. Thirty different compounds were identified by GC-MS hydrophobic substances (i.e., monoterpenes, sesquiterpenes, etc.) that have been previously associated with antibacterial activity. Those results were confirmed by in vivo antibacterial studies, which showed the antibacterial activity of the essential oil against Staphylococcus aureus and Escherichia coli. The study constitutes an important step for encouraging the development of experiments to confirm the therapeutic potential of essential oils since, in that case, not only was the activity evaluated, but these data was also reinforced with the chemical characterization of the extract using the reliable determination of the oil composition.

Apart from the application of chromatography techniques in the analysis of food matrices, this Special Issue also includes one application for the evaluation of biological and environmental samples. In this case, Banik et al. [11] carried out the study of volatile organic chemicals (VOCs) in cat urine and faces with the aim of discovering the components of those matrices responsible for their unpleasant odor. Authors have proposed a previous extraction using solid-phase micro-extraction followed by determination using GC-MS and subsequent identification by comparison with the NIST database. For fresh samples, 22 compounds were identified in urine and 64 in feces, whereas the number of volatile substances increased up to 34 in urine and decreased to 12 in feces for staled samples. The methodology facilitated the determination of trimethylamine, low-molecular organic acid, ketones, phenolic compounds, and aromatic heterocyclic N organic compounds, which are responsible for the bad odor; however, agreeable substances were also found. This study also shows the great versatility of chromatographic applications to solve environmental challenges, e.g., in the search of possible odor remediation that can reduce or mitigate the impact of cat residues, which is one of the most common pets around the world.

Finally, it is worth mentioning the review article published in this compilation which discussed the approaches developed so far for the evaluation of vitamin D and its derivatives in food matrices using chromatographic techniques [12]. In this exhaustive and critical revision of the literature related to the issue in question, the authors mentioned the importance of using sample preparation procedures prior to the application of chromatographic separations due to the great complexity of matrices. However, despite the importance of this step, it is remarkable that conventional approaches are the most common strategies in this kind of work, whereas miniaturized and novel sustainable approaches have been scarcely developed. Regarding the use of chromatographic techniques, LC in its different modalities, combined with UV and MS has been the most frequently used for the analysis of vitamin D derivatives, since the use of GC can isomerize the analytes, thus hampering the analysis. However, authors also highlight the importance of the application of SFC in this field. This chromatographic technique has gained great attention in recent years due to the advantages provided in terms of comprehensiveness, selectivity, and peak capacity, which are essential in the analysis of this group of compounds, considering the wide range of polarities that involves from ester forms until hydroxylated species.

3. Conclusions

The seven contributions included in this Special Issue highlighted the relevance of chromatographic techniques in the analysis of food and environmental applications and show the substantial advancements that involve the application of this techniques to achieve more selective and sensitive methodologies which therefore provide more efficient determinations. These improvements in the development of analytical methodologies not only guarantee the reliability of the data obtained, but also the application of more sustainable strategies that, in combination with miniaturized extraction procedures and the use of novel sustainable materials, constitute an important development regarding the use of greener approaches in the field of analytical chemistry.

LC, GC, and (more recently) SFC have become powerful techniques in addressing the challenges posed in varied areas such environment protection, contamination remediation, or food industry (including food technology, food safety, fraud, etc.). The articles compiled in this publication have demonstrated and analyzed the versatility of those techniques in terms of matrices (milk, plants, cheese, urine, and feces), as well as in terms of compounds (xenobiotics from different families, enzymes, secondary metabolites, and VOCs, among others). Additionally, it is worth mentioning the variety of methodologies or strategies that can be developed based on chromatographic techniques using targeted and untargeted analysis for addressing issues related to the identification of hazardous substances, unmasking fraud or adulteration, and for the characterization of species.

In conclusion, the articles published in this compilation are a representative sample of the most recent advances and applications of chromatographic techniques and show the current and future trends in fields pertaining to food and environmental analysis.