Capillary Electrophoresis in Food Analysis

Capillary Electrophoresis (CE) is a powerful separation and analysis technique that has been rapidly progressing since it was first introduced. The application range of CE is so diverse that it ranges from small analytes to large and complex macromolecules. This chapter aims to provide a deep understanding of the basic principles of CE. The first part of the chapter involves the theoretical basis, instrumentation, and separation mechanism of CE. The second part focuses on capillary electrophoretic separation modes and the third part describes the detection methods in CE. The fourth and final part covers capillary electrophoretic strategies for specific analyte groups.

This chapter introduces sample preparation techniques in Capillary Electrophoresis (CE) for food analysis. Food sample preparation prior to CE analysis aims to transfer target analytes from random statuses in the original food matrix to highly ordered pre-detection statuses, which is an entropy reduction procedure and cannot happen spontaneously. Generally, this is a time-consuming, labor-intensive, and error-prone step in complex sample analysis, especially in food analysis. Nevertheless, to match the fast analysis nature of CE, food samples have to be prepared efficiently in a relatively short time. Therefore, many highly efficient and fast sample preparation techniques were applied in CE for food analysis, including phase separation, fieldassisted extraction, membrane separation, chemical conversion, and online coupling of sample preparation/analysis techniques. The principles and operation of each of the above-listed sample preparation techniques and some application examples are shown in different sections. 

 Highly selective and sensitive analytical methods are necessary for food analysis because diverse components can be found in this complex sample matrix, sometimes occurring at only trace levels. Besides, simple and cost-effective methods are needed to meet the requirements of governmental food standards organizations and industries. Capillary Electrophoresis (CE) is a technique that meets these requirements offering high-resolution separations and high-throughput. It only demands small amounts of samples and chemicals for experiments and its versatility due to the different separation modes possible and the combination with different detection systems, has favored its application to determine diverse compounds in food analysis. This chapter summarizes significant issues and challenges involved in the determination of lipids, carbohydrates, and proteins, as well as recent advances in the analysis of these food components by several CE modes and detection systems.

These peptides themselves and especially as products of enzymatic or chemical cleavage of parental proteins, belong to the important components of foodstuffs. They significantly influence their nutritional, biological, technological, and functional properties. Some of these peptides were found to have effects on human health and nutrition, e.g., by affecting human digestive, endocrine, cardiovascular, immune, and nervous systems. Hence, qualitative and quantitative analysis of peptides in foods is of great importance. For the separation and quantification of peptides in foods, capillary electromigration methods represent one of the most suitable analytical methods. This chapter presents a comprehensive overview of the developments and applications of high performance capillary and microchip electromigration methods (zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography and electrochromatography) for separation and analysis of peptides in foods and food products in the time period since 2010 up to the middle of 2020. Various aspects of the application of capillary electromigration methods for peptide analysis in foods, such as sample preparation, peptide preseparation, preconcentration, derivatization, adsorption suppression, and detection, are described and discussed. Several particular applications of capillary electromigration methods for separation and analysis of peptides in various food samples of animal, plant, and microbial origin are demonstrated.

The relevance of amino acids analysis is widely recognized in different fields. In Food Science, the determination of amino acids is of special interest since it can provide valuable information related to the nutritional, quality, and safety properties of food samples. For this reason, the development of robust, efficient, sensitive and cost-effective analytical methodologies is essential. Among the different analytical techniques, capillary electrophoresis has shown great potential in the last decades as a powerful tool to carry out the analysis of amino acids in food samples. This chapter aims at providing a comprehensive overview of the most recent applications of capillary electrophoresis for the analysis of protein and nonprotein amino acids in foodstuffs. The main experimental conditions concerning the separation and detection of amino acids are discussed and given in tables. 

Vitamins are a series of trace compounds obtained from food that play important roles in human health. Vitamin analysis is essential for nutritional assessment and food production. A comprehensive overview of capillary electrophoresis for vitamins analysis is given. This chapter includes papers published since 1996 and can be seen as a guidance note of vitamins analysis using capillary electrophoresis. The analyses are discussed for water-soluble vitamins and fat-soluble vitamins according to different separation modes. In addition, various sample pretreatment methods avoiding matrix interferences with the analysis of vitamins are also described. Articles pertaining to different vitamins from a variety of food and beverages, dietary supplements, and pharmaceutical samples are included. This chapter highlights the unique performance of capillary electrophoresis for the qualitative analysis of vitamins in food. 

Polyphenols are naturally occurring compounds found in fruits, vegetables, cereals and beverages. Nowadays, there is a high interest in these compounds because of their potential health benefits associated with the protection against the development and progression of many degenerative diseases due to their antioxidant capacity. However, their composition changes both qualitatively and quantitatively depending on the natural source. Thus, the determination of these compounds is not straightforward. Among the different techniques employed for their analysis, capillary electrophoresis is a very interesting alternative due to its high separation efficiency, high resolution power, short analysis time and low consumption of samples and reagents. This chapter presents an overview of the recent developments and applications of capillary electrophoresis for the analysis of phenolic compounds from food samples, including articles published since 2010 to date. In addition, the characteristics of the most relevant developed methodologies using different separation modes are broadly discussed.

Electrophoretic approaches are increasingly used for the determination of food additives in real samples based on the easy operation modes and enhanced separation efficiency of Capillary Electrophoresis (CE). This chapter presents a summary of recent breakthroughs related to the development of different analytical strategies focused on enhancing the study of food samples and reviews the determination of food additives by CE, including some promising approaches. The effectiveness of these strategies to solve alimentary issues is also discussed.

Chiral analysis is a powerful tool in Food Science for quality and safety assessment since the enantiomeric composition of food samples can reveal adulterations, the effects of processing and storage or give valuable information on the bioactivity, traceability or even toxicity of foods. This chapter describes the potential of Capillary Electrophoresis in the chiral analysis of food and beverages. The separation modes used in CE for the chiral analysis of food samples are described, including different strategies for sample preparation and sensitivity enhancement. The most relevant applications developed in the period from 2010 to the present are depicted and the main conclusions and future prospects are outlined. 

The most significant advances in food analysis using microchip electrophoresis (ME) technology will be discussed in this book chapter, covering the works published from 2009 to 2019, which will be organized in three sections based on the detection mode employed: electrochemical and fluorescence detection, and bioanalytical-based approaches. The most innovative methodologies, relevant applications, and latest advances in instrumentation to achieve a truly portable lab-o- -a-chip will be discussed. Commercial instruments will also be briefly mentioned as a demonstration of the maturity of ME technology.

This chapter deals with the issue of food authenticity and applications of capillary electrophoresis in this field. An overview of food adulteration, including the frequency of adulteration of selected commodities and a list of methods used to prove authenticity or detect food adulteration, is presented. An overview of applications of capillary electrophoresis for food authentication is supplemented by specific cases described in more detail.

 Chemical hazards may be present in food due to their intended use during food production (i.e., residues), they may be intentionally added to food products to confer specific attributes (i.e., food additives), or they may simply occur at any of the stages of the food supply chain (i.e., contaminants). Since these chemical hazards represent a health risk to consumers, legislation has been developed to establish the maximum concentration levels of these substances in food, and to define control measures to monitor their presence in food products. In general, liquid chromatography (LC) and gas chromatography (GC) are used as analytical techniques in laboratories that are responsible for carrying out routine food safety analyses. During the last decades, capillary electrophoresis (CE) has been extensively investigated as an alternative (or complementary) separation tool to chromatographic techniques, and today, it is already a consolidated technique that can be implemented in routine food safety laboratories. This chapter presents the state of the art of CE in the field of chemical food safety and gives an overview of relevant applications in this area.

At present, dietary supplements are commercially available products, globally consumed as an addition to the usual diet. Considering that dietary supplements are a source of nutrients, they are widely utilized to improve human health and prevent various diseases; therefore they are expected to be safe. There is still no common definition regarding the role of supplements which cannot be considered functional foods nor drugs. Dietary ingredients in supplements are exempt from food additives or drugs regulations. For this reason, these supplements are marketed without any data on identity, including ingredient information, effectiveness, toxicology and safety. Therefore, efficacy and safety are necessary claims required to preserve consumer health. To face this imperative challenge, sensitive and selective analytical techniques capable of providing a full characterization of the supplements in terms of their components are needed. In the last decades, Capillary Electrophoresis (CE) has shown to be a powerful tool that offers solutions to almost any analytical issue arising in several application fields. Due to its simplicity of operation and versatility, it has become a complementary separation tool to other separation techniques such as gas and liquid chromatography in the analysis of dietary supplements. This chapter aims to give a comprehensive overview of the most important applications of CE for the analysis of dietary supplements in terms of their main key components.

The safety and quality of food products, which is one of the most significant issues today, is a cause of increasing concern for consumers. For this reason, food policies are tightly determined by the governments with new conditions and regulations. Systematic monitoring of chemical pollutants such as pesticides, toxins, environmental and industrial contaminants, and residues in food products is critical in protecting public health. Capillary Electrophoresis with mass spectrometry (CE-MS) is frequently used in food analysis to ensure food safety and food quality. In this review, an updated overview of the targeted analysis of residues, contaminants, exogenous toxic ingredients, endogenous toxic ingredients, bioactive components, carbohydrates, amino acids, peptides and proteins in different food matrices through CE-MS is presented. In addition, the advantages of CE-MS based non-targeted analysis and its effectiveness in the field of food safety and quality are discussed in the light of recent studies. From a future perspective, the role of CE-MS based food metabolomics in food science is discussed together with recent developments on metabolomics applications.