Rapid analysis of ascorbic and isoascorbic acids in fruit juice by capillary electrophoresis

Food Additives and Evolved Methods of Detection: A Review

Food additives are essential constituents of food products in the modern world. The necessity of food processing went up rapidly as to meet requirements including, imparting desirable properties like preservation, enhancement and regulation of color and taste. The methods of identification and analysis of such substances are crucial. With the advancement of technology, a variety of techniques are emerging for this purpose which have many advantages over the existing conventional ways. This review is on different kinds of additives used in the food industry and few prominent methods for their determination ranging from conventional chromatographic techniques to the recently evolved nano-sensor techniques.

Combining fluorescent quantum dots with transition metal oxide shell as core-shell nanocomposite for turn-on sensing of ascorbic acid

Ascorbic acid (AA) is an essential vitamin in humans, and numerous AA detection studies have been conducted. Most quantum dots (QDs)-based approaches depend on redox reactions involving AA, and they require the introduction of an intermediate (e.g., metal ions, OPD, TMB) or the assembly of fluorescent substances with nanosheets (such as MnO2) that can be degraded by AA. These methods are complex, unstable, and are susceptible to interferences. To address these problems, a core-shell fluorescence probe was developed for turn-on sensing of AA. The transition metal oxide shell FeOOH was generated around the surface of CuInZnS QDs to quench the fluorescence. In the presence of AA, the FeOOH shell was decomposed into Fe2+ and the fluorescence of QDs was recovered. Using a physical shell, the obtained nanocomposite realized direct AA detection, avoiding the effects of interfering substances caused by QDs exposure. Moreover, our probe showed great potential in point-of-care tests and was readily adapted for use as a smartphone-assisted paper sensor.

Using Cu2+ to regulate the emission feature of near-infrared fluorescent sensor with AIE: To detect ascorbic acid in food samples and its application in bioimaging

Conventional ascorbic acid (AA) detection methods such as chromatography, capillary electrophoresis, colorimetry, electrochemical detection, and enzymatic analysis require expensive equipment and complicated operation. Simple, rapid, and accurate AA detection is essential to inspect food quality, diagnose diseases, and assess immunity in humans. In this study, the first near-infrared fluorescence sensor DBHM with aggregation-induced emission was developed to detect AA under the involvement of Cu2+. The DBHM + Cu2+ sensor showed high sensitivity to AA with a limit of detection of 2.37 μM. The AA detection mechanism was investigated by optical studies, 1H NMR titration, high-resolution mass spectrometry, and infrared spectroscopy. AA was detected qualitatively and quantitatively by the DBHM + Cu2+ sensor in beverages, fruits, and Vitamin C tablets using a dual-mode (fluorescence and smartphone app) sensing platform. The new sensing system also showed low toxicity and excellent bioimaging in HeLa cells, C. elegans, and mice. This sensor could advance AA detection technology in the food industry and has potential bioimaging applications.

Electrochemical Detection of Ascorbic Acid in Oranges at MWCNT-AONP Nanocomposite Fabricated Electrode

Ascorbic acid (AA) is an essential vitamin in the body, influencing collagen formation, as well as norepinephrine, folic acids, tryptophan, tyrosine, lysine, and neuronal hormone metabolism. This work reports on electrochemical detection of ascorbic acid (AA) in oranges using screen-print carbon electrodes (SPCEs) fabricated with multi-walled carbon nanotube- antimony oxide nanoparticle (MWCNT-AONP) nanocomposite. The nanocomposite-modified electrode displayed enhanced electron transfer and a better electrocatalytic reaction towards AA compared to other fabricated electrodes. The current response at the nanocomposite-modified electrode was four times bigger than the bare electrode. The sensitivity and limit of detection (LOD) at the nanocomposite modified electrode was 0.3663 [AA]/µM and 140 nM, respectively, with linearity from 0.16–0.640 μM and regression value R² = 0.985, using square wave voltammetry (SWV) for AA detection. Two well-separated oxidation peaks were observed in a mixed system containing AA and serotonin (5-HT); and the sensitivity and LOD were 0.0224 [AA]/µA, and 5.85 µΜ, respectively, with a concentration range from 23 to 100 µM (R² = 0.9969) for AA detection. The proposed sensor outperformed other AA sensors reported in the literature. The fabricated electrode showed great applicability with excellent recoveries ranging from 99 to 107 %, with a mean relative standard deviation (RSD) value of 3.52 % (n = 3) towards detecting AA in fresh oranges.

Direct analysis of ascorbic acid in food beverage samples by flow injection analysis using reduced graphene oxide sensor

In this paper, a simple, sensitive and precise electroanalytical method was developed using flow injection analysis (FIA) with amperometric detection and reduced graphene oxide sensor for ascorbic acid determination in samples of multivitamin beverages, milk, fermented milk, and milk chocolate. The advantages of this sensor include a potential displacement of 450 mV and a 2-fold peak current increase for electrochemical oxidation of ascorbic acid, which resulted in a highly sensitive method. No interference of sample matrix was observed, avoiding solvent extraction procedures (samples were only diluted). The FIA allowed a high analytical frequency, approximately 96 injections per hour, together with adequate detection limit of 4.7 μmol L^-1. Good precision (RSD < 7%) and accuracy (recoveries between 91 and 108%) evidenced the robustness of the method. The method was compared with ultra-fast liquid chromatography (UFLC) obtaining statistically similar results (95% confidence level). The ascorbic acid content in samples varied from 0.065 to 2.53 mmol L^-1.

A stimuli-responsive fluorescence platform for simultaneous determination of d-isoascorbic acid and Tartaric acid based on Maillard reaction product

An activatable fluorescence monitoring platform based on a novel Maillard reaction product from d-glucose and L-arginine was prepared through a facile one-pot approach and applied for simultaneous detection of d-isoascorbic acid and tartaric acid. In this work, the new Maillard reaction product GLA was first obtained, and its fluorescence intensity can be effectively quenched by KMnO₄, resulting from a new complex (GLA-KMnO₄) formation between GLA and KMnO₄. Upon addition of d-isoascorbic acid or tartaric acid, an enhanced fluorescence was observed under the optimumed experimental conditions, indicating a stimuli-responsive fluorescence turn on platform for d-isoascorbic acid or tartaric acid can be developed. The corresponding experimental results showed that this turn on fluorescence sensing platform has a high sensitivity for d-isoascorbic acid or tartaric acid, because the detection limits were 5.9μM and 21.5μM, respectively. Additionally, this proposed sensing platform was applied to simultaneously detection of d-isoascorbic acid and tartaric acid in real tap water samples with satisfactory results.

An Ascorbic Acid Oxidase-based Sensing Platform for Stereoselective Interaction with Ascorbic Acid and Isoascorbic Acid

A simple enzyme-based nanohybrid material was fabricated via immobilizing ascorbic acid oxidase (AO) on the surface of flower-like electrodeposited gold nanoparticles (dpAu) and reduced graphene oxide (rGO) modified glassy carbon electrodes (GCEs). The composite material was used for stereoselective interaction with ascorbic acid (AA) and isoascorbic acid (IAA). Herein, AO was applied as a stereoselective selector, and the dpAu/rGO nanohybrid not only acted as a supporter for high loading of AO, but also served as the nanomaterial for signal amplification. The results showed obvious peak current differences between AA and IAA, indicating that this strategy could be employed to recognize AA and IAA. Under the optimum conditions, the sensor exhibited a good linear response to AA and IAA in a linear range of 1.0 × 10^-4 - 5.0 × 10^-3 M. This approach with the merits of simplicity and rapid response provided a promising perspective for identification of AA and IAA.

Enantioselective recognition of ascorbic acid and isoascorbic acid on HS-β-cyclodextrin/gold nanoparticles/hollow carbon microspheres hybrid modified electrodes

The HS-β-cyclodextrin/gold nanoparticles/hollow carbon microspheres hybrids were prepared to develop a simple strategy for electrochemical chiral analysis.

CE methods applied to the analysis of micronutrients in foods

This article reviews the applications of CE that are relevant to the analysis of small molecules in foods. CE has been applied to a wide range of important areas of food analysis and is rapidly being established as an alternative technique to chromatographic methods including HPLC and GC within analytical food and research laboratories. In recent years the analysis of food by CE has become more frequent and important and as such a variety of compounds have been separated and quantified. Although many other analytes have been detected by CE, this review will highlight areas relating primarily to the rather broad chemical classes of free amino acids, carbohydrates, organic acids, vitamins and a variety of antioxidants. In addition, information relating to the analyte, sample matrix, mode of CE employed, scope of the methodology and the detection and derivatization of the small molecules are considered and discussed.

Determination of organic acids by CE and CEC methods

A comprehensive overview of the analysis of low-molecular-mass organic acids employing electromigration methods in the capillary format is given. This review includes papers published since 2003 and can be seen as an update of the review paper published by Galli et al. in 2003. Tables included in this review contain application papers describing the determination of organic acids from a variety of fields like the analysis of food and beverages, environmental samples, samples from clinical origin, and from natural products.

A fast and reliable route integrating calibration and analysis protocols for water-soluble vitamin determination on microchip-electrochemistry platforms

A novel analytical route to determine water-soluble vitamins (B group and C) using single channel microchip-electrochemistry platforms is presented. The electrochemical detection protocol was carefully optimized, and it was shown that it was crucial to use 1 M nitric acid in the detector compartment to detect folic acid. A phosphate buffer (pH 6, 10 mM) and a separation voltage of 2 kV gave the complete separation of vitamins in less than 130 s, with good reproducibility (RSDs less than 10%) and accuracy (error less than 9%). In addition, a methodological innovation integrating calibration and analysis of water-soluble vitamins on the chip is also proposed. The strategy consisted in sequentially using both reservoirs (named calibration and analysis reservoirs) as well as a calibration factor (defined as signal/concentration of analyte). The analytical route required 350 s in the overall protocol (employing 130 s in calibration plus 130 s in analysis), an improvement over the times used in both conventional and microchip protocols.

Recent advances in the application of capillary electromigration methods for food analysis

This article reviews the latest developments in the application of capillary electromigration methods for the analysis of foods and food components. Nowadays, methods based on CE techniques are becoming widely used in food analytical and research laboratories. This review covers the application of CE to analyze amino acids, biogenic amines, peptides, proteins, DNAs, carbohydrates, phenols, polyphenols, pigments, toxins, pesticides, vitamins, additives, small organic and inorganic ions, chiral compounds, and other compounds in foods, as well as to investigate food interactions and food processing. The use of microchips as well as other foreseen trends in CE analysis of foods is discussed. Papers that were published during the period June 2002-June 2005 are included following the previous review by Frazier and Papadopoulou (Electrophoresis 2003, 24, 4095-4105).

Analysis of natural antioxidants by capillary electromigration methods

In this work, an exhaustive survey of capillary electromigration methods used to analyze natural antioxidants is presented together with some discussion of the use of these substances use as functional foods. This review provides an updated and exhaustive overview of the separation and identification by capillary electrophoresis of natural compounds with antioxidant activity found in natural matrices and/or foods. The compounds concerned are catechins, isoflavones, anthocyanins, phenolic acids, vitamins, as well as other less common natural substances that have shown antioxidant activity.