**3.6 Food analysis**

236 Macro to Nano Spectroscopy

same as the amount of carbon in the atmosphere (750 gigatons). However, a large proportion of rainwater DOC is still uncharacterized. A novel method for qualitatively characterizing DOC compounds in rainfall is to use fluorescence. A large proportion of DOC is fluorescent and this fraction can be used to characterize DOC compounds (Baker & Spencer, 2004, as cited in Muller, 2008), yet its full potential for analyzing rainwater DOC compounds has yet to be achieved. Fluorescence can be used to fingerprint fluorophores, identify DOC compounds, and detect small concentration levels which may have otherwise gone undetected, with just 0.04 ml samples. Given the importance of better characterization of rainwater DOC, and the presence of fluorescent DOC compounds, using fluorescence spectrophotometry, primarily sought to examine the fluorescent DOC compounds present in precipitation in Birmingham, UK has been investigated (Catherine et al., 2008). Furthermore, how the fluorescence of the identified DOC compounds varies with meteorological parameters, by assessing the variations with stratiform/convective storm types; examining the variations with air mass type and source area using back-trajectory analysis; and investigating variations with wind speed and wind direction have been investigated (). The results of this study demonstrate the utility of fluorescence analysis for identifying and characterizing rainwater DOC compounds. This research has revealed information regarding fluorescent rainwater DOC compounds in Birmingham, UK and provides evidence in support of using fluorescence spectrophotometry as a means of

Organic pollution originating from industrial, agricultural and municipal wastewater discharge has become a common environmental problem in many lakes, rivers, estuaries and coastal waters. The commonly-used methods to study the composition of dissolved organic matter (DOM) (nuclear magnetic resonance, gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, size exclusion chromatography, etc.) need complicated sample pretreatment procedures and are not suitable for on-line or real-time determination. Excitation-emission matrix (EEM) fluorescence spectroscopy has been suggested as a powerful tool to characterize aquatic DOM which could detect the specific fluorescent fractions in organic matter from different sources with much higher sensitivity (Coble et al., 1996, as cited in Guo, 2010). Therefore, wastewater dissolved organic matter (DOM) from different processing stages of a sewage treatment plant in Xiamen was characterized using fluorescence spectroscopy by Gue at al. (Guo et al., 2010). The results of this study showed that excitation emission matrix fluorescence of wastewater DOM from a sewage treatment plant revealed high concentration of degradable protein-like fluorescence and the occurrence of xenobiotic-like component. This technique provides a fast and sensitive way to monitor the qualitative and quantitative variation of DOM during

Perylene-3,4:9,10-tetracarboxylic bisimide, so-called perylene bisimide (PBI) is known as red vat dyes (*fluorescent dyes*), and has been applied to pigments such as automotive finishes due to its light-fastness, thermal stability, and chemical inertness . Perylene bisimide (PBI) is a fluorescent dye which has strong emission and high photostability. Although PBI has been widely used for industrial materials, the application of PBI in analytical fields was limited mainly due to its high hydrophobicity. In recent years, however, unique and useful analytical methods based on PBI platform are being successfully developed by utilizing the characteristic features of this compound including its high hydrophobicity. In this regard, the recent trend of environmental and biological analysis using PBI was reviewed by Soh &

qualitatively characterizing rainfall DOC.

the whole sewage treatment process.

Fluorescence spectroscopy is an instrumental technique whose theory and methodology has been widely exploited for studies of molecular structure and function. It is therefore applicable to address molecular problems in food. Since many foods exhibit auto fluorescence it is considered highly relevant for characterization purposes and highthroughput screening. The main advantages of molecular fluorescence spectroscopy are its sensitivity and selectivity, in addition to its ease of use, instrumental versatility, speed of analysis and its non-destructive character.

Recently, it has been shown that excitation-emission matrix (EEM) fluorescence spectroscopy and three-way statistical methods, concretely Parallel Factor Analysis (PARAFAC) can be used for distinguishing between wine samples of different appellations, or between wine samples obtained with different ageing procedure (Airado-Rodrguez et al., 2011). At first, excitation-emission matrices (EEMs) were obtained and examined with the aim of identifying the main families of fluorescent compounds. Then PARAFAC was applied for exploratory analysis and the scores of the four selected components were obtained. The set of sample score values obtained in the PARAFAC decomposition were plotted against each other, to visualize clustering trends of samples belonging to different appellations. The potential of the autofluorescence of wine, through its Excitation-emission matrices (EEMs), combined with the three-way method PARAFAC for the purpose of discrimination of wine according to the appellation of origin, is shown in this paper. Wine samples were monitored with rapid and non-destructive front face fluorescence spectroscopy, yielding information about the wine throughout its appellation and ageing conditions. PARAFAC revealed four groups of fluorophores that were responsible for the main fluorescence of Spanish wines. Two of them were assigned to benzoic-like phenolic acids and phenolic aldehydes, and to monomeric catequins and polymeric proanthocyanidin dimers, respectively. The exploration of the matrix of score values obtained by PARAFAC reveals some distribution trends of the samples according with their appellation.

Rapid measurements of milk properties and discrimination of milk origin are necessary techniques for quality control of milk products. A study was undertaken to evaluate the potential of using front face fluorescence spectroscopy (FFFS) and synchronous fluorescence spectroscopy (SFS) for monitoring the quality of forty-five ewe's milk samples originating from different feeding systems by Hammamia et al. (Hammamia et al., 2010). Whereas, the physicochemical analyses and fluorescence spectra were conducted on samples during lactation periods (the first 11 weeks). Results obtained showed a good discrimination among milk samples with regard to feeding systems given to the ewes throughout the lactation periods. In addition, a better discrimination was observed with front face fluorescence spectroscopy than with synchronous fluorescence spectroscopy.

Fumonisins (FBs) are worldwide distributed and produced by Fusarium verticillioides and Fusarium proliferatum, mainly in corn and corn-based products (Soriano & Dragacci, 2007, as cited in Silva et al., 2009). Although several other fumonisin analogues have been characterized, fumonisin B1 (FB1) remains the most abundant in naturally contaminated

Current Achievement and Future Potential of Fluorescence Spectroscopy 239

advances in the noble metal clusters open a promising field toward the development of a satisfying fluorescence probe. In this regard, recently biomolecule-stabilized Au nanoclusters were demonstrated as a novel fluorescence probe for sensitive and selective detection of glucose (Jin et al., 2011). The fluorescence of Au nanoclusters was found to be quenched effectively by the enzymatically generated hydrogen peroxide (H2O2). By virtue of the specific response, the present assay allowed for the selective determination of glucose in the range of 1.0×10-5 M to 0.5×10-3 M with a detection limit of 5.0×10-6 M. In addition, it has been demonstrated the application of the present approach in real serum samples, which suggested its great potential for diagnostic purposes. In comparison with previous approaches for glucose detection, this method required no complicated preparation procedure, and used only commercially available materials. It also exhibited environmentally friendly feature and good sensitivity. Furthermore, the present nanosensor possessed red emission and excellent biocompatibility, which presage more opportunities

Recently, metalloprotein design and semiconductor nanoparticles have been combined to generate a reagent for selective fluorescence imaging of Pb2+ ions in the presence red blood cells (Shete et al., 2009). A biosensor system based on semiconductor nanoparticles provides the photonic properties for small molecule measurement in and around red blood cells. Metalloprotein design was used to generate a Pb2+ ion selective receptor from a protein that is structurally homologous to a protein used previously in this biosensing system. This designed protein demonstrates a highly sensitive and selective biosensor that can reversibly detect Pb2+ ions in aqueous solutions. The modularity of semiconductor nanoparticle-based biosensors has allowed metalloprotein design and different semiconductor materials to be combined to significantly improve the detection of soluble, exchangeable Pb2+ ion

The development of artificial receptors for molecular recognition studies of zwitterion amino acids under the physiological conditions is a very important research area since it can help to understand the important roles of free amino acids in biological systems. In this regard, a new fluorescence macrocyclic receptor based on the Zn(II) complex of a C2 terpyridine and a crown ether has been developed for molecular recognition of zwitterion amino acids in water/DMF solution with remarkable selectivity towards L-aspartate (K =

Copper is an essential trace element, its deficiency is one of the causes of anemia, but it is toxic at higher concentration levels. The uptake of copper by human beings above a certain level is known to cause gastrointestinal catarrh, Wilson's disease, hypoglycemia, and dyslexia. Increases in copper concentration in water and plants have resulted from industrial and domestic waste discharge, refineries, disposal of mining washings, and the use of copper as a base compound for antifouling paints. Therefore, the trace copper content in water and food must be monitored on a daily basis. In this regard, a highly sensitive and selective optical sensor for the determination of trace amounts of Cu2+ based on fluorescence quenching has been developed (Aksuner et al., 2009). The sensing membrane was prepared by immobilization of a novel fluorescent Schiff base ligand 4-(1-phenyl-1-methylcyclobutane 3-yl)-2-(2-hydroxy-5-romobenzylidene) aminothiazole, on polyvinlyl chloride. The accuracy of the proposed sensor was confirmed by analyzing standard reference materials of natural water and peach leaves. The sensor was successfully applied for the determination of copper

for studying the biological systems in future applications.

concentrations to address inefficient Pb2+ ion chelation therapy.

4.5x104 M-1) and L-cysteine (K = 2.5x104 M-1) (Kwong et al., 2009).

Corn-based foods followed by fumonisin B2 (FB2).The problems and risks associated with fumonisin contamination have resulted in the development of precise, reliable and sensitive methods for its determination in corn and corn-based foods (Magan & Olsen, 2004, as cited in Silva et al., 2009). Therefore, the quality parameters in the analysis of FB1 and FB2 in cornbased products obtained with LC with fluorescence detector have been investigated (Silva et al., 2009). Furthermore, a comparison study between fluorescence detector (FD), mass spectrometry, and tandem mass spectrometry with a triple quadrupole (QqQ) analyzer using an electrospray ionization interface for the determination of fumonisin B1 and B2 in corn-based products has been performed. A comparative study of the three LC detectors, FD, single quadrupole, QqQ for the analysis of fumonisins in corn samples has been performed. The response achieved by the three detectors was sensitive enough to study the maximum contents established by the EU legislation. These LC detectors would be appropriate for quantification purposes but the acquisition of at least two transitions achieved with QqQ provided a univocal identification.

Low-molecular-weight compounds have been used widely as animal drugs, food additives, and pesticides, to achieve maximum productivity and profits directly or indirectly through food products. However, residues of such low-molecular-weight compounds in food products have been proven to be detrimental to human health. Therefore, development of a microsphere-based competitive fluorescence immunoassay for the determination of hazardous low-molecular-weight compounds in food has been described (Zou et al. 2008). In this method, antigens are covalently bound to carboxy-modified microspheres to compete monoclonal antibody with low-molecular- weight compounds in food samples; mouse IgG/fluorescein isothiocyanate conjugate is used as the fluorescent molecular probe. Thus, the hazardous low-molecular-weight compounds are quantified using a multiparameter flow cytometer. This method has been evaluated using clenbuterol as a model compound. It has a sensitivity of 0.01 ng/mL with dynamic range of 0.01–100 ng/ mL, and the concentration of clenbuterol providing 50% inhibition (IC50) is 1.1 ng/mL. The main advantages of this method are its high efficiency, biocompatibility, and selectivity, as well as ultralow trace sample consumption and low cost.

The aspects of fluorescence spectroscopy that may have value for solving problems in food science and technology have been summarized in a review article by Strasburg & Ludescher (Strasburg et al., 1995). In this review article, the techniques described, which depend on the measurement of the intensity, energy and polarization of fluorescence emission, have been illustrated by examples taken from the food science and related literature.
