Intrinsic Fluorescence Markers for Food Characteristics, Shelf Life, and Safety Estimation: Advanced Analytical Approach

Abstract

Food is a complex matrix of proteins, fats, minerals, vitamins, and other components. Various analytical methods are currently used for food testing. However, most of the used methods require sample preprocessing and expensive chemicals. New analytical methods are needed for quick and economic measurement of food quality and safety. Fluorescence spectroscopy is a simple and quick method to measure food quality, without sample preprocessing. This technique has been developed for food samples due to the application of a front-face measuring setup. Fluorescent compounds-fluorophores in the food samples are highly sensitive to their environment. Information about molecular structure and changes in food samples is obtained by the measurement of excitation-emission matrices of the endogenous fluorophores and by applying multivariate chemometric tools. Synchronous fluorescence spectroscopy is an advantageous screening mode used in food analysis. The fluorescent markers in food are amino acids tryptophan and tyrosine; the structural proteins collagen and elastin; the enzymes and co-enzymes NADH and FAD; vitamins; lipids; porphyrins; and mycotoxins in certain food types. The review provides information on the principles of the fluorescence measurements of food samples and the advantages of this method over the others. An analysis of the fluorescence spectroscopy applications in screening the various food types is provided.

Keywords: chemometrics; excitation–emission matrices; fluorescence spectroscopy; food analysis; intrinsic fluorophores.

Figure 1

Schematic presentation of the setup in the front-face fluorescence measurement of a solid or liquid food sample. The obtained spectral data (excitation–emission matrix) and their corresponding chemometric processing are also shown.

Figure 2

Schematic presentation of the pathway to obtain pure spectra of the food-containing intrinsic emitters. An example of a honey sample: (a,b) EEM in 2D and 1D presentation, (c) estimated emission profiles obtained by MCR-ALS.

Figure 3

Emission spectrum of the non-fat milk. The emission maxima, under excitation at 290 nm and 330 nm, correspond to tryptophan (blue) and vitamin A (red), respectively, as intrinsic markers.

Figure 4

The normalized fluorescence emission spectra obtained on the whole maize seed using the optical fiber. Solid and dashed lines denote control and aflatoxin B1-contaminanted Zea mays seeds, respectively. Excitation wavelength: 340 nm (reproduced from reference [59]).

Figure 5

EEM heatmaps for the first (a) and the second (b) PARAFAC component corresponding to phenolics, and the third PARAFAC component (c) corresponding to proteins. Intensity scale is in arbitrary units (reproduced from reference [85]).