Surface-enhanced Raman spectroscopy study of commercial fruit juices

Surface-enhanced Raman Spectroscopy (SERS) is a vibrational spectroscopy holding potentials for a rapid evaluation of quality and composition of food industry products without any need of sample preparation. In fact, SERS combines the advantages of the Raman effect such as the high specificity (ability to identify a given molecular species in the presence of many other chemicals) with the use of nanosized metallic materials enabling Raman signal enhancement. Among many nanomaterials, gold nanoparticles (GNPs) and their colloidal dispersions have attracted great interest for SERS applications due to their unique properties of small size, large surface area to volume ratio, high reactivity to the living cells, stability over high temperatures. In this frame, a low-cost home-made nanosized substrate has been designed and used for the investigation of commercial fruit juices. The substrate is based on home-made 50-nm sized GNPs. The use of the designed substrate has allowed us to observe the SERS spectra of commercial juices featuring a low-level of Raman signal with a commercial micro-Raman apparatus. Thanks to the use of a wavelet denoising procedure and background subtraction spectra with clear features have been obtained. Their quantitative analysis has enabled to evidence the presence of juice components of great importance for the quality evaluation of the products, such as fructose and pectin. The overall inspection of the results has confirmed the potentialities of SERS in food industry especially because of the use of home-made substrates well-suited to be employed for the eventual on-line product evaluation.