Screening of Antioxidant Properties of the Apple Juice Using the Front-Face Synchronous Fluorescence and Chemometrics
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Screening of Antioxidant Properties of the Apple Juice Using the Front-Face Synchronous Fluorescence and Chemometrics Katarzyna Włodarska 1 & Katarzyna Pawlak-Lemańska 1 & Igor Khmelinskii 2 & Ewa Sikorska 1
Received: 21 May 2016 / Accepted: 7 November 2016 # The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract Fluorescence spectroscopy is gaining increasing attention in food analysis due to its higher sensitivity and selectivity as compared to other spectroscopic techniques. Synchronous scanning fluorescence technique is particularly useful in studies of multi-fluorophoric food samples, providing a further improvement of selectivity by reduction in the spectral overlapping and suppressing light-scattering interferences. Presently, we study the feasibility of the prediction of the total phenolics, flavonoids, and antioxidant capacity using front-face synchronous fluorescence spectra of apple juices. Commercial apple juices from different product ranges were studied. Principal component analysis (PCA) applied to the unfolded synchronous fluorescence spectra was used to compare the fluorescence of the entire sample set. The regression analysis was performed using partial least squares (PLS1 and PLS2) methods on the unfolded total synchronous and on the single-offset synchronous fluorescence spectra. The best calibration models for all of the studied parameters were obtained using the PLS1 method for the single-offset synchronous spectra. The models for the prediction of the total flavonoid content had the best performance; the optimal model was obtained for the analysis of the synchronous fluorescence spectra at Δλ = 110 nm (R2 = 0.870, residual predictive deviation (RPD) = 2.7). The optimal calibration models for the
* Ewa Sikorska [email protected] 1
Faculty of Commodity Science, Poznań University of Economics and Business, al. Niepodległości 10, 61-875 Poznań, Poland
2
Universidade do Algarve, FCT, DQF and CIQA, Campus de Gambelas, 8005-139 Faro, Portugal
prediction of the total phenolic content (Δλ = 80 nm, R2 = 0.766, RPD = 2.0) and the total antioxidant capacity (Δλ = 70 nm, R2 = 0.787, RPD = 2.1) had only an approximate predictive ability. These results demonstrate that synchronous fluorescence could be a useful tool in fast semiquantitative screening for the antioxidant properties of the apple juices. Keywords Apple juice . Total phenolics . Total flavonoids . Synchronous fluorescence . Partial least squares regression
Introduction Phenolic compounds account for the metabolic activity and antioxidant properties of plant-based foods and for the putative health benefits to humans (Scalbert et al. 2005). Moreover, polyphenols affect organoleptic properties of foods: their color, flavor, astringency, and hardness (Robbins 2003). The assessment of polyphenolic compounds and their antioxidant activity is one of important aspects of quality studies of many foods. The HPLC method is mainly used for the assessment of individual phenolics, coupled with absorbance,
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