Katarzyna Włodarska

Explorative study of apple juice fluorescence in relation to antioxidant properties

Total fluorescence spectra (excitation-emission matrices, EEM) were recorded for a series of commercial apple juices, including clear and cloudy juices produced from concentrate, cloudy juices that were not from concentrate, and freshly squeezed juices. An exploratory study of the spectra with parallel factor analysis (PARAFAC) revealed three groups of fluorophores with different emission properties, and these properties were characterized by excitation/emission maxima at 270/315nm, (310, 370)/455nm, and 430/(550, 680)nm, respectively. A regression analysis of the total fluorescence spectra arranged into three-way arrays using N-way partial least squares regression methods (NPLS1 and NPLS2) and an analysis of the unfolded spectra by partial least squares methods (PLS1 and PLS2) revealed quantitative relations between the fluorescence and antioxidant properties of juices. The best models for the total phenolic contents and total antioxidant capacities were obtained by applying the NPLS1 method to the EEM. The model parameters were as follows: R(2)CV=0.802, RPD=2.3 for the total phenolic content and R(2)CV=0.808 and RPD=2.3 for the total antioxidant capacity. These results show the potential use of fluorescence spectroscopy for screening apple juices for their antioxidant properties.

Classification of commercial apple juices based on multivariate analysis of their chemical profiles

ABSTRACT Currently, a wide range of differently processed apple juices is available on the market. In this study the quality of commercial apple juices from four product categories was evaluated on the basis of their chemical profiles (total soluble solids, pH, titratable acidity, ratio of soluble solids to acidity, sugars, total phenolics content, and antioxidant activity) using multivariate methods. Principal component analysis has revealed, that the chemical parameters, such as titratable acidity, ratio of soluble solids to acidity, and pH (PC1) and sugars and total soluble solids (PC2) appears to be the parameters most differentiating the samples. Five classes of juices with similar chemical composition were detected using hierarchical cluster analysis. The exploratory analysis of the overall chemical profiles revealed that the juices clear from concentrate, cloudy not from concentrate and freshly squeezed, were easily distinguishable due to their unique properties. In contrast, cloudy juices from concentrate showed properties similar to juices of other classes. The classification based on k-nearest neighbors method had high sensitivity and low classification error for clear juices from concentrate and cloudy not from concentrate. The classification failed for the cloudy juices from concentrate.

Evaluation of Quality Parameters of Apple Juices Using Near-Infrared Spectroscopy and Chemometrics

Near-infrared (NIR) spectra were recorded for commercial apple juices. Analysis of these spectra using partial least squares (PLS) regression revealed quantitative relations between the spectra and quality- and taste-related properties of juices: soluble solids content (SSC), titratable acidity (TA), and the ratio of soluble solids content to titratable acidity (SSC/TA). Various spectral preprocessing methods were used for model optimization. The optimal spectral variables were chosen using the jack-knife-based method and different variants of the interval PLS (iPLS) method. The models were cross-validated and evaluated based on the determination coefficients (R2), root-mean-square error of cross-validation (RMSECV), and relative error (RE). The best model for the prediction of SSC (R2 = 0.881, RMSECV = 0.277 °Brix, and RE = 2.37%) was obtained for the first-derivative preprocessed spectra and jack-knife variable selection. The optimal model for TA (R2 = 0.761, RMSECV = 0.239 g/L, and RE = 4.55%) was obtained for smoothed spectra in the range of 6224–5350 cm−1. The best model for the SSC/TA (R2 = 0.843, RMSECV = 0.113, and RE = 5.04%) was obtained for the spectra without preprocessing in the range of 6224–5350 cm−1. The present results show the potential of the NIR spectroscopy for screening the important quality parameters of apple juices.

Motywy wyboru żywności przez konsumentów soków – badania pilotażowe

The aim of this study was to evaluate the food choice motives of consumers. Preliminary studies were carried out on a group of 96 consumers of juices based on the Food Choice Questionnaire. It is a tool, which enables the systematic measurement of the importance of diff erent food choices. The confi rmatory (CFA) and exploratory factor analysis (EFA) and hierarchical cluster analysis (HCA) methods were used for analysis of data. The results of factor analysis revealed 12 new groups of factors determining the choice of food. The most important factors infl uencing selection of food were: taste, worth the money and a positive eff ect on external appearance. Using hierarchical cluster analysis three segments of consumer were identifi ed, with diff erent attitudes towards food choices: engaged – enthusiasts of healthy nutrition, indiff erent – not attaching attention to what they eat and practical – focused on the price and availability of products. Segmentation of consumers with similar attitudes towards choice of food can help the producers in precise targeting of marketing messages to a selected group of consumers.