Non-destructive fluorescence spectroscopy for quality evaluation of almond oils extracted from roasted kernel

Abstract

Almond oils extracted from roasted kernels at different roasting times at 150 °C were analyzed to quantify quality parameters such as acidity, peroxide value, K₂₃₂, K₂₇₀, antioxidant activity and the oxidative stability index. The roasting process induced oxidation of the chemical compounds in the oil, resulting in increased acidity, peroxide value, K₂₃₂ and K₂₇₀. The antioxidant activity exhibited a decreasing trend over time, while the oxidative stability showed only slight changes. Excitation-emission matrices (EEMs) were directly scanned on almond oil samples. The combination of the EEMs with parallel factor analysis (PARAFAC) provided qualitative information about the main fluorophores and their evolution with the roasting time. Quantitative information was obtained using unfolded partial least squares (U-PLS), demonstrating the effectiveness of the fluorescence technique in combination with multivariate analysis to quantify analytical parameters in almond oils. Prediction models were developed, and subjected to external validation. The coefficients of determination in the external validation were higher than 0.94 for all parameters except k270.