Blueberries: an experimental study of their ripening using Raman spectroscopy at 1064 nm and a model for predicting anthocyanin content

A set of 28 lyophilized blueberry samples was measured by means of Raman spectroscopy. These samples were selected to represent three different ripening stages: unripe (m2), medium (m3), and mature (m5), respectively. The concentration of total anthocyanins (AT), and of delfinidins (DF), cyanidins (CY), petunidins (PT), and malvidins (MV) was available, which was previously measured by standard analytical techniques. The data set was processed by means of multivariate analysis. Three- and two-class cases were studied, depending on whether all ripening stages (m2+m3+m5) or the limited set (m2+m3) were considered. The processed spectra allowed to achieving qualitative and quantitative information. A qualitative assessment of ripening was obtained by means of Principal Component Analysis (PCA). Then, Partial Least Square (PLS) was used to build predictive models for quantitative assessment of anthocyanins.