Greece has a long tradition of table olive processing. In recent decades, the table olive industry has evolved into a dynamic sector of the Greek economy. Raman is an emerging spectroscopic technique that has found application in agri-food analysis due to rapid spectrum acquisition, noninvasiveness, and simple sample preparation. The effective control of fermentation requires on-line monitoring of process parameters to ensure the quality and safety of the final product. In this study, the efficiency of Raman spectroscopy as a rapid and non-destructive technique to monitor table olive fermentation was evaluated. Kalamata black olives were fermented in 7% (w/v) brine comprised of NaCl and KCl at a 1:1 ratio for 145 days. Three fermentations were performed, namely, (a) spontaneous fermentation with the indigenous microbiota and inoculated fermentations with (b) Lactiplantibacillus pentosus B281 and (c) a commercial starter culture (VegeStart-60) containing Lactiplantibacillus plantarum. Raman spectra were acquired during processing from the surface of olives from four spots of three different olive fruits. The spectra were analyzed using Partial Least Squares Regression (PLS-R) to estimate the counts of lactic acid bacteria (LAB), pH, and titratable acidity values directly from spectral data. In addition, Orthogonal Partial Least Squares Discriminant Analysis (Ortho PLS-DA) was employed to discriminate olive fruits between the beginning and the end of fermentation. The results showed that the most efficient PLS-R models provided R2 and RMSE scores for cross-validation of 0.60 and 0.61, 0.81 and 0.61, and 0.74 and 0.72 for LAB, pH, and titratable acidity, respectively. Moreover, Ortho PLS-DA successfully discriminated olive samples at the beginning and the end of the fermentation, providing promising perspectives for the use of Raman spectroscopy in on-line monitoring of table olive fermentation.
Acknowledgements: This work was funded by the Greek Ministry for Rural Development and Food, General Secretariat of Union Resources and Infrastructure, Special Agricultural Development Program (RAP) 2014-2022 (contract number Μ16ΣΥΝ-01086).
