Suivi de la stabilité physico-chimique et de la capacité antioxydante (pH, DPPH, TBARS) de matrices alimentaires (yaourt nature, huile d’olive) au cours de 21

Abstract

This work aims to evaluate and compare the stability of plain yogurt and olive oil, two staple products of the Mediterranean basin, over a 21-day storage period. The study focuses primarily on monitoring their degradation kinetics and the evolution of their antioxidant capacity. This approach allows analyzing the quality of these matrices using three simple and accessible spectrophotometric indicators: pH, the DPPH assay, and the TBARS index. The results showed a progressive decrease in yogurt pH from 5.37 to 4.72 within 21 days, reflecting a post-acidification linked to the residual activity of lactic ferments. Quantitative analysis of its antioxidant capacity revealed a non-monotonic profile, with an increase up to Day 14 due to the release of bioactive peptides from fermentative proteolysis, followed by a sharp drop at Day 21, in parallel with a 50% increase in the TBARS index signaling secondary lipid oxidation. For olive oil, the analysis highlighted that temperature is the determining factor in degradation. At 40 degrees Celsius, the antioxidant activity collapsed almost completely while the TBARS index increased exponentially, unlike storage at 4 degrees Celsius where degradation remained moderate. The very strong statistical correlations observed at 40 degrees Celsius confirm the internal consistency of these three indicators. It emerges from these results that, under the experimental conditions of our study, the pH-DPPH-TBARS triptych validates its effectiveness as a simple and relevant routine tool for comparative quality control. This dynamic highlights a progressive microbial post-acidification for yogurt and a critical thermal sensitivity for olive oil. This study outlines certain limitations related to the semi-quantitative nature of TBARS and the limited number of measurement points, opening perspectives to enrich the approach with the peroxide value and lactic ferment enumeration.