Drying temperature-dependent changes in grape seed bioactives and oxidative status: integrated HPLC/GC and multivariate analysis

Abstract: Drying temperature (40–80 °C) critically influences the stability of bioactive compounds in grape seeds and their functional responses. In this study, we evaluated the vitamin and phytosterol content of Boğazkere grape seeds using high-performance liquid chromatography (HPLC) and the fatty acid content using gas chromatography (GC). Antioxidant capacity was determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and the oxidative stress marker, malondialdehyde (MDA). Temperature-dependent and compound-specific alterations were observed: while selected vitamins and phytosterols showed distinct thermal susceptibilities, fatty acid profiles exhibited measurable remodeling. Antioxidant activity revealed non-linear dose- and temperature-dependent patterns, whereas MDA consistently decreased with increasing temperature, reflecting the reduced oxidative metabolism in dehydrated tissues. Multivariate analysis, including principal component analysis (PCA) and heatmap visualization, effectively discriminated temperature treatments and revealed correlations between compositional and functional parameters. The combined use of univariate and multivariate analyses revealed that the drying temperature reshaped not only individual bioactive compounds but also the overall biochemical profile of grape seeds. These findings establish a mechanistic link between thermal processing and bioactive stability, providing a chemical basis for optimizing grape seed valorization in food systems.