Comparative study of nutrient and antioxidant contents in by-products of peach and nectarine varieties

This study investigates the nutritional composition and antioxidant potential of industrial by-products derived from various cultivars of peaches ( Prunus persica ) and nectarines ( Prunus persica var. nucipersica ), specifically focusing on peels, kernels, and pulps, to evaluate their suitability as functional food ingredients. Ash analysis showed high levels across all by-products, with the highest content found in the peels (8.1–9.6%), followed by the kernels (7.5–8.2%) and the pulps (1.2–2.3%). Total dietary fiber (TDF) content in all matrices exceeded the threshold defined by Regulation (EC) No 1924/2006 for the "source of fiber" claim, although none of the by-products can be qualified as "high protein" ingredients (protein content: 2.9–7.8%). Quantification of total phenolic content (TPC) identified kernels as the richest source (376–591 mg GAE 100 g −1 ), followed by peels (239–439 mg GAE 100 g −1 ) and pulps (117–265 mg GAE 100 g −1 ). Among the varieties studied, Sweet Dream, Nectatinto, and Royal Summer exhibited superior phenolic profiles. Antioxidant capacity, evaluated using ABTS•⁺, DPPH • , and FRAP assays, confirmed that kernels and, to a lesser extent peels from Sweet Dream and Royal Summer enhanced antioxidant activity. Direct radical scavenging assays (ABTS •+ and DPPH • ) corroborated the trends observed with extract-based methods, highlighting nectarine variety Nectatinto as the variety with the most favourable antioxidant profile, followed by peach varieties Sweet Dream and Royal Summer. Stability processes showed that freeze-drying more effective than oven-drying in preserving phenolic compounds and antioxidant activity across all by-products and varieties. These findings underscore the potential of peach and nectarine by-products as valuable sources of bioactive compounds for incorporation into functional food formulations.