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.