Comparative Evaluation of Wild Plum (Prunus spinosa L.) Stone Fruits and Leaves: Insights into Nutritional Composition, Antioxidant Properties, and Polyphenol Profile

<i>Prunus spinosa</i> L. is a shrub with nutritional potential, yet limited information is available on the composition of its stone fruit and leaves. This study aimed to investigate and compare the macro and micronutrients, fatty acid profile, and lipophilic and hydrophilic antioxidant compounds in fruits and leaves, as well as their potential functional properties. The results revealed that leaves contain higher crude protein (10.94%) than fruits (6.46%) but lower crude fiber (13.86% compared to 22.16%). The iron (370.37 mg/kg) and manganese (43.57 mg/kg) were significantly higher (<i>p</i> < 0.05) in leaves than in fruits (44.87 versus 7.02 mg/kg). The fruits' lipid profile was rich in monounsaturated fatty acids (56.8%), whereas the leaves showed higher saturated fatty acids (38.3%) and polyunsaturated fatty acids (43.7%). The leaves also presented significantly higher n-3 content (25.2%) compared with fruits (1.80%). The antioxidant compounds were higher in the leaves, with total vitamin E exceeding 1268 mg/kg, primarily α-tocopherol (1214.98 mg/kg) isoform, lutein (409.38 mg/kg), and astaxanthin (3.74 mg/kg), compared with only 74.75 mg/kg total vitamin E in the fruits. The total hydroxycinnamic polyphenols in leaves were 92.63% higher in leaves than in fruits, with anthocyanins at 63.23% and flavonols at 95.82%. Although the leaves demonstrated superior antioxidant potential and mineral content compared to the fruits, making it a promising candidate for nutraceutical and functional food applications, the fruits maintained a healthier lipid profile suitable for dietary fat intake. This comparative analysis highlights the distinct nutritional and bioactive composition of <i>Prunus spinosa</i> co-products.