Evaluation of the Main Functional and Bromatological Properties of Walnut Kernels

Walnut kernels are highly valued for their mineral, vitamin, protein, lipid, and polyphenol content. To understand their nutritional value, quality, and potential for human consumption and industrial use, the chemical composition of different genotypes must be analyzed. The kernel composition of 41 walnut genotypes (31 Romanian, 8 Moldovan, and 2 American) from the Research Institute for Fruit Growing Pitesti germplasm collection in Romania was analyzed. The following parameters were analyzed: moisture, ash, sugars, lipids, polyphenols, tannins, flavonoids, carotenoids, and anthocyanins. The Moldovan genotypes exhibited the highest average kernel moisture and ash content, outperforming the Romanian average, while the individual American cultivars sat between them. Regarding sugar content, ‘Hartley’ cv. recorded the highest individual level, followed by the Romanian and Moldovan averages, whereas ‘Chandler’ cv. displayed lower values. For lipids and polyphenolic fractions, ‘Chandler’ cv. prominently surpassed both regional averages, while ‘Hartley’ cv. recorded values well below them, though both American cultivars excelled individually in anthocyanin accumulation. ATR-FTIR spectroscopy combined with second-derivative Savitzky–Golay preprocessing further supported the observed compositional variability. The most discriminative spectral regions were 3050–2800 cm−1 and 1800–900 cm−1, which are mainly associated with functional groups related to lipids, proteins, and carbohydrates. Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) identified distinct compositional groups, with lipid-related spectral features representing the main source of variability among the samples. These results emphasize the significant biochemical diversity among walnut genotypes and support the selection of cultivars with valuable nutritional and technological properties.