Chromatographic Determination and Antimicrobial Evaluation of Walnut (Juglans regia L.) Septa from Different Habitats

Walnut septum (WS), a major by-product of walnut processing, represents a promising source of bioactive compounds with potential antioxidant and antimicrobial properties. This study aimed to characterise the phytochemical composition of WS extracts from different habitat origins and evaluate their antimicrobial activity. Total amino acids were profiled by gas chromatography–mass spectrometry, while phenolic compounds were analysed using high-performance liquid chromatography. Both methods were evaluated according to ICH Q2 (R2) guidelines for analytical procedure validation. The results showed a complex composition of amino acids and polyphenols, including ellagic acid and quercitrin. However, it was clear that habitat variations in WS samples had a significant impact on the quantities and composition of phenolic compounds and total amino acids in WS extracts. Antimicrobial activity was assessed against Gram-positive and Gram-negative bacterial strains. Variations in antimicrobial efficacy were associated with differences in phenolic composition and content due to habitat differences in WS sample origins. Collectively, this study highlights the WS as a valuable agro-industrial by-product with potential applications as a natural source of antimicrobial compounds in food and pharmaceutical systems.