A Study of Juglone in Georgian Walnuts (Juglon regia) by Chromato-Mass Spectrometry

Abstract

The study concerns the identification and quantification of the biologically active naphthoquinone, juglone (5-hydroxy-1,4-naphthoquinone), in the walnut (Juglans regia), a species widespread in Georgia, using an ultra-high-performance liquid chromatograph. The relevance of this research lies in the need to valorize agri-food waste and adopt zero-waste principles, which constitute an important aspect of the circular economy. Walnut peel obtained during processing is considered a potentially rich source of juglone, which is used for its antimicrobial, anti-inflammatory, antifungal, and other effects. Mass spectrometric analysis identified juglone with a characteristic molecular mass (m/z 173 [M-H]). The effects of different extraction methods (ultrasound, classical, high pressure/temperature, hot extraction with reflux, lyophilization) and solvent on the yield of the target compound were compared. Quantitative data showed that the maximum juglone content was observed in the ethyl acetate extract of lyophilized walnut skin, exceeding that of the ethyl acetate extract of the sample dried at 40°C and of the raw skin. Relatively low concentrations were detected in the ultrasonic and classical extraction using 50% ethanol, while the minimum amount was found in the condensate formed during lyophilization. The results obtained indicate that walnut peel represents a promising raw material for juglone, and that lyophilization combined with ethyl acetate extraction can be considered the optimal technological approach for maximizing the extraction of the target compound. This study provides a basis for the targeted utilization of walnut agro-waste and for the optimization of technological processes aimed at obtaining bioactive compounds.