Comparative analysis of volatile profiles and antimicrobial activities of freeze-dried and oven-dried pomegranate seeds: implications for waste valorization in a circular economy

Abstract

Pomegranate (Punica granatum), an ancient and well-recognized fruit, is highly valued in traditional medicine and the food industry for its rich composition of phytochemicals. This research investigated the effect of freeze-drying (FD) and oven-drying (OD) on the aroma profile and antibacterial activity of pomegranate seed essential oils (EOs). The aromatic compounds were evaluated using four different extraction techniques—hydrodistillation (HD), supercritical fluid extraction (SFE), headspace solid-phase microextraction (HS-SPME), and simultaneous hydrodistillation extraction (SHDE) for comparison. Antibacterial activity of the EO was tested in 7 microorganisms, including 3 Gram-positive (Enterococcus faecalis, Staphylococcus aureus, Bacillus cereus), 3 Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae), and yeast (Candida albicans). A total 93 compounds (FD) and 55 compounds (OD) were identified, belonging to groups such as carbonyls, fatty acids, esters, furans, alcohols, lactones, and other unspecified categories. Furthermore, there were no significant differences in the antimicrobial properties of the EOs between the two drying methods. E. coli exhibited the highest resistance to the tested EOs as its growth remained uninhibited. K. pneumoniae and P. aeruginosa demonstrated resistance, with no inhibitory effects observed except at the highest concentrations tested (4550 μg∙g−1 and 4580 μg∙g−1). Among the Gram-positive bacteria, S. aureus was inhibited at 4550 μg∙g−1 and 4580 μg∙g−1, B. cereus at 4550 μg∙g−1 and 2425–4580 μg∙g−1, and E. faecalis at 2275 μg∙g−1 and 2425–4850 μg∙g−1, while C. albicans was the most susceptible (1138 μg∙g−1 and 1213 μg∙g−1). SFE proved effective in extracting fatty acids, particularly saturated fatty acids (SFAs), while HD and SHDE were most effective in extracting carbonyl compounds.