Constituents, Antioxidant and Antibacterial Abilities of Essential Oil of Dolichos lablab Flowers and Its Application as Food Preservative

Dolichos lablab flowers, as the dried buds of D. lablab L, was used as an ingredient in various dishes in China, and there were no studies on the constituents, antioxidant and antibacterial activity with the essential oil. The constituents, antioxidant and antibacterial ability of the essential oil of D. lablab flowers (EOF) obtained by hydro-distillation (HD) method were evaluated, and its efficacy in fresh pork preservation was studied. The 36 components were recognised, accounting for 96.46% of EOF. The proportion of oxygen-containing compounds in EOF was as high as 89.72%, of which fatty acid accounted for 65.82%. Among fatty acids, palmitic acid (33.86%), myristic acid (8.42%), lauric acid (5.42%) and 2E-dodecenoic acid (4.46%) were identified as the major compounds. EOF had an excellent antioxidant ability. The semi-radical scavenging concentrations (IC50) of EOF for 2,2-Diphenyl-1-picrylhydrazyl (DPPH⁻), 2,2′-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS⁺) and liposomal peroxidation were 3.09, 2.46 and 0.82 mg/mL. EOF also showed good antibacterial ability, including Bacillus subtilis, Listeria monocytogenes, Escherichia coli and Staphylococcus aureus. And the L. monocytogenes showed the highest sensitivity to EOF with the minimum inhibitory concentration (MIC) of 1.25 μg/mL and the minimum bactericidal concentration (MBC) of 2.5 μg/mL. Further research showed that EOF achieved its antibacterial effect by destroying the functional and structural integrity of cell membranes and cell walls of L. monocytogenes, leading to the leakage of alkaline phosphatase (AKP), nucleic acids and proteins, ultimately leading to L. monocytogenes death. The pork fresh-keeping results showed that 1.0% EOF extend the shelf-life of pork up to day 6, which was 2.00 times than the control during 7 days of refrigeration at 4°C. This study will provide the fundamental data support for future potential applications of EOF in food preservation.