Comparative Phytochemical Characterization and Total Phenolic Content of Aqueous Extracts of Azadirachta indica and Murraya koenigii with Isolation and Identification of Foodborne Microorganisms from Fresh Produce

Abstract

Background: Medicinal plants are an important source of bioactive phytochemicals with potential applications in food safety and antimicrobial therapy. Fresh fruits and vegetables are frequently contaminated with foodborne microorganisms, highlighting the need for natural antimicrobial agents. Comparative evaluation of phytochemical composition and antimicrobial potential of medicinal plants may provide valuable insights for food preservation and public health. Aim: The present study aimed to comparatively evaluate the phytochemical constituents and total phenolic content of aqueous extracts of Azadirachta indica (Neem) and Murraya koenigii (Curry leaves), and to investigate their antibacterial activity against foodborne bacterial isolates recovered from fresh produce. Methods: Aqueous extracts of neem and curry leaves were prepared using 10 g dried plant powder in 100 mL of distilled water. Qualitative phytochemical screening was performed to detect major secondary metabolites, while total phenolic content (TPC) was determined using the Folin-Ciocalteu method and expressed as mg gallic acid equivalents (GAE)/g extract. Fresh watermelon and tomato samples were microbiologically analyzed by total plate count and selective culture   techniques. Bacterial isolates were identified using cultural characteristics, Gram staining, IMViC, Triple Sugar Iron (TSI), catalase, and oxidase tests. Antibacterial activity was evaluated by the agar well diffusion method on Mueller-Hinton agar using extract concentrations of 100%, 75%, 50%, 25%, with streptomycin as the positive control. Results:  Both plants extracts contained alkaloids, flavonoids, phenols, tannins, saponins, terpenoids, and glycosides. Neem extract exhibited a substantially higher total phenolic content (81.8 mg GAE/g extract) than curry leaf extract (46.2 mg GAE/g extract). The total bacterial counts were 49.5 × 104   CFU/g in watermelon and 48.6 × 104   CFU/g in tomato samples. Escherichia coli was isolated from watermelon, whereas Salmonella spp. and fungal isolates were recovered from tomato samples. Both extracts demonstrated concentration-dependent antibacterial activity against E. coli, with neem extract exhibiting comparatively greater inhibitory activity, particularly at lower concentrations. Conclusions: The findings demonstrate that aqueous extracts of Azadirachta indica and Murraya koenigii are rich in bioactive phytochemicals and possess promising antibacterial activity against foodborne bacteria. The higher phenolic content and superior antibacterial efficacy of neem extract indicate its potential as a natural antimicrobial agent for food safety applications. These results provide a foundation for future investigations involving quantitative phytochemical analysis, antioxidant efficacy against a broader range of foodborne pathogens.