Study of Antimicrobial, Antioxidant and Cytotoxicity Properties of Selected Plant Extracts for Food Preservative Applications

An attempt has been made to evaluate antimicrobial, antioxidant and cytotoxicity properties of extracts from onion ( Allium cepa L. ), garlic ( Allium sativum ), leaves of guava ( Psidium guajava ), papaya ( Carica papaya ), tea ( Camellia sinensis ), baen ( Avicennia alba ) and keora ( Sonneratia apetala ), respectively to apply as natural preservatives for tomatoes. The air-dried plant materials of the respective plant species were subjected to ethanol-methanol extraction, concentrated and stored at 4 °C before use. The extracts were dissolved in 95% ethanol for analysis of antioxidant and antimicrobial properties. Of the extracts tested, tea extracts showed the highest zone of inhibition against several pathogenic bacteria ( E. coli 35.0±3.2 mm; P. aeruginosa 29.3±2.6 mm; S. typhi  28.4±2.1 mm and S. pyogenes 27.7±3.7 mm) using the disc diffusion method. In regard to DPPH free radical scavenging assay, keora and guava extracts showed the highest percentage of radical scavenging activity with the values of 89.64± 0.18 and 89.39± 0.88, respectively, which were in agreement with higher total antioxidant capacity (TAC) of these extracts obtained by the phosphomolybdenum method. Brine shrimp lethality bioassay for cytotoxicity assessment showed LC 50  of 132.54 ± 18.99 µ g/mL for the leaf extract of keora which was found to be most toxic among all studied extracts. The initial results indicated that the extracts could be used for food preservative applications based on the antimicrobial, antioxidant and cytotoxicity properties of the tested extracts. However, efficacy, stability and safety issues need to be addressed with both in vitro and in vivo studies.