Antioxidant and Antibacterial Activities of Onion Extract and Applications in Mixed Fruit and Vegetable Juice

Abstract

The objectives of this research were to evaluate the antioxidant and antibacterial activities of ethanolic onion extract from 3 varieties (Allium cepa Linn., Allium ascalonicum Linn. and Murraya koenigii) and application in mixed fruit and vegetable juice. Determination of chemical properties of onion extract included total phenolic compound, flavonoid, antioxidant activity by ferric ion reducing antioxidant power (FRAP) and 2, 2-diphenyl-1-picrylhydrazyl radical scavenging activity (DPPH) assays. Antibacterial activity against Bacillus cereus, Staphylococcus aureus, Escherichia coli O157:H7 and Salmonella Enteritidis was performed by determination of minimum inhibitory concentration (MIC) and antibacterial index (AI). Results showed that Allium ascalonicum Linn. (RO) extract contained the highest amount of total phenolic compound, flavonoid and antioxidant activity by FRAP and DPPH assays (17.22±2.24 µmol GAE/g DW, 3.10± 0.23 µmol QT/g DW, 5.65±0.44 µmol trolox/g DW and 6.27±0.21 mg vit C/g DW, respectively). All onion extracts were able to inhibit the growth of all tested bacteria except Salmonella Enteritidis with MIC between 0.125-1.75 g/mL and AI between 14.09-24.81. All onion extracts significantly (p£0.05) increased total phenolic compound and flavonoid contents in mixed fruit and vegetable juice. All onion extracts were able to inhibit the growth of B. cereus, S. aureus and E. coli O157:H7 approximately 2, 2 and 1.5 log CFU/mL in mixed fruit and vegetable juice, respectively, during the storage at 4 °C for 14 days.