Antioxidant Properties of Selected Plant Extracts and Application in Packaging as Antioxidant Cellulose‐Based Films for Vegetable Oil

Selected plant extracts including cinnamon, clove, ginger, green tea and thyme were investigated for their antioxidant activity by using both β‐carotene‐linoleate bleaching agar well diffusion and β‐carotene‐linoleate bleaching broth assays, and for radical scavenging activity against free radicals using a 2,2‐diphenyl‐1‐picrylhydrazyl assay. Undiluted plant extracts (except ginger oil) showed a yellow zone of β‐carotene ranging from 15.3 to 38.2 mm in diameter. At a concentration of 50 μL mL^‐1, thyme yielded the highest antioxidant activity (260%), followed by ginger (254%), cinnamon (108%), clove (106%) and green tea (101%), respectively. Conversely, at a plant extract concentration of 0.39 μL mL^‐1 solution in ethanol, green tea yielded the highest radical scavenging activity (94.3%), followed by clove (93.4%), cinnamon (91.1%), thyme (30.4%) and ginger (8.29%), respectively. The minimum oxidative bleaching inhibitory concentrations (MOBICs) of these plant extracts were determined using a β‐carotene‐linoleate bleaching broth dilution assay ranging from 0.195 to 50 μL mL^‐1. The MOBICs of plant extracts in a range of 0.195–1.56 μL mL^‐1 could reveal an ability to inhibit the oxidation of β‐carotene‐linoleate broth. Cellulose‐based film containing cinnamon, clove or green tea showed positive activity against β‐carotene‐linoleate oxidation and 2,2‐diphenyl‐1‐picrylhydrazyl radicals. Protective effects of plant extracts incorporated in cellulose‐based pouches in stabilizing soybean oil were tested by measuring their peroxide values and free fatty acid contents during accelerated storage. Green tea‐incorporated cellulose‐based pouches exhibited stronger antioxidant properties in soybean oil than do butylated hydroxyanisole‐incorporated cellulose‐based pouches. This study showed the potential use of plant extracts as antioxidants for food packaging application. Copyright © 2011 John Wiley & Sons, Ltd.