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 beta-carotene-linoleate bleaching agar well diffusion and beta-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 beta-carotene ranging from 15.3 to 38.2mm in diameter. At a concentration of 50 mu LmL-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 mu L 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 beta-carotene-linoleate bleaching broth dilution assay ranging from 0.195 to 50 mu LmL-1. The MOBICs of plant extracts in a range of 0.1951.56 mu LmL-1 could reveal an ability to inhibit the oxidation of beta-carotene-linoleate broth. Cellulose-based film containing cinnamon, clove or green tea showed positive activity against beta-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 (c) 2011 John Wiley & Sons, Ltd.