2.5.1. Inhibition of b-carotene bleaching
The antioxidant activity of mushroom extracts was evaluated by the b-carotene linoleate model system. A solution of
b-carotene was prepared by dissolving b-carotene (2 mg) in chloroform (10 ml). Two millilitres of this solution were pipetted into a 100 ml round-bottom flask. After the chloroform was removed at 40 C under vacuum, linoleic acid (40 mg), Tween 80 emulsifier (400 mg), and distilled water (100 ml) were added to the flask with vigorous shaking.
Aliquots (4.8 ml) of this emulsion were transferred into different test tubes containing different concentrations of the mushroom extracts (0.2 ml). The tubes were shaken and incubated at 50 C in a water bath. As soon as the emulsion was added to each tube, the zero time absorbance was measured at k = 470 nm using a spectrophotometer. Absorbance readings were then recorded at 20-min intervals until the control sample had changed colour. A blank, devoid of
b-carotene, was prepared for background subtraction. Lipid peroxidation (LPO) inhibition was calculated using the following equation: LPO inhibition = (b-carotene content after 2 h of assay/initial b-carotene content) 100. The extract concentration providing 50% antioxidant activity (EC50) was calculated from the graph of antioxidant activity percentage against extract concentration. TBHQ was used as standard (Barros & Baptista et al., 2007; Barros & Ferreira et al.,2007).