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 concen-
trations 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 con-
tent) 100. The extract concentration providing 50% antioxidant
activity (EC50) was calculated from the graph of antioxidant activ-
ity percentage against extract concentration. TBHQ was used as
standard (Barros & Baptista et al., 2007; Barros & Ferreira et al.,
2007).