A portable colorimeter (HunterLab, MiniScan XE, Reston, USA) was
used for measuring objective color using the L*, a* and b* scales of the
CIELab system. A D65 illuminant was used at an observation angle of
10° and a cell opening of 30 mm. The readings were obtained at three
different points, 30 min after the exposure of the samples to the
atmosphere.