Bleaching ornamental plant material: a brief review

Abstract

The Australian dried flower and foliage industry is expanding rapidly because of increasing demand overseas for unique native flora. The industry compliments the export of fresh, native cut flowers. Bleaching is an important step in the processing of plant material that is to be marketed, bleached or dyed. Profitability is dependant upon attainment of high white quality and on cost efficient utilisation of expensive bleaching chemicals. Sodium chlorite is an excellent bleaching agent because it is relatively selective for lignin. Hydrogen peroxide may be more practical for some plant materials because it is less expensive. Choice of an effective bleach activator, such as hypochlorous acid for chlorite bleach, is critical for cost efficient processing. Relative efficiency of different bleach regimes can be compared by assaying residual lignin using ultraviolet or fourier transform infrared spectroscopy. Multistage bleaching, where peroxide is used first to remove about 50% of lignin, followed by chlorite treatment, is likely to reduce processing costs.