Bleaching of Apple Pomace by Hydrogen Peroxide in Alkaline Conditions: Optimisation and Characterisation of the Products

Abstract

Dried apple pomace from a cider plant was bleached by sodium chlorite in acidic conditions, sodium hypochlorite or hydrogen peroxide in alkaline conditions. The most satisfactory treatment for intensity and evenness of the bleaching was hydrogen peroxide. Response surface methodology was used to study this treatment. Both pH and concentration of hydrogen peroxide had very significant effects on bleaching, yield and swelling capacity. At high pH values and peroxide concentration, white products were obtained with high swelling capacities but low yields. As effects were not linear, empirical second degree models were built to fit results of yield and swelling capacity. Equations were obtained with high significance and good predictive value. The alkaline peroxide treatment extracted polyphenols but also pectic materials from the apple pomace, while hemicelluloses and cellulose remained in the bleached material. Water absorption and retention were also increased, though less than swelling, and water uptake was faster.