Walnut shells bleaching using oxidizing and reducing agents

Abstract

Walnuts with dark-colored shells, with blackish brown spots that are more or less punctuated, have poor consumer acceptability. To improve the appearance and the commercial quality of shell nuts, certain bleaching processes are applied by means of several oxidizing and reducing agents. Walnuts Juglans Regia L, variety Calarasi and Cogalniceanu, harvest 2015, Exploitation Iargara, Moldova were analyzed. The determination of chromatic characteristics according to CIELAB and effects of the reaction parameters on the color of the whitened shell by the method of the response surfaces of the color variables L*, a* and b* was made. Walnuts bleaching was performed with oxidative bleaching agents (hydrogen peroxide, calcium hypochlorite, sodium perborate and Okorn 12) and reductants (sodium dithionite and sulphurous anhydride) at different concentrations, pH values and temperatures. Based on the analysis of the effects of the independent whitening parameters (the pH of the environment, the concentration of bleaching agents and the temperature of the bleaching medium) and their interactive effects on the chromatic profile and the whitening process of the nut shell it was found that the oxidative whitening agents are more effective. Taking into account the whitening activityof the agents and their toxic emissions, the whitening of walnuts can be done with sodium perborate(Cperborat=5%, τ=60 min, t=600C, pH=10), Okoron 12 (Cokoron12 =5%, τ=90 min, t=600C, pH=10) and with hydrogen peroxide (CH2O2=10%, CNaOH =2.2 %, t=600C, 90 min).