POLYPHENOLS AND NAPHTHOQUINONES EXTRACTION FROM WALNUTS PELLICULA: THE IMPACT ON KERNELS QUALITY

Abstract

Walnuts change their appearance during storage, becoming brown and bitter. The aim of this paper was to determine the polyphenols and naphthoquinones extraction process parameters from the pellicle of kernels, and to assess the influence of extraction on the walnuts quality. It was studied the influence of NaOH, ethanol and polygalacturonase on the polyphenols and naphthoquinones extraction from walnut kernels pellicle. Small amounts of enzyme, (0.011±0.001) %, contribute to the extraction of colored substances from the pellicle by destabilizing of biopolymer matrix. Hydration, volume increase, the destruction of the bio-polymeric matrix - all contributes to the extraction, also to the pellicle release from the kernels surface. The hydration degree increases as the amount of ethyl alcohol in the extract became < 7.5 %. The oxidized and colored components are extracted according to the exponential models: Y = Aekx, k ∈ (-0.40±0.06). The consecutive extraction of phenolic substances and naphthoquinones, carried out at room temperature, contributes to the improvement of colour and taste, increasing technological value of the processed walnuts.