Impact of treatment with oxidative bleaching agents on walnut (Juglans Regia L.) shell chromatic parameters

Abstract

Walnut meal is a nutrient-rich product and has a high nutritional value. Walnut meal is a product that can be used in food technology, in order to improve the nutritional quality, expand the range of confectionery products, and replaces the walnut kernel. Due to the dark color, the use of the walnut meal in the preparation of pastries would have a negative effect on the appearance of some final products and the whitening process would allow its use without negatively influencing the final product. The aim of the research is to whiten Juglans regial L. walnut meal as a valuable nutritious raw material. Hydrogen peroxide was used to bleach the walnut meal, and the pH, concentration of the whitening agent and the concentration of the meal were used as variable parameters of the bleaching process. The color descriptors (Whitening index, Saturation index, Total color difference, Browning index) were calculated to establish the optimal whitening conditions of the walnut meal. The obtained results showed that an alkaline medium, with the hydrogen peroxide concentration of 10% and 2.5% meal concentration allows obtaining the best color parameters in terms of Lightness (82.20) and Whitening Index (71.20). In addition, the study of walnut meal quality in terms of peroxide value evolution showed that the treatment with hydrogen peroxide does not affect in any way the value of the peroxide index of the lipids. The highest peroxide value (4.91 mmol/g oil) was recorded for the sample bleached in a 10% Hydrogen peroxide solution, with a pH of 10 against the 4.71 mmol/g oil for the unbleached sample.