The purpose was to detect substances that cause the gradual blackening of walnut kernels. The polyphenols from kernel's pellicle (walnuts of “Kogălniceanu” variety) were supposed to exhaustive ultrasonically-assisted extraction. For recognition of extracted polyphenols, HPLC system “Agilent 1200” with Single Quadrupole Mass Detector and with Diode Array Detector (DAD), was used. The separation of the extracted compounds was performed on the C18 column “Eclipse XDB”, 4.6x150mm, particle size 5μm, using the gradient of the mobile phases A and B at 25⁰C, with a flow rate of 0.5 mL/min. Phase A: water with 0.1% acetic acid; Phase B: acetonitrile with 0.1% acetic acid. The UV-Vis spectra were recorded in the range of 200-600nm. Chromatograms were analyzed at wavelengths λ1 = 280nm and λ2 = 360nm. Phenolic compounds were identified: Rt, min λmax, nm HM+, m/z Compound ω, % 3.44 230 501 2,3-Hexahydroxydiphenaloyl-glucose 17.9 ± 1.1 3.84 230 339 2,3-Hexahydroxydiphenic acid 2.6 ± 0.7 4.50 250 485 Digalloyl-glucose 6.4 ± 2.0 9.63 250 332 Galloyl-glucose 3.6 ± 1.3 11.30 280 579 Procyanidin dimmer 20.5 ± 2.5 12.62 280 291 Catechin 17.2 ± 2.4 13.16 280 291 Epicatechin 8.2 ± 1.4 14.25 250 941, 924 Pentagalloyl glucose 7.9 ± 1.7 14.99 280, 360 936 Casuarictin 8.2 ± 3.0 16.22 280, 360 303 Ellagic acid 7.6 ± 2.1 Conclusion: Biologically active polyphenols have an ambiguous effect on the quality and taste of walnuts. Having worked out their redox potential, they become a source of dark color and bitter taste. Their preventive extraction in an unoxidized state before technological processing can significantly improve the quality of such valuable food “wastes” as walnut cake.