Transfer of substances during the alcoholic maceration of green walnuts (Juglans regia L.)

Transfer of substances during the alcoholic maceration of green walnuts (Juglans regia L.). Green walnuts were extracted with 60 and 80 % ethanol respectively to produce walnut liqueurs. The transfer of primary and secondary metabolites was analytically monitored for four months. The extracts contained 9 to 9.5 g/l total sugar and 2.7 g/l total acidity. The 60 % variant released distinctly more minerals from the fruits. The maximum transfer of total polyphenols reached 8.3 g/l after six weeks. In this case no impact of the alcoholic strength was detectable. The colour of the extracts developed from light green to nearly black. Ellagitannins belong to the most important secondary metabolites of walnuts. The extracts contained 550 to 570 mg/l ellagitannins expressed as ellagic acid equivalents determined by RP-HPLC/UV Some ellagitannins could be determined by direct RP-HPLC combined with mass spectrometric detection and fragmentation (neg. ESI-MSn). Both extracts showed an intensive and typical walnut flavour, but the 80 % variant received a better sensory evaluation. Flavour analysis confirmed the stronger extraction of grassy and green compounds in the 60 % variant.