Traditional walnut liqueur – cocktail of phenolics F. Stampar, A. Solar, M. Hudina, R. Veberic, M. Colaric * Department of Agronomy, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia Received 1 November 2004; received in revised form 18 January 2005; accepted 18 January 2005 Abstract The phenolic composition in walnut husks of the Slovenian cultivar Elit, which is a basic material for the traditional making of walnut liqueur, was investigated by HPLC with a PDA detector. Four different samplings of green husks were performed on dif- ferent dates in order to compare the contents of phenolic compounds. The 2nd sampling coincided with the picking time of walnut fruits intended for the making of liqueur. Phenolic composition of walnut liqueur was investigated as well. Thirteen phenolic com- pounds were identified in walnut husks: chlorogenic acid, caffeic acid, ferulic acid, sinapic acid, gallic acid, ellagic acid, proto- catechuic acid, syringic acid, vanillic acid, catechin, epicatechin, myricetin, and juglone. In walnut liqueur, 1,4-naphthoquinone was also identified. The major phenolic in the husks was juglone with the highest content in the 2nd sampling; its content in walnut liqueur was low. The concentrations of individual phenolics in the liqueur were quite low compared with the contents in the green husks, due to the traditional way of making the liqueur. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Green husks; Juglans regia L.; Liqueur; Phenolic compounds; Walnut 1. Introduction Walnut is an old, traditionally important and widely spread species in Slovenia mainly grown in natural, arti- ficial (plantation) and rural populations (Solar, Hudina, & Stampar, 2001; Solar, Ivancic, Stampar, & Hudina, 2002; Solar, Stampar, & Smole, 1997). Green walnuts, shells, kernels and seeds, even bark and leaves, have been used in the pharmaceutical and cosmetic industries. Walnuts are used in human nutrition; also the young green walnuts are much appreciated in traditional folk medicine for the making of an alcoholic wholesome drink – walnut liqueur, which is riched in phenolic com- pounds and vitamins. This liqueur is made out of wal- nuts with green husk and just before the hardening of the endocarp. These fruits are left to steep in food-grade ethanol (see also Alamprese, Pompei, & Scaramuzzi, 2005). Walnut fruits and many walnut products, such as walnut liqueur, are rich in phenolic compounds (Prasad, 2003). Phenolic compounds play a number of crucial roles in the complex metabolism of plants and also of fruit trees. They are involved in physiological processes of fruit tree growth and development and affect different aspects of fruit pre- and post-harvest life (Usenik et al., 2004). Consumption of certain phenolics in the food is considered beneficial for human nutrition (Golding, McGlasson, Wyllie, & Leach, 2001). Epidemiological evidence shows that foods rich in phenolics derived from fruits is associated with lower risks of cancer and coro- nary heart disease, as well as cataracts, brain and im- mune dysfunction and stroke (Lattanzio, 2003). Phenolics also contribute to astringent but pleasant taste of the liqueur. Halvorsen et al. (2002) reported that walnuts have one of the highest contents of antioxidants among all 0308-8146/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2005.01.035 * Corresponding author. Tel.: +386 1 423 11 61; fax: +386 1 423 10 88. E-mail address: mateja.colaric@bf.uni-lj.si (M. Colaric). www.elsevier.com/locate/foodchem Food Chemistry 95 (2006) 627–631 Food Chemistry