MODEL STUDIES ON THE PRECURSORS AND FORMATION OF THE METALLIC SMELLING (E,Z)-2,6-NONADIENOL DURING THE MANUFACTURE AND STORAGE OF BUTTERMILK

Application of Aroma Extract Dilution Analysis to the volatiles genera ted from the degradation of 9-hydroperoxy-(E, Z,Z)-10,12,15 -octadecat rienoic acid under aqueous acidic conditions at room temperature, and in the presence of butter starter cultures, showed that the metallic-s melling (E,Z)-2,6-nonadienol (NDOH) was the most odour-active compound . Quantitative studies on its generation during storage of sweet-cream buttermilk which had been spiked with several potential precursors, s uggested the following reaction pathway for the formation of NDOH duri ng the manufacture of buttermilk: during fermentation of the sweet-cre am, the cc-linolenic acid present in the neutral triacylglycerides is peroxidized by lipoxygenases of the starter cultures into glyceryl 9-h ydroperoxy-(E,Z,Z)-10,12,15-octadecatrienoate. During separation of th e butterfat, the polar peroxide is transferred into the buttermilk and is subsequently cleaved into (E,Z)-2,6-nonadienal under the acidic co nditions in the buttermilk matrix. Reductases of the starter cultures, which are still active during storage, finally produce (E,Z)-2,6-nona dienol and the attendant metallic off-flavour. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.