pH dependent partitioning behaviour of food and beverage aroma compounds between air‐aqueous and organic‐aqueous matrices

Abstract

Aroma compounds in the Flavornet database were screened for ionizable functional groups such as carboxylic acids, aliphatic and aromatic amines, phenols, alcohols and thiols. Of the 738 aroma compounds listed in this database, 101 molecules have ionizable moieties with estimated monomeric aqueous pKa values ranging between 1.75 and 10.97. pH dependent effective air/water partitioning coefficients (Kaw,eff) and n‐octanol/water partitioning coefficients (Dow) were estimated for all ionizable aroma compounds over the pH range from 0 to 14. The ionizable aroma compounds display a broad range of Kaw,eff (1.8 × 10‐23 to 6.1 atm M‐1) and log Dow (‐6.2 to +7.2 units) values. For many aroma compounds, pH dependent ionization will have a significant effect on Kaw,eff and Dow, leading to variations in these physico‐chemical properties by up to 11 orders of magnitude over the composite pH range of common foods and beverages. Changes in food and beverage pH affect not only the relative contributions of neutral versus charged forms of ionizable aroma compounds (which directly affects analyte volatility and olfactory reception), but also partitioning between freely dissolved and sorbed forms of the analyte in solution (which indirectly affects analyte volatility). Copyright © 2015 John Wiley & Sons, Ltd.

Cooperative transitions involving hydrophobic polyelectrolytes

“…The p H range in which the transition occurs is over approximately 0.2 p H units, which is remarkably sharp and points to a highly cooperative transition (indeed M ≈ 11, see later). To compare, a typical monomer analog of an HPE, butyric acid in a demixed system of octanol and water, undergoes a transition from mainly soluble in octanol to mainly soluble in water over a p H range as broad as roughly 4 p H units ( 28 ), which also is obvious in Fig. 2 for M = 1.…”