Feasibility of the SPME method for the determination of the aroma retention capacity of proteose–peptone milk protein fraction at different pH values

The work aimed to develop a “true headspace-SPME–GC” method for evaluating the aroma retention capacity of the proteose–peptone (PP) milk protein fraction. The SPME analytical conditions were optimized in aqueous solution to which was added a blend containing seven aroma compounds from different chemical classes. The following parameters were tested: sample equilibrium time, fibre coating and fibre exposure time. The optimal equilibrium time was found to be 4 h and the DVB/CAR/PDMS fibre offered the highest sensitivity and repeatability. Finally, a 1 min fibre exposure time was chosen in order to avoid aroma competition and extraction phenomena. This method was then employed to evaluate the flavour binding capacity of PP aqueous systems at different pH values (6.8, 5.0 and 3.8). For all the pH conditions the retention capacity of the PP fraction gradually increased with hydrophobic chain length or overall hydrophobicity of the aroma compounds. Higher aroma binding capacity was found at pH 3.8.