In vitro and in vivo volatile flavour analysis of red kidney beans by proton transfer reaction-mass spectrometry

The volatile flavour released from red kidney beans was evaluated in vitro (in a model mouth system) and in vivo (in-nose). The dynamic release of the volatile flavour compounds was analysed by proton transfer reaction-mass spectrometry. The flavour compounds were identified by gas chromatography-mass spectrometry. Four masses (m/z 33, 45, 59 and 73; mass flavour compound+1) were predominantly measured in the headspace of the beans and selected for dynamic flavour release studies. Comparison of the four masses, identified compounds and their quantities present showed that the four masses probably correspond to methanol (m/z 33), 2-methylbutanal (m/z 45), 2,3-butanedione (m/z 59) and 2-methylpropanal/2-butanone (m/z 73). Three mastication rates were employed in in vitro analysis (0, 26 and 52 rpm) and two mastication rates in in vivo analysis (52 rpm and free chewing). In in vitro analysis, dynamic release patterns varied significantly among the compounds and the mastication rates (MANOVA, P<0.05). Increase in mastication rate from 0 to 52 rpm increased the maximum flavour concentrations measured by 50-400%. It also increased the persistence of the flavour compounds. The extent of the mastication effect varied among the compounds and, therefore, altered their proportions. Principal component analysis on the relative in vitro and in vivo data revealed that the normalised in vivo release curves were between those of the in vitro samples. This indicates that in vivo release was satisfactorily simulated by the in vitro technique.