Air-water interfacial properties of enzymatic wheat gluten hydrolyzates determine their foaming behavior (vol 55, pg 155, 2016)

© 2016 Elsevier Ltd The authors wish to express that, upon performing follow-up experiments to this work, we have noticed an error in the content of our paper. However, we'd like to stress that, although a correction seems the appropriate measure, the main conclusions of the paper remain unaltered. More specifically, the error has consequences for 2 Figures and some sentences in paragraph 3.3 (“Adsorption kinetics to the air-water interface”). In Fig. 4, only a minor adaptation in the x-axis is necessary. The x-axis title should say “Drop formation time (ms)” instead of “Drop formation time (log ms)”. In Fig. 5B, the slopes of the decrease in surface tension as a function of time are incorrect. Consequently, the correct values would affect some statements in paragraph 3.3 (more specifically, some of the correlations, as the reported values are incorrect), but do not impact the overall conclusions of our paper. A new version of Figure 5 is given below, as well as the complete paragraph 3.3, which is largely the same as in the original manuscript, but for the sake of clarity, is repeated here.(figure missing) Adsorption parameters for T2, T6, P2 and P6 at different protein concentrations [0.010%, 0.050% and 0.150% (wprot/v)]. A. Lag time, defined as the time when the surface tension starts to decrease. B. Negative slope of the decrease in surface tension as a function of the logarithmic drop formation time. Connecting letters represent significant differences at a significance level α = 0.05. 3.3 Adsorption kinetics to the air-water interface Adsorption kinetics of proteins at the air-water interface are typically determined with a drop volume tensiometer which measures surface tension starting from a drop formation time of 10 s. An MBP method which measures surface tension over a range of drop formation times (varying from 10 ms to 10 s) can provide additional information. Here, both techniques resulted in similar trends but the shorter drop formation times in the MBP allowed drawing some additional conclusions (drop volume tensiometer data not shown). The adsorption kinetics at the air-water interface measured with the MBP method at protein concentrations of 0.010%, 0.050% and 0.150% (wprot/v) showed large differences in lag time, i.e. the drop formation time at which the surface tension started to decrease (Figure 4). There were no significant differences (p > 0.01) in lag time between the different hydrolyzates at any given protein concentration (Figure 5A). However, lag time significantly (p < 0.01) decreased with protein concentration. At 0.150% (wprot/v), tension even decreased immediately and thus without any lag time. In order to compare the adsorption of the different samples at each concentration, the negative slope of the decrease in surface tension as a function of the logarithm of drop formation time was calculated (Figure 5B). There did not seem be a trend of a faster decrease of surface tension for a given sample at increasing protein concentrations. Thus, diffusion to the air-water interface (as represented by the lag times) seemed concentration-dependent, but this was not the case for the rate of adsorption. At most of the protein concentrations, no large differences in negative slope between the different samples were observed except at 0.010% (wprot/v). Here, the peptic hydrolyzates had a significantly higher negative slope than did the tryptic hydrolyzates. This indicates that the rate of their adsorption was higher. This effect did not go hand in hand with an increased FC for these samples at 0.010 probably due to the limited sensitivity of the foaming test. However, peptic hydrolyzates average wise were more hydrophobic than tryptic hydrolyzates (Section 3.2). This possibly explained their faster adsorption at low protein concentrations. There was a fairly good correlation between the calculated hydrophilic to hydrophobic ratio (Section 2.6) of the samples and their negative slopes of the decrease in surface tension as a function of drop formation time at 0.010% (R² = 0.715) and 0.050% (wprot/v) (R² = 0.875) (graphs not shown). In general, lag times decreased when protein concentrations increased, while there was no clear trend in terms of the rate of decrease of surface tension, as protein concentration increased for each sample. Differences in the negative slope of the decrease in surface tension between different samples at a given concentration could be linked to the above hydrophilic to hydrophobic ratio. The authors would like to apologise for any inconvenience caused.

Publication year:2016