Mayonnaises made with pungent and bitter EVOOs are not perceived as pungent or bitter (Experiment 1)
To investigate the potential effects of food constituents on EVOO perception, we first asked participants to evaluate the throat pungency and bitterness intensity of pure oils, presented in liquid form and three mayonnaises made with the corresponding oils. The first oil, a non-EVOO oil (HO), was a high oleic acid safflower oil, chosen to be the best match to EVOO regarding its lipid composition. The oil is highly refined to remove all but trace amounts of any components but triglycerides. It displayed little or no pungency or bitterness (see below). The second oil was an EVOO containing a low amount of OC (39 mg/kg of oil), and was weakly pungent and bitter. In these studies, it is referred to as LOC (Low OC). The third oil was an EVOO containing a high amount of OC (349 mg/kg of oil), was very pungent and moderately bitter, and referred to as HOC (High OC). To prepare a mayonnaise from each of the oils, 100 g of oil, 9 g of pH 7 bottled water and 8 g of egg yolk were combined following the procedures detailed in the Materials and Methods section. None of the additional ingredients often used in traditional mayonnaise recipes such as salt or lemon were used in our samples in order to limit gustatory stimulations other than those coming from the oils themselves. The six samples were all evaluated by the subjects within a testing session.
Focusing on the results of the 3 oils evaluation first, Fig. 2 (left panel) shows that participants judged the HOC oil strongly pungent (30.5 intensity rating), whereas HO and LOC oils were perceived as being only weakly pungent (2.6 and 4.7 respectively) and they were not significantly different from each other in intensity (p = 0.172). In contrast, the HOC oil was much more pungent than either of these (p < 0.0001). These results are consistent with previous work8 indicating a strong association between the amount of OC in EVOO and the oil level of throat pungency. The HOC oil was also judged clearly more bitter (19.3) than HO and LOC oils (2.5 and 5.5 respectively; p = 0.0041 between HO and LOC and p < 0.0001 for both oils compared to HOC) (Fig. 2 right panel) which is most likely due to higher content of bitter tasting phenolic compounds such as those mentioned in Fig. 1 in HOC oil (523 mg/kg total phenols as tyrosol equivalents) compared to LOC oil (201mg/kg total phenols as tyrosol equivalents).
Strikingly, when HOC was tested as a mayonnaise (HOC mayo; Fig. 2, left panel), its pungency almost entirely vanished (4.8 rating, p < 0.0001 compared to HOC oil). This mayonnaise was made of 90% oil and thus dilution cannot be responsible for the large loss in pungency intensity (-84%) relative to the pure HOC oil. The observed pungency suppression most likely reflects the fact that OC is no longer able to activate the TRPA1 receptors through which the sensation is mediated13. Similarly (Fig. 2, right panel), perceived bitterness of the HOC mayonnaise decreased markedly, although to a lesser extent (-37%) (rating 12.1, p < 0.0001 compared to HOC oil).
Egg yolk free model mixtures made with pungent and bitter EVOO maintains pungency and bitterness (Experiment 2)
The results of Experiment 1 could be due to direct binding of OC and other bitter phenolics to some of the egg yolk components (the most abundant being, protein (16%), lecithin (10%) and water (50%)). Alternatively, it could be due to the sequestration of OC and the bitter tasting compounds in the egg mayonnaise emulsion.
To study the observed phenomenon further, in Experiment 2, we prepared a water/oil emulsion displaying similar consistency to the mayonnaises used in Experiment 1, but free of egg yolk and thus of its components. For that, we replaced the egg yolk with a surfactant blend consisting of 0.4 g of Tween 80 and 0.6 g of Span 80 (see Materials and Methods for details). Participants evaluated the throat pungency and bitterness intensity of three model mixtures without egg yolk, each made with a different oil (HO, LOC and HOC). Sensory tests were conducted as described in the Materials and Methods section.
In contrast with the perceptual loss observed with the HOC mayonnaise in Experiment 1, the pungency (Fig. 3, left panel) and the bitterness (Fig. 3, right panel) of the model mixtures made with HOC oil was maintained. Indeed, in Experiment 1, LOC and HOC mayonnaises showed comparably low levels of pungency and were not distinguishable (p = 0.588), whereas in Experiment 2, pungency intensities of LOC mixture and HOC mixture were clearly different (p < 0.0001); they were much more aligned to the perceived intensities reported for the corresponding oils in liquid form (Experiment 1), with HOC oil triggering higher pungency than LOC oil. Similarly, the bitterness perception was not suppressed in the HOC mixture. The conclusion of Experiment 2 is that the pungency and bitterness reductions observed in Experiment 1 in the HOC mayonnaise were not replicated in an emulsion made without egg yolk. These results are consistent with the hypothesis that the suppression of EVOO pungency and bitterness observed in the mayonnaise samples is attributable to the presence of egg yolk and not due to a physical entrapment of the sensory compounds in the emulsion droplets.
Reduction in EVOO pungency in mayonnaise is positively correlated to the amount of egg yolk in the mixture (Experiment 3)
Experiment 3 was designed to evaluate quantitative differences in the suppression of pungency and bitterness in the presence of egg yolk. To accomplish this, we prepared four HOC mayonnaises with increasing amounts of egg yolk (1, 2, 4 and 8 g per 100 g of oil). For reference, many mayonnaise recipes recommend the use of 1 large egg yolk for 150 g of oil; this would correspond to approximately 12 g of egg yolk per 100 g of oil.
The results of this Experiment were straightforward for pungency perception. The more egg yolk incorporated into the mayonnaise the less pungent it was perceived (Fig. 4, left panel). Indeed, at 4 to 8 g egg yolk per oil sample, the pungency almost completely vanished. The relationship between bitterness intensity reduction and increasing amount of egg yolk was less apparent than with the throat pungency but the egg yolk appears to decrease bitterness perception as well (Fig. 4, right panel). The bitterness intensity evaluation obtained here at 8 g seems at odds with the general bitterness reduction trend of the Experiment for reasons that are not apparent. The results of Experiment 1 could be due to direct binding of OC and other bitter phenolics to some of the egg yolk components (the most abundant being, protein (16%), lecithin (10%) and water (50%)). Alternatively, it could be due to the sequestration of OC and the bitter tasting compounds in the egg mayonnaise emulsion.
Food proteins in model mixture cause major EVOO pungency and bitterness loss in a dose response manner (Experiment 4)
Proteins are known to bind to phenolic compounds. Since protein is a major component of egg yolk (16%), we hypothesized that they play the major role in EVOO pungency and bitterness suppression in mayonnaise. In Experiment 4, testing this supposition, participants evaluated the same model mixture as used in Experiment 2 (emulsion of EVOO high in OC with fixed concentration of surfactants), but here the test samples were prepared with increasing amounts of pure protein isolate. The goal was to determine whether the addition of pure protein isolate would reduce pungency and/or bitterness perception of the HOC mixture.
A whey protein isolate, characterized by a high content of proteins (> 95% protein on solids basis, of which 65% was β-lactoglobulin and 25% was α-lactalbumin) with a high dissolution factor in water was incorporated into our model mixture in increasing amount (0, 0.25, 0.5, 0.75 g and 1g protein per 100 g of HOC oil). The four samples were tested, as previously described in the Materials and Methods section.
The results of this Experiment were similar to those of Experiment 3. Increasing amount of proteins in the test samples elicited a reduction in perceived pungency and bitterness in a dose dependent manner (Fig. 5). A small addition of whey protein (0.25 g) into the mixture already produced a strong effect on the perceptual qualities of EVOO, with a loss of 52% pungency and a loss of 49% bitterness compare to the control (0 g protein). Additional proteins, with all other variables held constant, further suppressed both perceived pungency and bitterness. These results support the hypothesis that the presence of food proteins in the sample trigger sensory reduction due to interaction between the proteins and both OC (throat pungency inducing) and bitter tasting EVOO compounds.