Partitioning of caffeine and quinine in oil‐in‐water emulsions and effects on bitterness

Abstract

The bulk vegetable oil–water partition coefficient of caffeine and quinine was determined by a shake‐flask method as log Kow = −1.32 and 2.97. These values were consistent with the effect of oil concentration on the distribution of the bitterants in an oil‐in‐water emulsion (0–2 and 0–20 wt% oil stabilized with 0.125 and 1 wt% whey protein isolate, respectively). For example, in a 20% o/w emulsion, approximately 90% of the total caffeine remained in the aqueous phase, whereas in a 2% o/w emulsion, only ∼20% of the quinine remained in the aqueous phase. The intensity of the bitter taste of caffeine and quinine in emulsions was assessed by a large cohort (n = 100) of untrained participants. An increase in fat in the emulsions (from 0.5 wt% to 2 wt% oil emulsions stabilized with 0.125 wt% whey protein isolate) caused a significant decrease in perceived bitterness that was accompanied by a decrease in the aqueous concentration of the hydrophobic bitterant quinine Specifically, the bitterness of quinine was reduced ∼13% in the o/w emulsion with more fat, and this drop paralleled a drop in the aqueous concentration and was generally consistent with aqueous dose–response functions published elsewhere. For the hydrophilic bitterant caffeine, there was no significant change in the perceived bitterness or aqueous concentration with changing oil concentration. We conclude that the perceived bitterness of a hydrophobic bitterant like quinine in an emulsion depends on the aqueous concentration rather than the overall concentration.

Caffeine-Containing Emulsion: Influence of the HLB and Mixing Proportions, the Oil’s Chemical Composition, and the Existence of Caffeine on Emulsion Properties

“…Their ease of preparation, excellent performance, and outstanding stability make them highly appealing for large-scale production . Although some studies on caffeine emulsion in various systems, including emulsifier-free emulsions, multiple emulsions (W/O/W), O/W emulsions, and W/O emulsions, , have been reported, the impact of oil’s chemical composition on emulsions’ properties has not been explored for all formulations.…”

Advances in sensory science: From perception to consumer acceptance

“…Two studies were devoted to reducing perception of bitterness and oral burn. The findings were that (a) the perceived bitterness of quinine, a hydrophobic bitterant, in an emulsion depended on the aqueous‐phase concentration rather than the overall concentration, and an increase in fat in the emulsion caused a significant decrease in perceived bitterness (Tenney et al., 2023), and (b) oral burn of capsaicin in a protein solution was proportional to the non‐protein‐bound capsaicin concentration, rather than the total capsaicin concentration, and micellar casein solution was significantly more effective than the water rinse in reducing oral burn (Farah et al., 2023). Related to oral burn, reductions in taste, flavor, and mouthfeel intensity caused by oral burn might be more pronounced in liquid than in solid foods.…”