Sources of soapy off-flavor in clear acidic whey protein beverages

Clear acidic protein beverages are made with whey protein isolate (WPI) due to its solubility at pH 3.3. These beverages can display a soapy off-flavor, which is not detected at neutral pH. Our hypothesis was that medium chain fatty acids are the source of this off-flavor. WPI (14 duplicate lots) were rehydrated to 10% solids (w/v), subjected to descriptive sensory analysis, and evaluated at their original pH, as well as pH adjusted to 6.3 (pre-acidif) or to 3.3 (neutral) at 21°C. Solvent-assisted flavor evaporation with gas chromatography mass spectrometry and gas chromatography olfactometry were performed on six selected WPIs (three neutral and three pre-acidified), followed by quantitation of octanoic, decanoic, and dodecanoic acids using stable isotope dilution assays. Retronasal and orthonasal thresholds of these acids were determined at pH 6.3 and 3.3. Model systems of WPI with the three acids were generated to confirm soapy flavor. The average concentrations of the three acids in selected WPIs were as follows: C8 = 14.4 ± 2.0 ppm; C10 = 27.8 ± 2.39 ppm; C12 = 24.7 ± 2.20 ppm. Sensory detection thresholds for all three acids at pH 3.3 were lower than at pH 6.3 (p < 0.05). Trained panel profiling of model systems demonstrated that a combination of octanoic and decanoic acids within the concentration range documented in WPI at pH 3.3 caused a soapy flavor, which was not detected at pH 6.3. Identification of the sources of soapy off-flavor in clear, acidic protein beverages provides the baseline to reduce or eliminate this off-flavor. PRACTICAL APPLICATION: Clear acidic protein beverages are one category of protein beverages within the expanding world of protein beverages. Identification of the source of soapy off-flavor in clear, acidic whey protein beverages is useful for consistent delivery of protein beverages that are desirable to consumers.