Role of protein concentration and protein–saliva interactions in the astringency of whey proteins at low pH

Abstract

Whey protein beverages are adjusted to pH <4.5 to enhance clarity and stability, but this pH level is also associated with increased astringency. The goal of this investigation was to determine the effects of protein concentration on astringency and interactions between whey and salivary proteins. Whey protein beverages containing 0.25 to 13% (wt/wt) beta-lactoglobulin and 0.017% (wt/wt) sucralose at pH 2.6 to 4.2 were examined using descriptive sensory analysis. Controls were similar pH phosphate buffers at phosphate concentrations equivalent to the amount of phosphoric acid required to adjust the pH of the protein solution. Changes in astringency with protein concentration depended on pH. At pH 3.5, astringency significantly increased with protein concentration from 0.25 to 4% (wt/wt) and then remained constant from 4 to 13% (wt/wt). Conversely, at pH 2.6, astringency decreased with an increase in protein concentration [0.5-10% (wt/wt)]. This suggests a complex relationship that includes pH and buffering capacity of the beverages. Furthermore, saliva flow rates increased with increasing protein concentrations, showing that the physiological conditions in the mouth change with protein concentration. Maximum turbidity of whey protein-saliva mixtures was observed between pH 4.6 and 5.2. Both sensory evaluation and in vitro study of interactions between beta-LG and saliva indicate that astringency of whey proteins is a complex process determined by the extent of aggregation occurring in the mouth, which depends on the whey protein beverage pH and buffering capacity in addition to saliva flow rate.

Dynamic modelling of whey protein–saliva interactions in the mouth and relation to astringency in acidic beverages

“…Therefore, if whey proteinesaliva interactions determine astringency, the in vitro model should relate better to astringency. Kelly et al (2010) found no obvious relationship between astringency and turbidity on mixing whey proteins with saliva in a 1:1 ratio. In contrast, simple correlations have been observed between astringency and turbidity on mixing polyphenols with saliva (Monteleone et al, 2004).…”

“…It is notable, that as the concentration of whey protein in an acidic beverage is increased, astringency does not greatly increase (Childs & Drake, 2010;Kelly et al, 2010). For example, Kelly et al (2010) found that astringency reached a maximum in beverages containing 4e5% (w/w) protein, and did not increase with higher protein concentrations.…”

“…Later, it was shown that human salivary mucins form aggregates with b-lactoglobulin . Kelly et al (2010) provided further evidence of protein aggregation, measured as increased turbidity, when whey proteins are mixed with saliva. However, they found that a static turbidity measurement (as often used to model polyphenol-based astringency) did not give a simple correlation with protein-based astringency.…”

“…For example, Kelly et al (2010) found that astringency reached a maximum in beverages containing 4e5% (w/w) protein, and did not increase with higher protein concentrations. In contrast, sourness and cardboard flavour (Childs & Drake, 2010) of whey protein increases in proportion to protein concentration while consumer acceptance decreases (Childs & Drake, 2010).…”

Whey Protein Concentrate as a Substitute for Non-fat Dry Milk in Yogurt

“…Soukoulis, et al [25] reported that pH affected the flavor of yogurt when WPC were added in the formulation. Furthermore, other authors found that higher whey protein content in yogurts increased the buffering capacity in the product and also influenced the flavor perception [24,26,27].…”