Factors Regulating Astringency of Whey Protein-fortified Beverages

Abstract

Whey proteins are added to a variety of foods and beverages for functionality and added nutrition. A rapidly growing area of whey protein use in foods and beverages is the sports drink category. There are two categories of whey protein-fortified drinks: those at neutral pH and those at low pH. The drinks at low pH have a clear and refreshing appearance, compared to the shake-style drinks at neutral pH. Astringency is very pronounced at low pH. Thought to be caused by compounds in foods that bind with precipitate salivary proteins, astringency at high levels is an undesirable characteristic in foods and beverages. The mechanism of astringency of whey proteins is not understood and has not been investigated. Salivary flow rate, viscosity, and pH are a few variables that have been reported to alter perceived astringency of red wine, tannic acid, alum, chitosan, and cranberry juice.

In order to investigate factors regulating astringency of whey proteins, a market survey was conducted and a model beverage was formulated. Trained sensory panelists evaluated the viscosity and pH effects on astringency of whey protein-fortified model drinks (n=8). Changes in optical density of saliva and drink mixtures before and after centrifugation were also investigated to see if a relationship existed between aggregation, precipitation, and astringency. Increasing viscosity (1.6 mPa s – 7.7 mPa s) did not alter maximum intensity, time to maximum, duration, or area under the curve of astringency time-intensity profile. Significant changes were observed over the pH range investigated (pH 2.6 – 6.8). Acidic drinks were higher in astringency and sourness compared to the drink at neutral pH. Astringency decreased from pH 3.4 to pH 2.6. Saliva and drink mixtures showed that aggregation and precipitation were taking place, and the degree of precipitation correlated with perceived astringency. Electrostatic interactions between positively charged whey proteins at low pH and saliva proteins with low isoelectric points are thought to be responsible for aggregation and precipitation, resulting in the perception of astringency.