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    Comparative study of whey protein isolate gel and polydimethylsiloxane as tribological surfaces to differentiate friction properties of commercial yogurts

    Year: 2019

    Journal: Food Hydrocolloids, Volume 97, DEC

    Authors: Di Cicco, Francesca; Oosterlinck, Filip; Tromp, Hans; Sein, Arjen

    Organizations: DSM Food Specialties, Delft, the NetherlandsNetherlands Government

    Keywords: Tribology; Whey protein isolate gel; Polydimethylsiloxane; Counter-surface; Yogurt; Creaminess

    To predict in-mouth perception of semi-solid foods like yogurt, their lubricating behavior needs to be understood. In food industrial applications of oral tribology, it is preferable and more efficient to use a material with a hydrophilic surface to mimic the tongue in the in vitro setup. We investigated and compared whey protein isolate (WPI) gel and polydimethylsiloxane (PDMS), based on their physicochemical characteristics and their ability to discriminate the friction behavior of a set of commercial yogurts known to elicit different mouthfeels. Stiffness and wettability of WPI gel were more similar to the human tongue than PDMS. The friction factors of Newtonian fluids measured on WPI gel allowed to construct a master Stribeck curve; this was not the case for PDMS. The yogurts could be clearly discriminated when measured on WPI gel. Their friction factors in the mixed regime correlated to the fat content and to perceived creaminess. Yogurts' discrimination was not optimal on PDMS. The measurements on WPI gel, done in the speed range 1-0.001 m/s, were compared to a second speed range (0.2-0.002 m/s), believed to be more relevant for in-mouth conditions. Yet, the first speed range gave the best discrimination, also between samples with small differences in fat content (semi vs full-fat). Statistical analyses were performed on the datasets obtained using WPI gel, for a detailed characterization of its discriminative predictive power, demonstrating that the average friction in the mixed regime, and the slope in the mixed regime are the most discriminating features for tribological behavior.
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