The effect of viscosity on flavour, mouthfeel and koku enhancement by tastants and yeast extracts in beef broths

This study investigated the effect of viscosity on the dynamic sensory perception of savoury beef broths enriched with savoury enhancers to evaluate the effect of perceived thickness on the koku enhancement effect (i.e. thickness, flavour duration, and complexity). Beef broths were enriched with five combinations of tastants and taste enhancers [none (control); sodium chloride (NaCl); a combination of monosodium glutamate (MSG) and inosine monophosphate (IMP); yeast extract (Kokumax-100); a combination of yeast extract (Kokumax-100) with MSG and IMP]. Three levels of viscosity [low (ƞ=0.72 mPa.s); medium (ƞ=2.94 mPa.s); high (ƞ=12.65 mPa.s)] were obtained by adding different concentrations of locust bean gum (0.00, 0.20, 0.40 w/w%) to beef broths. Temporal-Check-All-That-Apply (TCATA) profiling showed that yeast extract with MSG-IMP enhanced the intensity, richness, body, and duration of savoury sensations of low-viscous beef broths, demonstrating a koku enhancement effect. Increasing the viscosity of broths decreased the perception of taste (i.e. saltiness and savouriness) and flavour (i.e. beef flavour) for most broths, demonstrating a cross-modal suppression of taste and flavour by viscosity. Only broths with yeast extract (Kokumax-100) with MSG-IMP demonstrated stable flavour and taste enhancement across all broth viscosity levels. Koku enhancement by yeast extract (Kokumax-100) with MSG-IMP, MSG-IMP, and NaCl was observed for mouthfeel properties in broths with low and medium viscosity, but not in broths with high viscosity suggesting a suppression of koku enhancement at high broth viscosity. We conclude that (i) yeast extract (Kokumax-100) produces koku enhancement in liquid savoury broths when combined with taste enhancers monosodium glutamate (MSG) and inosine monophosphate (IMP), and (ii) the magnitude of the koku enhancement depends on the presence of taste enhancers and is attenuated at higher broth viscosity.