Rheological investigations of beta glucan functionality: Interactions with mucin

The shear and extensional rheology of β-glucan and mucin mixtures have been studied as to probe the functionality-related thickening effects of consumed β-glucan during food digestion. Mucins, the main viscosity-inducing components of oral and gastrointestinal fluids, can increase the shear viscosity of β-glucan solutions, e.g. when 3% mucin is added into 1% β-glucan, the shear viscosity increases from 0.4 Pa s (1% β-glucan) to 2 Pa s at a shear rate of 0.1 s−1. The 3% mucin contributes 1.6 Pa s in the presence of β-glucan, which is nearly 16 times of the viscosity induced by 4% mucin alone at the same shear rate. Mucin affects the extensional viscosity in a similar way, e.g. incorporation of 2% mucin into a 2% β-glucan system increases the extensional viscosity from 4 Pa s to 8 Pa s. Substitution of β-glucan for an equal concentration of mucin results in the decrease of the shear and extensional viscosities: Α 4% β-glucan solution has a maximum extensional viscosity of 92 Pa s; substitution of 1% β-glucan for 1% mucin (1% mucin+3% β-glucan) reduces the maximum recorded extensional viscosity to 36 Pa s; this is further reduced down to 8 Pa s at 2% mucin+2% β-glucan, and then on to 4 Pa s at 3% mucin+1% β-glucan, and to 0.8 Pa s at 4% mucin. A similar trend is observed for the shear viscosities. The shear and extensional moduli and the extensional relaxation times also follow such patterns. The Trouton ratio values are lower than 100, that is they are not as high as in other food hydrocolloids; this strongly suggests a fine in vivo interplay between shear and extensional viscosities. The effect of mucin on β-glucan solutions rheology is primarily attributed to excluded-volume interactions, which increase the effective concentration of the glucans. The implications of the above on the rheology-related functionality of β-glucans are discussed.