Contrasting relationship between macro- and microviscosity of the gelatin- and starch-based suspensions and gels

The problem of correlation between rheological properties in macro- and micro- scales of media with biopolymers of polypeptide (gelatin) and polysaccharide (starch) nature is investigated. The viscosity of the biopolymer solutions with concentrations 0.5-5 wt% was estimated by standard rotational rheometry technique and with fluorescent molecular rotor at 15-50 A degrees C. Opposite trends were observed for relationship between microviscosity eta (m) and macroviscosity eta for two biopolymers: eta (m) << eta for gelatin and eta (m) >> eta for starch solutions. The temperature dependence of eta (m) followed the monoexponential decay law in all samples over the whole temperature range indicating insensitivity of microviscosity to gel mesh melting under heating. The dissimilarity of macro- and micro-rheological properties of gelatin and starch-containing media is discussed in terms of difference in architecture of the gels.