Bioactive and rheological properties of rose hip marmalade.

In this study, bioactive (total phenolic, antioxidant and antiradical activity) and rheological properties (steady and dynamic) of rose hip marmalade were investigated. Bioactive properties were determined in rose hip marmalade and extract. Extract had higher total phenolic content (38.5 mg GAE/g dry extract), antioxidant activity (124 mg AAE/g dry extract) and antiradical activity (49.98 %) than marmalade. Steady and dynamic rheological properties of the marmalade were determined at different temperature levels (5, 25 and 45 °C). Rose hip marmalade exhibited shear thinning behavior and Ostwald de Waele model best described flow behavior of the sample (R (2)  ≥ 0.9880) at different temperature levels. Consistency index and apparent viscosity values (η 50 ) at shear rate 50 s(-1) decreased with increase in temperature level. Viscoelastic properties were determined by oscillatory shear measurements and G' (storage modulus) values were found to be higher than G'' (loss modulus) values, indicating that the rose hip marmalade had a weak gel-like structure with solid-like behavior. G', G'', G (*) (complex modulus) and η* (complex viscosity) values decreased with increase in temperature level. Modified Cox-Merz rule was satisfactorily applied to correlate apparent and complex viscosity values of the rose hip marmalade at all temperatures studied.