engleski

Influence of pectin addition on rheological properties of Apple puree at loe temperatures

Rheological properties of food are important for determining process parameters and defining sensory characteristics of certain food products. Apple puree is heterogenic colloid system that was made by pastring of mashed and termical treated fruit. This paper deals with the influence of pectin, insoluble dry solid content and soluble dry solid content, shear and cooling rate on rheological properties of apple puree at low temperatures before and during freezing. Basic apple puree of Idared sort was made by blanshing in 10% sucrose solution and different puree combinations with addition of pectin (0, 2% and 0, 4%) with different esterification stage (62% and 71%). Rheological properties were measured by rotation viscosimeter with refrigeration unit. Dependance of shear rate and shear stress at 5°C and 0°C ; at constant shear rate by continuing and scale cooling were measured. The lowest sub-cooling temperature at which still shear occures (Tm) and the temperature after fast increasement of shear stress, apparent viscosity and lower temperature decreasement (Tk) were determined. It was proved that all apple purees are nonnewtonian pseudoplastic. Apparent viscosity and consistency coefficient were enhanced with the increasing content of higher stage esterification pectin while the lower esterification pectin had the opposite effect. The addition of pectin decreased the freezing temperature.

rheological properties, apple puree, low temperature, pectin

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