The role of sucrose and hydrocolloids on thermal transitions and viscoelastic response of starch pastes

KRÜGER, ALEJANDRA; FERRERO, CRISTINA; ZARITZKY, NOEMÍ E.

Puebla, México.

Congreso; Eight International Congress on Engineering and Food; 2000

International Association for Engineering and Food

The effect of sucrose (15%) and different hydrocolloids (1% xanthan gum, guar gum or sodium alginate) on gelatinization and glass transition temperatures of starch pastes (10%) were determined using Differential Scanning calorimetry (DSC). Measurements showed that glass transition temperatures of the maximum concentrated matrix (T´g) are below the usual frozen storage temperatures (= -20ºC) thus diffusion-controlled changes in quality. Sucrose had the main effect on the increase of gelatinization temperatures as well as on the decrease observed in glass transition values. Microscopic observations showed that sucrose and hydrocolloids limited the swelling of stach granules during gelatinization. Viscoelastic behavior of the frozen pastes was tested by oscillatory rheometry. An increase of the dynamic moduli G´ accompanied by the formation of a sponge-like estructure was observed in starch-sucrose samples without hydrocolloid after show freezing and during storage. The addition of hydrocolloids prevented the sponge formation however certain textural damage was syneresis. Hydrocolloid addition was beneficial from the technological point of view by decreasing textural damage during frozen storage at temperatures above T´g; its effect can not be attributed to modifications in the glass transition temperatures but to the lower molecular mobility induced in the rubbery state by increased viscosity