Effect of freezing rate and frozen storage on starch-sucrose-hydrocolloid systems

Model food systems based on starch (100 g kg(-1)), sucrose (150 g kg(-1)) a nd water (750 g kg(-1)) with and without the addition of a low proportion o f hydrocolloid (xanthan gum, guar gum or sodium alginate) were gelatinised, frozen at different rates and stored to analyse textural changes by oscill atory rheometry. Differential scanning calorimetry (DSC) was used to analys e gelatinisation, amylopectin retrogradation and glass transition temperatu res. Sucrose had a significant effect on the increase in the gelatinisation temperature as well as on the decrease observed in glass transition values . The onset temperature of the second step of the glass transition, corresp onding to the heat capacity change close to ice melting (denoted Tg(im) in the present work), ranged between -23.0 and -22.2 degreesC. Rheological vis coelastic tests showed an increase in the dynamic moduli G* and G' after sl ow freezing and during storage at -19 degreesC (T>Tg(im)) in starch-sucrose systems that is related to sponge formation due to amylose retrogradation. DSC studies confirmed that also amylopectin retrogradation occurs during s torage; however, samples containing gums did not develop the spongy appeara nce. Storage at the usual commercial temperatures (close to -18 degreesC, s lightly above Tg(im)) affects the quality of aqueous starch-sucrose pastes without gums owing to amylose and amylopectin retrogradation. However, when hydrocolloids are included in the formulations, the usual storage conditio ns allow the maintenance of acceptable textural attributes. (C) 2000 Societ y of Chemical Industry.