食品化学课件 Topic 2-4 FScN-4112-11 Tg applications.pdf

FScN 4112-11 Topic 1-4 Glass Transition Food Applications The Harry and Louise Revolution Dr Ted Labuza Department of Food Science and Nutrition University of Minnesota St Paul MN 55108 tplabuza@ /Ted_Labuza Slide # 1 Characteristics of the glassy and rubbery states. rubbery softer more flexible T lower modulus g glassy greater free volume temperature lower viscosity crisp, brittle fast reaction rates high viscosity sugar crystallization reduced free volume slow reaction rates high modulus lower heat capacity solids (%) Slide # 2 iso- elasticity lines affect mobility and texture 2 about 10 drop per 10°C T-Tg Decreasing storage modulus and local T °C viscosity glass transition line % solids % moisture Slide # 3 •  Stickiness •  caking •  Collapse due to flow under gravity •  Crystallization of sugars and starch •  Loss of crispness •  Protein aggregation •  Increased chemical reaction rates Slide # 4 Dry Food Crispness •  When gain