91C-42 |
Texture changes in chocolate cookies as a function of water activity |
J. M. AGUILERA1, L. Cadoche2, and C. Vega2. (1) Chemical and Bioprocess Engineering, Universidad Catolica de Chile, Vicuna Mackenna 4860, Macul, Santiago, Chile, (2) Chemical and Bioprocess Engineering, Catholic University of Chile, Vicuna Mackenna 4860, Macul, Santiago, Chile Texture changes in chocolate cookies as a function of water activity J.M. AGUILERA, L. Cadoche and C. Vega, Dept. of Chemical and Bioprocess Engineering, Universidad Católica de Chile, Vic. Mackenna 4860, Santiago, Chile A growing demand for cereal based foods has contributed to their strong market performance over the last decade. Texture is an important variable in consumer acceptance of these products as well as in shelf life and product quality. Two different textures can be found among cereal based foods: brittle products like snacks, and soft products like breads, cakes, etc. Temperature and humidity at which products are exposed play an important role in the type of textural behavior. The objective was to determine and model changes in textural parameters (hardness, crispness, flexural modulus and work to fracture) of chocolate cookies as a function of water activity (aw). Textural parameters were determined using a TA.XT2 Texture Analyser and a three-point bending cell. Glass transition temperature was measured with a Perkin-Elmer differential scanning calorimeter. Profiles of the force-deformation curves to fracture were thin and tall for aw < 0.33, and became progressively wider and shorter at higher aw. Hardness and crispness of cookies remained almost constant for aw < 0.33 with average values of 11 N and 26 N, respectively. A sharp drop in the values of these parameters was observed in the aw range of 0.33-0.65, coincidental with the change in fracture from brittle to ductile. The temperature of the transition is more than 50ºC lower than the Tg determined by DSC. The Fermi distribution described well the variations in texture properties of the chocolate cookies as a function of water activity. The aw characterizing the transition as derived from the model ranged between 0.45 and 0.78. Texture changes in chocolate cookies seem to be related to mechanical factors (brittle-ductile transition) rather than to a glass transition. We further elaborate on the importance of brittle-ductile transition.
Session 91C, Food Engineering: Food process engineering
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