Sensory texture of commercial biscuits as a function of water activity

The variation in sensory texture of four types of commercial biscuits as a function of water activity, using both a trained sensory panel and a consum er panel, was studied. The biscuits were: (a) like roasted bread, aerated a nd sweet; (b) cracker from whole-wheat flour; (c) cracker from normal flour ; (d) sweet biscuit, vanilla flavoured. Texture changes were discriminated better when tested in the mouth than manually. The transition from crisp to noncrisp was gradual and continuous, and could be adequately modeled using Fermi's equation. The sensory perception of crispiness loss depended on ho w it was measured: for 'crisp with molars' the loss occurred at a lower wat er activity than for 'noise'. The water activities at which consumers found the crispiness ideal were different for each type of biscuit, showing that the moisture content of a biscuit should be adjusted at particular values for each product to satisfy consumer preferences. The correlation of sensor y acceptability versus 'crispiness with molars' showed one of the biscuit t ypes to be an outlier, white the rest were well correlated. Differences bet ween biscuits in relation to their textural changes with a, can be explaine d by differences in their microstructure, degree of starch gelatinization a nd gluten development.