Influence of freeze-drying treatment on the texture of mushrooms and onions

In the present work the textural properties of mushroom and onion, fresh and after freeze-drying, were studied, to understand how this drying treatment influences the texture of these food products. The fresh products had average moisture contents of 90.25 % and 90.02 % (wet basis) and the freeze-dried ones had moisture contents of 7.01 % and 5.19 % (wet basis), for mushroom and onion, respectively. The texture profile analysis (TPA) to the samples of the fresh and freeze-dried mushrooms showed that neither of the samples analyzed possessed measurable adhesiveness, and that hardness decreased very much with drying, either in the cap or in the stalk. Chewiness also varied quite significantly with freeze-drying, contrarily to cohesiveness, which practically stayed the same. Springiness also decreased with drying, although not in a very significant way. When comparing the two parts of the mushroom, it was observed that the cap is much harder, has slightly lower cohesiveness and springiness and a little higher chewiness. From the TPA to the fresh onion and to the freeze-dried one it was possible to conclude that the hardness of the onion decreased very much from the fresh to the dried state. A similar behaviour was observed for the chewiness, which also decreased, but in a much less extent. On the other hand, cohesiveness increased slightly with drying. In relation to springiness, this property was not affected from drying, being the value in the fresh state quite similar to the value in the freeze-dried state.