Changes in texture, microstructure and nutritional quality of carrot slices during blanching and freezing

Thermal processing of vegetables has pronounced effects on the cell structu re, often lowering the final textural properties of the product. In order t o investigate the effect of thermal processing on carrot, slices were subje cted to different blanching and freezing treatments before frozen storage. Microwave-, steam- or water-blanched material was frozen and then stored at -24 degrees C. Steam-blanched carrots were subjected to blast freezing or cryogenic freezing at different temperatures before frozen storage. The inf luence of these process conditions on the texture (maximum load and slope), microstructure, dry matter, sugars, carotene and drip loss was investigate d. Microwave blanching differed from the other blanching methods by resulti ng in a heterogenic cell structure. The content of dry matter, carotene and sucrose was higher following microwave blanching. Blast freezing resulted in low maximum load which seemed to be caused by major tissue damage. Conce rning cryogenic freezing, lowering the temperature from -30 degrees C to -7 0 degrees C resulted in better preservation of the native microstructure to gether with an increase in maximum load, which was most pronounced after on e month of storage. No significant effect was observed when lowering the te mperature from -30 degrees C to -70 degrees C for any of the other measured parameters. (C) 1999 Society of Chemical Industry.