Effect of blanching in water and sugar solutions on texture and microstructure of sliced carrots

Thermal processing of vegetables has pronounced effects on the cell structure, often negatively affecting the final textural properties of the product. In order to study the effect of thermal processing and the protective effect of sugars on the tissue, sliced carrots were subjected to blanching treatments under different time and temperature combinations both in water and in 4% sugar solutions made of trehalose or maltose. The influence of these process conditions on mass transfer, texture, and microstructure (Cryo-scanning electron microscopy) was thus investigated. The total mass loss of all the samples blanched in water was associated to their cook value (C-100(18)) except for the overprocessed one (90 degrees C, 10 min) that showed a total mass change significantly lower due to water uptake. The use of trehalose and maltose in the blanching solution reduced the solute loss while increasing the water loss. Microstructural analysis of the differently blanched carrots showed detachments between adjacent cell walls as well as plasmolysis phenomena as the time and temperature of the thermal treatment were increased. A protective effect of both sugars on cell structures was observed mostly in the sample treated at 90 degrees C. At macroscopic level, textural changes upon blanching were observed by a penetration test. As blanching time was increased, samples processed at 75 degrees C showed a hardness increase, while those processed at 90 degrees C showed a hardness decrease. However, both trehalose and maltose did not exert significant effects on the textural properties of blanched carrots when compared with those blanched in water.