During blanching, there was rapid loss of turgor and membrane integrity which caused loosening and swelling of the cell walls ow- ing to breakdown of the cell wall and middle lamella (Canet et al.,
2005). It is clear that for HWB blanching, penetrating of heat in the stem lettuce tissues takes longer time, so the cell walls can be greatly damaged causing larger amount of nutrients (ions) loss due to leaching (Table 2). Ions in the polar/reactive sites of high polymer molecules or the ones forming bridges in the stem lettu- ces can also be leached off (Owen and Fennema, 1996; Karp, 1999). However, with MWB this is not the case because internal heat generation can easily penetrate in the vegetable tissues (Ra- mesh et al., 2002; Lin and Brewer, 2005). So, the electrical conduc- tivity of HWB samples was higher than that of NOB samples because only few ions remained in the samples after blanching.