To make good use of knives in the kitchen to keep in mind this principle of micro-oxidation (of course, is a popular and not strictly scientific explanation, so I do not want the engineers):
"Any contact, friction or movement of a metal blade with another body is solid or liquid surface always generates a micro heat (which of course you do not feel) to alter, in the case of food, the taste, flavor and sometimes consistency "
You could argue that only a very fine nose or palate can feel these changes: if you do not know the rule is so, but if you know it you will see that these changes are felt and how!
I invite you to do two tests, which will convince you (I won several bets with people disbelieving, making them blindly, ie without the tasters of the food was informed):
a - the pancake test
Make two omelettes with the same ingredients and the same amount of ingredients, cook them in two pans at once the same and equal to two fires, then sautéed and cut with a knife and a l 'other with a wooden spatula to spezzatela: simply test to compare two flavors on the palate, and feel very different! Seeing is believing.
b - Try a slice of salami
Sliced salami, a good season, before cutting it by a head with a knife properly as indicated below, and from the 'other end with an electric slicer and then you try to compare: you all say that they are two different sausages, with a taste of the far 'from a' more!
Even here, try it (this test the 'I did even with a group of professional tasters, saying they were two different sausages and nobody noticed it was the same salami!).