The type of detergent used during the DNA extraction process from a sample of kiwi cells is just one among many factors that influence the amount we can obtain. The type of fruit or vegetable used, the temperature of the water baths, the kind of alcohol added, as well as the mashing process prior to the extraction, all affect how much DNA will be liberated and then precipitated.

Out of plain curiosity, I repeated the same experiment, however, instead of mashed kiwi I used onion that I chopped in a blender. Three out of three trials were unsuccessful - although I used identical detergents, I was not able to precipitate a lot of DNA strands. Furthermore, the strands were short and slippery, and I couldn't take them out of the test tube.

There are two possible explanations - either onion is not a suitable vegetable to perform the experiment or the blades of the blender simply tore apart the DNA strands and they became too small to be taken out.