Why is it recommended to blanch onions before pickling them? I was recently looking for a recipe to pickle onions, and among several others I found this one. Skimming through the comments I came across the same question as I'm asking now, but without any other answer than the musings of the author of the recipe:

Pouring water over the onions is something I've always done without quite knowing why. A quick internet research shows that most picked onion recipes call for this, but without explanation.
Hot water is often pour over onions (that aren't going to be pickled or cooked) in order to tame their sharpness and soften them a little. But a pickling brine is so intense and sharp itself, perhaps it isn't necessary.

So I started wondering myself whether or not the latter part of the quote is true; is it necessary to blanch the onions before pickling them, as the pickling solution is so sharp in taste anyway?
The recipe in question mixes:

1 medium red onion, about 5 ounces
1/2 teaspoon sugar
1/2 teaspoon salt
3/4 cup rice vinegar, white wine vinegar, or apple cider vinegar

And then let it all rest in a jar for 30 min-2hrs before it is ready. It is supposed to keep for a couple of weeks in the refrigerator. The blanching of the onions happens before it is all put in the jar.
From  indiacurry.com :


  Blanching Vegetables for freezing or pickling
  
  Vegetables have a natural enzyme that continues to effect texture, color and flavor. Blanching stops the enzyme action
  The natural enzymes help vegetable to grow and mature until they are harvested. After the vegetables have been harvested, they continue to remain active even when frozen or pickled making the pickles to be tough, effect the color and flavor. Blanching stops the action of the enzymes.
  The purpose of blanching is not to sterilize or pasteurize vegetables. It may kill some but not all the surface micro-organisms
  
  Blanching is done by either scalding vegetables in rapidly boiling water, or in a steamer for a short time period. The vegetables must be scalded just long enough to stop the enzyme reaction, but not too long to make them soft and mushy by breaking up the cell-walls.
  Under-blanching stimulates enzyme activity and is worse than not blanching
  Over-blanching causes loss of texture, color, flavor and vitamins.
  Vegetables are blanched for freezing or making Indian pickles.