i just have to say that the lemon zest and toothpaste as used in cooking made complete sense to me.
When I was in HS (back in the 1970s), my big brother was the track team captain and I was a scorekeeper and announcer. The track "spirit team" (aka "track groupies") were supposed to bake for the team. We made cookies, fudge, cupcakes, etc. I made the icing from scratch. It was cooked in a double-boiler, not the ever popular lard whipped with insane amounts of sugar. I think the cupcakes were chocolate and I was trying to make mint icing. The concept was good, but the execution was lacking. The texture was grainy/gritty, resembling old fashioned toothpaste (not the gel kind) and kinda minty.
I was so embarrassed because the whole team was joking about the "toothpaste icing." I was a very sensitive child who did not take being the butt of the joke well. Other people's opinion mattered more to me than my own judgement. I am 56 y.o. and I still blush when I remember that bus ride home from the track meet. Now I'm more self confident and I like to think I can laugh at my own mistakes, so I'm sharing my "toothpaste icing story" for your amusement.