There are hot foods that contain no capsaicin, it is perfectly possible to have a very hot sauce that contains none.
https://en.wikipedia.org/wiki/HorseradishHorseradish (Armoracia rusticana, syn. Cochlearia armoracia) is a perennial plant of the family Brassicaceae (which also includes mustard, wasabi, broccoli, cabbage, and radish).
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The distinctive pungent taste of horseradish is from the compound allyl isothiocyanate.
https://en.wikipedia.org/wiki/Black_pepperPepper gets its spicy heat mostly from piperine derived from both the outer fruit and the seed. Black pepper contains between 4.6 and 9.7% piperine by mass, and white pepper slightly more than that.