לא הכהן אהרן מזרע מום בו אשר איש כל" לחם את בו מום 'ה אשי את להקריב יגש (כא כא) "להקריב יגש לא אלקיו
The Rambam (Bias Mikdash 8 1) lists ninety different blemishes that disqualify the Kohein that has them from serving in the Bais Hamidkash. The Chishukei Chemed writes: The Rokeach (320) brought that the mitzvah of meah brachos is meant intended to save Am Yisrael from one hundred curses. Ninety-eight of them are written in Parashas Ki Savo and two more are alluded in the passuk (Devarim 28:61): “Gam kol choli vechol makkah.” Based on this we can say that Chazal determined that we have to answer ninety amens a day to save us from the ninety blemishes that disqualify the Kohanim. (Kovetz Shu”t printed at the end of sefer Aleinu Leshabei’ach Vol. III, Teshuvah 78)
The dorshei reshumos added an allusion to this: המום is numerically equivalent to ninety-one which is equal to “אמן”. (Meoros Hadaf Hayomi Bechoros 43a)
