The gemara seems to conclude that by min b'sheino mino we follow ta'am, meaning that so long as the issur taste is realized in the heter, the food is assur. Tosafos discusses whether this concept is d'oraysa. The fact that Rava doesn't pick a number such as 60x or 100x, rather makes it dependent on the taste, leads Tosafos to say that the issue of ta'am k'ikar is d'oraysa. Tosafos rejects the opinion of Rashi in Chulin 98b who holds that we pasken ta'am k'ikar is only d'rabonon. In the long discussion, Tosafos also cites the opinion of R. Yosef D'orleans who says that although ta'am k'ikar is d'oraysa, it is only an issur aseh, a violation of a positive mitzvah for which there is no malkus. Rabbeinu Tam rejects this and holds that there would be malkus. The fundamental point in their argument is whether we consider ta'am k'ikar to be a new prohibition (Rabbeinu Yosef) or merely a giluy that this also qualifies as eating the item which is assur.
R. Akiva Eiger 78a asks why the gemara concludes from Reish Lakish that ta'am k'ikar is not d'oraysa from the fact that there is no malkus when the pigul, no'sar and ta'mei are mevatel each other. According to Rabbeinu Yosef that ta'am k'ikar is d'oraysa but there is no malkus since it is merely an a'seh, we could simply say here too that ta'am k'ikar is d'oraysa but there is no malkus? This is a very strong question on Rabbeinu Yosef because the gemara does seem to imply that we can't separate ta'am k'ikar being d'oraysa from the malkus. It is also intriguing that R. Akiva Eiger asks this question from Rabbeinu Yosef in Tosafos Chulin 99, rather than asking it from Tosafos on the very next page of Zevachim!
To me it seems that there is a very strong diyuk in Rashi that would answer both R. akiva eiger's question and Tosafos question. Tosafos (d.h. ma'siv) asks why do we challenge the gemara's proof from reish lakish that ta'am k'ikar isn't d'oraysa from the mishna that one can fulfill their mitzvah of matzah by eating a kezayis of matzah made from mostly rice flour (and a little wheat flour that gives ta'am in it). Why didn't the gemara ask from the myriad of places where we have a concept of ta'am k'ikar?
A careful reading of Rashi indicates that the gemara never meant to prove from Reish Lakish that ta'am k'ikar is not d'oraysa. It could be that Reish Lakish would submit that ta'am k'ikar is d'oraysa. The gemara was simply saying that we don't regard the ta'am to be as substantial as the ikar so that by merely eating a kezayis of something that has taste of issur he would get malkus. Rashi writes:
ושמע מינה נותן טעם ברוב לאו דאורייתא- הא דאמור רבנן בכל דוכתי איסור הנותן טעם בהיתר אוסרו ואף על פי שההיתר ברוב, לאו דאורייתא הוא ללקות עליו
Rashi clearly focuses on the malkus. Meaning, that it could very well be d'oraysa but there is no malkus since eating a kezayis of taste of issur isn't tantamount to eating a kezayis of actual issur. Based on this approach, Tosafos question is answered. The only clear case we can ask from is the mishna in chalah that allows one to fulfill matzah by eating a kezayis that only has a taste of wheat flour and not an actual kezayis of wheat flour. This indicates that ta'am k'ikar affects even the shiur, and doesn't just make the item assur. Based on this, R. Akiva Eiger's question is also answered. The gemara wasn't simply trying to say that ta'am k'ikar isn't d'oraysa. The gemara understands that even according to Reish Lakish, ta'am k'ikar may be d'oraysa. The gemara is only trying to say that eating a kezayis of ta'am issur doesn't warrant malkus. Therefore, there is no question from Rabbeinu Yosef who says that it is d'oraysa but an issur aseh because that is essentially what the gemara is trying to say - issur but no malkus.