The gemara 115b writes "achal maror l'chatza'in", i.e. one ate less than a k'zayis, then again less than a k'zayis. etc. within the shiur of k'dei achilas pras, "yatzah", one has fulfilled the mitzva. The term "yatzah" implies that this is a b'dieved act only. In other words, it sounds like l'chatchila one should/must swallow the entire k'zayis in one gulp! Interestingly, this halacha is not cited by the Rambam, and appears in Shulchan Aruch only with regard to matzah, where it is highlighted by the Magen Avraham. While it fits the language of the gemara, it difficult to see how swallowing an entire k'zayis in one shot is considered the regular "derech achila", but eating smaller bites is not. Sure enough, the Aruch haShulchan rejects the whole idea. In his view, the gemara simply means that eating with significant pauses, even within the context of k'dei achilas pras, is not a l'chatchila. However, eating in bites and swallowing a bit at a time would not be a problem.
Since we learn a hekesh of 15-15 connecting the mitzvah of achilas matzah with the mitzva of achila in sukkah on the first night, would anyone say that the k'zayis eaten on the first night of sukkot should be done in one gulp (like the MG"A)? The Mishna Berura in Hil Sukkah does say the k'zayis must be eaten within "kdei achilas pras", but does not make the logical jump to say in one gulp - I'm not sure why not.