Sholom Rav.

'Ochlim' is a verb - masculine plural. For example, 'We eat' is translated as 'Anu Ochlim'. I assumed that that is why, when referring to the plural of food , the Tana'im switch to 'Ochlin'. Otherwise 'Nun' is normally an Arama'ic suffix that is used in the Gemara. Then I checked with the Mishnah in Pesachim, which presents the text of the 'Mah Nishtanah' and found that all the verbs there - 'Ochlin', 'Matbilin' and 'Mesubin' - end with a 'Nun'. That being the case, we must say that it is a matter of dialect, and that this was the way the Tana'im spoke.

The Gemara in Bava Kama, commenting on the opening Mishnah there, which spells the word 'Chayav' - 'Chav' without a 'Yud', explains that it is a matter of dialect.

Be'Virchas Kol Tuv.

Eliezer Chrysler