פירוש על עבודה זרה 70:9

An earlier mishnah in this chapter began with a list of things owned by a non-Jew from which it was prohibited to derive benefit. This is a more stringent legal category than food which is merely prohibited to eat, the list which is contained in our mishnah. We will explain each item in this mishnah and why it is forbidden to eat. 1) Milk—if the non-Jew milked an animal without a Jew watching, he may have mixed into the milk, milk which comes from an non-kosher animal, such as a camel. 2) Bread and oil—this prohibition is not due to a fear of the bread or oil being truly non-kosher. Rather the Sages prohibited a Jew from eating non-Jewish bread or oil in order to prevent Jews from socializing with non-Jews. The Talmud relates that it is permitted to eat bread made by bakers (as opposed to private individuals) since that will not bring Jews and non-Jews together. The mishnah notes, in what is surely a later addition, that Rabbi and his court permitted Jews to consume non-Jewish oil. The “Rabbi” referred to here is Rabbi Judah Nesia, the grandson of Rabbi Judah the Prince who composed the