What types of bakery products are prohibited due to Pas Akum?
The grain: Only breads [or baked Mezonos products] that are made of the five grains [oat, spelt, wheat, barley, rye] are forbidden due to Pas Akum. However, bread made of legumes or rice [or potatoes] is not included in the prohibition of Pas Akum. Nevertheless, legume bread falls under the prohibition of Bishul Akum and thus is only permitted to be eaten if the legume bread is not fit for a kings table. Some Poskim however argue that legume bread is never fit for a kings table, and is hence never forbidden neither due to Pas Akum or Bishul Akum.
Dough of a gentile: The dough of a gentile is not considered Pas Akum, as the prohibition of Pas Akum only applies towards baked products of a gentile. [Thus, all dough products that are sold may be made by gentiles and do not require any Jewish intervention within the processing of the dough.]
If the dough was made by a Jew but was baked by a gentile, is it forbidden due to Pas Akum?
Yes. The bread is forbidden due to Pas Akum unless there was some Jewish intervention in the baking process, such as turning on or raising the flame or entering the bread into the oven.
Is yeast of a gentile forbidden due to Pas Akum?
No. The yeast of a gentile is not forbidden due to Pas Akum even if it was made form gentile baked products. Nevertheless, it requires a reliable Hashgacha due to that yeast can be derived from various sources, some of which are not Kosher.
 112/1; Rosh; Rabbeinu Yerucham
 Michaber ibid
The reason: As these foods are considered of significance and bring towards closeness amongst people. [Taz 112/2]
 Michaber ibid
 Rama ibid
 Bach 112; Rabbeinu Yerucham Nesiv 17/7; Tur; Levush, brought in Shach 112/5 and Taz 112/3
 Shach 112/1 that so is the implication of Michaber and Rama throughout the chapter; Rambam and Rashba brought in Beis Yosef; Toras Chatas 75/2 in name of many Achronim; Chachmas Adam 65/5; Hakashrus 19 footnote 9
Other opinions: Some Rishinim rule that the dough of a gentile also contains the prohibition of Pas Akum, and it hence must be made with Jewish involvement. [Ran, brought in Beis Yosef and Shach ibid]
 P”M 112 S.D. 1
 Beis Yosef 112; Taz 112/10; Beir Heiytiv 112/14