In literature, a persona can be one of two things: (1) a reflection of "one's inner self" in the text or (2) an exaggerated representation of one's self viewed externally (Dr. Wheeler, "Literary Terms and Definitions: P"). Another way to phrase it is that a persona is the narrator's voice within the work as a character that is distinct from the actual writer ("Persona Literary Term"). One example Dr. Wheeler gives us is the narrator in Geoffrey Chaucer's The Canterbury Tales. The narrator himself acts as a character, and his voice is separate from the voice of the writer. As a character, the narrator expresses his inner self.
Michael Pollan, author of The Omnivore's Dilemma: A Natural History of Four Meals, is a journalist, and as such most of his prose in the book are written in a distant, third person, factual, reporting style. Nevertheless, there are several places in which he inserts himself as a narrating character in the work, giving himself a persona through which he exposes the narrator's inner self. The most subtle examples are often found in the beginning of chapters, such as the beginning of chapter 1, "The Plant: Corner's Conquest." In chapter 1, he takes the reader on a visual journey through a supermarket, classifying all we see by flora and fauna. While the description starts out in third person, he soon uses first person "I" to place himself there in the store with his readers, as we see in the following sentence: "I'm not just talking about the produce section or the meat counter, either--the supermarket's flora and fauna" (p. 17). Using first person "I" is certainly an obvious way in which he inserts himself as a narrating character; however, even in this very second paragraph, he uses a subtle approach of pointing the reader to sections of the grocery store as if he was there with us, as we see in the following sentence, "Over there's your eggplant, onion, potato, and leek; here your apple, banana, and orange" (p. 17).
A second example of this subtle approach of being there as a narrating character, thereby creating a personal for himself, can be seen in chapter 2, "The Farm." Here, he opens the chapter with a vivid description of driving a tractor as if the reader sees him there, in the story, really driving the tractor as a narrating character. He further creates the illusion of himself being a character by using both the words "you" and "us" in this same descriptive paragraph, as we see in the following sentence: "... planting corn, you try to follow the groove in the soil laid down on the previous pass by a rolling disk at the end of a steel arm attached to the planter behind us" (p. 32). By using "you," he is including the reader in what he is doing and giving the reader instructional advice; by using "us," he is putting the reader on the tractor along with himself, which certainly shows he is placing himself in the story as a narrating character, creating a persona.
Other than using these more subtle approaches to creating a persona, he also creates a persona for himself anytime he uses the word "I," as briefly mentioned earlier. One example of using "I" in this same chapter is in the next paragraph in which he goes into further detail about the tractor he was driving in the earlier paragraph and who it belonged to, as we see in the clause, "The tractor I was driving ..." (p. 33). In the first chapter, we see him creating a personal for himself by using the word "I" when he starts discussing exactly what led him on this quest to figure out where what we eat comes from.
Creating for himself a persona is a useful way to make the reader more engaged in the text. As noted earlier, Pollan is a journalist, and journalism reporting can be very dry. As Pollan progresses deeper into the details he is disclosing, we can see how all of the details can very easily become very dry for the reader, no matter how important they may be. Therefore, creating a personal lightens the mood and makes his writing more entertaining, which ensures the reader will become more engaged with the very critical text. What's more, in creating a persona, he provides the opportunity to reveal his inner thoughts, which also helps the reader engage more with the text because reader and author share many of the same inner thoughts concerning the subject matter.