The Food and Drug Administration does not require adding flavor packs to the labeling of pasteurized juice (which includes the from-concentrate as well as the not-from-concentrate versions), because, "it is the orange," said Gunter.
Non-pasteurized juice must be labeled as such, with warnings about potential pathogens. These regulations have been in place since 1963, she said.
As for the New York City mothers, Gunter said, "I don't think there has been a large outcry."
"If consumers have the false impression that pasteurized orange juice is not heated or treated because they have a picture of an orange on the carton, then they are not informed," said Gunter.
"There's a lot of literature and movies taking the food manufacturers to task on food preparation," she said. "We have left the farms and it's just not possible to feed everybody. I love the raw-food crowd, but we cannot get that many oranges out to that many people before they go bad in refrigeration."
But Alissa Hamilton, a former food and policy fellow at the Institute of Agriculture and Trade, said that modern technology is so "sophisticated" that these flavor pack mixtures "don't exist in nature."
"They break it down into individual chemicals," she said. "The flavor of orange is one of the most complex and is made up of thousands of chemicals."
"They are fine-tuned so each company has its trademark flavor," said Hamilton, who is author of the 2009 book, "Squeezed: What You Don't Know About Orange Juice."."
One that is used in a variety of foods, including alcoholic beverages, chewing gum and as a solvent in perfumes, is ethyl butyrate.
According to Doug Kara, a spokesman for the FDA's food safety division, the chemical is "generally recognized as safe as a food additive for flavoring."
"The orange juice companies market their premium brands as fresh-squeezed and better than concentrated," said Hamilton. "But it's a heavily processed product."
She advises on the blog, Civil Eats, that the freshest orange juice can be bought in May when the bright and flavorful Valencia oranges are harvested and have "not spent months in storage."
She adds that consumers can eat a whole Florida orange, which is higher in vitamin C than processed juice and much tastier.
As for any health concerns, Hamilton said, "I don't know," but many of the oranges used for juice come from mega-producer Brazil, where regulation of pesticides is not as stringent as in the U.S.
Still, according to the FDA's Karas, "We do screening of imports, and imported foods need to meet the same standards as do foods grown or produced domestically."
Mothers such as 36-year-old Yujin Kim, who has a 3-year-old and a 4-month-old, said she is concerned about what is in her orange juice.
"It's not arsenic but still something I didn't know I was drinking, so I ended up researching juice machines and bought one today," said Kim, who lives in New York City. "I definitely will not be buying any juice from now on."
"It makes sense that they would need to add chemicals for it to last through the transit time and for the consumers to buy and store at home," she said. "It's just wrong that they aren't being transparent about it. We as a consumer have a right to know exactly what's in the foods we are buying."
Her friend, Murakhver, said she wrote to Whole Foods and got an email response, which she shared with ABCNews.com.
Whole Foods spokesman Julie Campbell wrote that she was unable to disclose the name of the company that makes its orange juice, "as that information is proprietary."
"Flavor Packs are typically made by fractional distilling the oil from orange peel; essentially concentrating the components," she wrote. "Flavor packs are used by other brands to standardize their products. We accomplish the same thing by blending orange juice from different varieties and parts of the season together."
"I don't know what that means," said Murakhver. "If how they make it is proprietary, there is no transparency."
Though Whole Foods later clarified directly to ABC News that it does not use flavor packets in the juice, Murakhver remained unsettled by what she said were the company's ambiguous statements to her.
"There hasn't been a day in the last three years that we've not had it in the fridge and at the top of the shopping list with the milk," she said. "We are going to get a juicer and eat fresh fruit every morning and try to get our sugar high from fresh fruit."
"I like vintage champagne, not vintage orange juice," she said.
This story was updated to clarify Whole Foods' position that it does not use flavor packets in its juices.