A new study by researchers in the US claims that the vitamin C content of popular ready-to-drink brands of orange juice can drop from 45 milligrams per cup to zero within four weeks after opening
The study, published in the April issue of the Journal of the American Dietetic Association, , was led by Carol Johnston, a professor of nutrition at ASU.
Johnston also found that frozen reconstituted orange juice contained more vitamin C than ready-to-drink juice, although the exact amounts depended on when the juice was consumed following purchase. She recommended that ready-to-drink orange juice should be purchased three to four weeks prior to the expiration date and consumed within one week of opening.
"We don't want people to stop drinking orange juice for any reason at all," Johnston said. "We just want them to know that the frozen concentrate orange juice contains more vitamin C and may be a better nutritional choice."
Johnston and her team analysed two brands of frozen juice and two brands of ready-to-drink juice and found that orange juice from concentrate contained 86 milligrams of vitamin C per fluid cup when first prepared, dropping to 39 to 46 milligrams after four weeks of storage. The study did not offer a recommendation as to whether consumers should choose frozen or ready-to-drink juice.
Ready-to-drink juices, on the other hand, start with 'significantly lower' amounts of vitamin C than frozen, according to the study - 27 to 65 milligrams per cup when the container is opened, and zero to 25 milligrams four weeks later.
Oxygen in the air is responsible for most vitamin C loss in packaged orange juice, meaning routine handling during the production process as well as storage in non-airtight containers after opening can reduce the amounts of vitamin C both before and after purchase.
"While the average person needs only about six milligrams per day of vitamin C to avoid health problems like scurvy, low intake of vitamin C can lead to fatigue, feelings of listlessness and may lead to more serious complications," Johnston said.
She added that previous studies had shown that vitamin C deficiencies among US adults had risen from five per cent to 16 per cent in the past 20 years, and the amount of vitamin C consumed by Americans had dropped 20 per cent since the mid-1970s.
During roughly the same period, Johnston noted, "increasing sales of pasteurised, ready-to-drink orange juice resulted in a marked shift in the industry" - the number of factories producing concentrates decreased and the number producing ready-to-drink juice increased.
According to the study, the vitamin C content of orange juice is "highly variable and dependent on, for example, the variety and maturity of the oranges, fresh fruit handling, processing factors and packaging. Pasteurised, ready to serve orange juice typically contains 25 per cent less vitamin C per serving than frozen concentrates, a result in part of heat destroying the vitamin C".