The ongoing debate in the food industry as to whether orange juice made from frozen concentrate has higher levels of active vitamin C than ready-to-drink orange juice continued this week when scientists in the US claimed that the former may be true, reports Reuters Health.
"Frozen concentrates have more vitamin C in them, quite a bit more, than ready-to-drink juices - since vitamin C is very easily destroyed and ready-to-drink orange juice goes through more processing than concentrates," said study lead author Dr Carol S. Johnston of Arizona State University East in Mesa.
Johnston and her co-author D. L. Bowling examined samples taken from different brands of orange juice sold in both frozen concentrate form and in ready-to-drink resealable cartons. Among the ready-to-drink samples, the researchers included both not-from-concentrate, pasteurised versions and from-concentrate, non-pasteurised versions.
The content of the type of vitamin C that can be readily absorbed by the body dropped in all of the juices over time, with levels falling an average of 2 per cent per day, Johnston and Bowling report in the April issue of the Journal of the American Dietetic Association .
However, the investigators noted that the ready-to-drink versions lost much more usable vitamin C during that period than did the frozen concentrates. When first prepared, the frozen concentrates contained 86 milligrams of vitamin C per fluid cup, which dropped to 39 to 46 milligrams after 4 weeks. The ready-to-drink juices contained anywhere from 27 to 65 milligrams per cup when unsealed and this dropped to 0 to 25 milligrams per cup at the expiration date 4 weeks later.
Overall, the various ready-to-drink samples contained between 75 per cent to 105 per cent of the readily absorbable vitamin C noted on their labels - a figure which dropped to between 25 per cent and 39 per cent by the end of the month. On the other hand, the frozen concentrates had 80 per cent of their vitamin C label claims on opening, dropping to 50 per cent after four weeks.
Johnston and Bowling concluded that ready-to-drink orange juice loses a lot of its usable vitamin C in the period of time that commonly elapses between a consumer's initial purchase and the time of consumption. They pointed out that the pasteurisation procedure -which many ready-to-drink orange juices undergo to destroy bacteria - gives this version a poorer running start due to the immediate heat destruction of vitamin C.
The degradation of vitamin C in this processing is further aggravated, they noted, by the type of plastic and wax containers in which ready-to-drink juices are packaged - leaving the juice's vitamin C content much more vulnerable to damaging air exposure over time than the vitamin C in frozen concentrates.
The researchers suggest that to maximise vitamin C consumption, consumers are best off drinking frozen concentrate orange juice within the first week after mixing it with water. They note that if consumers prefer the ease of ready-to-drink orange juice they should make sure to buy those juices three to four weeks before the expiration date, and drink it within the first week after opening the container.
"I hate to discourage people from getting orange juice, and you do get some vitamin C in ready-to-drink orange juice," Johnston told Reuters Health. "But I think if people knew that concentrate was a better product they would make the effort to get it.... And it's important because orange juice is a major source of vitamin C in the American diet and Americans are getting less and less in their diet. So they should try to get the best product."