Orange juice made from frozen concentrate can have higher levels of active vitamin C than ready-to-drink orange juice, say researchers from Arizona State University East in Mesa. And once reconstituted, the vitamin in frozen juices may keep its potency longer.
The research team 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, pasteurized versions and from-concentrate, non-pasteurized 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 day. But 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% to 105% of the readily absorbable vitamin C noted on their labels. This dropped to between 25% and 39% by the end of the month. On the other hand, the frozen concentrates had 80% of their vitamin C label claims on opening, dropping to 50% after 4 weeks.
The scientists conclude 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 point out that the pasteurization procedure--which many ready-to-drink orange juices undergo to destroy bacteria--gives this version a lower vitamin C content due to the immediate heat destruction of the nutrient.
The type of plastic and wax containers in which ready-to-drink juices are sold further aggravates the degradation of vitamin C. The packaging leaves 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 maximize vitamin C consumption, consumers are better 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 brands they should make sure to buy those juices 3 to 4 weeks before the expiration date, and drink it within the first week after opening the container.
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