Impacts of our environment on the L-ascorbic acid (vitamin C) in oranges
Evolution of the quantity of vitamin C in an anoxic environment
Who has never been told to drink their freshly pressed orange juice fast because vitamins 'escape'? That is exactly what I wanted to verify in this project of my first year of B. Sc.. The purpose of the experiment was to follow the evolution of the quantity of L-ascorbic acid contained in oranges, according to several treatments, (1) in a fully enclosed container, (2) in a container left open at room temperature, (3) in a closed container at 70°C (pasteurization temperature utilized in agri-food processes).
All experiments were done with test tubes filled with freshly pressed orange juice. The first tubes only contained orange juice (no air), the oxygen inside the juice was disregarded and they were closed with a lid. The second set of tubes were left open at room temperature (22°C). The third set was identical with the first one, but put in a 70°C bain-marie. Each experiment was carried out during 5 days. Each tube of a set was subject to a titration (diiodine) to assess the quantity of vitamin C, before and after the experiment, and averaged.
It appeared that only 35% of the quantity of vitamin C has oxidized over 5 days when the juice is left open at room temperature! Over 10% was degraded in 5 days when the juice was fully enclosed, which allows saying that the initial juice contained dissolved oxygen, or an oxidative element (hence the need of preservatives to be added to industrialized juices). When the third set was heated (70°C), it lost 35% of vitamin C in only 5 hours, and over 85% after 5 days, suggesting that pasteurized juices are poor in vitamin C, unless artificial L-ascorbic acid is added.
In short, you can press oranges and not drink it right away, not worrying about missing on vital vitamin C. If put it in your fridge, the juice will not only keep its vitamins, but won't go bad for a week either, given its acidity.
All experiments were done with test tubes filled with freshly pressed orange juice. The first tubes only contained orange juice (no air), the oxygen inside the juice was disregarded and they were closed with a lid. The second set of tubes were left open at room temperature (22°C). The third set was identical with the first one, but put in a 70°C bain-marie. Each experiment was carried out during 5 days. Each tube of a set was subject to a titration (diiodine) to assess the quantity of vitamin C, before and after the experiment, and averaged.
It appeared that only 35% of the quantity of vitamin C has oxidized over 5 days when the juice is left open at room temperature! Over 10% was degraded in 5 days when the juice was fully enclosed, which allows saying that the initial juice contained dissolved oxygen, or an oxidative element (hence the need of preservatives to be added to industrialized juices). When the third set was heated (70°C), it lost 35% of vitamin C in only 5 hours, and over 85% after 5 days, suggesting that pasteurized juices are poor in vitamin C, unless artificial L-ascorbic acid is added.
In short, you can press oranges and not drink it right away, not worrying about missing on vital vitamin C. If put it in your fridge, the juice will not only keep its vitamins, but won't go bad for a week either, given its acidity.