Question No.  19248 :
May I know if vitamins found in fruits will lose its effect after some time and how long might the vitamin stay after the fruits are cut? If the fruits are made into fresh juice, does it still contain as much vitamin as those found in the original fruit?

Vitamin C is one of the most unstable vitamins there is. When mixed with so many other ingredients (such as is the case for food), it is especially unstable and degrade to less active ingredients from the effects of temperature, light, humidity, and time. Vitamin C is not stable in water; after 8 hours in chlorinated tap water only 20% of the vitamin C remains. After the fruit is cut, the vitamin C near the cut surface exposed to air would be first oxidised and degrades. The rate of oxidation and degradation varies depending on the environmental condition, the type of fruit an its pH, the area of the cut surface as well as the time directly exposed to air. Ascorbic acid is vitamin C and this molecule is physiologically active. It is easily oxidised to its reduced form dehydroascorbic acid which is also physiologically active. However the reduced form is even more easily oxidised and is degraded into diketogulonic acid which has no vitamin C activity. The problem is that many of the analyses have included all three molecular types and represented as ascorbic acid. Since these analyses are not routinely accomplished, much of the food nutrient data is based on old techniques and possibly inaccurate information. If anything, the nutrient values will be reported as being higher than the actual value. No values are available for the actual processed food that is ready for consumption, except for fruits and vegetables that are eaten fresh and raw. However, even these have lost some of their nutrients because of the length of time and natural degradation that has been going on since harvesting. Storage conditions also do their harm on the nutrient values. Remember that the nutrients in food begin decreasing from the moment that they are harvested (and never increase). Known by most scientists, but virtually unknown by the public, is the fact that the ascorbic acid molecule has an asymmetric carbon atom. This means that ascorbic acid molecules could have two stereo-specific forms, namely the L-form and the D-form. Biosynthesis in plants produces the L-ascorbic acid, which is beneficial to our bodies. Ascorbic acids synthesised in the lab normally compose of 50% L-form and 50% D-form. The D-ascorbic acid is designated as useless and discarded by the body, as most research shows. People ingesting Vitamin C would only benefit from the L-ascorbic acid. In an orange, the Vitamin C is primarily the L form, and remains so in the surroundings of the orange. However, when the juice has been extracted from the orange for a period of days, the L changes to D and the juice will eventually even off at 50% D and 50% L Vitamin C content. Frozen concentrate orange juice, when thawed and water added, will produce exactly the same action. Investigations showed that many factors affected the vitamin C contents of citrus juices. They include: Production factors and climate conditions: High nitrogen fertilizer rates can lower vitamin C levels in citrus fruits. Proper potassium levels are also needed for good vitamin C levels.Areas with cool nights produce citrus fruits with higher vitamin C levels. Hot tropical areas produce fruit with lower levels of vitamin C. Environmental conditions that increase the acidity of citrus fruits also increase vitamin C levels. Maturity state and position on the tree: Vitamin C decreases during the ripening process. Immature fruit has the highest levels. The position on the tree also affects vitamin C levels. Since sunlight exposure enhances vitamin C levels, fruit positioned on the outside of the tree and on the south side have higher levels. Shaded inside fruit has the lowest. Type of citrus fruit (species and variety): Early maturing varieties have higher levels than late maturing types. Tangerines tend to have lower levels of vitamin C than oranges due to its lower acid levels. Studies have found that the peel had the highest levels of vitamin C followed by the pulp then the juice. Only 26% of vitamin C of a citrus fruit can be found in the juice. The peel had 53% and the pulp and rag had 21%. Parameters used for processing into different products: Frozen concentrated orange juice and reconstituted almost always have higher levels of vitamin C. This is most likely due to blending of early-season fruit with late season fruit. Canned single strength orange juice will have lower vitamin C levels due to heating during the canning process. Type of container: In cans, which are not used very much today, it was found that enamel-lined cans had higher losses of vitamin C than plain tin cans. This was due to residual oxygen and vitamin C reacting with the tin. Glass packed orange juice provides poor retention of vitamin C, losing 10% after 4 months of storage. Older cardboard cartons lost up to 20%. Today, most cartons have specially designed multi-layered oxygen and light barriers to protect both loss of vitamin C, flavour, and to enhance shelf-life. Frozen concentrated orange juice packed in foil-lined cardboard cans retained greater than 90% of their vitamin C after 12 months at -20°C. Here are some tips for vitamin C: Fresh, raw fruit usually contain the highest natural amount of vitamins, especially vitamin C. Heat, water and the air destroy some of the vitamins in fruit. They are especially vulnerable when cut open, so make sure you keep the fruit salad refrigerated and in a sealed container. Dried fruit does not contain as high a level of vitamin C, but it can actually have higher levels of iron, fibre, potassium, and magnesium. Frozen fruits can provide better nutrition in some cases than older raw fruit as they are generally frozen within hours of being picked. Tinned or canned fruit may be lower in nutrients, although added fruit juice can actually increase the levels of vitamin C. Orange and grapefruit juices contain more natural vitamin C than any other fruit juice. The vitamin C content of canned juices may deteriorate upon exposure to air, so be sure to refrigerate and tightly seal opened containers. Freshly squeezed juice contains more vitamin C than "made from concentrate" canned or frozen juices. Adding ascorbic acid, or vitamin C, to juice allows manufacturers to claim that the drink will give your child "100 % vitamin C". This health claim, however, can mask its sugary content and hides the fact that other essential nutrients are not included. Question Asked By:

Name: Daniel Toh

Age Group: 13 to 20

Occupation Type: Student

Education Level: Primary