Microcomponents antioxidants and vitamins

Ripe tomatoes are relatively rich in antioxidants: vitamin C (160-240mgkg-1), lycopene (30-200mgkg-1), provitamin A carotenes (6-9mgkg-1) and phenolic compounds; flavonoids (5-50mgkg-1); and phenolic acids (10-50mgkg-1).14 Also present in small quantities are vitamin E (5-20 mg kg-1) and trace elements such as copper (0.1-0.9mgkg-1), manganese (1-1.5mgkg-1) and zinc (1-2.4mgkg-1) which are present in several antioxidant enzymes. Most often the tomato variety is not indicated and the reported values are a mean concentration of the constituents in tomatoes found in local markets.

Whole red-ripe tomatoes contain nearly all the vitamin C activity in the reduced ascorbic acid form. Dehydroascorbic acid has been reported to consti tute 1-5% of the total ascorbic acid in tomatoes.15,16 The ascorbic acid concentration in fresh ripe tomatoes is about 25mg per 100g. Thus, a small tomato supplies about 40% of the adult US recommended daily allowance (RDA) of 60 mg and about two-thirds of the RDA of 40mg for children. A glass of tomato juice supplies about 35mg of ascorbic acid or about 60% of the adult RDA and 85% of the RDA for children.

Tomatoes are also a good source of vitamin A, present in the form of carotene. Fresh ripe tomatoes and tomato juice contain 1000 international units (IU) of vitamin A per 100g. Booker et al.17 gave a figure of 1150IU per 100g. On the basis of these figures, a small tomato or glass of juice should supply 20% or more of the adult recommended daily allowance (RDA) of 5000IU. It is clear, therefore, that in relation to the average consumption, the tomato makes a very important contribution to the vitamin A requirement of the human diet.

Tomatoes also provide small amounts of the B complex vitamins: thiamine, niacin and riboflavin. The content of thiamine, reported in various sources cited by Leoni,8 varies from 16 to 120mg per 100g of ripe fruits and juice. On this basis a small tomato contains only about one-tenth of the RDA for an adult man. The same sources indicated the riboflavin and niacin contents of tomatoes to be rather low (20-50 mg per 100g for riboflavin and less than 1mg for niacin). On the basis of these values it is evident that tomatoes make a very small contribution to the 1.7 mg of RDA of riboflavin and 20 mg of niacin required for adults.11 Cultivars and environmental conditions, such as exposure to light, are also important. From a practical standpoint the stage of ripeness is not an important consideration here because tomatoes are usually canned or consumed only when ripe and because of this the method of ripening seems to have little effect.

Was this article helpful?

0 0

Post a comment