Vegetable ascorbic acid content

Yahia EM, Soto G, Puga V and Steta M. 2001a. Hot air treatment effect on the postharvest quality and ascorbic acid content in tomato fruit. In Artes F, Gil MI and Conesa MA, editors. Improving Postharvest Technologies of Fruits, Vegetables and Ornamentals, Volume 2. Paris International Institute of Refrigeration, pp. 550-556. 

Ascorbic acid is probably the most labile bioactive compound in fruit juices and fruit and vegetable pieces, as we described in the first part of this chapter. Retention of this phytochemical after the nonthermal treatments ranged from 47% to 100%, depending on the intensity of the applied treatment and the product. For example, the greatest losses of vitamin C were found in fresh-cut red lettuce and melon treated with IR and HHP (Fan and others 2008 Wolbang and others 2008), respectively. However, the use of gamma radiation in various vegetables retained 100% of their total ascorbic acid content (Fan and others 2008). 

The ascorbic acid content of fruits and vegetables is markedly affected by variety, and to a lesser degree by maturity and climate. Increased exposure to sunlight and ripening on the plant generally enhances the vitamin C content of the edible portion. Ascorbic acid concentration within a fruit or vegetable often varies largely from part to part. 

Genetic Variation. The concentration of many individual nutrients in foods of plant origin is under genetic control. Baker (34) reviewed some examples of genetic manipulation that improved the quantity of )3-carotene in tomatoes, methionine in beans, and lysine in com. Variations of ascorbic acid content of different varieties of raw vegetables and fruits is notoriously high (35). Twofold variation in vitamin C concentration in different strains of a vegetable or a fmit is common and a fivefold variation can be found. Differences in ascorbic acid contents (35- to 300-fold) of different strains of a fmit were reported prior to 1950 (36). These reports have not been substantiated. 

Mabesa and Baldwin (139) found that frozen peas, cooked with or without water in microwave ovens or conventionally, varied in ascorbic acid content. When the same ratio of water to vegetable (1 4) was used in the microwave and conventional methods, ascorbic acid retentions were similar (70%), but lower than when no water was used in the microwave oven (retention >96% ). 

In a study of ascorbic acid retention in frozen cauliflower (Table IX) (140), the ascorbic acid content and retention in the vegetables cooked with no water was significantly higher (p<0.05) than those cooked with increasing proportions of water (0.25 1, 0.5 1, 1 1). However, the cauliflower cooked without water was not as palatable. 

Klein et al. (135) found that approximately one-half of the initial ascorbic acid in fresh raw spinach was retained in the cooked vegetable. The amount of water and vegetable (1 4) used in each method was constant, and cooking times were similar. No significant differences in ascorbic acid content between conventionally and microwave cooked spinach were found. 

Lutein and zeaxanthin are the dominant carotenoids in the human retina (112). They represent about 36% and 18% of the total carotenoid content of the retina, respectively (101). M. oleifera contains high amounts of lutein, 24.8 mg/100 g edible fresh leaves (39). Carotenoid types - a-carotene and 3-carotene are up to 4.5 and 34 mg/100 g, respectively, while lycopene is not present inM. oleifera (44). In fresh leaves of M. oleifera of Tanzania, vitamin C (ascorbic acid) content can be as high as 204 mg/100 g fresh weight (113). On the other hand, in Pakistan vitamin C contents range between 36 and 43 mg/100 g (4). In terms of cooking stability, when 20 mg samples are cooked in 400 ml of water, the vitamin C content loss can be as high as 98.5%. However, smaller losses of vitamin C are observed when M. oleifera sample is cooked in less water. Since most leafy vegetables are cooked prior to consumption, it is recommended that M. oleifera leaves be cooked in small amounts of water for short periods to minimise loss of vitamin C (113). Essential Oils... 

In a previous work, Di Scala and Crapiste (2005) studied the effect of temperature on some of the most important quality characteristics of individual pieces of red sweet pepper Capsicum annuum. L) during drying. Color and antioxidant content are among the main quality attributes of these vegetables besides textural and flavor attributes. Both carotenoids (provitamin A) pigments and ascorbic acid contents are related to pepper variety (Roura et al., 2001) and technological factors. 

Ascorbic acid (vitamin C) is utilized as a cofactor to stabilize the chloroplast stroma, in quenching free radicals and reacting with hydroxy radicals and in the biosynthesis of tartaric acid and oxalic acid (6), important organic acids in grapes, and many vegetables. The effect of CA on ascorbic acid content differs with commodity,... 

Szeto YT, Tomlinson B, and Benzie IFF (2002) Total antioxidant and ascorbic acid content of fresh fruits and vegetables implications for dietary planning and food preservation. British Journal of Nutrition 87 55-59. 

Thus, it is uncertain to what extent the apparent protective effects of fruit and vegetable consumption on risk of stomach cancer can be attributable to their phytoestrogen content. This appears not to have been studied directly, and other constituents such as ascorbic acid (vitamin C), a-tocopherol (vitamin E) and /1-carotene may be potentially protective. 

As has been explained in previous chapters, the antioxidant capacity of fruits and vegetables is a function of the amounts and types of phytochemicals that are present in the fresh tissues. However, the individual contribution to the total antioxidant capacity varies widely. Various studies have demonstrated that phenols and flavonoids contribute to a higher extent than ascorbic acid, carotenoids, and others to the antioxidant capacity of fmits and vegetables (Robles-Sanchez and others 2007). It has been observed that a given content of vitamin E in fruits contributes significantly more to the antioxidant capacity than the same content of ascorbic acid. 

This experiment is flexible in that students may choose the samples they wish to analyze. It is suggested that several fruits and vegetables as well as an unknown ascorbic acid sample be available for analysis. The vitamin C content of raw and cooked vegetables can also be measured and compared. Commercially available vitamin C tablets or multivitamin pills provide interesting samples for analysis. The time required for this experiment can be adjusted by controlling the number and type of samples. 

Fruits and vegetables are the most common food sources for vitamin C (15-18). In food, vitamin C exists as two vitamers L-ascorbic acid (AA) and its oxidation product, dehydro-L-ascor-bic acid (DHAA) (Fig. 1) (15,17-19). Total Vitamin C is the sum of the AA and the DHAA contents. A stereoisomer, isoascorbic acid (IAA) is often added to food as an antioxidant. Both LAA and its oxidation product, dehydroisoascorbic acid (DHIAA), can interfere in Total Vitamin C determinations. 

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