2. Variation among species and cultivars
While there have been many studies on the AA content of fruits and vegetables, relatively few have been reported on the content of the two forms of vitamin C, AA and DHA. The wide variation in the content of AA and DHA among
different species of fruits and vegetables are shown in Tables 1 and 2, respectively. Persim- mons and peppers show the highest amount of vitamin C among their groups. In general crucif-
erous vegetables contain higher content of AA and sulfur compounds than non-cruciferous veg- etables. Total sulfur content correlated well with the AA content of vegetables (Albrecht et al.,1991)
In cruciferous vegetables reduced glu- tathione would reduce DHA to AA. It is interest- ing to note that only DHA was detected in Swiss chard. When the sample was spiked with AA it was completely and immediately transformed to DHA, which was the only vitamin C form de- tected. This result could be associated with a high oxidase activity in the Swiss chard extracts (Gil et al., 1998). Vitamin C contents of fruits and vegetables are also variable among cultivars and tissues. Nelson et al. (1972) found a range from 19.3 to 71.5 mg/100g AA in six strawberry cultivars from four locations. Lee et al. (1995) reported a range from 64 to 168 mg/100g AA in five fresh pepper culti- vars. In citrus fruit, flavedo tissues contained four times higher AA content than the juice (Nagy, 1980). Usually skin tissues have more AA content to protect the fruit from outside stress caused by light and oxidation.
during growth, the lower the AA content of plant tissues (Harris, 1975). Temperature also influences the composition of plant tissues during growth and development. To- tal available heat and the extent of low and high temperatures are the most important factors in determining growth rate and chemical composi- tion of horticultural crops. Reuther and Nauer (unpublished report, 1972) showed that ‘Frost Satsuma’ mandarins contained more vitamin C when grown under cool temperatures (20–22°C day, 11–13°C night) than hot temperatures (30– 35°C day, 20–25°C night). Grapefruits grown in coastal areas of California generally contain more vitamin C than fruit grown in desert areas of California and Arizona.