Chemistry Reference
In-Depth Information
There is some evidence that the concentration of vitamin C in cow's
milk (Andersson and Oste 1994; Lindmark-Mansson and Akesson, 2000) and
goat's milk (Kondyli et al., 2007) changes with season. Andersson and Oste
(1994) found that in raw milk sampled in March or August, the concentration
of vitamin C was higher (2.0-2.7 mg/100 ml) than in samples collected in
October (1.2 mg/100 ml). Lindmark-Mansson and Akesson (2000) reported
that mean values for vitamin C were higher in July and September than in
January and March.
Ascorbic acid is considered to be the first line of defence against oxidiz-
ing species and consequently appears to be the vitamin lost most readily in
milk and cooking of foods (Bates, 1997). Loss of vitamin C is determined
primarily by the concentration of O
2
dissolved in milk and is greatly acceler-
ated by exposure to light and the presence of heavy metals such as Cu and Fe
(Scott et al., 1984). Andersson and Oste (1992a, b) observed that at a low
oxygen content (0.6 ppm), ascorbic acid decreased by about 50% after 1-2
weeks' storage with somewhat higher stability at 78C than at 23 or 358C. At
oxygen contents of 3.5-5.4 ppm the loss was much greater.
12.6.7.
Vitamin C Status and Requirements
In setting values for average population requirements and individual
nutrient intakes, the important question is, how do we differentiate between
preventing deficiency symptoms, ensuring an adequate intaike and promot-
ing optimal intake for the prevention of disease? The recommended dietary
allowance (RDA) of 60 mg/day in the United States (Food and Nutrition
Board, 1989), the reference nutrient intake (RNI) of 40 mg/day in the United
Kingdom (Department of Health, 1991) and the population reference intake
(PRI) of 45 mg/day in the EU were aimed at prevention of the clinical
deficiency state, scurvy. The Food and Nutrition Board (2000) established
an estimate average requirement (EAR) for vitamin C, which is the nutrient
intake value that is estimated to meet the requirements of half of a specific
gender and life-stage group, and was based on evidence that 75 mg/day
vitamin C can maintain near-maximal neutrophil concentration with minimal
urinary loss (Levine et al., 1996). Thus, the EAR for men aged 19-50 years is
75 mg/day, with a value of 60 mg/day for women, based on women having less
lean body mass and body water and a smaller body size than men. There are
no data on the distribution of vitamin C requirements in healthy adults;
therefore the US Food and Nutrition Board (2000) recommended daily
allowance (RDA) for vitamin C, which is the intake value considered to
meet the requirements of 97.5% of the relevant life-stage and gender popula-
tion group, be set at 90 mg/day for men and 75 mg/day for women (RDA
¼
EAR
þ
2CV), assuming a coefficient of variation (CV) of 10%. There is
