Ascorbic destruction

Another important food processing technology is pasteurisation. It consists of rapid heating to temperatures between 60 and 65°C in order to destroy microorganisms. Oxidoreductases are inactivated at the same time. As the heating is short, the destruction of antioxidants is only moderate. Losses of ascorbic acid are a good indicator of the destructive changes. Losses of ascorbic acid and carotenes are minimised by deaeration. 

Prevention of vascular disease is one of the goals of a study in progress in Sweden, in which newly diagnosed diabetic children have been randomized in a doubleblind study where one group receives placebo and the other a preparation containing ascorbic acid, )3-carotene, nicotinamide, selenium and vitamin E (Ludvigsson, 1992). Future research with antioxidants may attempt to prevent the onset of pancreatic beta-cell destruction in the prediabetic phase of susceptible individuals. 

The conversion of L-xylosone into L-ascorbic acid has been reversed by treating the latter with pert-naphthindan-2,3,4-trione hydrate184 2,3-dioxo-L-zj/fo-hexonic acid is formed and is decarboxylated to L-xylosone. It was suggested that the destruction of ascorbic acid in vivo by this mechanism might explain the relatively high requirements for the vitamin in many species. 

Some horticultural crops such as sweet potatoes, bananas, and pineapples can suffer from chilling injury at low temperatures (Lee and Kader 2000). Chilling injury causes accelerated losses in ascorbic acid content of chilling-sensitive crops. Destruction of ascorbic acid can occur before development of any visible symptoms of chilling injury (Lee and Kader 2000). 

Folate is a relatively unstable nutrient processing and storage conditions that promote oxidation are of particular concern since some of the forms of folate found in foods are easily oxidized. The reduced forms of folate (dihydro- and tetrahydrofolate) are oxidized to p-aminobenzoylglutamic acid and pterin-6-carboxylic acid, with a concomitant loss in vitamin activity. 5-Methyl-H4 folate can also be oxidized. Antioxidants (particularly ascorbic acid in the context of milk) can protect folate against destruction. The rate of the oxidative degradation of folate in foods depends on the derivative present and the food itself, particularly its pH, buffering capacity and concentration of catalytic trace elements and antioxidants. 

The stability of some vitamins is influenced by aw. In general, the stability of retinol (vitamin A), thiamin (vitamin Bj) and riboflavin (vitamin B2) decreases with increasing aw. At low av (below 0.40), metal ions do not have a catalytic effect on the destruction of ascorbic acid. The rate of loss of ascorbic acid increases exponentially as aw increases. The photodegradation of riboflavin (Chapter 6) is also accelerated by increasing aw. 

Chen, T.S.. R.G, Cooper "Thermal Destruction of Folacin Effect of Ascorbic Acid. 

Rutin, Ascorbic acid Tablet MLR Non-destructive quantitation method. Errors (SEP) less than 0.7%. Method validated using ICH-adapted guidelines 129... 

The fruit contains a fixed oil from 15 to 30% and a volatile essential oil up to 12%. The fruit also contains flavonoids, iodine, kaempferols, umbelliferone and stigmas-terol and ascorbic acid traces of aluminium, barium, lithium, copper, manganese, silicon and titanium. A non-destructive method of determining oil constituents has been described by Fehrmann et al. (1996). 

Groden, D., and Beck, E., 1979, H2O2 destruction by ascorbate-dependent systems from chloroplasts, Biochim. Biophys. Acta 546 4269435. 

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