Ascorbic acid, destruction

Kinetics of Ascorbic Acid Destruction During Processing and Storage... 

To predict nutrient deterioration, knowledge of the reaction rate as a function of temperature of storage or processing is needed. The kinetics of ascorbic acid destruction have been examined most extensively in model systems, with particular attention being given to intermediate moisture foods (17, 71,78,79). Most of the data available for vitamin C losses in actual food systems are insuflBcient to calculate the kinetic parameters needed to predict losses during heat treatment or storage. 

According to Lenz and Lund (72), kinetic models for destruction of food components are needed to improve products by minimizing quality changes for new product development and to predict shelf life during storage. Numerous reports and reviews of the kinetics of ascorbic acid destruction can be found in the literature (68-88). A brief overview is presented here to indicate the need for further research in this area. 

If the destruction of a component is presumed to be zero-order, a plot of C vs. t should give a straight line. Certain losses of vitamin C, particularly in frozen foods, are presumed to follow first-order kinetics (89). Labuza (76) observed that zero-order reaction rates for quahty losses may be assumed in some fluctuating temperature studies, but this may lead to a miscalculation of predicted changes. Therefore, from a theoretical standpoint, it is important that the proper order be used for predictions. In general, ascorbic acid destruction is assumed to be first-order, or pseudo first-order (17,27) except under specific conditions of heat and moisture (79). 

Some information regarding the Ea for ascorbic acid in food systems can be found in the literature. Kirk et al. (17) determined that the vitamin C destruction in a model dehydrated food system could be described by the first-order function. Rates of destruction were influenced by dw, moisture, and temperature of storage. Activation energies for TAA destruction at above 0.24 were approximately 18 kcal/mol, similar to those reported for RAA by Lee and Labuza (78). Lower EaS were reported at a s less than 0.24, suggesting a diflFerent mechanism for ascorbic acid destruction, perhaps by an anaerobic pathway. Rate constants were also influenced by the packaging used for the model food system, which may be attributed to the amount of dissolved oxygen present. 

Mechanism of Reaction Proposed in Relation to Water and Kinetics of L-(+)-ascorbic Acid Destruction... 

Rojas, A. M. Gerschenson, L. N. (1997). Influence of sj tem composition on ascorbic acid destruction at processing temperatures. J. Sci Food Agile., 74, 369-378. 

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). 

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