Acid ascorbic, loss

The bone becomes depleted of calcium salts when the urine is acidic over a relatively long period. This was shown by Goto (17) who fed rabbits large doses of hydrochloric acid. He then showed that urinary calcium loss occurred in concert with a marked reduction in mass of the skeletal system, and also that the total non-fat dry weight of bone decreased,implying a loss of bone matrix. A dose-dependent, dietary acid induced loss of labelled calcium from rat bone has been reported by Thorn and his coworkers (18). They demonstrated that in response to graded doses of ascorbic acid, cells in tissue culture, and bones in whole animals fed such doses were depleted of the labelled calcium. 

Vitamin C (ascorbic acid) is also a well-known antioxidant. It can readily lose a hydrogen atom from one of its enolic hydroxyls, leading to a resonance-stabilized radical. Vitamin C is acidic (hence ascorbic acid) because loss of a proton from the same hydroxyl leads to a resonance-stabilized anion (see Box 12.8). However, it appears that vitamin C does not act as an antioxidant in quite the same way as the other compounds mentioned above. 

Levarterenol bitartrate may be stored at pH 3.6 in a well-filled ampul in the presence of 0.1% NaHS03. Exposure to air, in an alkaline or neutral pH resulted in deterioration of the sample accompanied by a darkening of the solution to a brown color. Dilution of levarterenol in plasma, 5% dextrose, or saline containing ascorbic acid resulted in no significant loss of activity after 9 hours at room temperature. Saline diluent without ascorbic acid allowed loss of activity. Levarterenol as the bitartrate salt or in the free base form behaved similarly. 

A number of food additives and ingredients are available in encapsulated form, which include active agents such as citrous flavors, citric acid, ascorbic acid, spice extracts, and vegetable extracts. Encapsulation serves to enhance stabihty, reduce loss by volatilization and oxidative degradation, increase shelf-life, and impart better handling properties. Water-soluble carriers in common use for food additives are gum arabic, modified starches, maltodextrins and hydrolyzed gelatins. Encapsulation... 

Folic acid is quite stable. There is no destruction during blanching of vegetables, while cooking of meat gives only small losses. Losses in milk are apparently due to an oxidative process and parallel those of ascorbic acid. Ascorbate added to food preserves folic acid. 

In regard to the addition of antioxidants, ascorbic acid was tested to protect astaxanthin during 6 h of cell wall disruption step and using lactic acid at 65 C. Concentrations of ascorbic acid ranged from 0 to 18 mg per mL of lactic acid. Ascorbic acid prevented loss of astaxanthin, but its effect was relatively modest. Additionally, a-tocopherol was used during the extraction step with 100% ethyl lactate. As with ascorbic acid, concentrations ranged from 0 to 18 mg per mL of ethyl lactate and the studied action time was 6 h. With 12 mg of a-tocopherol, maximal amounts of astaxanthin were extracted after 1 h extraction time (a-tocopherol caused an increase of 11% in astaxanthin yield). Quantities above 12 mg did not seem to be effective. 

In acidic solution, the degradation results in the formation of furfural, furfuryl alcohol, 2-furoic acid, 3-hydroxyfurfural, furoin, 2-methyl-3,8-dihydroxychroman, ethylglyoxal, and several condensation products (36). Many metals, especially copper, cataly2e the oxidation of L-ascorbic acid. Oxalic acid and copper form a chelate complex which prevents the ascorbic acid-copper-complex formation and therefore oxalic acid inhibits effectively the oxidation of L-ascorbic acid. L-Ascorbic acid can also be stabilized with metaphosphoric acid, amino acids, 8-hydroxyquinoline, glycols, sugars, and trichloracetic acid (38). Another catalytic reaction which accounts for loss of L-ascorbic acid occurs with enzymes, eg, L-ascorbic acid oxidase, a copper protein-containing enzyme. 

The calcium form of EDTA instead of free EDTA is used in many food preparations to stabilize against such deleterious effects as rancidity, loss of ascorbic acid, loss of flavor, development of cloudiness, and discoloration. The causative metal ions are sequestered by displacing calcium from the chelate, and possible problems, such as depletion of body calcium from ingestion of any excess of the free chelant, had it been used, are avoided. 

Ascorbic acid is a reasonably strong reducing agent. The biochemical and physiological functions of ascorbic acid most likely derive from its reducing properties—it functions as an electron carrier. Loss of one electron due to interactions with oxygen or metal ions leads to semidehydro-L-ascorbate, a reactive free radical (Figure 18.30) that can be reduced back to L-ascorbic acid by various enzymes in animals and plants. A characteristic reaction of ascorbic acid is its oxidation to dehydro-L-aseorbie add. Ascorbic acid and dehydroascor-bic acid form an effective redox system. 

The important commercial feature of these juices, especially significant with blackcurrant and tomato juices, is their ascorbic acid (or vitamin C) content, of which loss by oxidation is known to be accelerated both by heat and by metal (particularly copper) contamination. The effect of copper has been carefully investigated for pure ascorbic acid", and more recently ascorbic acid in blackcurrant juice and model systems. There are, however, oxidation inhibitors of different kinds (which may themselves be heat-sensitive) present in various fruits, which give differing results. The presence of metals will also affect flavours", may cause discoloration, and may give rise to clouding effects, as in apple juice. ... 

Approaching the matter from an entirely different angle, a semiquantitative estimation of ascorbic acid or total iodine-reducing substances might provide a suitable basis. Delays in handling involve rather marked losses of ascorbic acid. Kramer and Mahoney (20) have observed a relationship between quality and the amount of iodine-reducible substances remaining in lima beans. 

C Ascorbic acid Coenzyme in hydroxylation of proline and lysine in collagen synthesis antioxidant enhances absorption of iron Scurvy—impaired wound healing, loss of dental cement, subcutaneous hemorrhage... 

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. 

Evaporation is the oldest process for the concentration of liquid foods. Temperatures are higher compared to those of the more modern membrane filtration or freeze concentration processes. Tocopherols, carotenes, ascorbic acid, flavonoids and other phenolic antioxidants are partially destroyed by heating. Therefore, it is necessary to minimise the time needed for evaporation, and heating to the evaporation temperature should be carried out very rapidly. The temperature may be decreased if the pressure is reduced. The process is then more expensive, but losses of antioxidants become substantially lower. 

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). 

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