Discoloration, inhibition

Phenolic acids occur naturally in higher plants, usually as free adds, glycosides, esters, or in insoluble-bound form in a complex mixture of other phenolic compounds. The presence of phenolic acids in food products has been associated with astringency, discoloration, inhibition of enzyme activity, and antioxidant properties, among others [15]. A major portion of phenohc acids present in almond was found in the form of soluble esters. Wijeratne et al. [16] reported that the total amounts of identified free phenolic acids were 16.3, 14[ig/g and a trace amount in skin, shell, and whole seed extracts, respectively, whereas the amounts for total esterified phenolic acids were 279.6,967.1, and 40.3 [ig/g, respectively. 

Under atmospheric conditions, 3-aminophenol is the most stable of the three isomers. Both 2- and 4-aminophenol are unstable they darken on exposure to air and light and should be stored in brown glass containers, preferably in an atmosphere of nitrogen. The use of activated iron oxide in a separate cellophane bag inside the storage container (116), or the addition of staimous chloride (117), or sodium bisulfite (118) inhibits the discoloration of aminophenols. The salts, especially the hydrochlorides, are more resistant to oxidation and should be used where possible. 

Fluorouracil Inhibition of the enzyme thymidylate synthase, the rate-limiting step in thymidine formation. Dose-limiting Myelosuppression and mucositis with bolus administration Diarrhea and hand-foot syndrome with continuous infusion Additional toxicities Skin discoloration, nail changes, photosensitivity, and neurologic toxicity... 

New developments are hydroxylamines and lactones (for processing stability), which operate at an earlier stage during stabilisation. Lactone (benzofuranone) chemistry has been identified as commercially viable, and marks a revolutionary advance in comparison to hindered phenols and phosphites [18]. New lactone chemistry (Figure 10.1) provides enhanced additive compatibility, reduced taste and odour (organoleptics), resistance to irradiation-induced oxidation, and inhibition of gas fade discoloration. The commercial introduction of fundamentally new types of stabilisers for commodity and engineering polymers is not expected in the near future. 

The function of sodium nitrite, NaN02, as a food additive is two-fold (1) it inhibits the oxidation of blood, preventing the discoloring of red meat, and (2) it prevents the growth of botulism bacteria. There is now some controversy regarding this food additive because nitrites are suspected of combining with amines under the acidic conditions of the stomach to produce carcinogenic nitrosoamines. 

Tetracyclines inhibit P. acnes, reduce the amount of keratin in sebaceous follicles, and have antiinflammatory properties (inhibiting chemotaxis, phagocytosis, complement activation, and cell-mediated immunity). Drawbacks to tetracyclines include hepatotoxicity and predisposition to infections (e.g., vaginal candidiasis). Other adverse effects include GI disturbances, photosensitivity, tooth discoloration in children, and inhibition of skeletal growth in the developing fetus. Tetracyclines must not be combined with systemic retinoids because of an increased risk of intracranial hypertension. / Tetracycline is the least expensive agent in this class and is often... 

Foliar tests Cotton and other plants grown in the greenhouse received a foliar treatment in early stages. Effects such as growth inhibition, distortions (epinasty), chlorosis, discoloration, etc., were recorded. 

Figure 4. Inhibition of discoloration vs. ultraviolet-absorber concentration (Fade-ometer exposure)...

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