Apple browning

When an apple is cut, its surface is exposed to oxygen in the air. Iron-containing chemicals inside the apple react with the oxygen and turn the apple brown. This is an oxidation reaction. Keeping cut apples cold will slow down the rate of the chemical reaction that makes them turn brown. Adding lemon juice or orange juice to them will also slow down this process. That is because the juice is an antioxidant and the citric acid acts as an inhibitor. 

When an apple is sliced, the inside part of the apple is surrounded by air. Air contains oxygen molecules. Oxygen molecules in the air combine with molecules in the apple to turn the apple brown. 

Real-World Question How can the chemical reaction that turns apples brown be prevented ... 

Fig. 6.50 Browning of apple. (From http //study.com/dmages/multimages/16/apple browning.png).

Brown E R, McIntosh K A, Smith F W, Manfra M J and Dennis C L 1993 Measurements of optical-heterodyne conversion in low-temperature grown GaAs Appl. Rhys. Lett. 62 1206-8... 

Brown, C. W. Obremski, R. J. Multicomponent Quantitative Analysis, Appl. Spectrosc. Rev. 1984, 20, 373M18. 

In the production of opalescent or natural-type apple juice, ascorbic acid is added to the fmit pulp before pressing, or to the juice as it comes from the press, to retain more of the apple flavor (4). Ascorbic acid addition and pasteurization of the juice as soon as possible after pressing prevent polyphenol oxidation, which causes browning and contributes to pulp flocculation. 

Natural style juices that contain the cloud are increasing in popularity, especiaHy apple juices, because these retain more fresh flavor if processed carefuUy. Optimum processing conditions chill the fmit to 4°C before milling, add 500 ppm ascorbic acid to retard browning, press under nitrogen, and flash pasteurize the juice as quickly as possible (4). 

Vacuum Flow When gas flows under high vacuum conditions or through very small openings, the continuum hypothesis is no longer appropriate if the channel dimension is not very large compared to the mean free path of the gas. When the mean free path is comparable to the channel dimension, flow is dominated by collisions of molecules with the wall, rather than by colhsions between molecules. An approximate expression based on Brown, et al. J. Appl. Phys., 17, 802-813 [1946]) for the mean free path is... 

FIG. 6-12 Correction factor for PoiseiiiUe s equation at low pressures. Curve A experimental curve for glass capillaries and smooth metal tubes. (From Brown, et al, J. Appl. Phys., 17, 802 [1.946].) Curve B experimental curve for iron pipe (From Biggie, Couiiesy of E. I. du Pont de Nemours [Pg.641]

K Sjdlander, K Karplus, M Brown, R Hughey, A Krogh, IS Mian, D Haussler. Dirichlet mixtures A method for improved detection of weak but significant protein sequence homology. Comput Appl Biosci 12 327-345, 1996. 

Brown, iVl. A., and Brix, K. A. (1998). Review of health consequences from high-, mtermedi ate- and low-level exposure to organophospborus nerve agents. /. Appl. Toxicol. 18, 393-4i)8. 

Donahue, S.M., Brown, C.W., Scott, M.J., "Analysis of Deoxyribonucleotides with Principal Component and Partial Least-Squares Regression of UV Spectra after Fourier Processing", Appl. Spec. 1990 (44) 407-413. 

The arguments against nonclassical ions are summed up in Brown, H.C. The Nonclassical Ion Problem Plenum NY, 1977. This book also includes rebuttals by Schleyer, P.v.R. See also Brown, H.C. Pure Appl. Chem., 1982, 54, 1783. 

For reviews, see Hoffmann, R.W. Niel, G. Schlapbach, A. Pure Appl. Chem., 1990, 62 1993 Pelter, A. Smith, K. Brown, H.C. Borane Reagents Academic Press NY, 1988, p 310. For a review of allylic boranes, see Bubnov, Yu.N. Pure Appl. Chem., 1987, 21, 89, For an example that proceeds with asymmetric induction, see Buynak, J.D. Geng, B Uang, S. Strickland, J.B. Tetrahedron Lett., 1994, 35, 985. 

Bredt DS, Snyder SEl Nitric oxide, a novel neuronal messenger. Neuron 8 3—11, 1992 Brouette T, Anton R Clinical review of inhalants. Am J Addict 10 79-94, 2001 Brown ES, Nejtek VA, Perantie DC, et al Quetiapine in bipolar disorder and cocaine dependence. Bipolar Disord4 406 11, 2002 Bushnell PJ, Evans EIL, Palmes ED Effects of toluene inhalation on carbon dioxide production and locomotor activity in mice. Fundam Appl Toxicol 5 971-977, 1983... 

Brown, H. C., The Reactions of Alkali Metal Hydrides and Boro-hydrides with Lewis Acids of Boron and Aluminum, Congr. Lect., 17th Int. Congr. Pure Appl. Chem. p. 167. Butterworths, London, 1960. 

Brown HC, Zaidlewicz M (2001) In Organic Syntheses via Boranes, Vol 2. Aldrich Chemical Company, Milwaukee, p 118 Yamamoto Y, Asao N (1993) Chem Rev 93 2207 Bubnov YN (1987) Pure Appl Chem 59 895... 

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