Browning of apples

Rouet-Mayer, M.-S., Ralambosoa, J., and Philippon, J. (1990). Roles of o-quinones and their polymers in the enzymic browning of apples. Phytochem. 29,435-440. 

Le Tien, C. et al., Milk protein coatings prevent oxidative browning of apples and potatoes, J. Food Sci., 66, 512, 2001. 

In plant and animal cells, many enzymes are compartmentalized, and several are also immobilized, greatly slowing down reactions. After the cells have been mechanically damaged, some reactions may proceed fast. A well-known example is the rapid enzymatic browning of apple tissue after the apple has been cut here, the cutting allows an enzyme, polyphenoloxidase, to reach its substrate, mainly chlorogenic acid. 

Inhibits enzymatic browning of apples, potatoes etc. Mp 188-190° dec. (hydrate). 

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

Goupy P, Amiot MJ, Richard-Forget F, Duprat F, Aubert S and Nicolas J. 1995. Enzymatic browning of model solutions and apple phenolic extracts by apple polyphenoloxidase. J Food Sci 60 497—501, 505. 

Jeon M and Zhao Y. 2005. Honey in combination with vacuum impregnation to prevent enzymatic browning of fresh-cut apples. Int J Food Sci Nutr 56(3) 165—176. 

Symptoms Browning of foliage on the side of a plant facing the prevailing wind. Individual leaf margins or tips may be markedly browner than the leaf centers. Apples and other fruit may show a red/ brown russeting on the skin surface. 

In most studies of DPO activity, the main objective is usually a simple comparison of the potential of a particular tissue to undergo enzyme-catalyzed browning, for example, a comparison of the potential for enzymic browning of different apple or mushroom cultivars. Related to this are comparative studies of different inhibitors and processing regimes to control enzymic browning. In these circumstances, it is usually sufficient to provide comparative measurements rather than absolute values of enzyme activity, in which case results can be expressed in arbitrary units such as AmV/min for 02 electrode assays or AA/min for spectrophotometric assays. If more precise units are required, the 02 electrode results should be expressed as Anmol 02/min/(j.g protein. 

Phenolic compounds are of interest due to their potential contribution to the taste (astrin-gency, bitterness, and sourness) and formation of off-flavor in foods, including tea, coffee, and various fruit juices, during storage. Their influence on the appearance of food products, such as haze formation and discoloration associated with browning in apple and grape products, is also significant. Furthermore, analysis of these phenolic compounds can permit taxonomic classification of the source of foods. The importance of each phenolic compound and its association with the quality of various foods is described further in Sec. IV, on food applications. 

The phenolic composition of apple consists of cinnamic acids, flavonols, dihydrochalcones, and flavan-3-ols (50,56). In the apple fruit processing industry, hydroxycinnamic acid derivatives and flavan-3-ols are important due to their contribution to the astringency, haze, and browning in apple juice and cider. Chlorogenic acid represents the major hydroxycinnamic acid derivative. The flavan-3-ols (catechins) are present in the monomeric form as well as in oligomeric and polymeric forms (procyanidins) in apple and apple products (56). 

IH Kim, HS Lee. Evaluation of polyphosphate for the control of nonenzymic browning in apple juice. Foods Biotechnol Korea 6 309-313,1997. 

The colour of a soft drink or fruit juice may be assessed in a number of ways. If the product is clear it can simply be carried out by measuring the absorbance of the product at one or more wavelengths. The actual values chosen will depend on the particular colour of the product. For a yellow product, such as apple juice, wavelengths of 465, 430 or 420 ntn are often chosen to assess the colour. These values can then be expressed in European brewing convention (EBC) units by multiplication by a factor of 25. The actual Brix value chosen to assess the colour depends on the country however, levels between 11 and 12 are often taken as the norm. If dealing with a red-coloured product, then the assessment is generally carried out at 520 nm. Absorbance values are sometimes also taken at 420 nm in red or black juices to assess the brownness of the product. The two absorbance values are often used to express a colour ratio, which gives an indication of colour versus brownness ... 

All the fabulous success stories and the terrible disasters that can occur in kitchens around the world can be blamed on chemical reactions. Cakes are light and fluffy because the baking soda in the batter reacts with an acid to produce carbon dioxide, a gas. When sugar is heated, it turns into dark brown, gooey caramel. The cut surfaces of apples and bananas turn brown because they react with oxygen in the air. All of these are examples of chemical reactions in the kitchen. 

FIG. 18 Schematic layout of a two-compartment configuration using bipolar (bmp) and anionic (a) membranes proposed to inhibit enzymatic browning of cloudy apple juice (Tronc et al., 1998) via preliminary acidification to pH 2.0 and subsequent de-acidification to pH 3.5 by reverting flow of HCl and apple juice streams. 

What color are the apple pieces when they are first sliced How long does it take for the apple slices to turn brown Which apple slice turns brown first Do all of the apple slices turn brown ... 

These large, complex molecules are called enzymes. The piece of apple that is left in the air turns brown because of these enzyme molecules. 

The two pieces of apple that are in the bowl of cold water do not turn brown because each piece is surrounded by water molecules. The water molecules keep oxygen molecules from adding to molecules in the apple. 

The piece of apple that is rubbed with lemon juice does not turn brown because molecules in the lemon juice change the enzymes in the apple. When the enzymes are changed, they cannot cause the oxygen molecules to add to molecules in the apple. Lemon or citrus juice may be added to fresh fruit in a fruit salad to keep the fruit from turning brown. 

Remove one of the pieces of apple that is in the bowl of cold water. Does it turn brown after sitting in the air for thirty minutes ... 

ASK AN ADULT TO HELP YOU CUT AN APPLE INTO PIECES. Put a piece of apple in a bowl of hot water. Remove the piece of apple after five minutes. Does this piece of apple turn brown when exposed to air Even though this piece of apple is now exposed to oxygen molecules it should not turn brown since the heat changes the enzyme molecules. 

FIGURE 9.3 Principal component axes defining a new set of basis vectors for the measurement space defined by the variables X, Y, and Z. The third principal component describes only noise in the data. (From Brown, S., Appl. Spectrosc., 49 (12), 14A-30A, 1995. With permission.)... 

Maillard reactions are responsible for the browning of sugars in the presence of amino acids. They are one of the key routes to flavour compounds in the whole of food science. In practice, any browning in foods is due to the Maillard reaction except where it is enzymic, e.g. the browning of a cut apple is enzymic and hence not a Maillard reaction. 

To prevent non-enzymatic browning, the fruit can be dipped in a 5% solution of citric acid (or in lemon juice). This is especially advisable in the case of sliced and diced apples where the acid content is low. The acid allows the light colour to be retained, while at the same time improving the taste of the pieces of apple. The colour of the fruit can be made even lighter by adding ascorbic acid to the dip. 

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