Apple juice browning

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). 

Ozoglu H and Bayindirli A. 2004. Inhibition of enzymatic browning in cloudy apple juice with selected antibrowning agents. Food Control 13 213-221. 

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 ... 

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. 

Tronc, J.S., Lamarche, F., and Makhlouf, J. 1998. Effect of pH variation by electrodialysis on the inhibition of enzymic browning in cloudy apple juice. J. Agric.Food Chem. 46, 829-833. 

Inhibition of Enzymatic Browning in Cloudy Apple Juice.603... 

FIGURE 21.20 Electrodialysis cells for inhibiting enzymatic browning in cloudy apple juice, (a) Electroacidification step and (b) electro-alkalinization step. CEM, cation-exchange membrane BPM, bipolar membrane AEM, anion-exchange membrane. 

Tronc J-S, Lamarche F, and Makhlouf J. Enzymatic browning inhibition in cloudy apple juice by electrodialysis. J. Food Sci. 1997 62 75-78. 

Sydenham, E.W., Vismer, H.F., Marasas, W.F.O., Brown, N.L., Schlechter, M., and Rheeder, J.P. 1997. The influence of deck storage and initial processing on patulin levels in apple juice. Food Addit. Contam. 14, 429-434. 

The extent and mode of bioconversions of pectic substances in situ, their solubilization and depolymerization effect consistency, cloud behaviour, pressing characteristics, juice release, soluble solids, clarification, haze formation and browning potential. We have been studying plant cell wall degradation with pure and well characterized enzymes and from the results of these studies we are now able to better define the various stages in cell wall degradation and to understand implications for fruit processing. This will be demonstrated in apple juice production and stabilization of apricot nectar. 

Quoc, A.L., Mondor, M., Lamarche, F., Ippersiel, D., Bazinet, L., and Makhloul, J. 2006. Effect of a combination of electrodialysis with bipolar membranes and mild heat treatment on the browning and opalescence stability of cloudy apple juice. Food Res. Int. 39, 755-760. 

Gui, F. et al. Change of polyphenol oxidase activity, color, and browning degree during storage of cloudy apple juice treated by supercritical carbon dioxide, Eur. Food Res. Technol., 223, 427, 2006. 

O Beime, D. Effect of pH on nonenzymatic browning during storage in apple juice concentrate prepared from bramley s seedling apples, J. Food Sci., 51, 1073, 1986. 

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