In Bramley's Seedling, adjustment of juice pH affected darkening in apple juice concentrate during storage in the order pH 2.0 > pH 3.0 > pH 4.0. Darkening was also greater in model systems corresponding to juice at pH 3.0 compared with pH 4.0. The rapid darkening in concentrate of this cultivar appeared to be due to high rates of Maillard browning reactions rather than to other forms of nonenzymic browning.
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D. O’Beirne (1986) studied this question.