Studies on the occurrence of non-enzymatic browning during the storage of cloudy apple juice

120 day storage experiment at 4 degrees C, 22 degrees C and 40 degrees C of cloudy apple juice without AA added or juice with 0.006% or 0.024% (w/w) AA added was conducted. The content of polyphenols, 5-(hydroxymethyl)furaldehyde (5-HMF), ascorbic acid, and the color were assessed by HPLC and other analysis techniques. The formation of new particles in juice during storage was studied by electronic scan microscope and mastersizer. During the storage period of juice, the L value decreased and the a-value increased with prolonged storage time and increased temperature. The color change of the juice was acute during the initial 45 day storage period and then remained constant. The degree of non-enzymatic browning as well as the loss of tannin, epicatechin, chlorogenic acid, ascorbic acid and the mean polymerization degree of proanthocyanidins in the juice increased as the storage time was prolonged and temperature was increased. The color change (Delta E) of juice during the storage was caused mainly by the oxidation and polymerization of polyphenols but not by the degradation of ascorbic acid (R-2 for Delta E and total phenolic compounds loss was 0.7273, and for Delta E and TVC loss was 0.0081 respectively) and could be avoided by storing juice at a lower temperature. Delta E between juice with 0.006% (w/w) AA added and with 0.024% (w/w) AA added had no significant difference but was significantly lower than the juice without AA added. The addition of 0.006% (w/w) AA to juice could inhibit the oxidation and polymerization of phenolic compounds and inhibit the formation of new smaller particles. The b-value and the content of 5-HMF of juice with 0.024% (w/w) AA added were higher than of juice with 0.006% (w/w) AA added.