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

In freshly produced commercial citrus juice, aseptically filled in TetraBrik cartons, it has been demonstrated that nonenzymatic browning was mainly due to carbonyl compounds formed from L-ascorbic acid degradation. Contribution from sugar-amine reactions is negligible as evident from the constant total sugar content of degraded samples. The presence of amino acids and possibly other amino compounds, however, enhance browning. Although formation of 5-hydroxymethyl-furaldehyde (5-HMF) has been detected in degraded juice samples, its presence could not be used as an index of browning. 5-HMF has been found to be unreactive in the browning process in citrus juices and its contribution to browning in this type of products is insignificant, if not negligible. Increasing the L-ascorbic acid concentration extends the nutritional value of the product but also increases the severity of browning. Hence where L-ascorbic acid is added as an antioxidant in foods, care should be taken so that the amount added is just proportional to the level of oxygen present or to the amount of oxidizable substances. (C) 2000 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.