PlantL-ascorbic acid: chemistry, function, metabolism, bioavailability and effects of processing

✍ Scribed by Davey, Mark W; Montagu, Marc Van; Inz�, Dirk; Sanmartin, Maite; Kanellis, Angelos; Smirnoff, Nicholas; Benzie, Iris J?J; Strain, John J; Favell, Derek; Fletcher, John

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 437 KB
• Volume: 80
• Category: Article
• ISSN: 0022-5142
• DOI: 10.1002/(sici)1097-0010(20000515)80:7<825::aid-jsfa598>3.0.co;2-6

✦ Synopsis

Humans are unable to synthesise L-ascorbic acid (L-AA, ascorbate, vitamin C), and are thus entirely dependent upon dietary sources to meet needs. In both plant and animal metabolism, the biological functions of L-ascorbic acid are centred around the antioxidant properties of this molecule. Considerable evidence has been accruing in the last two decades of the importance of L-AA in protecting not only the plant from oxidative stress, but also mammals from various chronic diseases that have their origins in oxidative stress. Evidence suggests that the plasma levels of L-AA in large sections of the population are sub-optimal for the health protective effects of this vitamin.

Until quite recently, little focus has been given to improving the L-AA content of plant foods, either in terms of the amounts present in commercial crop varieties, or in minimising losses prior to ingestion. Further, while L-AA biosynthesis in animals was elucidated in the 1960s, 1 it is only very recently that a distinct biosynthetic route for plants has been proposed. 2 The characterisation of this new pathway will undoubtedly provide the necessary focus and impetus to enable fundamental questions on plant L-AA metabolism to be resolved.

This review focuses on the role of L-AA in metabolism and the latest studies regarding its biosynthesis, tissue compartmentalisation, turnover and catabolism. These inter-relationships are considered in relation to the potential to improve the L-AA content of crops. Methodology for the reliable analysis of L-AA in plant foods is brie¯y reviewed. The concentrations found in common food sources and the effects of processing, or storage prior to consumption are discussed. Finally the factors that determine the bioavailability of L-AA and how it may be improved are considered, as well as the most important future research needs.