Accumulation of carbohydrates and pungent principles in characteristic seed and set grown onion varieties (Allium cepa L.)

Abstract

The profile of carbohydrates of onions (Allium cepa L.), mainly consisting of fructooligosaccharides (FOS), has a strong impact on digestibility, processability and storability. This study focused on the accumulation of FOS and pungent principles in onions during bulb maturation. Different onion varieties were grown from both, seeds
and sets. Total FOS concentrations in onions of cv. ‘Sturon’ were higher when grown from sets than from seeds throughout the entire maturation period, reaching final levels of 75.7 ± 2.2 and 61.8 ± 11.8 g/L FOS, respectively. Higher levels in set grown onions might be due to their earlier emergence, thus resulting in an extended photosynthetically active period (+12% total sunshine hours). However, seed grown, so-called dehydrator onions (cv. ‘Stardust’) had significantly higher FOS contents than set grown cv. ‘Sturon’ onions at all sampling points (final FOS level: 129.3 ± 16.6 g/L), indicating cultivar-dependant accumulation. Furthermore, dehydrator onions accumulated FOS with highest molecular weight and a unique FOS distribution, allowing clear discrimination of such dehydrator cultivars. Besides carbohydrates, pungency as indicated by pyruvic acid levels was shown to be determined by sulphurous fertilization and its timing.