Influence of varietal onion composition on yield and quality of onion juice

Onions (Allium cepa L.) are indispensable components of many food formulations, and dried onion powders significantly contribute to flavour of savoury foodstuff. Due to the large variation in carbohydrate composition of onions, the selection of suitable cultivars is most important for producers of onion juice. The present doctoral thesis revealed the relationship between compositional differences in onions based on both, cultivar selection and propagation method. The differentiation between carbohydrate profiles of so-called dehydrator onions, being particularly high in fructooligosaccharides (FOS), and of common onion cultivars, containing high amounts of reducing sugars, was achieved by anion exchange chromatography (HPAEC)and ultra high performance liquid chromatography (UHPLC). Further, set grown onions were shown to have higher concentrations of total soluble solids, dry matter, and FOS, when being compared to regular seed grown onions. Differences between seed and set grown onion were found to be due to higher sunshine exposure during growth. Dehydrator onions were characterized by a differing biosynthetic accumulation pattern, yielding in higher polymerized FOS (maximum degree of polymerisation was 20 monosaccharides). The cultivation method and cultivar selection were found to be decisive when aiming at high yields of dry matter and FOS.