Fructans and major compounds in onion cultivars (Allium cepa)

The moisture, ash, protein, Brix degree, glucose, fructose, sucrose, total fructans and total sugar, total and insoluble fibre contents were quantified in five traditional onion cultivars from Tenerife (Guayonje, San Juan de la Rambla, Carrizal Alto, Carrizal Bajo and Masca) and a commercial cultivar (Texas Early Grano 502). The ratio between insoluble and soluble dietary fibre (IDF:SDF) and between glucose and fructose (G:F) were also determined. There were differences between cultivars in all the studied variables except for the IDF:SDF ratio. Carrizal Bajo and Carrizal Alto presented the highest moisture content and lowest protein, fibre, sugars and total fructans contents. In contrast, the Texas cultivar had the highest total and insoluble fibre and glucose contents, the Masca cultivar had the highest ash and protein contents, the Guayonje cultivar had the highest fructose and total sugar contents, and the San Juan de la Rambla had the highest Brix degree and total fructan contents. Significant differences in many of the parameters analyzed were observed between the two seed origins for the Guayonje and San Juan de la Rambla cultivars. Many correlations were observed between the parameters analyzed. The onion samples tended to be classified according to the cultivar when applying discriminant analysis.