Beet fiber is a fibrous by-product of the beet sugar industry. Efficient production of arabino-oligosaccharides (AOs) and feruloylated arabino-oligosaccharides (FA-AOs), which are AOs esterified with ferulic acid, from beet fiber was investigated. Under hydrothermal conditions at a reaction temperature from 160 degrees C to 180 degrees C for a reaction time of 5-15 min, solubilization of the beet fiber occurred in the range of 58-63 wt%. In the soluble fraction, galactose and arabinose as well as their oligomers have been detected. It is notable that various characteristic glycosides, which consist of ferulic acid and AOs or galacto-oligosaccharides (GOs), were obtained from the arabinan or galactan side chains of the pectin present in the beet fiber. The total yield of AOs and FA-AOs reached 84% at 160 degrees C for 12 mm, which was determined as arabinose units contained in the beet fiber. Almost all the ferulic acid present in the beet fiber was recovered as ferulate esters of oligosaccharides such as AOs or GOs via hydrothermal treatment. (C) 2013 Elsevier B.V. All rights reserved.