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The enzymatic transgalactosylation during lactulose hydrolysis was studied using the beta-galactosidase from Kluyveromyces lactis and an initial lactulose concentration of 250 g/L. During hydrolysis of lactulose, the formation of two novel trisaccharides was followed by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). A maximum trisaccharide yield of 14.05% was observed at 91.9% of lactulose hydrolysis. The two novel trisaccharides obtained by transglycosylation of lactulose were isolated and fully characterized by an extensive nuclear magnetic resonance (NMR) study. Complete structure elucidation and full proton and carbon assignment were carried out using 1D ( 1H, 13C, and 1D TOCSY) and 2D (gCOSY, TOCSY, ROESY, gHSQC, and gHMBC) NMR experiments. The trisaccharides were shown to be lactulose-based structures; the main one has a Gal unit linked to C-6 of the galactose moiety, and the other one has a Gal unit linked to C-1 of the fructose moiety. Transglycosylation of lactulose allows for the obtention of galacto-oligosaccharides with new glycosidic structures and would open new routes to the synthesis of prebiotics.

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The presence of Amadori compounds in commercial dehydrated fruits has been shown through HPLC analysis of the corresponding 2-furoylmethyl-amino acids obtained by acid hydrolysis. Furosine (2-furoylmethyl-lysine) was the main 2-furoylmethyl derivative observed in dried figs and apricot samples, whereas in prunes and dates similar amounts of furosine and 2-furoylmethyl-gamma-aminobutyric acid were detected. A considerable variation of 2-furoylmethyl-amino acid contents among commercial raisin samples was observed. 2-Furoylmethyl-gamma-aminobutyric acid and 2-furoylmethyl-arginine, the most abundant 2-furoylmethyl-amino acids, ranged between 9.9 and 75.8 mg/100 g sample and 10.0 and 62.5 mg/100 g sample, respectively. Most of the Amadori compounds present in raisins seem to have originated during the commercial shelf life period rather than during processing. Determination of 2-furoylmethyl-amino acids could be used as a method of controlling commercial dehydrated fruit and selecting storage conditions.