Tetra- and penta-fructooligosaccharide (FOS) isomers assessment in onion bulb tissues: effect of temperature and storage time

Tetra- and penta-fructooligosaccharide (FOS) isomers and their hydrolysis parameters-% hydrolysis, hydrolysis rate constant (k(obs)) and half-lifes (t(1/2)) in onion bulb tissues kept for 6 months at 10. 15. and 20 degreesC. were investigated. The hydrolysis of the tetra- and pentaFOS isomers ranged between 67% and 86% and isomers of b type 4b and 515 were hydrolyzed preferentially. The k(obs) showed large variation from 5 x 10(-3) week(-1) (lowest value) to 82 x 10(-3) week(-1) (highest value), while the half-life t(1/2) of the isomers ranged between 8.5 and 16.6 weeks. DP 4 content showed close correlation at 15 and 20 degreesC but different at 10 degreesC. At 10 degreesC, DP 4 isomers decreased sharply during the first 2 months but remained stable during the last 4 months. At 15 and 20 degreesC. DP 4 increased slightly within the first month, and then decreased during the second month. During the last 4 months, the 4a isomer remained stable, while 4b and 4c increased slightly. PentaFOS isomers varied in a similar fashion to tetraFOS isomers. At 10 degreesC. DP 5 isomers decreased sharply during the first 2 months and remained stable during the last 4 months except for a slight increase observed during month 3 for 5b and 5c + 5d. At 15 and 20 degreesC, they showed a similar pattern to those of the tetra-isomers. It was concluded that pentaFOS isomers are preferentially hydrolyzed with respect to tetraFOS isomers. because they have a relatively high content of fructosyl ends chain. Results also allow us to distinguish that the DP xb (type b) isomers are preferentiatlly hydrolyzed. (C) 2004 Elsevier Ltd. All rights reserved.