KINETICS AND HYDROLYSIS PARAMETERS OFTOTAL FRUCTOOLIGOSACCHARIDES OF ONION BULBS: EFFECTS OF TEMPERATURE REGIMESAND CULTIVARS NOUREDDINE BENKEBLIA 1,2,3 , NORIO SHIOMI 1 and MITSURU OSAKI 2 1 Department of Food and Nutrition Sciences Graduate School of Dairy Science Research Rakuno Gakuen University 582 Bunkyodai Midorimachi, Ebetsu, Hokkaido, 069-8501, Japan 2 Graduate School of Agriculture Hokkaido University Kita 9, Nishi 9, Kita-Ku, Sapporo, 060-8589, Japan Received for Publication February 8, 2006 Accepted for Publication March 15, 2006 ABSTRACT This work studied the percentage of hydrolysis, observed hydrolysis rate constant (k obs ), half-life time (t 1/2 ) and kinetics of degradation of the total fructooligosaccharides (FOS) of three different onion bulb cultivars (Yellow Spanish, Red Amposta and Tenshin) kept during 6 months under three tem- perature regimes, 10, 15 and 20C. The percentage of hydrolysis of FOS was higher at 20C than at 10C and ranged from 47 to 58% at 10C, from 63 to 68% at 15C and from 74 to 83% at 20C. The k obs ranged from 27 ¥ 10 -3 to 36 ¥ 10 -3 / week at 10C and from 41 ¥ 10 -3 /week to 47 ¥ 10 -3 /week at 15C, while at 20C, it was high and was about k obs 56 ¥ 10 -3 /week.. The t 1/2 decreased when temperature increased, and varied from 19.5 to 26.0 weeks at 10C, from 14.6 to 16.8 weeks at 15C and from 9.4 to 12.3 weeks at 20C, indicating that high degree of polymerization (DP) FOS have shorter lives than low DP FOS. Linear regression and kinetics of hydrolysis have shown that FOS hydrolysis is higher at 20C, with a coefficient of regression ranging between 0.87 and 0.99. Apparently, FOS hydrolysis is temperature independent, and storage time had more effect on the higher DP FOS than on the lower DP FOS. INTRODUCTION About 80% of onion bulb dry matter consists of nonstructural carbohy- drates (Benkeblia et al. 2002). The predominant carbohydrates are glucose, 3 Corresponding author. TEL: +81-0-11-388-4754; FAX: +81-0-11-387-5848; EMAIL: ben-nour@ rakuno.ac.jp Journal of Food Biochemistry 31 (2007) 14–27. All Rights Reserved. © 2007, The Author(s) Journal compilation © 2007, Blackwell Publishing 14