Variation in 1-fructo-exohydrolase (1-FEH) and 1-kestose-hydrolysing (1-KH) activities and fructo-oligosaccharide (FOS) status in onion bulbs. Influence of temperature and storage time

Effects of storage temperature and duration on 1-fructo-exohydrolase (1-FEH) and 1-kestose-hydrolysing (1-KH) activities and trisaccharide (Tri) and fructo-oligosaccharide (FOS) status in onion bulbs var Tenshin kept for 24 weeks at 10 and 20degreesC were investigated. 1-FEH activity peaked sharply after 10 weeks and seemed to be triggered by a decrease in sucrose content. 1-KH activity increased during the first 8 weeks and remained stable during the last 8 weeks. Contents of Tri, FOS and total FOS decreased abruptly during the first 8 weeks; however, at 10degreesC, contents of Tri, FOS (DP 3-12) and total FOS were lower than those at 20degreesC. The consumption rate of fructo-oligosaccharides also appeared to be higher at 20degreesC than at 10degreesC, despite the slight degradation in activities observed at this low temperature. 1-FEH seems to be under the control of a triggering signal which induces its activity, and sucrose seems to be this biochemical signal which initiates dormancy release and the onset of sprouting, as found previously. Thus changes in carbohydrates seem to be a strong indicator of the end of the dormant state of the bulb and the beginning of the sprouting period. (C) 2004 Society of Chemical Industry.