The Metabolism of the Fructooligosaccharides in Onion Bulbs: A Comprehensive Review

Abstract

In the past two decades, there has been vast expansion in the research of fructooligosaccharides (FOS), including their chemistry, biochemistry and enzymology in higher plants. However, in spite of these considerable advances in fructan science, many other aspects of the mechanisms of fructan metabolism have not been fully understood. The bulbing and yield of dry onion cultivars vary, but they depend on the contents of the high dry matter and non-structural carbohydrates (fructooligosaccharides) which contribute to keepability. The knowledge of the mechanisms of the synthesis and the degradation of the FOS occurring during growth and storage are of great interest. Important progress has been made in the research area of onion FOS, and in addition to their role as accessible reserve carbohydrates in bulbs during sprouting, FOS participate in many physiological processes of production, protection and preservation of the bulbs. This review aims to contribute to a better understanding of the metabolism of FOS in onion bulbs, based on recent investigations. The activities of the main enzymes involved in the synthesis and the hydrolysis of the FOS during the pre-harvest (growth) and post-harvest (storage) life of the bulbs are reviewed, although present knowledge is too limited to explain clearly the mechanisms triggering the enzymes activities or the mechanisms by which FOS contribute to quality and long keepability of the bulbs.

Analysis of Varietal Differences in the Fructo-oligosaccharide Accumulation Profile among Onion (<i>Allium cepa</i> L.) Cultivars Grown by Spring-sown Cultivation

“…Onions have been reported to accumulate both types of FOSs (Darbyshire and Henry, 1978;Shiomi et al, 1991Shiomi et al, , 1997. A detailed FOS biosynthetic pathway, which includes the key metabolic enzymes and the chemical composition and structure of each type of FOS, has also been reported (Benkeblia et al, 2003Fujishima et al, 2005;Shiomi et al, 2005). However, the differences in FOS composition and contents between common Japanese onion cultivars have not been comprehensively described.…”

“…Previous studies reported that onions accumulate FOSs with DP9 to DP10 or more (Darbyshire and Henry, 1979;Downes and Terry, 2010;Shiomi et al, 2005;Vågen and Slimestad, 2008), while Vågen and Slimestad (2008) reported that some varieties mainly accumulated mono and disaccharides. However, few studies have focused on the contributing factors behind varietal differences in sugar and FOS composition.…”

“…According to statistical data provided by the Ministry of Agriculture, Forestry hydrate, as storage carbohydrates Henry, 1978, 1979;Shiomi et al, 2005). Sugars (mono and disaccharides, and FOSs) comprise up to 80% of the total dry weight of an onion bulb (Benkeblia et al, 2003;Kahane et al, 2001;Shiomi et al, 2005).…”

Fructooligosaccharides changes during maturation in inflorescences and seeds of onion (Allium cepa L. ‘W202’)

“…Despite the substantial volume of literature available on fructooligosaccharides and their metabolism in onion bulb tissues reviewed by Shiomi et al (2005), none investigated fructan variation or accumulation in either inflorescence or seeds during their development and maturation. For example, Kuo et al (1988) reported only the content of raffinose oligosaccharides and sucrose in various Gramineae and Leguminosae species, and found that sucrose content varied widely from 3.4 (beet seeds) to 72.7 mg g -1 dry weight (soybean seeds).…”

Food Biochemical Study on Fructans and Related Synthesis Enzymes

“…35) 3. Post-harvest metabolism of fructo-oligosaccharides in onion and asparagus plants Alongside the studies on fructo oligodsaccharide accumulation during seed development 36) and bulbing, 37) we also studied the main enzyme activities involved in the synthesis and the hydrolysis of fructo oligosaccharides during the pre harvest 38) (growth), and post harvest 38,39) (storage) life of onion bulbs and asparagus spears, 40) although present knowledge is insufficient to clearly explain the mechanisms triggering enzymes or the mechanisms by which fructo oligosaccharides contribute to bulb quality and perishability. 39) Storage of onion bulbs for 6 months causes a decrease 41,42) in the contents of glucose, fructose and sucrose, as shown by Fig.…”