Dependence of Fructooligosaccharide Content on Activity of Fructooligosaccharide‐Metabolizing Enzymes in Yacon (Smallanthus sonchifolius) Tuberous Roots during Storage

Abstract

Tuberous roots of yacon (Smallanthus sonchifolius) accumulate about 10%, on a fresh weight basis, of inulin-type fructooligosacharides (FOSs), known as a food ingredient with various healthy benefits. However, we have a great difficulty to ensure these benefits because FOSs with a lower degree of polymerization (DP) decreased remarkably, and fructose increased when the tuberous roots were stored after harvesting even under previously recommended storage conditions of low temperature with high humidity. In the present study, to elucidate the involvement of FOS-metabolizing enzymes in FOS reduction during storage at 90% relative humidity and 8 degrees C, we extracted a crude protein from yacon tuberous roots and measured the activities of invertase (beta-fructofuranosidase, EC 3.2.1.26), sucrose:sucrose 1-fructosyltransferase (1-SST, EC 2.4.1.99), fructan:fructan 1-fructosyltransferase (1-FFT, EC 2.4.1.100), and fructan 1-exohydrolase (1-FEH, EC 3.2.1.80). The enzyme activities acting on sucrose, both invertase and 1-SST, were weakened after storage for a month. In addition, the activity of 1-FEH acting on short FOSs such as 1-kestose (GF(2)) and 1-nystose (GF(3)) was higher than that of 1-FFT. These results suggest that the continuous decline in FOSs of low DP during storage was dependent mainly on the 1-FEH activity. On the other hand, FOSs with a DP of >or= 9 only slightly decreased in stored yacon tuberous roots during storage, though distinct 1-FEH activity was observed in vitro toward a high-DP inulin-type substrate, indicating that highly polymerized FOSs content was unlikely to be closely connected with the 1-FEH activity.

Influence of the Addition of Ovalbumin and Emulsifier on the Physical Properties and Stability of Yacon (Smallanthus sonchifolius) Juice Foams Prepared for Foam Mat Drying Process

“…This tuberous root has high water content and low energy value, and unlike other tuberous species that store carbohydrates as starch, it presents fructooligosaccharides (FOS) as the main storage sugar (Narai-Kanayama et al 2007). The presence of FOS, particularly inulin, classifies yacon as a potentially functional food with prebiotic activity forasmuch as these components are poorly broken by the digestive enzymes, stimulating the development and activity of microorganisms that are beneficial to human health, known as probiotics (Ojansivu et al 2011;Campos et al 2012).…”

Smallanthus sonchifolius

“…The results indicate that partial hydrolysis of oligofructans starts shortly after harvest. In another study, during storage of yacon tuberous roots at low or room temperature, their fructooligosaccharides (FOSs) content signifi cantly decreased, whereas the fructose content increased, indicating that the extent of the changes was dependent on temperature (Narai-Kanayama et al 2006 ). Freezing storage at −20 °C was able to prevent the decline of FOSs in tuberous roots.…”

Cloning of a CDNA Encoding the Sucrose: Sucrose 1-Fructosyltransferase (1-SST) from Yacon and its Expression in Transgenic Rice

“…In contrast with most edible roots, yacon tuberous root stores its carbohydrates in the form of inulin type fructans and contains 60% of dry matter (7). Previously, enzyme activities related to the inulin type fructan metabolism, such as 1-SSt, 1-FFt and 1-FEH, had been observed in yacon (12). Fructans are extracted from fruits and vegetables like bananas, onions, chicory root and asparagus.…”