Polysaccharides of nutritional interest in jicama (Pachyrhizus erosus) during root development

Abstract

Jicama root applications have focused on their nutraceutical properties without clearly specifying which compounds are related to this effect. Thus, the aim of the present study was to identify the changes in polysaccharides of nutraceutical interest in two commercial jicama roots (YS - Yellow Seed; PS - Purple Seed) during four stages of maturation, focusing on starch, fructooligosaccharides, and pectin (via galacturonic acid), and on their glycemic index, with the goal of determining, if possible, the best cost-effectiveness between jicama growing stages and nutraceutical effect. Both materials (YS, PS) presented similar growth rates (0.069 and 0.072 cm/day) and final sizes (12.7 ± 1.25, 12.3 ± 1.63 cm). Changes in size were accompanied by changes in protein, fiber, ashes, lipids, and carbohydrates, after 106 or 127 days of growing. It was also found that fructose content was higher than glucose during the maturing stages, possibly because of the hydrolysis of fructooligosaccharides or sucrose for starch production. Concerning inulin, its levels decreased (<6.0%), after the first days (YS: 13.4% ± 0.7%; PS: 8.4% ± 0.2%, 106 days); however, during development, the presence of other fructooligosaccharides was observed (nystose-YS 106 days 15.8% ± 0.9% and PS-106 days 18.5% ± 0.1%), while galacturonic acid and native starch levels increased, which must be related to the jicama's low glycemic index found (<25%), and their nutraceutical properties. This work proves the presence of inulin in jicama roots by analytical methods, its dependence on root development and classifies jicama as a low glycemic index food, supporting its nutraceutical character.

Keywords: inulin; jicama root development; nutraceutical polysaccharides; pectin; starch.

FIGURE 1

Jicama equatorial axis (diameter)

FIGURE 2

Changes in jicama's diameter during development. YS: Yellow seed; PS: Purple seed. The growth rate was evaluated from the slope of the diameter – days curve. Values with different letters in each group (YS or PS) are significant different (p <.05)

FIGURE 3

Proximate analysis results (%, db‐ dry base) of the two jicama materials at different stages of growth; YS: Yellow seed; PS: Purple seed. (a) % Protein, (b) % Crude Fiber, (c) % Ash, (d) % Lipid and (e) % Carbohydrates. Bars with different small letters are significantly different inside the group (YS or PS). Bars with different capital letters are significantly different between the same developmental stage

FIGURE 4

Carbohydrate composition (% db‐ dry base) of two jicama materials (YS and PS) in different growing stages; YS: Yellow seed; PS: Purple seed; (a) % Reducing Sugar; (b) % Nonreducing Sugar; (c) % Soluble Fiber; (d) % Starch. Bars with different small letters are significantly different inside the group (YS or PS)

FIGURE 5

HPLC chromatograms of two jicama materials (YS and PS) evaluated at different growing stages. YS: Yellow seed; PS: Purple seed. Retention times: inulin (In): 11.9 ± 0.05 min; nystose (Nys): 12.7 ± 0.08, sucrose (Suc): 14.8 ± 0.02 min; glucose (Glc): 17.4 ± 0.01 min; fructose (Fru): 21.3 ± 0.01 min; Determination in Hamilton Ca⁺² column

FIGURE 6

Galacturonic acid (GalA) detection by HPLC (RT: 14.1 ± 0.3 min) on two jicama materials (YS and PS) at different growing stages. YS: Yellow seed; PS: Purple seed; RT: retention time. Determination on Agilent HI‐PLEX‐H column

FIGURE 7

Estimated glycemic index (eIG) in jicama during different growing stages. The mean value ±SD is presented. Bars with different small letters are significantly different inside the group (YS or PS). Bars with different capital letters are significantly different between the same developmental stage