extraction and determination of fructans (oligofructoses and
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University of Food Technologies, Department of Organic Chemistry and Microbiology, 26 Maritza Blvd., Plovdiv, Bulgaria
E-mail address: [email protected], [email protected]
Abstract Тhe continuous ethanol and water extractions of medicinal plants Cichorium
intybus, Inula helenium, Taraxacum officinalis and Helianthus tuberosus
accumulating inulin-type fructans in their underground parts – roots and tubers
were carried out. The extraction efficiency of inulin and oligofructoses was
followed by TLC. The amount of extracted fructans was determinated by the
spectrophotometric method based on the Seliwanoff reaction with resorcinol as
the absorbance of resulting compound was measured at 480 nm. It was obtained
that the average fructan content was as follows: Cichorium intybus е 33 %, в
Inula helenium - 42-44 %, Helianthus tuberosus – 69 % и Taraxacum officinalis –
34 %, which make them rich sources of soluble dietary fiber, when they were
used in dietary food products.
Introduction Inulin is a polydisperse linear polysaccharide, member of fructan family and serves
as a reserve carbohydrate in underground part of plants from the Compositae
(Astraceae) family such as Cichorium intybus (chicory), Inula helenium (elecampane),
Taraxacum officinalis (dandelion) and Helianthus tuberosus (Jerusalem artichoke).
Inulin consists mainly of β-(2→1) fructosyl fructose units (Fm), and usually but not
always the chain terminate with α-glucopyranose unit (1→2) (GFn) at the reducing end
(Figure 1). A small percentage of inulin molecules have a terminal fructoside unit
found primarily in the pyranose form in aqueous solution. The degree of
polymerization (DP) of inulin varies from 2 to 70 and depends on plant species,
harvesting time and post-harvest conditions. Molecules with DP<10 are called
oligofructoses or fructooligosaccharides (FOSs) and are a subgroup of inulin. The
maximum amount of low- and high-molecular fructans (75-85%) is found in
topinambur as the greater part of topinambur is a low-molecular fraction. Inulin and
FOSs are classified as soluble dietary fiber. They act as prebiotic as stimulate growth
of Bifidobacteria, low glucose blood level, improve mineral absorbtion and possess
immunomodulation effects. Inulin has been increasingly used in various foods due to
its beneficial nutritional attributes . Along with positive healthy effect inulin acts as
texture modifier, decreases caloric value and improves nutritional properties of food.
Material and methods: Moisture content of the dried ground tubers and roots were determinated according AOAC 945.32 method as the drying
process was carried out at 105 °C for 3 hours..
The extraction process was carried as follows: 0,45 g dry sample (roots or tubers) was extracted three times with 95 %
ethanol (40, 40, 20 ml) to obtain low-molecular fraction composed of fructose and FOSs. High-molecular fraction (inulin)
was then extracted by three following water extraction (40, 40, 20 ml). The extraction level of oligofructoses in the ethanol
extracts and of inulin in water extracts were monitored by TLC to observe the extraction rate of fructans and to observe
inulin fractions. Thin-layer chromatography (TLC) was performed on silica gel 60 F254 plates (Merck) with: 1) n-
BuOH:EtOH:H2O (5:3:2) (v/v) as an eluent and the plates were dipped into a detecting reagent diphenylamine-aniline-
acetone-H3PO4; 2) BuOH:i-PrOH:H2O:CH3COOH (7:5:4:2) (v/v) – mobile phase and detecting reagent – diphenylamine-
aniline-H3PO4 acetone (1:1:5:50).
The fructan content in ethanol and water extracts were analyzed spectrophotometrically at 480 nm by resorcinol-
thiourea reagent.
Conclusion
Inulin and oligofructoses content in some medicinal plants has been defined by TLC
and spectrophotometric methods of analysis. From the obtained results we can
conclude that Helianthus tuberosus is the richest source of fructan (50-70 g/100 g),
but the FOSs fractions dominate in the both extracts. Water fractions obtained from
Taraxacum ollicinale consists of short chain-oligofructoses and very small amount of
inulin. The greatest content of high-molecular inulin (40-42 g/100 g) is characteristic
of elecampane. The fructan content in all of the investigated plants increases during
the autumn. The rich content of FOSs and inulin in these plants made them a source of
prebiotics which improve the digestion function and enriches colon with
Bifidobacteria.
Figure 1. Chemical structure of Inulin
(GFm) (Fn)
Number Name of the plant Moisture
content ±SD, %
CV, %
1. Inula helenium L. (elecampane) 8,50 ±0,23 0,15
2 Cichorium intybus L (common chicory) 7,76±0,38 0,24
3 Taraxacum ollicinale Web. (dandelion) 8,46±0,26 0,12
4 Helianthus tuberosus L. (Jerusalem artichoke) 9,66 ±0,3 0,19
Table 1. Moisture content in the roots and tubers of the medicinal plants
0,000
0,050
0,100
0,150
0,200
0,250
0,300
0,350
0,400
320 360 400 440 480 520 560 600 640 680
THEHTWCIECIWTOETOWIHEIHWIHW10IHE10
Abs
Wavelength, nm
No Species Date of
taking
samples
Underground
part
Low molecular
fraction (fructose
and FOSs), g/100 g
High-molecular
fraction (inulin)
g/100 g
Fructan,
g/100 g
1 Inula helenium L 11.11 rootstock 10,9 ±2,2 32,0±2,0
42,9±2,1
2 Inula helenium L 04.10.10 roots 8,3±1,5 32,7± 0,5 41,0±1,8
3 Cichorium intybus L. 04.11
11.11
roots
-
12,1±2,5
16,1 ± 0,06
21,2 ±1,5
33,3 ±2,0
4 Taraxacum officinale Web. 06.11.11 roots 10,7±0,7 23,9±4,2 34,6±2,4
5 Helianthus tuberosus L. 06.09.11 tubers 6,4 ±0,4
43,5±2,5 49,9± 1,4
6 Helianthus tuberosus L. 2010 tubers flour 45,4 ±2,2
23,9±1,0
69,3±2,5
Table 2. Fructan content (g/100 g dw) in underground organs of Composite Family (Astraceae) plants
Figure 3. Absorption spectrum of the complex compounds formed by
interaction of fructans with concentration 1 mg/ml with resorcinol
SD – standard error; CV – coefficient of variation
Figure 2. Thin layer chromatography of inulin and FOSs extraction
Helianthus tuberosus L. Inula helenium L.
Taraxacum officinale Web.
Fructose
Sucrose
FOSs Inulin
Ethnol extracts Water extracts