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Xylo-oligosaccharides isolated from ragi (Eleusine coracana) bran: determination of their structure and function

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Title Xylo-oligosaccharides isolated from ragi (Eleusine coracana)
bran: determination of their structure and function
 
Creator Veenashri, B.R.
 
Subject 07 Enzyme Biochemistry
05 Ragi (Finger Millet)
 
Description Xylo- oligosaccharides (XOS) are emerging group of prebiotics which are gaining immense
attention across the globe. Arabinoxylans which are enriched in cereal and millet brans are
one of the ideal sources to obtain xylo-oligosaccharides by endoxylanase treatment. Finger
millet, also known as ragi, has very high amount of arabinoxylans and has not been exploited
for the isolation, purification and functional characterization of XOS, hence the present
study. XOS were obtained from water unextractable polysaccharides by xylanase treatment.
Sugar composition of XOS revealed the presence of arabinose and xylose in a relative ratios
of 1: 2.4.Cinnamic acid derivatives such as ferulic acid and coumaric acids are found to be
major bound phenolic acids in XOS. Finger millet XOS were separated into neutral (~70%,
eluted with water, fraction 1) as well as bound phenolic containing XOS {~20 -25%, eluted
with methanol/water (1:1), fraction 2}on Amberlite XAD-2 adsorption chromatography.
Fraction 2 was further purified on Sephadex LH-20 into three peaks i.e two minor and one
major peak. Major peak was structurally characterized by 1H NMR and signals were observed
in the range of 3.0-5.0 ppm which are typical of XOS. Signals at 5.3 ppm (H-1) indicated the
presence of α- arabinose furanosyl moiety. Signals falling in the range of (a) 6-8 ppm (H-1 to
H-5 of ferulic acid), (b) 3.85 (O- methyl group present in the ferulic acid) and (c) 2.10 (Oacetyl
groups substituted to xylose) were typical of feruloylated /acetylated XOS. FT- IR
absorbance observed at 3600-3200 cm-1 (stretching of the hydroxyl groups both XOS as well
as phenolic hydroxyl groups), 1731cm -1 (ester group of ferulic acid), 1596 cm -1 (phenyl ring
group) and 1253 cm-1 (conjugated double bonds of ferulic acid) substantiated 1H NMR
studies. However the major peak was resolved into two peaks on LC- ESI-MS- TOF
indicating the m/z values as 728 (Feruloylated arabino xylotetraose) and with a low signal
intensity at m/z 567( O- acetylated feruloyl arabino xylobiose).Antioxidant activity of the
feruloyl XOS derived from ragi bran was compared with feruloyl XOS derived from wheat,
maize and rice brans by using three different methods i.e. (i) DPPH, (ii)FRAP as well as (iii)
β-carotene emulsion assays. Relatively higher anti-oxidant capacity was exhibited by ragi
XOS as compared to XOS of cereal brans by DPPH and FRAP assays. α- amylase and α-
glucosidase are the key enzymes that have been targeted as potential candidates for
modulation of type-2 diabetes associated post prandial hyperglycemia. Tannins, phenolic
acids, WSP and XOS were isolated from finger millet bran in 3, 2.4, 0.8 and 7% yields
respectively and were taken individually as well as collectively at a concentration of 50 μg
and 10 μg for the inhibition of α– amylase and α– glucosidase respectively. The inhibition of
these enzymes is of mixed type and was more pronounced when the inhibitors taken together
rather than individually. This study clearly indicated the potential of ragi bran derived
tannins, phenolic acids, WSP and XOS with respect to the inhibition of both α– amylase and
α– glucosidase.
 
Contributor Muralikrishna, G.
 
Date 2015
 
Type Thesis
NonPeerReviewed
 
Format application/pdf
 
Language en
 
Rights —
 
Identifier http://ir.cftri.com/12180/1/VEENASHRI.%20B.%20R%2C%20Ph.D%20Thesis.pdf
Veenashri, B.R. (2015) Xylo-oligosaccharides isolated from ragi (Eleusine coracana) bran: determination of their structure and function. PhD thesis, University of Mysore.