Biochemical and Molecular Studies for Elucidation of the Role of Isoflavones in the Improvement of Flavour Quality of Soybean
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Date
2016
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Division of Biochemistry ICAR-Indian Agricultural Research Institute New Delhi
Abstract
Soybean (Glycine max (L.) Merr) is a nutrient rich crop but has limited consumer
acceptability due to the presence of off-flavour leading to its limited use in various
food products. Small aldehydes and ketones are mainly responsible for this offflavour.
These compounds are produced via sequential action of lipoxygenase (LOX)
and hydroperoxide lyase on PUFAs abundantly present in soybean. Increasing the
inherent antioxidant potential of soybean seeds is currently being envisaged as a
promising strategy to control off-flavour. Isoflavones are one of the various
antioxidants present in soybean considered responsible for its health benefits.
Isoflavone come under the class of polyphenolic compounds and are of different
chemical forms. In soybean genistein, daidzein and their glycosidic forms are the
major isoflavones present. In addition to these small amounts of glycitein and its
derivatives are also present. Due to the inhibitory effect of the isoflavone on
lipoxygenase activity and inherent antioxidant potential; an increased content of
isoflavones can help in controlling off-flavour. In the present study, the isoflavone
content and composition in seed samples of 17 soybean genotypes was determined
with a total isoflavone content ranging from 155.53µg/g for PUSA 40 to 1151.26µg/g
for Bragg. Further, to find the correlation between isoflavone profile and lipid
peroxidation, TBA number and carbonyl value, known indices of off-flavour were
calculated in these genotypes. The results showed a significant negative correlation of
these parameters with genistein: daidzein ratio. Two contrasting genotypes of soybean
viz. Bragg (high isoflavone) and PUSA 40 (low isoflavone) were selected on the basis
of total isoflavone content and gene expression analysis was done for the two
isoforms of isoflavone synthase (IFS1 and IFS2) which is a key enzyme involved in
isoflavone biosynthesis, at various stages of seed development. Expression studies
revealed a higher expression of IFS2 in Bragg as compared to PUSA 40 towards later
stages of seed development. Besides, expression of IFS2 showed positive correlation
with total isoflavone content at all the stages examined. Furthermore, the level of
IFS2 expression increased 8.6 fold at 55 DAF w.r.t. the level at 35 DAF in Bragg but
a continuous decrease in its expression was observed in PUSA 40 from 35 DAF to 55
DAF. Also, a 1566bp cDNA sequence encoding IFS2 was cloned, characterized and
submitted to NCBI (GenBank Acc. No. KT581120.1). In-silico characterization of
IFS2 revealed 521 amino acid long protein with a 10 amino acid long cytochrome
P450 cysteine heme-iron ligand signature sequence. The information generated from
this study can further be used for the development of ‘High-isoflavone’ soybeans with
improved nutritional and flavour characteristics.
Description
t-9407
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