Article Number: PRJA45923613

Vol. 1 Issue 1, pp: (1-16), March 2016.
Article Number: PRJA45923613
Copyright ©2016
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Full Length Research Paper


Isolation, characterisation and in vitro evaluation of the antioxidant properties of α-lipoic acid from de-oiled rice bran.

Surashree Sen Gupta1* and Mahua Ghosh1

1Department of Chemical Technology, University of Calcutta, Kolkata, West Bengal 700 009, India.

*Corresponding author. Email:

This article has been retracted at the request of the publisher. A Chemist noticed an error which was communicated to the corresponding author and the editors of the journal. The manuscript was then re-assigned to three external reviewers. Here are some of their comments:

  • FIRST REVIEWER’s COMMENTS: It is common knowledge for identification of a compound that one needs to provide at least the following basic data, including 1H- and 13C-NMR, elementary analysis, HRMS and IR. However, most of the mentioned data are missing in the manuscript. 1H-NMR spectrum is vague and the assignment of peaks is not correct, such as the authors claimed “The signals at δ 0.76 – 0.80 ppm referred to the methyl group (-CH3)”, but there is no methyl group in the structure of alpha-lipoic acid; It is also very strange that the authors assigned peak in 1H-NMR spectrum to a carbonyl group, which doesn’t have protons, see  “The 1H NMR spectrum of α-lipoic acid showed the presence of a typical carbonyl group at δ 2.025 – 2.098 ppm associated with the carboxylic acid group …”;  the chemical shift of carboxyl group should be around 10-15 ppm, how it could appeared around 4.36 ppm, see “the hydroxyl proton (-OH) of the carboxylic acid group which yielded a minor signal at δ 4.36 ppm” ?  In addition, the target compound is a chiral one, but the authors didn’t provide any proof regarding the chirality of the compound.
    Spectral characterization is completely wrong

Apologies are offered to readers and the entire scientific community that these errors were not detected during peer review period. 

 Received: January 20, 2016  Accepted: February 22, 2016  Published: February 26, 2016


α-lipoic acid was isolated from de-oiled rice bran by solvent extraction, followed by purification. α-lipoic acid was isolated using ten different solvents/solvent mixtures. A 1:10 proportion of de-oiled bran and solvents/solvent mixture was maintained. The mixtures were intensely blended followed by ultrasonication. Finally, they were purified by protein removal and treatment with alkali. The most effective solvent system for maximum yield of α-lipoic acid was water:ethanol (2:1) which yielded an amount of (0.43+0.02)% α-lipoic acid. Identity of the isolated and purified product was confirmed by HPLC, FTIR, NMR and GC analysis methods. HPLC retention time at 2.96 minutes and GC retention time at 19.80 minutes were obtained which were similar to those of the procured standard α-lipoic acid. FTIR and NMR techniques confirmed the atypical S–S linkage of α-lipoic acid, its carboxylic acid group and the ring structure. Finally varying concentrations of α-lipoic acid were prepared in water and their antioxidant efficacy were analysed by virtue of seven in vitro assay entities. A positive outcome was observed with α-lipoic acid in response to all the antioxidant assays performed. A concentration of 0.1% α-lipoic acid indicated to be the most effective one in terms of providing maximum antioxidant potency.

Key words: α-lipoic acid; antioxidant; isolation; purification; rice bran; solvent extraction.