Lac pigments

Structural identification and biological activity of six new Shellolic esters from Lac

Six new sesquiterpenoid esters, named Shellolic ester A-F (1-6), along with four known Lac dyes (7-10) were isolated from methanol extract of the secretions of Laccifer lacca. Their structures were established on the basis of spectroscopic analyses (IR, HR-ESI-MS, 1D and 2D NMR) and by comparison with published data. Biological activities evaluation of the isolates showed that they were inactive against human cancer cell lines (HepG2, MCF-7, Hela and C6) and LPS-treated RAW264.7, which is well consistent with that Lac resin used as nontoxic material in agriculture applications, pharmaceutical formulations, and food additives. However, compound 2, 4, 7, 9, 10 were found to be considerable active against B. subtilis, E. coli, and S. aureus microorganisms. The results complements the current knowledge about Lac produced from China. Meanwhile, Our present study further reveals that Lac resin are edible with no toxicity and physiologically harmless at the level employed as an excipient.

Antimicrobial Efficacy of Methylated Lac Dye, an Anthraquinone Derivative

A natural red dye which is produced by the tiny insects Kerria lacca while feeding on host trees is popularly known as lac dye. Lac dye is a mixture of at least five closely related pure compounds all being anthraquinone derivatives designated as laccaic acid A, B, C, D and E. Anthraquinones isolated from different natural sources and reported to have potent antimicrobial activity. The lac dye, which is also a mixture of anthraquinone derivatives, is expected to exhibit antifungal and antibacterial activity. Lac dye cannot be used as antibacterial and antifungal agent due to its low water solubility and high polarity. Therefore, it is modified into its methyl derivative to enhance its bio-efficacy. Methylated lac dye is characterized with the help of TLC, UV-Vis spectroscopy and FT-IR, NMR analysis. An in vitro spore germination assay was carried out to evaluate the antifungal efficacy of methylated lac dye against some phytopathogenic fungi which commonly caused a various foliar diseases in crop plants viz., Alternaria solani, Curvularia lunata, Erysiphe pisi, Helminthosporium oryzae and Verticillium sp. Among the tested fungi, Verticillum sp. showed highest sensitivity, which showed 100% inhibition at 750 and 1000 µg/ml as compared to control. However, E. pisi an obligate parasite also showed varied sensitivity but at 1000 µg/ml showed 100% spore germination as compared to control. Methylated lac dye also showed strong antibacterial properties against Ralstonia solanacearum at very low concentration (40 and 50 µg/ml). Hence, lac dye may serve as potent antifungal and antibacterial agent in plant disease management.

Conformations and spectroscopic properties of laccaic acid A in the gas phase and in implicit water

Conformations and spectroscopic properties of laccaic acid A (lacA) were studied by means of the experimental and theoretical approaches. The minimum energy conformers of lacA in the gas phase and in implicit water obtained from the B3LYP/6-311G(d,p) calculations displayed the same orientation of the COOH and OH groups on the anthraquinone-based component. The intramolecular hydrogen bonds (H-bonds) formed between the COOH, C=O and OH groups are very strong. In contrast, the orientations of the Ph(OH)CH(2)CH(2)NHCOCH(3) substituent moiety on the anthraquinone-based component in the gas phase and in implicit water are completely different. The substituent prefers to bind with the anthraquinone-based component in the gas phase while it moves away from the anthraquinone-based component in implicit water. The calculated IR spectra of the two lowest-lying energy conformers of lacA in the gas phase fit to the experimental FTIR spectrum. The full assignments of the vibrational modes with the correlated vibrational wavenumbers of those conformers were proposed here, for the first time. The intramolecular H-bond formations in lacA can cause the shift of the vibrational wavenumber for the COOH, C=O, OH and NH groups as compared to the normal vibrations of these groups. The NMR spectra showed that the stabilities of the two lowest-lying energy conformers of lacA in the gas phase are comparable and this is consistent with their computational energies. The UV-Vis spectra of the lowest-lying energy conformers of lacA in implicit water were compared with the experimental UV-Vis spectrum. The calculations suggested that the electronic transition in the visible region involves with the singlet π→π(*) excitation which the electron density transfers to a COOH group on the anthraquinone ring.

Analysis of natural food pigments by capillary electrophoresis

Lac, cochineal, safflower, gardenia, Monascus and elderberry pigments are used as food color additives in Japan. These natural pigments can be analyzed by capillary electrophoresis (CE). CE has several advantages over thin layer chromatography, gas chromatography and high-performance liquid chromatography, such as low capillary cost, reduced operating costs, small sample amounts, low production of waste materials and short analysis time. CE is shown to be a useful technique for the analysis of these natural food pigments and the pigments extracted from commercial food samples by solid-phase extraction method.

Separation of lac dye components by high-speed counter-current chromatography

High-speed counter-current chromatography has been successfully applied to the separation of the lac dye components. A 25-mg quantity of the sample was separated using a two-phase solvent system composed of tert.-butyl methyl ether-n-butanol-acetonitrile-water (2:2:1:5). The fractions were analyzed by high-performance liquid chromatography and electrospray tandem mass spectrometry. The separation yielded 2.6 mg of 97.2% pure laccaic acid C, 9.5 mg of 98.1% pure laccaic acid A, 3.6 mg of 98.2% pure laccaic acid B, and 0.5 mg of a 95.0% pure anthraquinonedicarboxylic acid with a molecular mass of 360.