‘Ohmic heating’ method backed for natural colour production

By Nathan Gray contact

- Last updated on GMT

Ohmic heating methods have the potential for use in the industrial production of natural colours.
Ohmic heating methods have the potential for use in the industrial production of natural colours.

Related tags: Color, Rice

The use of ohmic heating technologies, which pass electrical currents through foods to heat them, could provide opportunities for the industrial scale production of natural food colourants, researchers have suggested. 

The new study, published inInnovative Food Science & Emerging Technologies, investigated the potential of ohmic heating (OHM) to assist in the extraction of natural colours from their sources – using the extraction of anthocyanins from black rice bran as a model.

Led by Patiwit Loypimai from Mahasarakham University, Thailand, the team investigated the physical quality, bioactive and anthocyanin contents of colourant powder obtained from black rice bran using OHM to assist the solvent extraction – finding that the OHM method gave a higher yield of colourant powder than that obtained by steam-assisted solvent extraction methods and that the physical properties of the colourant were acceptable for commercial use.

The colourant powder prepared by ohmic heating assisted had higher colourant yield, anthocyanin pigments, and bioactive compounds than conventional methods,”​ wrote Loypimai and colleagues – adding that their findings suggest “that ohmic heating could be applied to develop industrial production​ scale of natural colourants. 

Natural potential

The authors tested the potential of ohmic heating using black glutinous rice bran (Oryza sativa​ L.) that has been suggested as a potential source of dark purple anthocyanin pigments.

Loypimai and his colleagues investigated the quality aspects and bioactive compounds of colourant powder obtained from rice bran extracted by ohmic heating (OHM) assisted solvent extraction – testing four different levels of electric field strengths (E) of 50, 100, 150, and 200 V cm– 1​.

“The results showed that OHM assisted solvent extraction was a promising method offering both high yield and high concentration of bioactive compounds,”​ said the team. 

Indeed, they found that the solubility, bulk density, and colour values of the colourant powder of all treatments were comparable – adding that the colourant powder obtained from the bran extracted using OHM with 30% moisture content (E=100, 150, and 200) and 40% moisture content (E = 50, 100, 150) had the highest level of bioactive compounds.

“The OHM gave a higher yield of colourant powder than that obtained by steam-assisted solvent extraction methods,”​ the team concluded.

Source: Innovative Food Science & Emerging Technologies
Volume 27, February 2015, Pages 102–110, doi: 10.1016/j.ifset.2014.12.009
“Ohmic heating-assisted extraction of anthocyanins from black rice bran to prepare a natural food colourant”
Authors: Patiwit Loypimai, et al

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