The study, published in Food Research International, evaluates the suitability of the natural food colouring anthocyanin as a pre-extrusion colouring for rice flour, noting that its retention as a pre-extrusion colour is mainly dependant on the extrusion cooking parameters.
The authors, led by Professor Rekha Singhal from the Institute of Chemical Technology, India, also reported that sodium carbonate reduced the retention of anthocyanin in the rice extrudates, and recommended metallized polyester as the most suitable packaging for the coloured extrudates.
“These attractive natural colouring pigments are water-soluble and this property facilitates their incorporation into numerous aqueous food systems,” said Singhal and her colleagues.
“[However], to the best of our knowledge, stability of added anthocyanins as pre-extrusion colouring has not yet been reported in literature,” they added.
Prof. Singhal and her team reported that the retention of anthocyanin colourant in rice extrudates coloured prior to extrusion improved with an increase in the moisture content of feed material, and screw speed and decreased with an increase in dye temperature.
They added that the addition of one per cent citric acid increased retention of anthocyanin by 20 per cent, but sodium bicarbonates decreased retention by 50 per cent.
They said that the amount of the natural colourant needed for extrusion cooking was reduced by 25 per cent with the addition of one per cent citric acid to rice flour prior to extrusion.
The demand for natural colourings has been intensified “with increasing public concern on the safety of synthetic colourants,” said Singhal and her team.
Such increased prominence in the use of natural colours has been also strengthened by the requirement that all food products containing the six colours so-called Southampton colours – cocktails of which were linked to hyperactivity in children – carry a warning label, which came into force on 20 July last year.
The researchers noted that anthocyanins are natural colouring compounds, widely found in fruits, berries and flowers. The research findings may help to reduce the amount of the natural colourant needed in foods.
Source: Food Research International
Published online ahead of print, doi: 10.1016/j.foodres.2011.05.017
“Stability of anthocyanins as pre-extrusion colouring of rice extrudates”
Authors: A.V. Durge, S. Sarkar, R.S. Singhal