The Effect of Different Lycopene Dyeing Solutions on Rice Colour Stability

Lycopene is a bright red substance that belongs to a group of naturally occurring pigments known as carotenoids, being the most efficient antioxidant of this group. Tomatoes are the major source of natural lycopene in the human diet, but synthetic lycopene is commonly used as a food ingredient. In this experiment, three varieties of Portuguese “Carolino” rice (Oryza sativa L., subsp. japonica) were coloured by saturated solutions of lycopene powder (10% of purity, with starch as excipient), with vinegar (56,5% w/w), ethanol (99,0% w/w), rice bran oil (92% w/w) and water (100% w/w). Colour was measured after colouring and after 21, 42, 63 days of storage. The antioxidant properties of dyed rice were also evaluated at 0 and 63 storage days. The antioxidant activity of most of dyed rice samples did not significantly changed over time. Results showed that vinegar and water conferred a redder colour to the rice kernels and ethanol led to the lower red colour values immediately after dyeing. Red colour intensity of all samples steadily decreased over time. Samples that used water and vinegar still presented at day 63 an evident orange colour, that was considered an appealing sensory attribute being an alternative to conventional white rice.