This study’s main goal was to search for natural dyes of a plant origin. Two different plants, Calendula officinalis and Centaurea cyanus, were studied. Several extraction solvents (such as ethanol, methanol and other solvent mixtures) were tested, and for the centaurea flowers, different pH levels were also tested (1, 4, 6, 8 and 10). The bioactivity of the extracts was analysed in terms of colour, anthocyanin and carotene content, antioxidant activity and total phenolic compounds. Tests to the photo and thermal stability of the extracts were performed to understand their resistance to variations of temperature and light conditions. From the obtained results it was possible to determine the best extraction process and understand in which food types these extracts could be better used in. For the calendula dyes, methanol was the best extraction solvent, and it was concluded that the extracts have a high resistance to both thermal and photo degradation. In case of the centaurea dyes, it was verified that the best extraction solvent was a mixture of ethanol and water acidified with HCl (60:40), with a pH level of 1. Contrary to the calendula extracts, these didn’t show a promising resistance level to the external conditions studied.

Mestrado em Engenharia Alimentar - Instituto Superior de Agronomia