Synergic effect of water-soluble components on the colouring strength of saffron spice

The purpose of this work was to study the synergic effect of water-soluble components of saffron, such as picrocrocin and kaempferol-3-glucoside, on its colouring strength (E1%1cm 440 nm). Picrocrocin and kaempferol-3-glucoside were added to an aqueous solution of crocetin esters in different molar ratios and different pH conditions. Interesting increments in the colouring strength were found because of the addition of picrocrocin to crocetin esters at molar ratios equal or higher than 1:1. These increments were even higher when kaempferol-3-glucoside was added up to get 1:1, 2:1 and 5:1 molar ratios. Neither in saffron extracts nor in crocetin ester solutions, important increments in the colouring strength were found when pH was modified from 2 to 11. The same result was observed in the mixtures of picrocrocin or kaempferol-3-glucoside with crocetin esters.