Stability of saffron extracts at different pH levels
Saffron spice (Crocus sativus L.) plays an important role in cookery and food industry due to its coloring properties, pleasant bitter taste and characteristic aroma. These features are mainly related to a group of crocetin esters, picrocrocin and safranal, respectively. Although information on the loss of coloring strength (E1% ⁄ 1cm440 nm) of saffron under different storage conditions is available, data published about stability of saffron compounds are scarce. Further knowledge about the effect of pH on each crocetin ester, picrocrocin and safranal in saffron aqueous extracts would provide important information for developing applications in cookery and food industry as well as for their storage. The aim of this work was to study the stability of coloring strength and of individual crocetin esters, picrocrocin and safranal in different pH aqueous extracts stored in natural light or in the dark for 10 days. Saffron in buffer solutions at pH levels: 3.0, 4.0, 5.0, 6.0, 7.0 and 8.0, plus a saffron solution in water (pH 4.8) were stored in such light conditions at 35±2°C. Coloring strength were daily measured by UV-vis spectroscopy. Concentration of compounds were also daily determined by high-performance liquid chromatography with diode-array detection (HPLC-DAD). An integral method was used to obtain the kinetic parameters. First order kinetic parameters for the loss of coloring strength and individual crocetin ester degradation were obtained, whereas second-order ones were assessed for picrocrocin degradation. A pH dependence of E1% ⁄ 1cm440 nm, crocetin esters, picrocrocin and their degradation were observed. The greatest stability of E1% ⁄ 1cm440 nm and major crocetin esters happened at pH levels ≥5.0, regardless the light presence. Higher stability of crocetin esters was observed in saffron extracts with buffer solutions compared with saffron extracts in water. Picrocrocin showed the lowest degradation rates in extracts stored at pH 6.0 and 7.0 in dark conditions. A kinetic model was not found for safranal since its concentration during storage showed irregular increments and decrements.
Moratalla-López, N., Martínez, V., Lorenzo, C., Poggi, L.M., Sánchez, A.M. and Alonso, G.L. (2020). Stability of saffron extracts at different pH levels. Acta Hortic. 1287, 419-428
Crocus sativus L., kinetics, crocetin esters, picrocrocin, safranal