Stability kinetics of orevactaene pigments produced by Epicoccum nigrum in solid-state fermentation

Orevactaene yellow pigment was produced by solid-state fermentation of broken rice using Epicoccum nigrum. The pigment was extracted using water as a solvent and subjected to stability studies at different temperatures (30, 40, 60, and 80 degrees C), pH (4, 6, and 8), sterilization, and sunlight exposure treatment. The observed data were fitted in the first-order kinetic model. Yellow pigment stability was found to vary at different temperatures studied. At 30 degrees C, only a 4% decrease in color intensity was observed after 2 h; at 40 degrees C, an 8% decrease was observed, and at 80 degrees C and pH 6.0, 17% of color intensity was lost. These results showed that the orevactaene pigment produced by E. nigrum is heat-sensitive and changes in color intensity should be expected in heat-processed products. After 180 min at 80 degrees C, yellow pigments maintained 82 and 76% of the initial color at pH 6 and 8, while a 65% decrease in color intensity was observed at 80 degrees C, pH 4. Autoclaving resulted in 69% decay and exposure of pigment to sunlight for 2 h showed 1% decay. The half-life period of the pigment at different temperatures varied from 82.5 to 5.25 h. The decimal reduction time decreased from 275 to 17.5 h with an increase in the temperature. Thermodynamic parameters for pigment decay at pH 6.0 were represented in terms of enthalpy triangle H, activation energy E-a, free energy triangle G, and entropy triangle S. The values observed were 44.52-44.93, 48.48, 96.60-105.18 kJ/mol, and -170.50 to -171.85 J/mol/K, respectively. All these parameters help in predicting the quality changes in terms of appearance during thermal processing and optimizing the process.