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

Abstract

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°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°C, only a 4% decrease in color intensity was observed after 2 h; at 40°C, an 8% decrease was observed, and at 80°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°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°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 ∆H, activation energy E a, free energy ∆G, and entropy ∆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.

Keywords

• microbial pigment
• thermal degradation
• kinetic modeling
• activation energy
• thermodynamics