Improved yield of UV and heat-stable Monascus yellow pigment by statistical optimization of solid-state fermentation conditions and extraction process

Abstract

Monascus species are well-known for their ability to produce biocolorants. A high-performing strain, M. purpureus F2–19, was recently developed by genome shuffling. Here, the entire bioprocess, starting from solid-state fermentation conditions to the extraction method, was statistically optimized to improve yellow pigment yield by the strain. Among culture conditions, monosodium glutamate concentration (used as nitrogen source), moisture content, and incubation period significantly influenced pigment production using less expensive broken rice as a substrate. Post-optimization, a yield of 1548.4 ± 14.6 AU/g was achieved, representing a 9.7-fold increase over the primary condition. The statistical model developed using central composite design of response surface methodology (CCD-RSM) is highly significant, with a P value of <0.0001. Similarly, a significant model (P < 0.0001) for extraction improved pigment yield further by 1.16-fold (actual output: 1796.4 ± 13.4 AU/g). The pigment remained highly stable with a preservation rate of ∼90 % after 2.5 h exposure to a high temperature of 100 °C or UV light (254 nm). Even autoclaving at 121 °C for 15 min preserved 96.9 % of the pigment. These values are higher than reported for other commercial microbial yellow pigments, riboflavin, β-carotene, or lutein, thus highlighting its potential as a natural food colorant. Liquid chromatography-mass spectrometry (LC-MS) of the pigment identified nine distinct yellow compounds, with monascin being the most abundant. Thus, the optimized bioprocess would facilitate economical large-scale production of the yellow pigment; but its implementation still requires efficient selection of bioreactors and optimizations of scaling-up, especially the heat and mass transfer parameters.