Monascus ruber ICMP 15220 fermentation for the production of pigments : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Bioprocess Engineering at Massey University, New Zealand
Edible pigments of Monascus species have an established history of use in certain Asiatic
foods. This work focused on development and optimization of production of the red
pigments of Monascus ruber ICMP 15220. This particular Monascus strain had not been
Suitable media compositions for growth and pigment production were first
evaluated on agar plates. Media that contained glucose and monosodium glutamate
(MSG) as carbon and nitrogen sources, respectively, were found to be most suitable for
red colour production and became the basis for further studies. Both submerged culture
and solid-state fermentations were assessed for pigment production.
In submerged culture, a fully defined medium with 10 g L-1 glucose and a carbon
to nitrogen mass ratio of 9 : 1 at 30oC proved to be the most productive for the target red
pigments. This medium used MSG as the nitrogen source. Attempts were made to replace
MSG with less expensive inorganic nitrogen sources, but no suitable replacement was
found. Biomass and pigment productivity were evaluated on a variety of carbon sources,
but ethanol was confirmed to be best.
Solid-state fermentation on steamed rice proved to be remarkably more productive
for the target pigment than the submerged fermentation. Solid-state fermentation did not
require supplemental nitrogen to attain a high productivity. The C : N ratio for attaining
the peak pigment productivity in solid-state culture proved to be entirely different from
the value that had been found to be optimal in submerged culture. In view of its superior
characteristics, the solid-state fermentation was optimized in packed-bed bioreactors. A
central composite experimental design was used for the optimization that focused on the
initial moisture content of the substrate and aeration rate in the bed as the main operation
parameters. In 18 cm deep packed beds of steamed rice, the optimal fermentation
conditions were at 30oC, an initial moisture content of 70%, and aeration with humidified
air (97 – 99% relative humidity) at a flow rate of 0.14 L/min.
In all cases, the production of pigments was growth associated. Under optimal
conditions in the packed-bed bioreactor, the red pigment productivity was nearly
3.4×104-fold greater than in the best case submerged culture. The stability of the pigments
produced under the various conditions was characterized with respect to ambient light,
pH, and heat.