Production of Monascus pigment by solid state culture on adlay

Abstract

Angkak is a natural red colourant which is usually made by culturing Monascus spp. on cooked rice. Changing from rice to other raw materials which are richer in nutrients could increase pigment yield. Adlay (Chinese pearl barley) has been used as a health food supplement and in traditional Chinese medicine and could be used as a new substrate for angkak production. Evidence also exists that mycotoxin formation during the culture of Monascus on adlay is less. The main objective of these studies was to increase Monascus pigment production by its culture on different types of adlay and to develop a continuous process for solid-state fermentation. Adlay angkak had higher concentrations of red pigments than rice angkak when Monascus was cultured on cooked grains with 50% water content in 250 Erlenmeyer flasks. Maximum red pigment production on cooked whole grain adlay was obtained at a moisture content of 60 %. Adding sugar to adlay increased the pigment formation and fructose was better than glucose and sucrose. Adding a nitrogen source had more effect on the pigment production of adlay angkak than a carbon source. Adding histidine was superior to using monosodium glutamate (MSG) and sodium nitrate. Red pigment production was increased from 9.5 to 77 OD units per gram of dry matter when 2% histidine was added to adlay. Co-culture of Monascus with yeast only slightly increased the pigment yield. Puffed adlay material was found to be a superior material for angkak production compared to whole grains. Optimization of the production process on 100 g puffed adlay showed that adding 4 g histidine, 20 g sugar and 200 g of water increased the pigment concentration 10 fold in fixed tray bioreactors. Oxygen transport limitation in a static bed normally limits angkak production to a layer of a few cm. Fine particles formed a bed which gave more problems with oxygen transport than whole grain particles. Mixing the bed can overcome such problems but cooked whole grain adlay was difficult to mix due to its high adhesivity. It was discovered that cooked puffed adlay at a moisture content of 60% gave high productivity yet low adhesitivity, and could be mixed easily. A rotating drum bioreactor was used to produce angkak on puffed adlay. In a continuously rotating culture at low speed, cells were damaged by shear. An intermittently rotating reactor gave poorer mixing but higher yield. The best condition was an intermittent speed with a low rotating speed and frequency of rotation. Solid state culture on ground adlay showed severe transport limitations. The use of audible sound and ultrasound enhanced pigment formation in ground adlay. The penetration of the pigment into a bed exposed to audible sound vibration was limited to a thin layer of material near the surface, whereas at the optimum power and exposure times the use of ultrasound doubled the pigment yield. Submerged culture on ground adlay was successfully performed in miniaturized stirred bioreactors. Increased agitation intensity improved yield, possibly indicating that oxygen transfer is limited in the miniature bioreactors. The use of puffed grain during solid state culture and ground grain during submerged culture both have advantages for the production of angkak. Both of them can be applied in both batch and continuous processes. The particles of puffed grain make it possible to rotate the substrate during fermentation due to puffed adlay having a reduced stickiness. Overall, a production process based on the use of puffed grain in a solid state fermentation is better than one based on ground grain in a submerged culture because as the water demand of the process will be lower, there will be less waste generation and product stability will be higher. The addition of chemical supplements such as histidine, MSG and octanoic acid to a fermentation in a rotating system could further increase pigment formation.