Monascus

Fungi of the Monascus genus grow in substrates rich in carbohydrates. In Asian countries, Monascus spp. are grown in steamed rice and the whole mass is eaten fresh, dried, ground, or incorporated into other foods. Pigments of these fungi are polyketide; six have been isolated and show a range of colors: yellow (monascin and ankaflavin), orange (monascorubrin and rubropunctamine), and red (monascoru-bramine and rubropunctamine) (Figure 9.9). The major source of red pigments in Asia is M. purpureus.3-58-59

1. Commercial Production

Monascus pigments are produced in Japan, China, and Taiwan in the traditional way with the Koji process. In this process, solid substrates (e.g., rice, wheat, soybeans, corn, and other grains) are inoculated. Fermentation in the solid state of the Koji process may be combined with a second stage of submerged culture, the Moromi process, by which products such as rice wine and soy sauce are produced.59

2. Studies on Fermentation Process

Early processes of Monascus-pigment production were unsatisfactory because the fungus produced an antibiotic (monascidin A), which is undesirable as a food ingredient.

Today, new strains and process conditions have been achieved to avoid production of the antibiotic. In particular, the M. purpureas is considered appropriate for solidstate fermentation. Additionally, different substrates and processes have been introduced to improve the quality and quantity of Monascus pigments (Table 9.10).60-68 The importance of mixing and of the levels of O2 and CO2 has been established. In the fermentation process the oxygen and carbon dioxide levels must be carefully controlled; by maintaining CO2 at 0.02 atm, pigment production is increased from 130 to 204 mg/g of rice solids when oxygen is increased from 0.01 to 0.50 atm. On the other hand, increments in CO2, while constantly maintaining the O2 levels, decrease pigment production. Implementation of improved systems with aeration and continuous feeding promises pigments of high quality and quantity. Interestingly, red pigments react with amino groups forming water-soluble compounds that additionally have greater thermostability and photostability than the parent compounds. Moreover, certain fermentation conditions favor the extracellular production of pigments, thus diminishing the downstream expense.59,61 Another aspect of importance is the use of solid waste products, such as sugarcane bagasse, for pigment produc-tion.60-62'63

It has been established that ankaflavin synthesis is favored at pH 4.0. Moreover, ammonium- and peptone-containing cultures produce higher total monascoru-bramine than those with nitrate as the nitrogen source. Thus, pH and nitrogen sources are variables that may be controlled for selective production of Monascus pigments.69

3. Applications

Monascus pigments are soluble in ethanol and slightly soluble in water. Color depends on pH: ethanol solutions are orange at pH 3.0 to 4.0, red at 5.0 to 6.0, and purplish-red at pH 7.0 to 9.0. They are light sensitive, more stable in 70% alcohol than in water, and thermostable up to 100°C in neutral or alkaline conditions.3,59 These pigments have been suggested as colorants for processed meats, marine products, jellies, jam, ice cream, tomato ketchup, koji, soy sauce, and kamboko. Currently, Monascus pigments are not permitted in the United States.

In meat products (sausage and pâté), red pigments have greater sensitivity than yellow fraction; evaluation has been carried out by light exposure for 50 days or 100°C/8 h. Monascus pigments are better colorants than traditional food additives such as nitrite salts.70

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