Studies On Thermal Stability Of Monascus Pigments

Monascus pigments are natural pigments fermentated by Monascus spp. They are mixture of kinds of red and yellow single pigment, Application of Monascus pigments to replace nitrates in meat is concerned particularly now. Monascus pigments is sensitive to light, high temperature, acid-base and heavy metal ions, especially in manufacturing of meat products, discoloration of meat products which added to Monascus pigments in heating process have bad effect of the product. Based on studies of the basic physical and chemical effects on the absorbance and chroma of monascus pigments, red pigments and yellow pigments were separated and prepared by TLC. After purity analysis and preliminary structure identification, thermal degradation characteristics were studied between red pigments and yellow pigment. Evaluation method of monascus pigments thermal stability was established, thermal stability of red pigments RP3 and yellow pigments YP1 were determined by this method. The main research results were as follows:1,Effect of light,high temperature,acid-base,salt concentration and heavy metal ions on stability of Monascus pigments were studied. Continuous illumination had significant effects on stability of monascus pigments, preserving rate decreased significantly in continuous illumination. Monascus pigments was stable in avoid light storge. Under the condition of pH 3-10, the stability of the pigment could maintain. Heavy metal ions had ignificant effects on stability of monascus pigments, Precipitation appeared when the monascus pigments were coexistenced with these heavy metal ions such as Cu²⁺, Fe³⁺. Chroma decreased with the increase of salt concentration. monascus pigments had a good stability under 100℃, while above of this temperature, stability of monascus pigments were obviously decreased with the increase of heating temperature and time.Thermal degradation dynamic model of monascus pigments was established. It was proved that it was in accordence with first order reaction kinetics. In heating process, Lightness of monascus pigments was increased with the prolongation of heating time, and the higher the heating temperature was, the lower of the decreasing. At the same time, reddishness of monascus pigments was also decreased with the prolongation of heating time, and the yellowness were increased with the increase of heating temperature.2,Changing trend of monascus pigments chroma in storage after different temperature heating was different. Preserving rate of monascus pigments decreased relatively slow in avoid light storage, the preserving rate was more than 85 percents after 90 days storage while the preserving rate of light storage was no more than 10 percents. Lightness was increased with the prolongation of storage time. Reddishness and yellowness were decreased with the prolongation of storage time. Storage of illumination has a poorer stability than avoid light storage.3,TLC was established to separate four red components and three yellow components from monascus pigments, toluene, ethyl acetate and formic acid(7: 3: 1, v/v)was used to separate red components while n-hexane, ethyl acetate and petroleum ether(30: 17: 5, v/v) was used to separate yellow components from monascus pigments. RP3 of red components and YP1 of yellow components were puritied proved by HPLC. After studied on the thermal degradation characteristics, YP1's thermal stability was better than that of RP3' s, after heating 40 minutes of 121℃, preserving rate of YP1 was 71.3%, while that of RP3 was only 45.2%. The thermal degradation kinetics of these two components accord with first order reaction kinetics model, the activation energy of RP3 and YP1 were 77.3826KJ/mol and 87.5049KJ/mol.4,Based on the effect of characteristic absorption peak and absorption value in heating time,heating temperature and concentration of monascus pigments, evaluation method of monascus pigments thermal stability was established. The testing condition was recommended as absorption 0.46-1.05, heating temperature 120℃, heating time 40min, difference of monascus pigments thermal stability could be measured by this method.