| Monascus pigments are the secondary metabolites produced by Monascus spp via submerged and solid-state fermentation.In our country,as food coloringagent,it has been used in the fields of foods for more than two thousand years.Monascus pigments can be divided into red pigment,orange pigment and yellow pigment according to the tone.At present,the demand of yellow pigment in the domestic market account for about 60%.In addition,compared with synthetic pigment and plant pigment,monascus yellow pigment has the advantages of low-cost production,high safety,high stability,and physiological activities,including anti-inflammatory,anti-tumor and antioxidant.Based on this,in this study,the mutant strain M.purpureus H14 producing water-soluble monascus yellow pigment is used as the research object to investigate the separation process and effect of water-soluble monascus yellow pigment by macroporous adsorption resin.The environmental stability,chemical structure and cellular antioxidant activity of the yellow pigment were studied.Finally,the effects of the pigment on the quality,sensory properties and storage quality of rice noodles were studied.The results of this study are showed as follows:(1)The adsorption and desorption properties of seven resins as adsorption media for water-soluble yellow monascus pigment were investigated,and static and dynamic adsorption separation systems were established.Macroporous resinLX-3020 was determined as the best adsorption resin for the separation of water-soluble yellow monascus pigmen.The optimal static adsorption conditions were temperature 25℃,solidliquid ratio 1:25～1:30,low acid conditions(pH=4),adsorption capacity of 370.75 U/g,pigment adsorption rate up to 80.61%.The optimal static desorption conditions were temperature 25℃,70%(v/v)ethanol-water eluent,low alkaline conditions(pH=8),and the pigment desorption rate was up to 93.30%.When the dynamic conditions were set as feeding concentration 50 U/mL and feeding flow rate and desorption flow rate lbv/h,the maximum recovery was 75.21%.Finally,the adsorption and desorption mechanism of the yellow pigment on the macroporous resin LX-3020 was analyzed through the isothermal adsorption and adsorption kinetics equation fitting curve,indicating that the multimolecular layer adsorption of pigment molecules on the resin and the adsorption of pigment molecules on the resin is mainly chemical adsorption.(2)The water-soluble yellow monascus pigmen has good stability to environmental factors such as pH,heat,light and metal ions.The water-soluble yellow monascus pigmen is C21H27NO7S.The overall color stability of the pigment is good,has been yellow color(except in high concentration of Ca2+,Cu2+ ionic solution);The pigment has good color stability in the range of pH 4-8,25-100℃ heat treatment,illumination,Na+,K+and other metal ions.Finally,UHPLC-ESI-MS analysis showed that the yellow pigment was composed of monascusone B and C21H27NO7S,respectively.Based on the alcoholsolubility of monascusone B,the water-soluble yellow monascus pigmen was determined as C21H27NO7S.(3)Monascus yellow pigment C21H27NO7S has good cellular antioxidant activity.At the concentration of 2.5 mg/mL,the scavenging rate of 1,1-diphenyl-2-trinitrophenylhydrazine(DPPH)free radical reached 93.32%VC unit.At 1.5 mg/mL,the scavenging rate of 2,2’diazo-di-3-ethylbenzothiazol-6-sulfonic acid(ABTS)radical reached 71.99 VC units.At 2.5 mg/mL,the total antioxidant capacity of water-soluble yellow monascus pigmen reached 64.16%of VC unit.Cell experiments showed that the water-soluble yellow monascus pigmen was not toxic to HUVECs.According to the results of ROS detection,the H2O2 group had high fluorescence intensity and a large number of ROS,while the protected group had low fluorescence and fewer fluorescent spots.By semiquantitativeanalysis of fluorescence intensity,the fluorescence intensity of H2O2 was significantly higher than that of the control group,while the fluorescence intensity ofthe protection group decreased significantly and returned to the normal level.The SOD content of the protected group was 693.15U/mg,which was significantly higher than that of the H2O2 group 403.53U/mg.The MDA content in the protected group reached 2.03nmol/mg protein,while the MDA content in the H2O2 group was significantly lower than 6.46nmol/mg.These results indicated that water-soluble yellow monascus pigment could reduce the intracellular ROS level.The antioxidant capacity of HUVEC after oxidative damage can be improved by increasing SOD level in HUVEC cells,alleviating peroxidation damage of cellular lipids and decreasing MDA content.(4)The addition of water-soluble yellow monascus’ pigment can significantly change the texture,cooking,color difference and sensory characteristics of rice noodles.Firstly,the effects of different pigment additions on the quality characteristics of rice noodles were studied.The results showed that when the supplemental level of water-soluble yellow monascus pigment was 200 mg/100 g,L*value decreased by 10.14%to 78.52,a*value and b*value increased to 9.55(5.41 times)and 73.63(6.74 times),respectively.Hardness,adhesion and chewiness decreased by 24.35%、77.35%and 34.49%,respectively.However,when the supplemental level was 120 mg/100 g,the flavor changes were the most significant and the score was the highest,indicating that the water-soluble yellow monascus pigment could significantly affect the sensory properties of rice noodles.Finally,compared with theblank group,the total number of colonies of rice noodles enriched with 120 mg/100 g water-soluble yellow monascus pigment was reduced by about 90%when placed at 30℃for 48 h,indicating that adding water-soluble yellow monascus pigment could increase the shelf life of rice noodles in storage. |
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