| Monascus pigments are the important secondary metabolites of Monascus fermented products,which have been used as natural food colorants for centuries in China.Monascus pigments include red pigments,yellow pigments and orange pigments.As is reported these pigments exhibit a wide range of biological attributes.However,the water-solubility of them is poor and they are sensitive to light.which greatly limit their applications in food industry.The polysaccharide-protein complexes have been used as effective food delivery,in order to improve the water solubility and stability of bioactive molecules.The effect of interactions among components of the delivery system on the functional properties of bioactive molecules are few reported.This paper mainly focus on the effect of carrageenan(Car)on the binding properties of Ankaflavin(AK)to bovine serum albumin(BSA),and the mechanism of antioxidant synergism of BSA-Monascus pigments(Mps)-Car system are also explored.The main conclusions are as follows:(1)The fluorescence emission of BSA was quenched through a static quenching mechanism when BSA-AK and BSA-AK-Car complexes formed.The binding of AK to BSA was mainly promoted by hydrophobic interaction and hydrogen bond,while BSA-AK-Car system were maintained by electrostatic interaction,van der Waals force and hydrogen bond.The K_avalue of BSA-AK-Car system was slightly higher than that of BSA-AK system,indicating that the binding affinity of ternary system was stronger than that of binary system.The binding interactions disturbed the microenvironment of Trp and Tyr residues,namely,the increase of hydrophobicity around the fluorophore after AK and/or Car binding to BSA(2)The specific binding site of AK to BSA was located in site I.And the binding region of Car to BSA was in domainⅢ,which changed after AK bond to BSA.(3)Theα-helix content of native BSA was 44.42%,which was reduced to37.40%when AK bound to BSA.An increase inα-helix content was observed upon the addition of Car.The content ofα-helix were 46.12%and 44.71%for BSA-AK-ι-Car system and BSA-AK-κ-Car system,respectively.The results showed that Car prevented AK from inducing conformational changes of BSA,and there was no effect on expansion of BSA structure of the addition of Car.(4)The scavenging rate of superoxide anion radicals of Mps was 42.02%at the concentration of 1.0 mg/m L,while that of BSA(10 mg/m L)was 69.42%.The binary system(BSA-Mps)showed a slightly lower antioxidant activity(63.61%),indicating the occurrence of antagonistic effect.The free radical scavenging rate of BSA-Mps-κ-Car system and BSA-Mps-ι-Car system were 82.59%and 80.07%,respectively,when Car(1.5 mg/m L)was added.These results demonstrated that the addition of Car could improve the free radical scavenging ability of BSA-Mps system.(5)The effect of Mps and/or Car on free radical-induced oxidative damage of BSA was evaluated.Mps increases the carbonyl content and decreases the protein sulfhydryl content during oxidative damage,and does not inhibit the exposure of hydrophobic cavities cause by conformational changes of BSA.Car can reduce the carbonyl content,and inhibit the decrease of sulfhydryl group content in BSA oxidation process.Meanwhile,Car can inhibit the exposure of hydrophobic cavities which cause by conformational changes of BSA,suggesting that Car could protect proteins from oxidative damage. |
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