Study On The Interaction Of Five Food Colorants With BSA By Multispectral Techniques

Food colorants are often used for maintaining and improving the food color appearance,when they are absorbed into the circulatory system and bind to serum albumin,the distribution and free concentration will be considerably influenced,accordingly,the vital information of food colorants would be obtained by analyzing their binding properties.Acid red 92(AR92),acid red 26(AR26),acid black 1(AB1),acid green 9(AG9)and acid blue 9(AB9)are common food colorants,the multispectral techniques were adopted to investigate the interactions of the five food colorants with bovine serum albumin(BSA),and-limiting law was combined for a further disscussion.The effects of salt concentrations on interaction of five food colourants with BSA were discussed at different pH(4.8,5.5,6.3 and 7.4;7.4 for BSA – AR92 system)and/or temperatures(293,298,304 and 310 K).All the KSV values for the BSA-AR92 / AR26 / AB1 / AG9 / AB9 system were negatively correlated with the temperature,and their Kq values were higher than the maximum scatter collision quenching constant of quenchers with biomolecule(2.0×1010 L·mol-1·s-1);the RLS intensities of BSA were heightening with the addition of AG9 / AB9.It suggested that the fluorescence quenching mechanism of BSA by the five food colourants was a static quenching.The binding constant K and the binding-site number n were also calculated,the comparison of of K values under the same condition indicated that the binding affinity of five food colourants with BSA in the following order: AR92 > AR26 > AB1 > AG9 > AB9;and the value of n approximately equal to 1 indicated that only one binding site exist on BSA for the five food colourants,respectively.The displacement experiments showed that AR92 binds to site I(subdomain IIA)on BSA;the investigation of alcohol impacts on the binding of BSA with five food colourants further confirmed the fact that they can combine the only site on BSA specifically.The thermodynamic parameters such as ?G0 < 0,?H0 < 0,?S0 > 0 demonstrated that the main driving force for BSA interacting with AR92 / AR26 / AB1 spontaneously was a static electricity;and for the BSA-AG9 / AB9 system,when salt concentrations(ionic strength)increased to a certain extent,the dominated force for the interaction of BSA with AG9 / AB9 would be transformed to non-electrostatic force(hydrogen bonding and van der Waals interaction)from the static electricity,resulting in that the mobility/local motion of AG9 / AB9 complexed with protein was retarded,and meanwhile,enthalpy-entropy compensation(EEC)was observed from the BSA-AG9 / AB9 system.Combining-limiting law,the modulation of ionic strength to the binding of AR26 / AB1 / AG9 / AB9 with BSA was analyzed,and the related parameters were calculated.The results displayed that the local charge rather than the overall or surface charge of BSA played a key role in dominating the interaction strength of BSA-AR26 / AB1 / AG9 / AB9 system.The change values of Hurea in the absence and presence of AG9 / AB9 was analyzed to discuss the structural stability of BSA.Furthermore,AR92 / AR26 / AB1 / AG9 / AB9-induced conformational changes of BSA were also analyzed.