Effects Of Different Factors On Starch-Fatty Acid-Protein Interaction And Its Mechanism

Starch,protein and lipid are the macronutrient in food.The changes of their structural and interactions in the process of food processing will have an important impact on the quality of food,such as texture,flavor,digestibility and so on.At present,there are many studies on the interaction of starch-lipid,starch-protein and protein-lipid binary systems,but these studies are not enough to reveal the interaction among starch,lipid and protein and their influence on the microstructure and functional properties of starch when they are presence together.Although there are studies on the starch-lipid-protein ternary interaction,the limited researches are not enough to reveal the rule and mechanism of the ternary interaction.In this paper,the influence of ion strength,pH value and complex temperature on the interaction of starch,lipid and protein ternary system was studied.The properties of the formed ternary complex are systematically analyzed by a variety of characterization methods,and the influence mechanism of complex conditions on the ternary interaction is clarified in this paper.The main results are as follows:1.A model system was constructed with wheat starch,β-lactoglobulin,fatty acids(lauric acid,myristic acid,palmitic acid,stearic acid)as raw materials to study the effect of NaCl on the interaction between starch-lipid and starch-lipid-protein.The results showed that lauric acid and myristic acid could form more complex with wheat starchy and the ability of forming complex of lauric acid was higher than that of myristic acid.In this experiment,only a small amount of wheat starch-palmitic acid and wheat starch-stearic acid complex was formed.The low solubility of palmitic acid and stearic acid,and to some extent myristic acid,in water caused these fatty acids to mostly self-aggregate.The presence of NaCl promoted the formation of wheat starch-lauric acid complexes and,to a lesser extent complexes with myristic acid,but had little effect on the formation of wheat starch-palmitic acid and wheat starch-stearic acid complexes.Solubility of fatty acids in aqueous medium was proposed to be a major factor for the formation of starch-fatty acid complexes.In the presence of β-lactoglobulin,the viscosity of the system can be significantly influenced,and the amount of starch-fatty acid-β-lactoglobulin complex formed in NaCl solution was less than that in aqueous medium.0.05M of NaCl solution resulted in the lowest viscosity and the least amount of ternary complex,which may be due to the change of starch dispersion in the system and starch-starch or starch-protein cross-linking,thus affecting the interaction between starch and fatty acids.2.The effect of pH on interactions between wheat starch,lauric acid andβ-lactoglobulin in a model system was investigate.Results from the Rapid Visco Analyser(RVA)showed that viscosity peaks appeared during the cooling stage and that their intensity increased gradually with increasing pH in the wheat starch-lauric acid binary system.With the wheat starch-lauric acid-β-lactoglobulin ternary system,the cooling viscosity peaks occurred throughout the pH range,and the change in intensity was not as evident as in binary systems.Results from differential scanning calorimetry(DSC),X-ray diffraction(XRD)and Raman spectroscopy showed that higher pH can promote the formation of both wheat starch-lauric acid binary and wheat starch-lauric acid-β-lactoglobulin ternary complexes,attributed to greater solubility of lauric acid.Moreover,the swelling power and the amylose leached increased when wheat starch was in alkaline conditions.The limited effect of pH variation on the formation of ternary complexes compared with binary complexes is proposed to be due to the pH buffering effect of β-lactoglobulin,which attenuates the influence of pH on the formation of complex.3.The aim of this chapter was to investigate the effect of cooling rate and complex temperature on interactions between wheat starch,lauric acid and β-lactoglobulin with Rapid Visco Analyse as a measuring instrument.Results from RVA,DSC and Raman showed that increasing cooling rate and complex temperature can facilitated the formation of both binary and ternary complexes,Under the high cooling rate,the retrogradation of amylose was rapid,leading to the formation of amylose single-helix structure with regarding fatty acids as the crystallization point,thus large amount of complexes formed.Higher complexation temperature lead to better dispersity and chain mobility of amylose and fatty acid in system which resulted in more complex formed.Thermostability was improved with lowering cooling rate and increasing temperature,due to enough time for arrangement of wheat starch-lauric acid or wheat starch-lauric acid-β-lactoglobulin complexes into a highly ordered crystalline structure and the increase of the hydrophobic interactions taking place inside the cavity of the amylose helix respectively.4.The effects of different amount of lauric acid on the foramation of wheat starch-lauric acid binary and wheat starch-β-lactoglobulin-lauric acid ternary complex were studied.Two different addition sequences of β-lactoglobulin were included in the study of ternary system.The results of RVA,DSC,XRD and Raman showed that the formation of wheat starch-lauric acid binary and wheat starch-β-lactoglobulin-lauric acid ternary complex increased first and then reached saturation with increasing the lauric acid content.The amount of lauric acid needed for the binary system and ternary system to reach saturation was different.The ΔT(Tc-To)of the complex melting increased with the increase of fatty acid content,which may be related to the different degree of polymerization of amylose.Regardless of the order of β-lactoglobulin addition,the number of complexes in ternary systems samples were always larger than that in binary system samples under the same amount of lauric acid.For the two kinds of addition sequence of β-lactoglobulin,the amount of complex formed by mixing starch,lauric acid and β-lactoglobulin first and then undergo RVA process was larger than that of adding β-lactoglobulin after the gelatinization of starch and lauric acid mixture,indicating that when starch,β-lactoglobulin and lauric acid are mixed together and then heated,the interaction between starch and fatty acid was prior to that of fatty acid and protein.That is,fatty acids preferentially form starch-lipid binary and starch-lipid-protein ternary complexes,rather than fatty acid-protein complexes.