Interactions Between Polymerized Whey Protein And Polysaccharides And Its Impact On The Gelation Properties And Application

This dissertation was part of the project "Research and development oftechnology and application of whey protein" financially supported by the program of"Twelfth Five-Year" of the Ministry of Science and Technology of China.Gelation property is one of the most important functional properties of wheyprotein concentrate, whey protein isolate and β-lactoglobulin. Both whey protein andpolysaccharide can gel in food systems. Presence of hydrocolloids especially anionicpolysaccharide during the cold gelation of whey protein presents another degree ofcomplexity of milk protein systems. Therefore, the objectives of this disteration wereto study the interactions between whey protein and pectin/inulin and its effect on thegelation properties of the system. Normally, whey protein was first heated and thenmixed with other polysaccharide in the food system. In this disteration, we not onlystudied the commonly used manner in which pectin/inulin added, but also comparedwith the manner where whey protein was mixed with pectin/inulin first and thenheated together. Finally, on the basis of investigation of the interaction between wheyprotein and pctin/inulin, Chinese-style Greek yoghurts with higher protein contentwere developed and compared with a commercial sample. Therefore, the presentstudy focuses on the following aspects:(1) interactions between WP/PWP and pectinand the effects on gelation and rheologial properties of whey protein;(2) interactionsbetween WP/PWP and inulin and the effects on gelation and rheologial properties ofwhey protein;(3) development of Chinese-style symbiotic Greek yoghurt. WP andpectin/inulin system refers to mixture where whey protein mixed with pectin/inulin first and then heated together while the other one was whey protein heated first andthen mixed with pectin/inulin.Effects of whey protein content (4-8%, w/v), pectin level (0.1-0.5%, w/v), pH(7-9) and ionic strength (50-200mM) on the Ca2+-induced gelation properties ofheated/unheated whey protein and pectin mixtures were investigated. Heated wheyprotein and pectin mixture was prepared by heating the mix at85oC for30min atcertain pH, while another one was prepared by heating whey protein alone and thenmixed with pectin. Turbidity, surface Zeta potential, mean particle size and textureproperty of the Ca2+-induced gels were analyzed. Results indicated that gelationoccurred after heating the mix of whey protein solution (8%) at pH7with0.3%to0.5%pectin without adding Ca2+. Protein concentration significantly affected turbidityand pectin addition slightly increased its value. Whey protein-pectin dispersionsshowed more negative charges than protein alone. However, no significant differencewas observed between the two types (p>0.05). Three peaks with different averagediameter depending on the protein concentration and pH were observed in the sizedistribution by volume for the control. As pectin increased, peak corresponding todenatured β-lactoglobulin shifted slightly towards larger particles. Gels could beformed for all the dispersions of pre-heated whey protein solution (4%, pH7.0) withwide range of pectin (0.1-0.5%) in the presence of Ca2+(100-200mM). Hardnessvalues were significantly increased with increasing pectin concentration at all Ca2+levels. The highest value of hardness was at100mM (p<0.05).Effects of pectin concentration, pectin DE value and pH on the flow behaviorunder various shear rate and temperature of WP/PWP (8%, w/v) and pectin wereinvestgated. Results indicated that all the factors did not affect the flow behaviorsignifivantly, and the type was shear-thinning fitted with Sisko equation (R2>0.99)and Arrhenius equation. With the increasing pectin addition, gelation time decreased.Effects of protein concentration (4-8%, w/v), inulin concentration (1-5%, w/v) and ionic strength (10-50mM) on Ca2+-induced interactions between whey protein(WP) and inulin mixture (pH7.0) heated at85oC for30min were investigated. Theinteractions were analyzed for turbidity, particle size, Zeta potential, apparentviscosity and texture profile. Interaction properties were also compared with mixtureof polymerized whey protein (PWP) and inulin in which whey protein was heated firstand then mixed with inulin. Results indicated that the dispersion became more opaquewith increasing protein but no significant difference was detected regarding the wayinulin added (p<0.05). Three peaks at about40,900and5000nm were observed insize distribution by volume. Compared with the control, there was a small shifttowards larger size with increasing inulin level in the width of peak corresponding todenatured whey protein. Zeta potential values for all samples fell in the ranges of-10to-30mV independent of the manner in which inulin added. Increasing inulinresulted in less negative Zeta potential and smaller repulsive force between particlesfor both types of mixtures. As protein and inulin increased, apparent viscosityincreased and combination of PWP and inulin showed significant higher values(p<0.05) than WP and inulin mixtures. It was not sufficient to form cold gels for allsamples at the level of10mM Ca2+. Compared with the control, the mixtures of PWPwith inulin showed higher water holding capacity may due to the ability of occludingwater of inulin microcrystals (p<0.05). WP/inulin mixture showed significant higherhardness (p<0.05) than PWP/inulin due to possible microcrystal seeds maintained insolutions when heated at80oC for30min. Results indicated that interactions may beoccurred between whey protein and inulin in the model system.Effect of inulin addition level on the flow behavior of WP/PWP (8%, w/v) andinulin mixtures under various shear rate and temperature were studied. Resultsindicated that inulin addition manner and addition level did not change the flow typesignificantly which was shear-thinning fitted with Sisko and Arrhenius equations.Effect of inulin addition level on the storage and loss modulis of whey protein (15%, w/v) were investigated, results indicated that inulin addition improved the onset pointof whey protein.Effects of different levels of PWP on the properties of yoghurts includingphysiochemical properties, syneresis, viscosity, texture, lactobacillus population,sensory evaluation and microstructure were studied. The results indicated thatyoghurts with0.4%PWP and0.3%pectin showed the highest pH value (4.60±0.07)and the lowest titratable acidity (67.90±9.69oT), highest viscosity and cohesivenessvalues (p<0.01). The population of the lactobacillus combined was about1010CFUmL-1, and the sensory evaluation score was higher than the commercial sample,which was above3.5for each individual attribute. The microstructure analysis ofyoghurts showed that yoghurt with0.4%PWP and0.3%pectin displayed uniformedand denser network.On the basis of optimation of levels of polymerized whey protein and pectin,Chieses style symbiotic Greek yoghut with three different protein supplements (wheyprotein concentrate, skim milk powder and whole milk powder) were prepared. Theprototype was analyzed for physiochemical, textural, sensory properties and probioticsurvivability and compared with a commercial sample. Experimental yoghurts weresignificantly higher in pH, protein content, hardness, and viscosity (p<0.01).Microstructure indicated a uniform and denser protein network. Probiotics remainedstable for Bifidobacterium during storage of10weeks.This study systematically investigated the interactions between whey protein andpectin/inulin and its effect on the gelation and rheologial properties of whey protein.The results may provide useful information in functional dairy foods for furtherapplications of whey protein.