Effects Of Ultrasound Pretreatment On The Mechanical Properties And Microstructure Of Whey Protein Emulsion Gels

Whey protein emulsion gel has exceptional nutritional and functional qualities.Therefore,it has potential application in feeding the growing population.Recent studies have identified that nonthermal technique such as ultrasound can be used as a pretreatment technique to improve the functional qualities of whey protein.The ultrasound works by generating acoustic wavelength and is environmentally friendly and low cost.However,developing emulsion gels with whey protein pretreated by ultrasound is scarce.This current research aimed to fathom the effect of ultrasound pretreatment on whey protein emulsion gels by analyzing their mechanical and microstructure properties which are very essential in properties of protein emulsion gels.To accomplish the above objectives different experiments were carried on whey protein.In the first experiment,the effect of the sequential dual frequency ultrasound pretreatment(SEDFU)on the mechanical and microstructure of whey protein emulsion gels was assessed.Results showed that SEDFU pretreatment led to the unfolding of whey protein based on circular dichroism and fluorescence spectra.Moreover,the storage modulus(G'),hardness and water holding capacity(WHC)of whey protein emulsion gel(WPEG)were improved after SEDFU pretreatment.The CLSM and SEM showed that the WPEG was a typical aggregated particulate gel.Ultrasound pretreatment of WPEG at the frequency of 20/28 k Hz for 10 min resulted in better gel properties and microstructure.Its G',hardness and WHC increased by 184,58.7 and 20.1% respectively and its microstructure showed fine network when compared with the control.In the second experiment,the mechanical and microstructure properties of whey protein emulsion gels were compared between the mono frequency and the dual frequency(sequential and simultaneous modes)ultrasounds.The results indicated that ultrasound could improve mechanical properties and change the microstructure of whey protein emulsion gel when compared with the control.Ultrasound resulted to a decline in ?-helix and increasing in random coil thereby exposing more tryptophan residues.As storage modulus(G'),texture(hardness)and WHC were negatively correlated with ?-helix content,they had positive correlation with random coil content.The highest effect among the ultrasound pretreatments was seen with the dual frequency ultrasounds.It was indicated that the composite of oil droplet particulate aggregate network and protein aggregate network in the microstructure of emulsion gel might have resulted from enhanced molecular interactions of protein by ultrasound pretreatment.In experiment three which was the final,the effect of p H,ionic strength(Na Cl)and protein concentration on rheology,hardness,WHC and microstructure of emulsion gels after ultrasound pretreatment was studied.The results indicated that the rheology,hardness and WHC increased with increase in p H,ionic strength(Na Cl)and protein concentrations.Whey emulsion gels formed at p H 3 were less elastic compared with p H 5 and 7.Addition of Na Cl at all levels improved the mechanical parameters,and the highest effect was observed at Na Cl 0.1 M.Higher protein-protein interactions was observed at protein concentration of 10 % which significantly(p<0.05)led to an increase in rheology,hardness and WHC.The microstructure was porous and less consistent at p H 3 but more compact networks were formed at p H 5 and 7.In Conclusion,the overall results showed that the application of ultrasound as a pretreatment technique could improve the mechanical and microstructure of whey protein emulsion gels which can be beneficial in developing foods with high functional and nutritional qualities.Findings from this thesis could be a step forward in developing or designing suitable functional foods with health benefit.