Characterization of ethanol induced protein gels by ultra-small angle x-ray scattering and rheological measurements

Protein gels;x-ray scattering

Uzun, Suzan

关键词: Protein gels;    x-ray scattering;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/95465/UZUN-DISSERTATION-2016.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Gelation is one of the main functions of food proteins. Protein gelation has been utilized to improve physical properties of protein-based products or for delivery of bioactive compounds. On the other hand, the control of gelation is very important to prevent formation of gel network which may affect performance of the process or final physicochemical properties of product. In this research, gelation mechanism of two different proteins, zein and whey protein, were examined in ethanol-water mixture.Zein is an amphiphilic protamine which is capable of self-assembly into distinctly different structures. Self-assembly of zein at high protein concentrations was studied in binary solvent systems of ethanol and water. Ultra-small angle X-ray scattering (USAXS) was used to characterize zein ensembles formed in aqueous ethanol. The results showed that zein assemblies possessed three levels of structural hierarchy. Zein formed rod-like structures at one dimension (1D) which self-assembled into two dimensional (2D) platelet-like structures. Platelet-like structures were organized to form spherical assemblies. In presence of oleic acid, zein interacted with oleic acid by forming 1D structure different than rod shape and larger platelet-like structures compared to 2D zein assemblies. Oleic acid facilitated formation of spherical structures with smooth surfaces. It was observed that self-assembly caused transition from sol to gel state in some conditions which depended on protein concentration and ethanol content of solution. Rheological measurements showed how the viscoelastic properties of zein samples altered with gelation and gel stiffness was increased as the protein concentration was increased. Oleic acid incorporated gels significantly higher storage modulus than zein gels. Raman spectroscopy suggests that gelation was driven by transition from α-helix to β-sheet conformation.The aggregation and gelation behavior of whey protein in alcohol-water mixture was investigated with rheological measurements. To examine the effect of whey protein composition, whey protein concentrate (WPC) and whey protein isolate (WPI) were used. Instant gelation of WPI in ethanol-water mixture was observed at 10% (w/v) and above protein concentrations where the gel stiffness increased as ethanol content of solution was increased. WPC showed different viscoelastic properties in varying ethanol contents than WPI counterparts. The gel network established in 20% WPC collapsed by further addition of ethanol to adjust final ethanol content to 60% (v/v). Ethanol-induced protein gelation mechanism was utilized for stabilization of lutein-in-safflower oil emulsions in whey protein gel matrix. Stabilization of droplets were achieved for both nanoscale and microscale droplets. As the process does not involve any heat treatments, lutein was well-preserved throughout the process. X-ray diffraction data showed no evidence of lutein crystallization, suggesting that lutein remained dispersed within the oil droplets.The results of this study demonstrated that proteins could form gel network in presence of ethanol. This research can help to control of structure formation through self-assembly in zein film production and to formulate hydrophobic or hydrophilic compound incorporated protein gel delivery systems.