Development and characterization of whey based alpha-lactalbumin protein nanotubes for food applications

Abstract

Alpha-lactalbumin (α-La) is one of the major proteins in whey. When partially hydrolyzed with protease, it produces nanotubular structures by self-assembly process. The aim of this PhD thesis is to develop and characterize whey based α-La nanotubes. In this study, purification of α-La from whey using ultrafiltration and chromatography, development of protein nanotubes with standard and purified α-La fractions, their characterization by microscopic, optical and spectrophotometric methods, analysis of hydrolysis process, and investigation of these nanotubes in relation to food applications were presented. Lactose was eliminated and proteins were concentrated in whey powder by diafiltration assisted ultrafiltration prior to chromatography. α-La and besides β- lactoglobulin were purified individually from whey protein concentrate with high purity (95–99 %). The obtained protein nanotubes were longer than 100 nm up to few microns with ~20 nm width in bundled, rod and chain-like fashions. Remarkable conformational changes occurred in the protein secondary structure during nanotube formation. Calcium to protein ratio critically affected nanotube formation and stability. Both hydrolysis and nanotube growth triggered gelation, but stiffer gel network was obtained with nanotubes. Viscoelasticity and stiffness were improved by blending with cellulose. As the calcium content increased the transparent appearance of the gels got turbid due to aggregation. α-La nanotubes were stable up to ~ 60 °C. The nanotubular gels entrapped a coloring agent by enhancing transparency. Binding of catechin to nanotubes was occured as reversible with low stability. α-La nanotubes and gels can be used as functional ingredients in food processing involving low and moderate heat treatments.