טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentShpigelman Avi
SubjectNano-Delivery by Beta-Lactoglobulin, and Protection of EGCG
from Green Tea, for Preventive Medicine
DepartmentDepartment of Biotechnology
Supervisor Professor Yoav Livney
Full Thesis textFull thesis text - English Version


Abstract

The major green tea catechin, (-)-Epigallocatechin-3-gallate (EGCG), is water soluble, bitter, astringent and relatively unstable in neutral and alkaline solutions. Animal and human studies indicate that the consumption of green tea products with high levels of EGCG may have desirable effects towards prevention of cancer, cardiovascular and metabolic syndrome diseases, neurodegenerative diseases and more. Because most of the population does not ingest the amounts of EGCG required for beneficial effects, it is highly desirable to enrich foods and beverages  with this compound, but the enrichment is limited by the sensitivity of EGCG to oxidation and its undesirable sensorial properties.

In this study we developed a novel method of nanoencapsulation of polyphenolic compounds like EGCG using partially denatured β-lactoglobulin (β-Lg) as a carrier. Using spectroscopic methods we found that optimal nano-entrapment is obtained when EGCG is added to preheated (75-85°C, 20 min) β-Lg solution during cooling and vortexing. Molecular level complexation was confirmed by IR absorbance spectrum of freeze dried nanoparticles. The thermally-induced protein-EGCG co-assemblies were smaller than 50nm, thus excellent transparency was maintained, enabling their application in clear beverages. Good loading efficiency (~70%) dependent on β-Lg concentration was obtained. The complexation did not hamper the protein’s colloidal stability and most importantly the complexes conferred considerable protection to EGCG against oxidative degradation.

The nano-entrapment dramatically suppressed the bitterness and astringency of EGCG, thus significantly promoting the possibility of industrial application. Simulated gastric digestion of β-Lg-EGCG nanoparticles showed limited release of EGCG, suggesting they could potentially be used as vehicles for protection of EGCG in the stomach, and for its sustained release in the intestine.

Protection of EGCG by sugars against degradation was also studied. Using a rapid method we developed for evaluating the degradation rate of EGCG by absorbance spectroscopy we found that various sugars provided different levels of protection at identical weight percentage, and that the combination of sugars and β-Lg nanocomplexes provided larger protection for EGCG than each protective component alone. It was suggested that the concentration dependent protection resulted from a combination of mechanisms, including: (1) reduced aqueous O2 solubility, (2) scavenging of reactive oxygen species, and (3) chelation of traces of transition metal ions, which is suggested to be the main reason for the difference among the sugars. The combined effects of sugars, especially fructose, and β-Lg complexation provided an effective protection to EGCG, which may be applied in enrichment of clear beverages for preventive medicine.