טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentWeltsch-Cohen Galit
SubjectSol-Gel Enzymatic Doping for Aroma Compounds Release
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Robert Armon
Professor Emeritus Carlos Dosoretz
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Aroma is one of the major components determining wine quality. The floral aroma of grapes has been found to originate mainly from substances named monoterpenes. The majority of monoterpenes are glycosidically conjugated. In this form monoterpenes do not contribute to grape aroma. The glycosidic form can be enzymatically hydrolyzed to its sugar moiety and the corresponding monoterpene. These enzymes act sequentially in two stages: at first, a-rhamnosidase (a-L-rha), a-arabinosidase (a-L-ara) and b-apiosidase cleave the terminal sugar. Subsequently, the release of monoterpene takes place following the action of b-glucosidase (bG). Wine milieu is not ideal for the activity of enzymes controlling the release of monoterpenes. The sol-gel process provides many advantages to entrapped enzymes: structure preservation, protection to chemical surrounding, stabilization and entrapment of multiple enzyme systems. These characteristics fit well in the role glycosidases play in releasing aromatic precursors. The main goal of the current research was to amalgamate the advantages that can be obtained from entrapment of enzymatic chain in sol-gel matrices aimed to enhance the flavor of various wine types. The use of PGS - Poly(Glyceryl Silicate) as a precursor of sol-gel matrix solved problems that rose when traditional precursors (i.e. TMOS, TEOS or MTMOS) were used. Initially, bG was separated from NOVOZYM 188, an enzymatic commercial preparation. Increase in substrate concentration revealed ‘substrate inhibition’ phenomenon. Once bG enzyme was entrapped in PGS, the inhibition phenomenon diminished. Subsequently, LALLZYME BETA (enzymatic complex, a blend a blend of bG, a-L-rha, a-L-ara, b-apiosidase and pectinases) was entrapped in PGS. The activity recovery was: bG-60%; a-L-rha-82%; a-L-ara-48%. Distribution of entrapped enzymes within the matrices was found to be homogenous. Entrapment was found to diminish the inhibitory effect of ethanol and glucose. PGS matrices showed a solid shelf life of at least ten months. Finally, the activity of doped PGS matrices was examined with natural substrate - a wine model. The research focused on the release of four monoterpenes: linalool, geraniol, nerol and a-terpineol. Hydrolysis of the glycosidic terpenes occurred as revealed by gas-chromatographic analysis (GC-FID). The study demonstrated that entrapped enzymes don’t leach out from doped matrices, and the entire activity occurred only inside the sol-gel matrix. The present study opens the door to a wide range of applications, that can use a variety of entrapped enzymes in sol-gel matrices in order to preserve or improve the quality of different products that contain glycosidic aroma and flavor compounds able to be released enzymatically.