Doctor of Philosophy (PhD)
Urease enzyme was crystallized almost a century ago, and to this day its intrinsic stability is not ideal for everyday applications. This work introduces a new process by which a naturally encapsulated material, watermelon seed powder (WMSP), is characterized for its stability and activity. WMSP enzymatic activity has been measured for over a year at various storage conditions—exposed to ambient atmosphere for a year, WMSP retained above 90% activity. In aqueous conditions, the enzyme maintained above 60% activity after two months; with the addition of a preservative that number stays at about 90%. There is a pH shift of the maximum activity at 8.1 pH in addition to a broadening of the activity curve allowing for a wider range of reactions.
In Chapter 3, immobilization techniques were employed on these powders, enhancing their usability and in turn presented some interesting dynamics. One of the techniques physically encapsulated the WMSP inside a porous resin, essentially creating a urea-ammonia exchange resin. These particles were subject to 10 cycles of urea hydrolysis, without any change in the urea-urease clock reaction. The agar immobilized WMSPs exhibited a behavior called quorum sensing. That is a biological communication process by which bacteria express certain genes when a “quorum” or sufficient number are in proximity of each other. With certain parameters, the particles will not clock individually, but when in a cluster of particles, the autocatalysis occurs. This property was then coupled with a hydrogel polymerization that gels in basic conditions. The WMSP particles in principle are biofilm generating analogues. Lastly, Chapter 4 presents an application of WMSP as a base generator for several adhesive formulations and outlines some potential future uses of WMSP.
Mai, Anthony Quan Quoc, "Characterization, Immobilization, and Polymer Related Applications of Watermelon Seed Powder, a Practical Source of Urease Enzyme" (2021). LSU Doctoral Dissertations. 5464.
Pojman, John A.