Microgel enzyme recovery can cut manufacturing costs

InTech, Jun 2004

IN A DISCOVERY THAT MAY SAVE food and beverage manufacturers big money, scientists created a microgel that can recycle enzymes for repeated uses.

Manufacturers routinely use enzymes to catalyze important reactions, such as the breakdown of sugars to create lactose-free milk or cheese products. In many cases, users embed industrial enzymes in a solid, synthetic matrix to easily separate them from their chemical product after a reaction takes place. But embedded enzymes may eventually leach from a matrix. The chemical cross-linking reaction used to attach the enzymes to the matrix also can inadvertently inactivate the enzymes, rendering them useless. In addition, large chemicals cannot enter a dense matrix to react with embedded enzymes.

The microgel created by Carnegie Mellon University scientists could potentially recover any enzyme, which could save manufacturers money.

"By enabling efficient enzyme recovery, this microgel system overcomes significant obstacles in using natural enzymes in laboratory and industrial settings," said Bruce Armitage, associate professor of chemistry at Carnegie Mellon University, who developed the recoverable enzymatic microgel in collaboration with chemistry professor Gary Patterson and graduate students Rong Cao and Zhenyu Gu.

The enzyme connects tightly to the microgel matrix, but remains fully functional, Armitage said. Molecules can diffuse into the porous microgel and undergo chemical reaction when they encounter an enzyme. The product can then diffuse out of the microgel. Separation of the product from the enzyme takes advantage of the fact that the microgel particles precipitate from solution at a low temperature. After removing the product, you can resuspend the microgel particles by adding fresh water and heating the solution.

"The complete recoverability of the enzymatic activity is encouraging, and we are excited about extending this concept to other enzymcs," Armitage said. In addition to the food and dairy industries, enzymes see use in a wide variety of applications, including DNA testing in forensic labs, clinical tests for diagnosing diseases, and synthesis of new pharmaceutical agents.

Armitage and Patterson relied on bio-molecular recognition to create their microgel particles. For each particle, single DNA strands helped create a three-way junction (TWJ) that looks like spokes of a wheel. To the end of each spoke, they tethered a strand of peptide nucleic acid (PNA), a synthetic material that recognizes and binds to DNA. They then irreversibly attached enzyme complexes to the tips of up to four PNA strands in a way that led to cross-linking of different TWJs, resulting in the microgel. At room temperature, individual microgel particles suspend in solution, but lowering the temperature causes the microgel particles to cluster together and precipitate from solution.

To test these enzymatic microgel particles, the Carnegie Mellon chemists used an analogue of lactose that changes color when broken down by the microgel enzyme. When the investigators added this substrate to the microgel, a yellow color instantly appeared, indicating the reaction's success. Once the reaction was complete, the scientists lowered the temperature, causing the microgel particles to precipitate. The product remained in solution and separated simply by pouring the liquid into a separate container.