Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/30/2003
Publication Date: 2/7/2004
Citation: Truong, V.-D., Clare, D.A., Catignani, G.L., Swaisgood, H.E. 2004. Crosslinking and rheological changes of whey proteins treated with microbial transglutaminase. Journal of Agricultural and Food Chemistry. 52:1170-1176. Interpretive Summary: Whey proteins recovered from cheese processing have been used in many foods as a protein supplement, filler/water binder, thickening agent, and gelling agent. However, the gel formation of whey proteins upon heating limits their utilization in several thermally processed food products. This study examined the application of a biochemical method involving microbial enzyme transglutaminase in modifying the gelling properties of whey proteins. We found that modified whey proteins with a wide range of gelling properties can be produced by varying the enzyme-protein ratios for the crosslinking reaction. Whey proteins that did not gel even up to 95 deg C were obtained. This process can be applied to produce nongelling or heat-stable whey proteins for various food applications.
Technical Abstract: Modification of the functionality of whey proteins using microbial transglutaminase (TGase) has been the subject of recent studies. However, changes in rheological properties of whey proteins as affected by extensive crosslinking with TGase are not well studied. The factors affecting crosslinking of whey protein isolates (WPI) using both soluble and immobilized TGase were examined and the rheological properties of the modified proteins were characterized. The enzyme was immobilized on aminopropyl glass beads by selective adsorption of the biotinylated enzyme on avidin that had been previously immobilized. WPI solutions were crosslinked using enzyme/substrate ratios of 0.12-10 units of activity/g WPI in a jacketed bioreactor with continuous circulation. Gel point temperature of WPI solutions treated with 0.12 units of immobilized TGase/g was slightly decreased, but gel strength was unaffected. However, increasing the enzyme/substrate ratio resulted in extensive crosslinking of WPI that was manifested by increases in apparent viscosity and changes in the gelation properties. Using 10 units of soluble TGase/g resulted in extensive crosslinking of alpha lactalbumin and beta-lactoglobulin in WPI, as evidenced by SDS-PAGE and Western blotting results. Interestingly, the gelling point of WPI solutions increased from 68 deg C at 0 min to 94 deg C after a 4 h reaction, and the gel strength was drastically decreased (lower storage modulus, G'). Thus, extensive intra- and inter-chain crosslinking probably caused formation of polymers that were too large for effective network development. These results suggest that a process could be developed to produce heat-stable whey proteins for various food applications.