Hardening Mechanism of Protein Bars
Principal Investigators: Donald J. McMahon, Utah State University
Co-Investigators: Shaun Adams, Utah State University
Bill McManus, Utah State University
Use of hydrolyzed proteins is known to delay hardening of high protein nutrition bars. Bars were formulated using ratios of 0, 25, 50, 75, or 100% partially hydrolyzed whey protein isolate (HWPI) to non-hydrolyzed whey protein isolate (WPI) in one experiment, and either WPI or HWPI combined with high fructose corn syrup (HFCS) or sorbitol syrup (SS) in a second experiment along with vegetable shortening such that initial aw was 0.59 for HWPI bars and 0.64 for WPI bars. After mixing, the dough was extruded into bars and stored at 32 °C for accelerated shelf life testing. Hardness, color and microstructure were measured during 42 d of storage. Bars initially had similar hardness of ~3.4 N that increased during storage. Bars with HWPI were softest with hardness at 37 d of 10 to 15 N compared to almost 100 N for bars with WPI. Water activity increased for WPI bars to 0.69 by 34 d. Bars became darker during storage depending on amount of Maillard browning reactants, i.e., HWPI/HFCS bars >> HWPI/SS > WPI/HFCS bars > WPI/SS bars. Bar microstructure at d 2 showed protein and fat dispersed in particulate form throughout the carbohydrate syrup within the bar matrix. During storage, a single non-lipid phase developed in HWPI bars while in WPI bars a phase separation occurred between protein and carbohydrate. We propose such phase separation initiates bar hardening and promotes subsequent protein aggregation. Successful formulation of HPN bars depends on cosolvent properties of the polyol/sugar towards the proteins and their preferential exclusion from the solvation layer surrounding the proteins.
McMahon, D.J. 2009. Hardening of High Protien Nutrition Bars and Sugar/Polyol-Protein Phase Separation. Western Dairy Center Annual Meeting. May 6, Utah State University, Logan.