Whey proteins serve as a structural component and source of protein in foods. When used in protein bars, whey proteins can contribute to a reduction in shelf life as a consequence of bar hardening. Bar hardening has been associated with water migration between phases and formation of a protein network in bars over time. One approach to ameliorate bar hardening is to form whey protein meso-structures that are not susceptible to water migration or protein network formation. We hypothesize such structures can be formed by using berry polyphenols to initiate whey protein aggregation that leads to formation of inert particles. Whey protein-cranberry polyphenol (WP-CP) particles were formed by adding 200 g of whey protein isolate (WPI) to 1 L of cranberry juice during continuous stirring. After mixing for 4 h, particles were pelleted (7,000 x g for 40 min), re-suspended at 0.01 g/mL in water, and spray dried. Bars were made with WP-CP particles or unmodified WPI. Textural properties were assessed using transient creep-recovery testing which measured the maximum compliance (J_max, indicating bar firmness) and percent creep-recovery (bar viscoelasticity). The WP-CP particles contained up to 2 mg/g of total phenolics, and the particle size ranged from 10 to 100 µm. Bars produced with WPI had a smaller J_max (more rigid) of 0.000053 Pa⁻¹ compared with 0.0023 Pa⁻¹ J_max for bars formulated with WP-CP particles. Bars formed with the WP-CP had a reduced percent recovery of 2.5% compared with 28.6% for bars made with WPI. Greater percent recovery indicates a more elastic system and possible network formation. Bars were placed in accelerated shelf life tests that imitate 3 weeks of storage at room temperature. The bars with WP-CP particles remained less rigid and more viscous (J_max of 0.0039 Pa⁻¹ and 10.9% creep recovery) than control whey protein bars (J_max 0.000012 Pa⁻¹ and 57.5% creep recovery). All differences between bars were found to be statistically significant at the P < 0.01 level. Rheological properties are consistent with WP-CP particles acting as inactive fillers and preventing formation of a protein network. These results suggest that WP-CP particles can be used to extend shelf life of protein bars and offer additional health benefits from plant polyphenols.