Abstract: L-Histidine (L-His) was added as a functional enhancer of protein gels to whey protein isolate in aqueous solutions to prepare heat-induced gels. The effects of L-His on the structure and gel properties of whey protein were investigated. The results showed that aggregates with a diameter of about 1 700 nm and a very small specific surface area, which were found to be almost uncharged, were formed at the isoelectric point (pI 5.2) of whey protein. However, the aggregate size was ~400 nm at pH away from the pI. L-His inhibited whey protein aggregation, reduced the aggregate size but dramatically increased the specific surface area, promoted protein unfolding and increased the amount of charge carried by the protein molecule. Whey protein formed a heat-induced white gel with a low water-holding capacity (WHC) at the pI, whereas the gels formed at other pH values were yellow with higher WHC than at the pI and the yellowness was increased as pH was farther away from the pI. Despite having no obvious impact on the color, L-His significantly enhanced the WHC (P < 0.05) and improved the textural properties of gels. More notably, the elasticity and chewiness of the gels that were formed at pH 7.59 and 9.74 were significantly improved by L-His (P < 0.05). These changes in gel functional properties could be mainly attributed to the fact that L-His could impel the rearrangement of hydrogen bonds, disulfide bridges and hydrophobic interactions involved the gel matrix. Overall, L-His changed the structure of whey protein and improved the gel properties, and its effect was affected by pH.

Key words: whey protein; pH; L-histidine; structure; gel properties