Influence Of Lactose Content On The Aging Of Whey Protein Isolate(WPI) And The Investigation On Ageing Mechanism

Thanks to its predominant functionality and high nutritional value, WPI( Whey Protein Isolate) is widely applied to the food manufacture industry as a good ingredient. Supported by high added value and driven by market requirement, the global market of WPI has continued to increased over the past decade, which attributed to amount of powder delivery in international trade. In view of a protein content up to 90% in WPI, whose thermal sensibility is also relatively high, the storage condition during its global transportation and transition can lead to a deterioration of powder properties and a reduction in its commercial value. In order to control the powder aging during storage and increase powder shelf-life, diafiltration was carried out to reduce the lactose content to 0.26% successfully in WPI, then the structural and functional changes in the aging process of the two protein powder were analyzed comparatively so as to probe into its mechanism, aiming to investigate the interest of delactosed WPI on the property of storage stability.The two powders were stored in controlled conditions at 40 ° C 、 60 ° C,with their control at 4 ° C, and then sampled periodically. Powder aging is mainly induced by Maillard Reaction during storage,especially at high temperature such as 60 ° C, where the Brownness Index of normal WPI can raise to 106.1, while the one of delactosed WPI only raised to 60.1.It is indicated that 1.3% reduction of lactose content in WPI can limite the progress of Maillard reaction. Meanwhile, a thermal treatment at 80 ° C was implemented on the two stored WPI in solutions for evaluating their heat-induced gelling property, which has been shown decreased with the storage degree augment. Nevertheless, the loss of gelling peripteries in delactosed WPI was much less than that of normal WPI.It has been shown that in the presence of higher lactose content, proteins of WPI powder denatured more rapidly(totally desaturated after 4weeks)with higher protein lactosylation(at last 7 lactose addition)when stored at 40 ° C, while the native protein still exist in delactosed WPI after 12 weeks’ storage,during which aging was contributed mostly by the Maillard reaction.The lactose content had a more significant effect in high temperature storage(60 ° C). These desaturated protein trend to cause polymerization of proteins, it is likely that this alteration was driven by the unfolding of the secondary structure, due to the conversion from α-helix to β-sheet conformation as shown by FTIR interpreted with PCA, CD.And then, the transition of protein polymerization from a soluble aggregate formed by hydrophobic interaction、hydrogen bond、disulfide to insoluble state formed by other covalent bonds after two weeks’ storage in normal WPI, while the aggregate in delactosed WPI stay still soluble when stored for 8 weeks.Diafiltration to produce delactosed WPI in this research project has been shown to control powder aging effectively through improving powder storage stability and increasing shelf-life. Even though there is only 1.3% reduction of lactose content between the two WPI, it still has a significance difference on the aging rate and Maillard reaction limit. The aging patheway and mechanism was investigated at the same time, the aim to decrease the functionality loss in WPI which caused by aging during storage was achieved successfully as well.