Gelation And De-gelation Of Whey Protein Systems

The alkali cold gelation of whey proteins is studied due to its fascinating rheological gelation profiles, as well as to investigate the existence of an alkali dissolution threshold for protein hydrogels with the protein concentration. Alkali cold gelation is achieved by first producing soluble protein aggregates followed by a sudden increase of the pH. At pH>11.6, there is a de-gelation step with time following an initial quick gelation step. The dynamic transition involves only the formation of non-covalent interactions between the initial covalently crosslinked aggregates; first they are formed but later on they are destroyed. This mechanistic hypothesis is verified by adding NaCl, SDS and NEM in addition to alkali. A sharp transition of the system modulus can be achieved due to non-covalent interactions on soluble disulfide crosslinked aggregates in a narrow protein concentration range. For studing the reasons of the huge difference of modulus transition during alkali cold gelation after NEM added, Tryptophan and 8-Anilinonaphthalene-l-sulfonic acid ammonium salt (ANS) fluoremetry and dynamic particle size of soluble aggregates with or without NEM were measured, found that NEM stabled the aggregates and formed more covalent interactions between WPI aggregates. The zeta-potential measurements showed that the aggregates with NEM have high absolute zeta-potential. The particle size of solubilizing gel during the alkali cold-gelation and SDS-PAGE verified that the aggregates with NEM had larger intitial particle size and this change were contributed by convalent interactions.