Studies On The Enzymatic Modification, Application And Gelation Mechanism Of Wheat Gluten

In this paper, the effect on rheological behavior of wheat gluten by the combined treatment of partial hydrolysis protease and subsequent microbial transglutaminase (TGase) cross-linking were studied; Changes in the structure of wheat gluten were analyzed to clarify the mechanism of how the combined treatment of alcalase-based partial hydrolysis and TGase cross-linking affect the properties of wheat gluten; Subsequently, effect on the boiling resistance capacity of pork meatballs by adding the modified wheat gluten were studied. In addition, changes in the chemical interactions and protein conformation in the process of heat-induced wheat gluten gels formation were studied. The main conclusions were as follows:Wheat gluten were partial hydrolyzed by Trypsin, Alcalase and Neutrase-based, respectively. The effect of partial hydrolysis and TGase cross-linking composite modification on wheat gluten rheological behavior were studied. Results showed that the storage modulus (Gf) of the composite modified wheat gluten increased by 31.7%, 58.2%, and 19.6%, respectively, compared with TGase modified wheat gluten.The effect of combining treatment by Alcalase-based partial hydrolysis and TGase cross-linking on the structure of wheat gluten were studied. Restults showed that the wheat gluten thermal denaturation temperature (Tg) was significantly increased from 54.43 to 57.69℃, combined action of partial hydrolysis degree (DH) 0.187% and cross-linking, suggesting the modified wheat gluten had a more stable structure. SDS-PAGE profiles revealed that polymers of wheat gluten were formed when treated by combination of Alcalase-based partial hydrolysis and TGase cross-linking, while excessive hydrolysis resulted in high-molecular-weight subunits degrading to smaller petides (< 31kDa). The analysis of free SH and surface hydrophobicity suggested that an appropriate degree of hydrolysis allowed wheat gluten structure to unfold and expose more sites for TGase cross-linking. The secondary structure analysis showed hydrolysis of 0.187% led to a reduction in a-helix and β-turn contents, and an increase in β-sheet and random coil contents. In addition, the a-helix to p-sheet ratio decreased from 0.608 to 0.522, which suggested that a more flexible wheat gluten structure was formed after the hydrolysis. SEM images revealed that hydrolysis at an appropriate degree made it suitable for TGase cross-linking wheat gluten to form a 3D network.Efects of modified wheat gluten (MWG) on boiling resistance capacity of pork meatballs were investigated. Results revealed that the addition of MWG effectively decreased the cooking loss rate by 49.16%, and increased the rate of yield and water holding capacity of pork meatballs by 15.48% and 18.27%, respectively, when treated at a high temperature for a long period of time (100℃,30 min); In addition, meatballs textural properties, such as the hardness, springiness, and chewiness, were significantly increased by 97.05%,6.68%, and 121.96%, respectively. The results showed that MWG had a better capacity on improving boiling resistance capacity. Rheological behavior and SDS-PAGE analysis indicated that MWG might interact with myofibrillar proteins, resulting in the formation of a more stable and compact gel network, which could, in turn, improve the cooking characteristics and textural properties of meatballs. The addition of vegetable proteins resulted in a reduction in free water content and an increase in bound water content, which led to a major improvement in water holding capacity.The formation of wheat gluten gels was attribuated to the interactions between proteins, which included covalent interactions (such as disulfide bonds) and non-covalent interactions (such as ionic bonds, hydrogen bonds, and hydrophobic interactions). Rheological behavior, SDS-PAGE, UV spectroscopy, and FTIR measurements suggested that wheat gluten unfolded during heat treatment; subsequently unfolded protein chains aggregated via disulfide bonds and hydrophobic interactions, and the aggregates agglomerated into a three-dimensional network. The major change in the secondary structure during gelation was a significant transition towards a β-sheet-like structure. The proportion of intermolecular β-sheets due to protein aggregation increased by 16.22% in the process of wheat gluten gelation at 90℃. In brief, thermal unfolding and aggregation were the two essential processes involved in wheat gluten gelation. During heating, wheat gluten unfolded, and the hydrophobic regions and free SH groups exposed. When the gelation temperature was higher than 60℃, a crosslinking reaction among the wheat gluten molecules occurred with increased heating temperatures; the G’value of wheat gluten gel continuously increased during the cooling process, which might be attributed to the formation of new disulfide bonds or hydrogen bonds.