Food Protein Films Formed By Enzyme Modification And Its Mechanism

Edible films from biopolymers including polysaccharide and protein have attracted a lot of attention recently, due to increased demands of consumers for both higher quality and longer shelf foods in combination with environmental needs for reduction of disposable packaging amounts. Moreover, protein films have more appeals due to biodegradability, edible and nutritious properties as well as good barrier characteristics against gas, organic vapor and oil, as compared to synthetic films.Transglutaminase (TGase) catalyzes acyl transfer reactions between γ-carboxamide groups of glutaminyl residents of proteins or polypeptides (acyl donors) and primary amines of compounds (acyl acceptors, such as free amino groups as in lysyl side-chains). Mang reports showed that TGase treatment can induced casein (or casein micelles), soy protein as well as gelatin to form gels or films. However, the research of this technique has been limited by the TGase source for many years. The development and industrial production of microbial TGase (MTGase) have made it possible to exploit TGase in food field.So, the development of biodegradable films by TGase has wide and potential application prospect.The influence of TGase treatment on the properties of the cast films from several food proteins including soy protein isolates (SPI-1, SPI-2), sodium caseinate (NaCas-1, NaCas-2), whey protein concentrate (WPC), gelatin (G-1, G-2), wheat gluten (WG) and peanut protein isolate (PPI) were investigated in this dissertation. Main results are as follows:TGase treatment significantly increased (P ≤ 0.05) the TS, E and S₀ values of most of protein films by 13.1%-36.2%, 43.0%-440.5% and 2.4%-216.1%, respectively, and simultaneously significantly decreased the MC, TSM and transparency values. The extent of TGase modification on the properties of cast films was related with the nature of protein. SDS-PAGE analyses showed that TGase treatment decreased the solubility of protein films in water. Scanning electric microscopy (SEM) analyses showed that the TGase-modified films had rougher surfaces as compared to the control, but more homogeneous and compact cross-sections. TGase treatment decreased the in vitro digestibility of TGase-modified films as compared with control films.TGase treatment significantly decreased moisture adsorption rate and balance moisture content of SPI, NaCas and gelatin films. The moisture adsorption rate and sorption isothermdata, were mathematically fitted to Peleg's Equation (M(t) = M₀+t/(k₁+k₂t)) and GAB(Guggenheim-Anderson-de Boer) model, respectively.