Biochemical and Rheological Characterization of Peanut Proteins Crosslinked with Microbial Transglutaminase

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Title: Biochemical and Rheological Characterization of Peanut Proteins Crosslinked with Microbial Transglutaminase
Author: Gharst, Gregory A.
Advisors: Tim Sanders, Committee Chair
Abstract: Initially, the rheological behaviors of aqueous peanut flour dispersions were characterized across a range of conditions, including controlled heating and cooling rates under both large and small-strain deformations. Fat content influenced the rheological patterns, as dispersions of higher fat flours were less viscous than lower fat flours. A roast effect was also displayed, especially for dispersions of the higher fat flours in which light roast flours were more viscous than dark roast flours. Dispersions of low fat peanut flours were more viscous than soy at higher temperatures (>75°C). Centrifugal separation revealed that the insoluble material of all dispersions primarily contributed to the observed rheological responses. SDS-PAGE was used to characterize the soluble and insoluble proteins making up the various dispersions. In the second study, we investigated the polymerization of peanut proteins treated with microbial transglutaminase (TGase). TGase is an enzyme that promotes protein crosslinking reactions through an acyl transferase mechanism involving protein-bound glutaminyl residues and primary amines including the -amino group of lysine residues in soy, myosin, gluten, oat globulin, casein and whey. Herein, we report exogenous TGase catalysis of several peanut protein fractions, including purified Ara h 1. SDS-PAGE banding patterns revealed the formation of high molecular weight polymers while catalysis of Ara h 1 resulted in distinct dimer formation. Crosslinking effects were accomplished in the presence and absence of the reducing reagent, dithiothreitol. Ortho-phthaldialdehyde assays (OPA), used to quantify the degree of polymerization, indicated ˜21% and ˜30% protein coupling using either cold hexane extracted peanut protein fractions or lightly roasted peanut flour dispersions, respectively. Rheological measurements established that TGase-modified light roast peanut flour-12% fat exhibited lowered viscosity readings compared to non-treated dispersions. In the third study, light roast-12% fat peanut flour (PF), a high protein ingredient prepared after partial extraction of oil from roasted peanut seed, was polymerized by TGase resulting in modification of functional properties such as viscosity, gelation, solubility, and water holding capacity. These experiments were conducted with either TGase treated or untreated 20% w/w PF dispersions containing 0.5% or 1.0% w/w amidated pectin (AP). Gelation occurred at higher temperatures (˜78°C) using PF dispersions treated with TGase compared to dispersions devoid of enzyme (˜68°C). The addition of 0.5% AP to PF dispersions minimized shifts in gel point temperature and increased the apparent viscosity of all samples, especially those treated with TGase. High molecular weight polymers were formed in TGase treated PF dispersions both in the presence and absence of AP; however, polymer formation was more rapid in PF dispersions without AP. OPA data indicated ˜40% protein coupling in PF dispersions treated with TGase compared to ˜20% in those containing both AP and TGase. In the final study, light roast-12% fat peanut flour (PF) is a high protein food ingredient. Recently, we observed that TGase crosslinked peanut proteins and changed the functional characteristics of the final product. Polymer formation was observed in TGase treated PF-casein (CN) dispersions and occurred more rapidly with increasing concentrations of CN. Upon heating, the gelation temperature of all TGase-treated PF-CN dispersions increased. Moreover, the viscosity and yield stress of TGase treated PF-CN dispersions were less than in non-TGase treated controls. TGase treated PF + 5% CN dispersions increased in water holding capacity after 24 hr incubation at 37°C. Casein proved to be an effective co-substrate with PF, and enzymatic processing changed several rheological characteristics including gelation temperature, viscosity, yield stress, and WHC. Collectively, these data suggest the potential use of PF-PF, PF-AP, and PF-CN polymers in high protein peanut-based food products.
Date: 2007-06-20
Degree: PhD
Discipline: Food Science

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