Jeffrey A. Byars

Chemistry and Physical Properties of Melt-Processed and Solution-Cross-Linked Corn Zein

Corn zein was cross-linked with glutaraldehyde (GDA) using glacial acetic acid (HAc) as catalyst. The objectives are to evaluate the swelling characteristics of GDA cross-linked zein gels in water, ethanol, and their combinations. Similar formulations, upon solvent evaporation, form films. The mechanical properties of the films are compared to compression molded tensile bars from GDA melt-processed zein as a second objective. Chemistry of the cross-linking reaction was based on the aldehyde binding characteristics defined by use of fluorescence spectroscopy; sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) to demonstrate the cross-linking reaction; FTIR to observe absorption differences of the cross-linked product; differential scanning calorimetry, dynamic mechanical analysis and thermogravimetric analysis to assess thermal properties; and the use of Instron Universal Testing Machine to evaluate mechanical properties. A reaction mechanism for acid catalyzed GDA cross-linking of zein is proposed. Thermal and mechanical properties of tensile bars cut from either film or formed by compression molding were similar, where both showed increased tensile strengths, ductility and stiffness when compared with unmodified controls. Samples that were reacted with 8% GDA by weight based on weight of zein from either process retained their integrity when tensile bars from each were subjected to boiling water for 10 min or soaking in either water or HAc for 24 h. The melt-processed, cross-linked zein is a more environmentally friendly method that would eliminate the need for HAc recovery.

Jet cooking of waxy maize starch: Solution rheology and molecular weight degradation of amylopectin

ABSTRACT The effect of processing conditions in an excess steam jet cooker on the degradation of waxy maize starch was studied. The temperature of the steam, the flow rate of the starch slurry, and the concentration of starch were determined to influence the extent of degradation. The viscosity of concentrated solutions of the jet-cooked product and the intrinsic viscosity of dilute solutions were used as measures of the extent of molecular degradation. The viscosity decreased at higher reaction temperatures, and at higher team-to-starch ratios. Multiple passes through the jet cooker decreased the viscosity dramatically for the first two passes, but little additional change was observed for further passes. The results show that mechanical and thermal degradation effects are both important in the jet cooking of waxy maize starch, although the primary effect is due to mechanical degradation.

Preparation of starch-stabilized silver nanoparticles from amylose–sodium palmitate inclusion complexes

Starch-stabilized silver nanoparticles (AgNP) were prepared from amylose-sodium palmitate helical inclusion complexes by first converting sodium palmitate within the amylose helix to silver palmitate by an ion-exchange reaction with silver nitrate, and then reducing the complexed silver palmitate salt with NaBH(4). This process yielded stable aqueous solutions that could be dried and then re-dispersed in water for end-use applications. Reaction products were characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), UV-VIS spectroscopy, X-ray diffraction, TEM, SEM and light microscopy. Addition of acid to reduce the pH of aqueous starch-AgNP solutions produced an increase in viscosity, and nearly quantitative precipitation of starch-AgNP was observed at low pH. Smaller AgNP and higher conversions of silver nitrate to water-soluble starch-AgNP were obtained in this process, as compared with a process carried out under similar conditions using a commercial soluble starch as a stabilizer.

Rheological characterization of solutions and thin films made from amylose-hexadecylammonium chloride inclusion complexes and polyvinyl alcohol

The rheological properties of aqueous solutions and films made from blends of polyvinyl alcohol (PVOH) and amylose-hexadecylammonium chloride inclusion complexes (Hex-Am) were investigated to better understand the polymer interactions and processing parameters. Aqueous solutions of Hex-Am displayed non-Newtonian shear thinning characteristics, becoming highly viscous at 4.2% solids and forming a strong mechanical gel at 10% solids. Cationic Hex-Am was observed to have dramatically different rheological temperature response profiles from anionic amylose-sodium palmitate inclusion complexes, displaying a precipitous increase in viscosity upon cooling from 95°C to 50°C. Aqueous solution blends of 1:1 PVOH/Hex-Am lack this precipitous increase in viscosity, indicating that PVOH reduces amylose-chain entanglement. Films cast from varying blends of Hex-Am and PVOH were thermostable to 200°C, and displayed decreasing storage modulus with increasing concentrations of PVOH in film blends. Films cast from Hex-Am/PVOH absorb water vapor at lower rates than their constitutive polymers.

The effect of cooling conditions on jet-cooked normal corn starch dispersions

When aqueous dispersions of normal corn starch are jet-cooked under excess steam conditions, the properties of the final product depend on the manner in which the cooked dispersion is cooled. Phase separation of amylose and amylopectin dramatically alters the final properties, and the extent of phase separation depends on the processing history of the sample. The aim of this study was to determine the effects of cooling rate, stirring rate and starch concentration on the rheology and microstructure of the cooled dispersion. A Rapid Visco Analyser was used to obtain a range of cooling profiles and stirring rates. Rheological measurements showed that samples that were stirred during cooling formed stronger gels than unstirred samples. Light microscopy revealed that after cooling, both irregular, amorphous particles and spherical or toroidal crystalline particles were observed in various proportions depending on starch concentration, cooling rate and stirring during cooling.

Jet-Cooked High Amylose Corn Starch and Shortening Composites for Use in Cake Icings

Butter cream is an all-purpose icing that is used to both ice and decorate cakes. Cream icings contain up to 40% shortening. As consumers become aware of the need to reduce fat in their diet, the demand for healthy, flavorful, and low-fat food increases. High-amylose corn starch was cooked in an excess-steam jet cooker in the presence of oleic acid. Amylose formed helical inclusion complexes with the fatty acid. Shortening was added at different levels to jet-cooked starch. The resulting starch-lipid composites (SLC) had 0%, 8%, 16%, and 24% fat. The composites were used to substitute shortening in the preparation of cake icings with 1% to 13% fat. SLC icings were formulated by either keeping the total solids constant, or the starch and sugar to water ratio constant as the fat level was reduced. The effect of fat and formulation of shortening and SLC icings on the physical and rheological characteristics were studied. It was found that low-fat SLC icings can be prepared by optimizing the formulation. Practical Application:  This study indicates potential new applications for SLC that benefit the confectionary industry by generating new products offering healthy alternatives to the consumers.

Effect of amylopectin on the rheological properties of aqueous dispersions of starch–sodium palmitate complexes

Aqueous dispersions of normal and high-amylose corn starch were steam jet cooked and blended with aqueous solutions of sodium palmitate to give starch containing amylose-sodium palmitate inclusion complexes. Partial conversion of complexed sodium palmitate to palmitic acid by addition of acetic acid led to the formation of gels. Blends of inclusion complexes prepared from normal and high-amylose corn starch were used to vary the amylose:amylopectin ratio of the gels, and the linear viscoelastic moduli were found to decrease with decreasing amylose:amylopectin ratio. Precipitation of the complexed starch at low pH showed that most of the amylopectin was not part of the gel network. The elastic modulus of the gels was shown to decrease sharply between 74 and 85 °C, and the transition temperature increased strongly with decreasing amylose:amylopectin ratio.

Constitutive modeling of β-glucan/amylodextrin blends

Abstract Accurate constitutive equations are required for the understanding of many food processes. The purpose of this work was to test the ability of constitutive equations to model the rheological behavior of β-glucan/amylodextrin blends in a range of flows. The predictions of the K-BKZ, Giesekus, Phan-Thien–Tanner and Bird–Carreau models were compared to experimental results in steady shear, startup of steady shear, stress relaxation and biaxial extension flows. The K-BKZ model yielded the most accurate predictions across the range of flows. The Giesekus and Phan-Thien–Tanner models gave good results in shear flows, but failed to predict the correct strain dependence in stress relaxation. The Bird–Carreau model did not capture many features of the flow behavior. The results indicate the need to test thoroughly constitutive equations before using them to model food processes.

Physical, Rheological, Functional, and Film Properties of a Novel Emulsifier: Frost Grape Polysaccharide from Vitis riparia Michx

A novel emulsifier, Frost grape polysaccharide (FGP), isolated from natural exudate of the species Vitis riparia Michx, was physically and rheologically characterized. The determination of the physical, structural, thermodynamic, emulsification, film, and rheological properties of FGP provide essential details for the commercial adoption of this novel plant polysaccharide. FGP is capable of producing exceptionally stable emulsions when compared with the industrially ubiquitous gum arabic (GA). The FGP isolate contained a negligible amount of nitrogen (0.03%), indicating that it does not contain an associated glycoprotein, unlike GA. Solutions of FGP have a high degree of thermostability, displaying no loss in viscosity with temperature cycling and no thermal degradation when held at 90 °C. FGP is an excellent film former, producing high tensile strength films which remain intact at temperatures up to 200 °C. This work identified a number of potential food and pharmaceutical applications where FGP is significantly superior to GA.

Rheological Studies on the Reaction of Zein with Polyethylenemaleic Anhydride

There continues to be interest in developing solvent-resistant articles from biobased renewable materials to successfully compete with petrochemical products. It was previously shown that reaction of zein with polyethylenemaleic anhydride (PEMA) provides articles that are solvent resistant. The gelation kinetics for the reaction of PEMA with zein was investigated rheologically to better understand this chemistry. The reaction of the nucleophilic groups on zein with the anhydrides on PEMA is the main cause for the gelation reaction. The gelation time was defined as being the point when the elastic modulus (G′) and viscous modulus (G″) cross. In this work, the rate of reaction, in terms of time to gelation, was studied in N,N-dimethylformamide solution for which the amount of PEMA, the reaction temperature, and the overall reaction concentration were varied. Exponential relationships were found between the gelation time and % PEMA, temperature, and % solids, as well as between elastic modulus with either % ...