Perry K.W. Ng

Natural Biopolymer-Based Nanocomposite Films for Packaging Applications

Concerns on environmental waste problems caused by non-biodegradable petrochemical-based plastic packaging materials as well as the consumers demand for high quality food products has caused an increasing interest in developing biodegradable packaging materials using annually renewable natural biopolymers such as polysaccharides and proteins. Inherent shortcomings of natural polymer-based packaging materials such as low mechanical properties and low water resistance can be recovered by applying a nanocomposite technology. Polymer nanocomposites, especially natural biopolymer-layered silicate nanocomposites, exhibit markedly improved packaging properties due to their nanometer size dispersion. These improvements include increased modulus and strength, decreased gas permeability, and increased water resistance. Additionally, biologically active ingredients can be added to impart the desired functional properties to the resulting packaging materials. Consequently, natural biopolymer-based nanocomposite packaging materials with bio-functional properties have a huge potential for application in the active food packaging industry. In this review, recent advances in the preparation of natural biopolymer-based films and their nanocomposites, and their potential use in packaging applications are addressed.

The beneficial plant growth-promoting association of Rhizobium leguminosarum bv. trifolii with rice roots

his paper summarizes a multinational collaborative project to search for natural, intimate associations between rhizobia and rice (Oryza sativa L.), assess their impact on plant growth, and exploit those combinations that can enhance grain yield with less dependence on inputs of nitrogen (N) fertilizer. Diverse, indigenous populations of Rhizobium leguminosarum bv. trifolii (the clover root-nodule endosymbiont) intimately colonize rice roots in the Egyptian Nile delta where this cereal has been rotated successfully with berseem clover (Trifolium alexandrinum L.) since antiquity. Laboratory and greenhouse studies have shown with certain rhizobial strain-rice variety combinations that the association promotes root and shoot growth thereby significantly improving seedling vigour that carries over to significant increases in grain yield at maturity. Three field inoculation trials in the Nile delta indicated that a few strain-variety combinations significantly increased rice grain yield, agronomic fertilizer N-use efficiency and harvest index. The benefits of this association leading to greater production of vegetative and reproductive biomass more likely involve rhizobial modulation of the plants root architecture for more efficient acquisition of certain soil nutrients [e.g. N, phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), zinc (Zn), sodium (Na) and molybdenum (Mo)] rather than biological N 2 fixation.

Characterization of storage proteins in different soybean varieties and their relationship to tofu yield and texture

Abstract The contribution of the total soybean proteins, the storage proteins [glycinin (11S) and β-conglycinin (7S) fractions] and their respective subunits to tofu yield and texture was studied. Protein contents were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) coupled with densitometry and reversed phase-high performance liquid chromatography (RP-HPLC), for seven soybean varieties, and correlated to tofu yield and texture. Results from SDS-PAGE, coupled with densitometry, showed that the 11S fraction proteins ( r =0.863, P r =0.917, P r =0.775, P r =−0.832, P

Effects of Selected Process Parameters on Expansion and Mechanical Properties of Wheat Flour and Whole Cornmeal Extrudates

Mechanical properties of cereal extrudates are recognized by consumers as quality criteria. These properties are affected by process variables. The effect of process variables, such as water injection rate, barrel temperature, and screw speed on the expansion and selected mechanical properties of wheat flour and whole cornmeal extrudates was determined. A laboratory-scale twin-screw extruder with an L/D ratio of 25.0 was used. The cross-sectional expansion, the specific length, and the elastic moduli and breaking strength in bending and compression were measured. Water injection rate and barrel temperature significantly affected the cross-sectional expansion index (SEI) (P < 0.01), specific length (P < 0.01), elastic modulus in compression (P < 0.05), and breaking strength in bending (P < 0.05). The SEI was increased with a decrease in water injection rate and/or an increase in barrel temperature. The elastic modulus and breaking strength in bending decreased with the decrease in water injection rate. The SME input, which was dependent on the process variables tested, also influenced the expansion and mechanical properties of extrudates. The higher the SME input was, the lower the elastic moduli and breaking strength were. This result confirmed that the texture of extruded product was controlled by changing the SME input.

Rheological behavior of undeveloped and developed wheat dough

ABSTRACT Undeveloped wheat dough is essentially wheat flour that has become fully hydrated without being deformed. The rheological properties of this material were compared to dough (developed dough) made using the standard method involving a farinograph. Flow behavior of undeveloped and developed dough samples made from hard and soft wheat flours were tested using creep tests, frequency sweep oscillatory tests, and temperature sweep oscillatory tests. All experiments showed that the undeveloped dough requires less resistance for deformation than developed dough. The differences are due to the energy input received by the developed dough and the influence of this factor in forming the protein matrix associated with developed dough. To attain a comparable state as the dough made in the farinograph, an energy input must be applied to the undeveloped dough material. Understanding the differences between undeveloped and developed dough may lead to new products, equipment, and processes in the bakery industry.

Effects of industrial pasta drying temperatures on starch properties and pasta quality

Abstract Effects of industrial pasta drying temperatures on various starch properties and the quality of pasta were investigated. A short cut pasta (fusilli) was processed from durum semolina and dried by high temperature (HT) and very high temperature (VHT) drying cycles. Starch properties were examined by Rapid Visco Analyzer, differential scanning calorimeter, X-ray diffractometer and polarized light microscope. Cooking quality was evaluated by determining cooking loss (CL) into cooking water, total organic matter (TOM) in washing water after cooking, and sensory evaluation. The X-ray diffractograms of semolina samples showed typical A-type diffraction patterns. The diffractograms of pasta products using HT and VHT drying were similar. However, an additional small peak appeared at about 2θ=20° for both drying cycles, indicating the formation of a V-type X-ray diffraction pattern. All starch granules of semolina displayed a clear “Maltese cross” under polarized light, but approximately 20% of starch granules of HT- and VHT-dried pasta samples either partially or completely lost their birefringence. Starch from VHT-dried pasta had greater RVA peak viscosity and breakdown viscosity than HT-dried pasta. Both gelatinization enthalpy and peak temperature of HT-dried pasta were significantly lower than those of VHT-dried pasta. The HT-dried pasta had lower quality scores based on TOM and CL values and sensory evaluation as compared with the VHT-dried pasta. The present study indicated that the changes in starch during HT and VHT drying may affect the pasta cooking quality.

Effect of extrusion cooking on the physicochemical properties, resistant starch, phenolic content and antioxidant capacities of green banana flour

Green banana flour was extruded through a co-rotating twin-screw extruder with constant barrel temperature. The objectives of this study were to determine the effect of extrusion cooking variables (feed moisture, FM, 20% and 50%; screw speed, SS, 200 and 400rpm) and storing of the extruded flours at 4°C for 24h on the physicochemical properties, resistant starch (RS), pasting properties and antioxidant capacities. Extrusion cooking at higher FM and lower SS increased the amylose content, which was expressed in highest RS content. Water adsorption index (WAI) and pasting properties were increased, while water solubility index (WSI), total phenolic content (TPC) and antioxidant activities (FRAP, ABTS(+), DPPH) in free and bound phenolics were decreased compared to the other extruded samples. Storing the extruded flours at 4°C for 24h prior to oven drying was the main factor leading to a further increase in the content of amylose, RS, TPC and WSI values, as well as pasting properties - in particular peak viscosity. Compared to native banana flour, extrusion cooking caused significant changes in all studied properties of the extruded flours, except for soluble DF and antioxidant capacity (ABTS(+) and DPPH) of bound phenolics.

Relationship Between Rheological Properties and Microstructural Characteristics of Nondeveloped, Partially Developed, and Developed Doughs

ABSTRACT Farinography and mixography are two commonly used procedures for evaluating dough properties. These procedures, however, cannot separate hydration and energy input during dough development, both of which are critically important for understanding fundamental rheological properties of dough. A rheometer and laser scanning confocal microscopy (LSCM) were used to study the relationship between rheological properties and microstructural characteristics of developed (by farinograph with both shear and extensional deformations), of partially developed (by rheometer with either shear or extensional deformation), and of nondeveloped (no deformation) dough samples of wheat flours. Rheological data revealed that developed dough had the highest G* (most elastic or strong), followed by doughs partially developed with extensional deformation, and then shear deformation, and finally by nondeveloped dough. The LSCM z-sectioning (scanning of different layers of the sample) and the analysis of amount of protein m...

Effects of Transglutaminase Enzyme on Fundamental Rheological Properties of Sound and Bug-Damaged Wheat Flour Doughs

ABSTRACT Transglutaminase (TG) catalyzes the formation of nondisulfide covalent crosslinks between peptide-bound glutaminyl residues and e-amino groups of lysine residues in proteins. Crosslinks among wheat gluten proteins by TG are of particular interest because of their high glutamine content. Depolymerization of wheat gluten proteins by proteolytic enzymes associated with bug damage causes rapid deterioration of dough properties and bread quality. The aim of the present study was to investigate the possibility of using TG to regain gluten strength adversely affected by wheat bug proteases. A heavily bug-damaged (Eurygaster spp.) wheat flour was blended with sound cv. Augusta or cv. Sharpshooter flours. Dynamic rheological measurements, involving a frequency sweep at a fixed shear stress, were performed after 0, 30, and 60 min of incubation on doughs made from sound or blended flour samples. The complex moduli (G* values) of Augusta and Sharpshooter doughs blended with 10% bug-damaged flour decreased si...

Effects of extrusion on dietary fiber and isoflavone contents of wheat extrudates enriched with wet okara.

ABSTRACT Okara is the residue left after soymilk or tofu production. In North America, okara is used either as animal feed, fertilizer, or landfill. The purpose of this study was to use wet okara to produce and enrich extruded cereal products and to study the effects of extrusion on the dietary fiber and isoflavone contents. Wet okara was combined with soft wheat flour to produce two different formulations (33.3 and 40% okara) and extruded using four combinations of two screw configurations and two temperature profiles. Various physicochemical properties, dietary fiber by enzymatic-gravimetric method, and isoflavone content by HPLC were analyzed. The radial expansion ratio decreased as fiber content increased. On the other hand, both bulk density and breaking strength increased as fiber content increased. Combining okara with soft wheat flour resulted in increased protein, dietary fiber, and isoflavone contents compared with soft wheat flour alone. Extrusion of the formulations resulted in decreased insol...