Rheological and Ultrastructural Properties and Particle Size Distribution of Soymilk as Affected by Processing Methods

Soymilk was prepared from boiled and unboiled comminuted suspensions of dehulled soybean and water using pressurized homogenization (one pass and two pass). Particle size showed significant differences between soymilks homogenized by one pass and two pass. Apparent viscosities and total solid contents showed significant differences between boiled and unboiled treatments. Soymilks exhibited pseudoplastic and thixotropic behavior and Arrhenius model was fitted to express temperature dependence of apparent viscosity. Microscopic images showed hydrated, separated, uniformly distributed, and homogeneous particles in boiled two-pass soymilk as they were disrupted easily and it was selected as the best treatment for processing soymilk containing all of the soybean solids.     

Particle Size Distribution in Tomato Concentrate and Effects on Rheological Properties

The particle size distribution of a tomato concentrate was determined by wet sieving. Wet sieve fractions were then investigated by microscopy and a method based on laser diffraction. Both methods showed that the size of many particles was considerably larger (up to two to three times) than the diameter of the pores through which they have passed during wet sieving. This was explained by the deformability of the tomato cell wall. Effects of particle size distribution on rheological properties were studied by standardizing wet sieve fractions (dry matter, pH). Highest values for yield stress and apparent viscosity were found for the 90–125 and 125–180 μm wet sieve fractions.     

Intrinsic Viscosity of Tomato Serum as Affected by Methods of Determination and Methods of Processing Concentrates

Magnitudes of intrinsic viscosity of tomato serum determined from the slopes of three equations were not identical, but they showed common trends. Intrinsic viscosities of serums from concentrates obtained by evaporation of juice were lower than those obtained by evaporation of serum and reverse osmosis concentration of serum. Their magnitudes also were lower for serums from diluted and sheared concentrates.     

Effect of Tomato Paste on Rheological Properties and Particle Size Distribution of Model Oil-in-Water Emulsions

The role of tomato paste in stabilizing model o/w salad dressing formulations pre-stabilized with xanthan and propylene glycol alginate was studied at levels of tomato paste ranging from 3 to 12% using creep measurements, steady shear measurements and particle size measurements. The addition of tomato paste shifted the particle size distribution to lower values; this distribution was a function of aging time. Creep and steady shear measurements showed an increase in rheological parameters and an increase in viscosity, respectively, suggesting that at higher or equal levels of 6% tomato paste the stability of the o/w emulsion was enhanced significantly.     

Foaming Properties of Proteins as Affected by Concentration

Commercial sodium caseinate and whey protein isolate were evaluated at protein concentrations 0.25 to 16% with ovalbumin solutions as reference. Logarithmic models were developed to express the effect of protein concentration on foam expansion and serum drainage. The kinetics of gas release from milk protein-stabilized foams followed a three-phase pattern. Low foam collapse rates were observed in initial and final phases while rapid collapse occurred during the transition phase. No transition was observed for ovalbumin-stabilized foams. Globally, foam collapse rate increased with increasing protein concentration. Apparent viscosity of protein-stabilized foams increased with concentration to a maximum; beyond which, a reverse trend was observed. Maximum viscosities of milk protein foams were at concentrations & lt;0.5%, while ovalbumin foams showed maximum viscosity around 2% protein.     

Effect of Wheat Bran Particle Size on Dough Rheological Properties

Commercial hard red spring, hard red winter, soft white and durum wheat brans were used to investigate the effect of wheat bran particle size on the rheological properties of doughs. Wheat brans were first coarsely ground and passed through a bran finisher to remove additional endosperm and aleurone layers. These processes increased total dietary fibre content and decreased starch content of the wheat bran samples. Three particle size distributions, for each wheat bran class, were obtained by further grinding (not by sifting) of the bran samples by different experimental mills. Coarse bran can retain significantly more water than medium or fine bran as measured by a centrifuge method, but bran particle size had no significant effect on dough water absorption. Addition of wheat bran into bread dough systems increased dough water absorption rate, reduced mixing time and decreased dough mixing tolerance as measured by farinograph. Fine particle size wheat bran decreased dough mixing tolerance and reduced mixing time compared to coarse bran. Dough containing fine particle size bran exhibited more strength than dough containing coarse bran after a 180-min rest period as measured by the extensigraph. © 1997 SCI.     

Determination of Rheological Behavior of Tomato Concentrates Using Back Extrusion

The back extrusion testing technique can be a very useful tool in assessing the rheological behavior of non-Newtonian fluids (e.g. tomato concentrates). In this procedure, an Instron Model 1122 Universal Testing Machine (with stainless steel, solid rod attachment) was used to measure the forces developed as diluted tomato paste was back extruded in a simple piston/annular cylinder geometry. Assuming power law behavior, the force-distance data for extrusions at different piston velocities were analyzed to yield the dimensionless flow behavior index (n) and the consistency coefficient (k) for each sample. Back extrusion measurements were performed on hot break and cold break tomato concentrates with different % total solids. For comparison, rheological measurements were also done on a set of samples with a Carri-Med Controlled Stress Rheometer.     

Hydrophilic and Rheological Properties of Brewer's Yeast Protein Concentrates

Protein solubility (PS), water-holding capacity (WHC), viscosity and gelling properties were studied in brewer's yeast protein concentrates prepared by 3 procedures: isoeletric precipitation of protein (I-PC), extraction with 0.5M NaClO₄(P-PC) or with 3% sodium trimetaphosphate (TMP-PC). PS was higher for TMP-PC and lower for P-PC at pH 4 to 12. WHC increased with increasing pH in all concentrates, but was higher for TMP-PC. The presence of NaCl (0.1 M and 1.0M) reduced to 50% the WHC of TMP-PC. Gelling properties of a 10% protein dispersion were studied in the TMP-PC preparation. Hardness and fracturability of the gel (TA-XT2 texturometer) was 35 and 31 gf, respectively. Apparent viscosity of a 3% dispersion at pH 7.0 was lower for I-PC and higher but similar for TMP-PC and P-PC. All concentrates showed pseudoplastic rheological behavior.     

Rheological Properties of Chymosin-Induced Skim Milk Gels as Affected by Milk Storage Time and Temperature

Fundamental dynamic rheological tests were used to measure the rigidity (|G*|) and viscoelasticity (tan δ) of gels made from skim milk samples that were (1) never cooled, (2) stored at 4°C, or 3) stored at 4°C and then rewarmed to 25°C. Milk cooled and held at 4°C prior to gel formation produced gels with lower |G*| and higher tan(δ) than fresh milk gels. Chilled milk samples that were rewarmed to 25°C for 16h prior to gel formation produced gels with rheological properties similar to fresh milk gels. The solubilization of β-casein during cold storage was hypothesized to be the cause of observed differences in gel rheology.     

Foaming and Emulsifying Properties of Whey Protein Concentrates As Affected by Lipid Composition

Freeze-dried WPC, containing 35 and 75% protein were manufactured by pretreating whey with calcium chloride and heat. These and commercial WPC were subjected to proximate analysis and lipid classes, phospholipid classes, free fatty acids (FFA), and monoacylglycerols (MAG) composition were determined. Solubility, thermal, foaming, and emulsifying properties of the WPC were studied. Pretreatment increased calcium and phosphorus contents and decreased the contents of all other minerals. The pretreatment had no effect on solubility, denaturation enthalpy, and onset temperature of denaturation of WPC. These values were comparable to those of commercial WPC. Foaming capacity and emulsion stability were unaffected, but foam stability increased and emulsifying capacity decreased due to pretreatment. Overall, total lipids and lipid class contents of experimental WPC were too low to affect surface properties of WPC.     

Rheological Properties and Microstructure of Acid Milk Gels as Affected by Fat Content and Heat Treatment

Gels were made from recombined milks containing 0, 1.5 or 3.5% fat that were heated at 75, 80 or 90°C for 30 min, followed by acidification with glucono-8-lactone at 30°C. The rheological and microstructural properties of acid gels were investigated using dynamic low-amplitude oscillatory rheology and confocal scanning laser microscopy (CSLM). Heating milks, at temperatures ≥80°C, increased the storage moduli (G′) and decreased the gelation time. Recombined milks containing high fat (3.5%) had higher G′ than gels made from low-fat or skim milk. Milk heat treatment resulted in gels with a cross-linked microstructure. Recombined fat globules appeared to be embedded in the protein matrix.     

Thermal Aggregation and Dynamic Rheological Properties of Pacific Whiting and Cod Myosins as Affected by Heating Rate

Thermal aggregation of cod myosin and Pacific whiting myosin were compared at different heating rates. Turbidity of Pacific whiting started to increase at 30°C and decreased at >50°C, and fluorescence intensity of ANS-myosin of both species was greater at slower heating rates at 20–80°C. Storage modulus (G′) of cod myosin gradually increased as temperature increased resulting in more elastic gel at slower heating rates. G′ of whiting myosin rapidly increased at 30°C, maximized at 45–48°C and decreased afterward. The onset temperature of a decreased G′ shifted from 45°C to 49°C as heating rate increased from 0.5 to 2°C/min. Whiting myosin heated at 2°C/min retained more myosin heavy chain.     

Particle Size of Water Insoluble Tomato Solids Measured by Laser Instrumentation

Particle size distributions of tomato paste and catsup water insoluble solids (WIS) were measured using an instrument based on laser light-scattering principles. Materials and procedures employed are described and examples of WIS size distributions and surface areas are shown.     

Rheological Relationships Between Surimi Sol and Gel as Affected by Ingredients

Rheological properties of surimi sol showed that consistency index (K) was surimi concentration-dependent, as it decreased with increased level of ingredients except for carrageenan which increased K value. The flow behavior index and textural properties appeared to be a function of type and level of ingredients. Unlike starch and synergistic carrageenan, egg albumin, oil and i-carrageenan did not show a composite reinforcing effect. K values measured by rotational cylindrical spindle viscometry more closely correlated with textural properties (r = 0.87 for compressive force; r = 0.87 for shear force) than did other viscometries studied.     

In Situ Particle Size Reduction of Alfalfa and Timothy Hay as Influenced by Form and Particle Size

Our objectives were to characterize particle size reduction of alfalfa and timothy hay by in situ incubation. Alfalfa and timothy hay were chopped at .64-cm theoretical length of cut. Subsamples were dry sieved through a 3.2-mm screen, yielding particles > 3.2 and < 3.2 mm, and another subsample ground (5.0 mm). Each forage treatment was placed in polyester bags and ruminally incubated for up to 100 h. Original and residues were wet sieved. Change in geometric mean diameter (initial to lowest) with time for both forages was less as particle size decreased from chopped to ground; however, percent change was similar between chopped and ground and between sieved > 3.2 and < 3.2 mm. Regression of geometric mean diameter on time for alfalfa exhibited quadratic relationships for all particle categories. For timothy, ground and sieved > 3.2 mm exhibited linear, whereas chopped and sieved < 3.2 mm exhibited quadratic relationships with time. Large particle fractions for both forages were reduced proportionately more than particle fractions that were small initially. Particle size distribution showed particles > 1.18 mm accounted for 63.0 to 98.4% of the initial DM, which was reduced to 14.9 to 24.1% by 100 h. Microbial fermentation and detrition associated with ruminal movements appear to contribute substantially to particle breakdown.     

Rheological,Textural and Flavour Properties of Yellow Mustard Sauce as Affected by Modified Starch,Xanthan and Guar Gum

Influence of a modified starch-gum thickening system on the rheological, textural and flavour properties of yellow mustard sauce was studied. The rheological measurements indicated that the sauces exhibited a weak gel-like, strong shear thinning behaviour. Dynamic viscoelasticity measurements showed that the sauces with modified starch (MS) and xanthan gum (XG) presented superior viscoelastic properties to those with MS and guar gum (GG) samples. All tested sauces showed non-Newtonian, pseudoplastic and thixotropic fluids characteristics. Parameters such as hardness, springiness, cohesiveness, gumminess and spreadability were used to evaluate the textural properties, and the results indicated that MS/XG was more influential than MS/GG on the textural properties. Sensory analysis suggested that 0.4 % MS/0.3 % XG, 0.4 % MS/0.4 % XG and 0.4 % MS/0.4 % GG were superior thickeners for the yellow mustard sauces. The flavours of these three sample groups with the highest sensory scores and a sample with only MS were analysed by an electronic nose, which showed that the electronic nose was able to distinguish their differences.     

Flow Properties of Tomato Concentrates: Effect of Serum Viscosity and Pulp Content

Shear rate-shear stress data were obtained on tomato serum samples at 5.6, 10, 15, and 20° Brix, and on 28 concentrates prepared from the serum samples and containing different amounts of pulp: +30%, +20%, +10%, normal, ?10%, ?20%, and ?30%. Serum samples were Newtonian fluids while concentrates were shear-thinning non-Newtonian fluids. Apparent viscosities of concentrates increased linearly with pulp content expressed as weight %, volume %, or the weight ratio of pulp to serum. Apparent viscosity of the concentrates (η₁₀₀ conc) was related to the viscosity of serum (η serum) and pulp content (P) by the expression: η₁₀₀ cone =η serum + A * P ** B. The contribution of pulp content to η₁₀₀ cone was much more than that of serum. η serum was well correlated with pectin content by the expression: η serum = A₁+ B₁ (Pectin) ** C₁.     

Activity and Mobility of Water in Sweetened Whole Soy Concentrates and Their Rheological Properties

Intermediate moisture systems were formulated with dehulled, blanched soybeans and four nutritive sweeteners (sucrose, glucose, fructose, sucrose/glucose). Soy content and sucrose/water ratio were varied. Water activity, water mobility (NMR) and rheological properties were determined. All three parameters were strongly influenced by the sweetener. All samples showed non-Newtonian behavior. Soy content and sucrose/water ratio had a stronger influence on rheology than on water properties.