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.     

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.     

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.     

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.     

芒果浓缩汁的流变学特性

研究了不同质量分数的芒果浓缩汁在不同温度下的流变学特性.回归分析发现,在研究的温度和质量分数范围内,芒果浓缩汁表现为Herschel-Bulkley流体,温度对黏度的影响可用阿伦尼鸟兹方程表示,质量分数对黏度的影响可用幂函数表示,推导出了温度和质量分数对浓缩芒果汁黏度综合影响的方程.随着芒果浓缩汁质量分数的提高,体系的静态屈服应力值也增大.     

Particle Size Distribution of Natural Peanut Butter and Its Dynamic Rheological Properties

This study compared the dynamic rheological properties of natural peanut butter with commercial peanut butter at 25°C. The natural peanut butter was produced using ultra-high speed grinding (?20,000 rpm) at different grinding times (2–5 min) from peanuts of China and India. Multimodal particle size distribution was observed for all the samples. The linear viscoelastic region obtained from stress sweep test of the peanut butter produced at 2–3 min fell within the linear viscoelastic region of commercial peanut butter of 0.1–11 Pa. Longer grinding time (3.5–5 min) produced a shorter and lower linear viscoelastic region of 0.03–3 Pa. The storage modulus, G′ is an increasing function of particle size distribution. All peanut butter samples exhibited elastic properties.     

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.     

番茄浆料的流变特性

对不同浓度的番茄浆料在30～60℃时的流变学性质进行了研究.结果显示,番茄浆料为假塑体系,屈服应力值的范围比较宽(40～140Pa).通过回归分析得到数学模型K=K0exp(Ea/RT)和K=Aexp(BC).可以分别用来描述温度和浓度对番茄浆料稠度系数的影响.利用这些方程,可以预测实际加工过程中不同温度和不同浓度条件下番茄浆料的粘度.     

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.     

动态超高压均质对蛋清蛋白溶液的粒度和流变性影响

本实验以10%的蛋清蛋白溶液为研究对象,采用动态超高压均质处理,研究蛋清蛋白溶液平均粒度和流变性的变化。研究表明,10%的蛋清蛋白溶液的平均粒度随着压力的增加而出现明显减小的现象,其经过超高压均质后,由非牛顿流体的胀塑性流体转变为假塑性流体,均质后的蛋清蛋白溶液的表观黏度明显升高。     

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.     

Selected Rheological Characteristics and Physicochemical Properties of Vegetable Oil Affected by Heating

Estimating oxidative stability with successive heating temperatures provides a qualitative assessment of oil in the food industry. As one of the prime factors contributing to oil characteristics, the flow behavior of highly refined sesame oil and mustard oil were determined experimentally between the temperatures 25 and 85°C. The variation of viscosity with temperature was fitted in two variable empirical equations and the mathematical models were compared. Various physicochemical parameters of the oils like conductivity, density, viscosity, ultrasonic velocity, saponification value, iodine value, and free fatty acid content were observed to estimate their characteristics and stability on heating to cooking temperature. The physical and chemical parameters were compared and correlated between the oils to analyze the oxidative stability at different times of heating. A novel relation was demarcated between ultrasonic velocity and the chemical parameters. The study helped in the identification of the best oil suited for repeated cycles of heating.     

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.     

番茄汁液流变性质的关联

对经45、32、24和16目筛网过筛所得番茄汁液的流变性质进行了研究。采用旋转式粘度计测定了番茄汁的剪切速率-剪应力数据。通过剪切速率-剪应力实验数据的关联发现,番茄汁液的流变行为可用Bingham模型表征。确定了不同温度和不同网目下番茄汁液的稠度指数和屈服应力。同时也建立了不同网目下番茄汁液的表观粘度与温度函数关系的关联式。     

番茄浆料的流变特性研究

对不同浓度(15、18、20和24°Brix)的番茄浆料分别在30、40、50和60℃时的流变学性质进行了研究。结果显示,番茄浆料为假塑体系,屈服应力值的范围比较宽(40-140pa)。通过回归分析,发现数学模型,K=koexp(Ea/RT)和K=Aexp(BC),可以分别用来描述温度和浓度对番茄浆料稠度系数的影响。在实验条件下,实验值能够很好地拟合模型。并且推导出温度和浓度同时对番茄浆粘度影响的方程。利用这些方程,可以预测实际加工中不同温度和不同浓度下番茄浆料的粘度。