EFFECT OF PECTIN CONTENT ON FLOW PROPERTIES OF MANGO PULP CONCENTRATES

The effect of pectin on the flow properties of mango pulp concentrates was studied using a coaxial cylindrical viscometer in the temperature (T) range 303-343°K. The variables were soluble solid content(C) 16-30°Brix, pectin content (C_pec, range 0.0323-0.0349 dry wt fraction) for the shear rate (γ) range 9.0-250 s^-1. Mango pulp concentrates behaved as pseudoplastic fluids in the entire pectin content range with a flow behaviour index of 0.286. A model relating shear stress () with the above variables is presented:     

Effect of Cloud Particle Characteristics on the Viscosity of Cloudy Apple Juice

ABSTRACT: Particle size, shape, and volume fraction as well as soluble pectin content and electro-viscous effects on cloudy apple juice viscosity were investigated. Particle characteristics were micrographically determined by electron microscopy. More than 2300 particles were digitalized and statistically analyzed. Cloudy apple juice resulted in a suspension of irregular shape particles ranging from 0.25 to 5 μm in size. A 10 °Brix juice had a particle volume fraction of φ₀= 3.93 ∞ 10^-3. Relative viscosity values were fitted to the generalized Sudduth equation. Intrinsic viscosity resulted 5.8 times greater than the theoretical value predicted by Einstein (α= 2.5). This was attributed to the first electro-viscous effect. Results also indicate that the effect of particle non-sphericity on cloudy apple juice viscosity can be neglected. Soluble pectin was found to increase juice viscosity significantly. Combined effects result in a strong linear increase of relative viscosity.     

EFFECT OF PHYSICAL PROPERTIES OF FOOD PARTICLES ON THE DEGREE OF GRAININESS PERCEIVED IN THE MOUTH

Nineteen food materials were pulverized and passed through standard sieves to prepare samples with different particle sizes (23–500 μm). Each sample was tested for physical properties, and sensory evaluation tests were conducted to obtain the graininess threshold value and the degree of graininess discrimination. The graininess threshold value tended to decrease and the degree of graininess discrimination tended to increase with increasing degree of circularity, with decreasing solubility, with decreasing water absorption rate- particle size coefficient, and with increasing WK₂/K₁. The degree of graininess discrimination tended to increase with increasing particle size and increasing WK₂. With a multiple-regression analysis, the graininess threshold value was expressed by six physical properties, and the degree of graininess discrimination was expressed by eight physical properties, each with high contribution rates.     

TEXTURAL PARAMETERS IN COMPRESSION TESTING OF A GEL MADE FROM FRESH AND FROZEN FISH MINCE

The relation between deformability modulus and yield stress is evaluated in compression testing of a model product made from fresh and frozen stored mince of cod. The experiments were performed with a compression rate of 120 mm/min. Preliminary experiments showed decreasing values of yield stress when compression rates were below 50 mm/min. Two moduli were calculated from the slope of the compression curve; α₁, initially (small deformations) and α₂ in a linear part of the curve shortly before rupture of the gel. α₂ was linearly related to yield stress in gels of different water content, and in gels made from fresh and frozen raw material. α₁ showed different relations to yield stress depending on quality of the raw material.     

RHEOLOGICAL INDICES OF FRUIT CONTENT IN JAMS: EFFECT OF FORMULATION ON FLOW PLASTICITY OF SHEARED STRAWBERRY AND PEACH JAMS

The effect of formulation factors on Casson yield values measured at low shear rates (0.08 ≤γ≤ 1.01s^-1) (σ₀₁) and at medium shear rates (2.58 ≤γ≤ 387.30s^-1) (σ₀₂) was analyzed in previously sheared strawberry and peach jams. Twenty three samples of each fruit jam were prepared according to a second order composite rotatable design. Composition ranges were: fruit content, 25–55%; soluble solids content, 60–70° Brix; added pectin in strawberry jams, 0.3–0.7% and in peach jams, 0.1–0.5%. Variation of σ₀₁ values in strawberry jams depended mainly on the interactions between fruit and soluble solids and between fruit and pectin, while in peach jams, it depended on fruit-soluble solids and soluble solids-pectin interactions. Patterns of change of σ₀₂ values with composition were similar to those observed for σ₀₁ in both strawberry and peach jams. Predictive power of σ₀₁ and σ₀₂ values for estimation of fruit content was low, but taken in conjunction with soluble solids content and total pectin values, 79.5% of the variability of fruit content in strawberry jams and 91.1% of same in peach jams could be explained.     

Osmotic Dehydration of Tomato in Sucrose Solutions: Fick's Law Classical Modeling

ABSTRACT:  Osmotic dehydration of tomato was modeled by the classical Fick's law including shrinkage, convective resistance at the interface and the presence of water bulk flow. Tomato slices having 8 mm thickness were osmotically dehydrated in sucrose solutions at 50, 60, and 70 °Brix and at 35, 45, and 55 °C. Other experiments were done in a 70 °Brix sucrose solution at 35 °C with tomato slices of 4, 6, and 8 mm thickness and at different motion levels (velocities 0, 0.053, and 0.107 m/s). Tomato weight, water content, and °Brix of the products were measured as a function of processing time (20, 40, 80, 160, and 320 min). Results showed that temperature, concentration, thickness, and solution movement significantly influenced water loss and sucrose gain during the osmotic dehydration of tomato. The model predicted the modifications of soluble solid content and water content as a function of time in close agreement with the experimental data. Experimental Sherwood number correlations for sucrose and water were determined as Sh _s = 1.3 Re ^0.5 Sc _s^0.15 and Sh _w = 0.11 Re ^0.5 Sc _w^0.5, respectively. The effective diffusion coefficients of water (4.97 10⁻¹¹– 2.10 10⁻¹⁰ m²/s) and sucrose (3.18 10⁻¹¹– 1.69 10⁻¹⁰ m²/s) depended only on temperature through an Arrhenius-type relationship.     

RHEOLOGICAL BEHAVIOR OF PROCESSED MUSTARD. II. STORAGE EFFECTS

Samples of processed yellow mustard with three different particle size distributions (slightly-coarse, standard, and fine) were prepared according to a standard formulation and pilot-plant replication of the commercial methodology and stored for 3 months at 5°C, 25°C, and 45°C. After 3-month storage at 45°C, all samples showed visible liquid separation (syneresis) and aggregation of colloidal particles, as indicated by increase in d _pop and decrease in % colloids. The fine milled samples exhibited syneresis and an increase in d _pop after 3-month storage even at 25°C. The bimodal distribution did not show significant changes as a result of aggregation. In general, increase in d _pop increased apparent viscosity (η _ap ), flow behavior index (n) from the Herschel-Bulkley model, and exponent n" from the loss modulus (G") power law equation. As d _pop increased, Bingham yield stress _o), plastic apparent viscosity (η _p ), shear stress constant (A) from the Weltman stress decay model, yield stress (_o) and consistency index (m) from the Herschel-Bulkley model, exponent n' from the storage modulus (G') power law equation, and minimum values of loss tangent (tan δ) decreased. In heterodisperse semi-solid foods such as processed mustard, the particle size distribution influences the structure (i.e., packing) and the rheological behavior. Therefore, time and temperature dependent instabilities such as syneresis may be minimized by controlling particle size distribution during processing.     

COMPARISON OF STEADY SHEAR RHEOLOGICAL PROPERTIES AND SMALL AMPLITUDE DYNAMIC VISCOELASTIC PROPERTIES OF FLUID FOOD MATERIALS

Small amplitude dynamic viscoelastic properties of apple butter, mustard, tub margarine, and mayonnaise are compared with their respective properties in steady shear flow in the range of shear rates and frequencies of 0.1-100 sec⁻¹ using a Rheometrics Mechanical Spectrometer. Comparison of dynamic and steady viscosities shows that dynamic viscosities (η*) are much larger than steady viscosities (η). Consequently the Cox-Merz rule is not obeyed. Moreover the obvious nonlinearity suggests that shift-factor type relationships are not obeyed either. The in-phase (η') component of the dynamic viscosity shows similar behavior when compared to the steady viscosity (η).
Comparison of G'/ω² and Ψ₁ also suggests that any of the results predicted by classical theories of viscoelasticity are not obeyed. G'/ω² is always much larger than Ψ₁ and the relationship between these two material functions is nonlinear.     

The Effect of Protein Particle Size Reduction on the Physical Properties of CO2-Precipitated Casein Films

ABSTRACT:  Casein precipitated with high pressure-CO₂ (CO₂CAS) has unique properties compared to commercial acid-precipitated casein. CO₂CAS is less water-soluble and films made from it are less susceptible to high humidity environments; however, the films are also opaque and hazy. The appearance of CO₂CAS films is important especially if applied as a food coating. To improve the appearance properties, the particle size of CO₂CAS film plasticized with glycerol was reduced. The effect of protein particle size reduction on tensile properties, water vapor permeability (WVP), and gloss was studied using ASTM methodology. As particle size of the CO₂CAS was reduced from 126 μm to 111 μm, tensile strength and modulus of the films increased, while WVP decreased. With the same particle reduction, gloss increased from 55.3 gloss units on average to 73 gloss units, but films were still hazy. With a particle size less than 86 μm, CO₂CAS films were glossy and transparent, however, tensile strength decreased and WVP increased. Depending on desired application, the properties of CO₂CAS films can be optimized by changing particle size.     

FLOW PROPERTIES OF BABACO (CARICA PENTAGONA) PUREES AND CONCENTRATES

A power law model describes adequately the rheological behaviour of Babaco purees and concentrates while a Herschel-Bulkley model describes concentrates only. A single equation η_a=α x cβ x exp (E_a/RT), combining the effects of temperature and concentration on apparent viscosity (η_a100), was used to describe rheological behaviour.     

RHEOLOGICAL BEHAVIOUR OF BUTTER AT SMALL DEFORMATIONS

Thirteen continuously churned commercial butter samples were evaluated for rheological properties at small deformations. The methods performed included dynamic experiments in shear and compression, stress relaxation in shear and static compression at 5–20C each. Linear viscoelastic behaviour was observed up to a critical strain of 0.001. The structure breakdown due to shear strains between 0.001 and 0.01 was found to be fully recoverable. No qualitative differences in the rheological behaviour were observed between the samples. Temperature-induced variations were mainly ascribed to changes in the solid fat content. Correlations between selected rheological measures in the linear viscoelastic region (i.e., complex modulus G* [Pa], relaxation modulus G(t) | _t ≃ 0[Pa], and modulus of deformability M_D[Pa]) were found to be causal and only slightly affected by the solid fat content.     

EFFECT OF UNIMODAL PARTICLE SIZE AND PULP CONTENT ON RHEOLOGICAL PROPERTIES OF TOMATO PUREE

The vane method in controlled shear stress mode was used to determine the yield stress and the shear rate—shear stress data of tomato purees containing 10–35% pulp of two different average particle sizes: 0.34 and 0.71 mm. Consistency index and apparent viscosity increased significantly with pulp content and decreased with average particle size. The effect of pulp weight fraction (P) on relative viscosity (η_r) could be described by the single parameter equation: η_r= [1 – (P/A)]⁻², while the effect of particle diameter on η_r could be described using Peclet number. Magnitudes of yield stress determined directly by the vane method were higher than those obtained by using the Casson model, and were proportional to the square of pulp content. Reduced Casson yield stress—P data on purees of both particle sizes followd a single curve. Effects of pulp content and particle size on vane yield stress and apparent viscosity were evident from the correlation forms with high values of R².     

PULSED ELECTRIC FIELD TREATMENT OF LIQUID WHOLE EGG INOCULATED WITH SALMONELLA ENTERITIDIS

The effects of pulsed electric fields (PEF) on the inactivation of Salmonella Enteritidis inoculated into liquid whole egg (LWE) and on the physical properties and the shelf-life of LWE were studied. PEF processing conditions were 1.2 mL/s flow rate, 200 pps frequency, 2.12 μs pulse duration, 25 kV/cm electric field strength, and 250 μs total treatment time. The PEF processing caused up to 1 log₁₀ cfu/mL reduction in S. Enteritidis population in LWE. The PEF-treated samples were subjected to heat at 55C for 3.5 min to inactivate the remaining bacteria without denaturing the LWE. The combination of PEF and heat treatments led to a 4.3 log₁₀ cfu/mL reduction in S. Enteritidis population (P < 0.05 ) and caused no significant change in viscosity, electrical conductivity, color, pH, and Brix, relative to control samples (P > 0.05 ). The PEF + 55C treated LWE samples presented significantly longer shelf-life at 4C compared with the control and heat treated samples (P < 0.05 ).     

The air drying behaviour of fresh and osmotically dehydrated banana slices

Ripe banana, cut to 10mm thick slabs were osmotically treated in sugar solutions of 35, 50 and 65° Brix for 36h. The initial moisture content fell from a value of 3.13kg H₂O DM to 2.19, 1.63 and 1.16kg H₂O kg⁻¹ for treatment in the three solutions, respectively. These slabs, with Total Soluble Solids (TSS) contents of 26, 34 and 39° Brix, respectively, as well as freshly cut but untreated slabs (15° Brix) were air dried in a cabinet type tray drier to near equilibrium conditions at fixed temperatures from 40 to 80°C and at a constant air speed of 0.62m s⁻¹. Drying was found to occur in the falling rate period only for both banana types and two drying constants K₁ and K₂ were established for a first and second falling rate period of drying. Increasing the drying air temperature significantly enhanced the drying rate and the K-values, except at 80°C when the rates fell, possibly because of case hardening of the slabs. Reducing the slab thickness also improved the drying rate, but increasing the air speed to 1.03m s⁻¹ did not have any profound effect. As the sugar content of the banana slabs increased through the osmotic treatment, drying rates fell. Calculated apparent moisture diffusivities at 60°C ranged from 34.8× 10⁻¹⁰ m² s⁻¹ (fresh slab) to 8.8×10⁻¹⁰ m² s⁻¹ for dried (39° Brix) slabs. The moisture diffusivity was significantly lowered as the moisture content dropped in drying and with increased levels of sugar. Previously osmosed and then air dried banana slabs showed appealing colour and texture compared to the fresh banana.     

RHEOLOGICAL AND CHEMICAL PROPERTIES OF MOZZARELLA CHEESE

Dynamic viscoelastic parameters and chemical properties of Mozzarella cheese produced using a "no-brine" cheese making method with 3 different cooking temperatures (38, 41, and 44C) were determined. Samples were stored for 3 weeks at 4C before dynamic mechanical analysis at 22C. G', G" and tan δ were 5.8 – 6.4 × 10⁵ dyne/cm², 1.9 – 2.1 × 10⁵ dyne/cm², and 0.33 – 0.35, respectively, at 1% strain and 10 rad/s. The percentage of intact α_s-casein and β-casein were 38–40% and 33–35% of total protein in the cheese, respectively. The range of cooking temperatures used in this experiment had little effect on dynamic viscoelastic properties or the amount of intact protein for the cheese.     

UNIAXIAL COMPRESSION AND STRESS RELAXATION TESTS ON ALGINATE GELS

The rheological behavior of alginate gels was analyzed using uniaxial compression and stress relaxation tests. The engineering compressive stress (σ_E)-deformation (ɛ_E curves were found to be concave upward and independent of the crosshead speed (V_t for V_t≥ 120 mm/min. By considering all the stress (σ_E)-time (t) data for t greater than 10 times the average loading period, the viscoelastic response of these gels was described by means of a 3-element Maxwell body characterized by a relaxation time of 300 s. Such gels exhibited an apparent linear viscoelastic solid behavior for ɛ_E≤ 8% and a nonlinear one for larger deformations. However, for ɛ_E>32% their solid viscoelastic behavior tended to a liquid one. Empirical models allowed the viscoelastic properties, as well permanent deformation, of these gels to be quantitatively described as functions of the deformation applied and/or loading rate.     

THIXOTROPY OF ORANGE CONCENTRATE AND QUINCE PUREE

Orange juice with pulp and pectins is thixotropic at soluble solids concentrations of 55 and 60 Brix in the range of temperatures from 0 to 20C and shear rate from 7.2 to 57.6 s⁻¹. Quince purée is thixotropic at soluble solids concentrations of 12.3 to 28 °Brix in the range of temperatures between 0 to 20C and shear rate from 7.2 to 57.6 s⁻¹. The thixotropic behaviour of orange juice and quince purée increases with increasing concentration and decreasing temperature and they can be described by the kinetic model proposed by Figoni and Shoemaker (1983):

The thixotropic structure of orange juice was destroyed by applying a shear rate of 57.6 s⁻¹ for 5 min, and for quince purée for 10 min. Quince purée shows a greater thixotropic character than orange juice, because it has a higher content of fiber, pulp and pectins and also because it shows a microscopic structure consisting of long particles and heterogeneous fibers.     

MECHANICAL PROPERTIES OF AERATED CONFECTIONERY

Mechanical properties, including an extensional modulus, penetration modulus and cut force, of an aerated confectionery nougat were measured instrumentally as a function of nougat density in the range 0.66–1.12 g/mL. Despite the fact that the material was not a true cellular solid, the properties were adequately modeled by the expression C₁(ρ-ρ_c)ⁿ with n = 3 as befits a closed-cell foam. The critical density, ρ_c, appeared to correspond to the density at random close packing for spherical air cells, i.e., an air cell fraction of ≈ 0.6.     

CARBOISIYL AND FATTY ACID ANALYSIS OF ANTELOPE AND BEEF FAT

Characterization of kidney fat from twelve antelope and four beef was accomplished by monocarbonyl, ketoglyceride and fatty acid analysis. Antelope lipids are highly saturated, possessing strong odor and flavor characteristics which many people find objectionable. The antelope fat had a stearic acid content of 42% and an oleic acid content of only 20% while beef fat contained 28% stearic and 34% oleic acid. The lipid was further analyzed by reacting on a 2, 4-DNPH Celite impregnated column. The derivatives were separated from unreacted lip-id, and monocarbonyls and ketoglycerides fractionated using column chromatography. The ratio of monocarbonyls to ketoglycerides was about 1:3 in beef and 1:1 in antelope. Amounts of monocarbonyls average 0.70 μM/g of fat for beef and 1.47 μM/g of fat for antelope. Further analysis of the monocarbonyls indicated 7% methyl ketones, 70% saturated aldehydes, 18% enals and 6% 2,4 dienals in beef while antelope had 15%, 70%, 11% and 4%, respectively. Major constituents of the saturated aldehydes were C₂ through C₈ for both species and C₁₀ for beef while the major methyl ketones were C₃ through C₇ for both species. Methyl ketone, saturated aldehyde and enal fractions showed similar trends in composition with short-chain components higher in antelope and long-chain components higher in beef. Considerable variation occurred among animals of the same species.     

COMPARATIVE STUDY OF STRUCTURAL CHARACTERISTICS AND THERMAL BEHAVIOR OF WHEY AND ISOLATE SOYBEAN PROTEINS

Electrophoretic profiles, sulfhydryl(SH)/disulfide (SS) groups content, and surface hydrophobicity (H₀) values of whey soybean proteins (WSP) and native soy isolates (NSI) were determined. WSP, composed mainly by Kunitz trypsin inhibitor (KTI), and lectin (L), has a H₀ value of 24.0 ± 1.0, which is 6.8 times lower than that of NSI ones, and SH/SS groups content in the same range of NSI. The thermal behavior of WSP and NSI was studied by differential scanning calorimetry (DSC). The WSP thermogram in water, similar to NSI, showed two main peaks (Tp values: 74.0 ± 0.5 C and 90.4 ± 0.8C) attributed to thermal denaturation of KTI and L, respectively. These endotherms are slightly affected by μ, whereas those of NSI are strongly affected (Tp of 7S and 11S peaks increase 17C and 20C respectively, by increasing NaCl concentration from 0 to 1M). WSP has low Ho values not noticeably affected by ionic strength changes, whereas NSI has higher Ho, that increase in saline media and favor intermolecular hydrophobic interactions. The consequent low tendency to protein aggregation by hydrophobic interactions in WSP would explain their lower thermal stability at high μ. Control proteins of both preparations (7S and 11S enriched fractions for NSI, and purified trypsin inhibitors, urease and lectin for WSP) were use to confirm these results.