Texture Changes During the Ripening of Port Salut Argentino Cheese in 2 Sampling Zones

ABSTRACT: Texture changes during ripening of Port Salut Argentino cheese for different sampling zones were studied. Compression relaxation tests were performed and results were analyzed using both Maxwellian and Peleg's models. Elastic equilibrium modulus obtained from the Maxwellian model decreased from 1.22 to 0.11 10⁴Pa during ripening. The constants derived from Peleg's model, k₁ and k₂, diminished with ripening time from 1.18 to 0.71 min and from 1.27 to 1.12, respectively. Asymptotic equilibrium modulus from Peleg's model decreased from 0.95 to 0.07 10⁴Pa during ripening. Rate parameters derived from a 1st order kinetics applied to both equilibrium moduli showed that the decrease was faster in the external zone (0.0846 d⁻¹) than in the central zone (0.0368 d⁻¹). The correlation between equilibrium moduli, salt concentration, moisture content, and maturation indexes was obtained with a determination coefficient of 0.76.     

THE RHEOLOGICAL PROPERTIES of RICE GRAIN

For rice kernels uniaxial compressive modulus function, the time-temperature and time-moisture content shift factors, the bulk compressive creep modulus, the uniaxial compressive stress relaxation modulus, and the uniaxial compressive failure stress were experimentally determined, while the shear modulus and Poisson's ratio were calculated from the available experimental data.
Uniaxial compression tests were carried out at deformation rates of 0.254.0.0508 and 0.0127 cm per min for five temperatures in 11C increments from 25 to 69C for each of the four moisture levels of 12, 17, 22 and 29% (d.b.). Stress relaxation and bulk compression tests were performed at the same four moisture levels and at the temperature of 25C.
Master curves for uniaxial compressive modulus and failure strength were developed as functions of reduced time where the temperature and moisture effects were transformed to equivalent time effects by the method of reduced variables. the brown rice kernel was found to have only one time-temperature and one time-moisture shift function showing that the material is thermo- and hydro-rheologically simple.     

Effect of air movement on peanut pod moisture variation during storage

Peanut pods (kernels in shell) were stored in 1 m³ containers under conditions which were completely sealed or purged with about 0·3 m³/min of room air for 3 months. The moisture content of 100 pods was measured before and after storage. No difference was found in pod to pod moisture variation between purged and sealed storage, although there was considerable difference in the average moisture content. It was also found that the variability in moisture content in the shell is about three times that in the kernel. These results suggest possible reasons why some kernels in a mass deteriorate despite acceptable average conditions.     

CHANGES IN EQUILIBRIUM MODULUS AND αsl-CASEIN BREAKDOWN DURING THE RIPENING OF PORT SALUT ARGENTINO CHEESE AS AFFECTED BY FROZEN STORAGE

The effect of the freezing, frozen storage and thawing on textural parameters and α_sl-casein breakdown during the ripening of Port Salut Argentino cheese was studied. Moisture content, salt concentration, casein profiles and asymptotic equilibrium modulus were monitored in control cheeses ripened at 5C and in cheeses, stored at -22C for 30 days, thawed and ripened at 5C, for different ripening times (1, 6, 13, 27 and 56 days) and two sampling zones (central and external). The freezing process significantly increased the rate of α_sl-casein and α_sl-I-casein hydrolysis. This process may affect the susceptibility of α_sl-casein to chymosin attack and also the availability of hydrolytic enzymes released by damaged microorganisms, which may contribute to the faster hydrolysis of α_sl-I-casein. The freezing process did not significantly affect the decay rates of asymptotic equilibrium modulus. First order kinetics constants for decay of the asymptotic equilibrium modulus were 3.71 10^-2day^-1 (control cheeses, central zone), 8.48 10^-2 day^-1 (control cheeses, external zone), 4.52 10^-2 day^-1 (frozen cheeses, central zone), and 11.43 10^-2 day^-1 (frozen cheeses, external zone). Significant differences in the decay rates of asymptotic equilibrium modulus were found between central and external zones in control and frozen cheeses primarily due to differences in moisture contents of the sampling zones.     

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.     

Micromechanical properties of almond kernels with various moisture content levels

Almond fruits are subjected to various mechanical stresses throughout production, from harvest to processing, storage and packaging. Kernel properties play an important role in reducing mechanical damage such as scratches and penetration of shell pieces. Knowledge of kernel properties under various conditions of the fruit can assist in optimising post-harvest and processing lines to minimise kernel damage and thus maximise final kernel quality. Kernel moisture content is one of the main attributes affecting the kernel’s response to mechanical processing. Increasing the kernel moisture content to an optimum level through wetting fruit prior to processing can lead to a reduced percentage of damaged kernel. Water added to the structure of kernels acted as a plasticiser and helped the kernels to absorb the mechanical load instead of fracturing and breaking into pieces. In this study, tests were conducted on almond kernels with different moisture content levels from 5.52 to 14.09g/100g wet basis. Kernels from a Nonpareil variety were tested in dried and wetted conditions. Test results showed that kernels with higher moisture content were able to undergo a larger deformation at a given force value in comparison with dry kernels. Average deformation for dry samples was from 0.12 mm, which increased to an average of 0.25 mm in wetted samples. The effect of skin on the mechanical properties of the kernels (with and without skin) was studied using a mechanical tester. The test results showed a peak force value in samples tested with skin in comparison with the kernels tested without skin.     

Effect of micronisation and electromagnetic radiation on physical and mechanical properties of Canadian barley

The effect of micronisation (high‐intensity infrared heating) and microwave radiation of normal barley (NB), high‐amylose barley (HAB) and waxy barley (WB) on the physical and mechanical properties was studied. Samples were tempered to 42–45% moisture content and then subjected to infrared or microwave radiation to reduce the moisture content to approximately 10%. The grain surface temperature during radiation was maintained at 100 °C. The changes in physical and mechanical properties were compared with unprocessed samples. Thermal radiation increased slightly the volume of the kernels because of the diffusion of water vapour from inside to the outer surface. These changes resulted in a decrease in particle and bulk densities. Thermal radiation affected the Hunter colour values, as well. The mechanical properties including bio‐yield point, modulus of elasticity and breakage susceptibility were affected by micronisation and microwave heating.     

COMPARISON OF MECHANICAL TESTS FOR EVALUATING TEXTURAL CHANGES IN POTATOES DURING THERMAL SOFTENING

The changes in the texture of cylindrical samples of potato tissues immersed in water at 60, 70, 80 and 90C for up to 80 min were monitored at each temperature in terms of tangent modulus of elasticity in axial and radial compression tests, and elasticity and viscosity parameters in creep and stress relaxation tests. The magnitude of all mechanical test parameters decreased with an increase in heating time and temperature. The creep and stress relaxation responses of individual potato samples were adequately represented by respective mechanical models (R²= 0.94 to 0.99). The mechanical test parameters followed apparent first-order degradation kinetics due to the effect of thermal softening, and the rate constant was used as an index of the sensitivity of a mechanical test. The radial compression test was relatively more sensitive than the axial test. Based on an overall comparison, the parameters from creep and stress relaxation tests were found to be the most sensitive in describing the textural changes during thermal softening of potatoes.     

Chitosan globules

We prepared chitosan globules to use as a structural unit or as a means of controlled ingredient release in food products. Globules were fabricated by coagulating drops of chitosan solutions (1–2% w/w chitosan in 3.8–5.6% w/w citric acid solution) in 1 N NaOH. The chitosan solutions, dropped from a 2.9 mm diameter tube, resulted in ellipsoidal globules with diameters of 3.7–5.1 mm and an opaque, whitish appearance similar to that of cooked white rice. The globules contained more than 98% water, about half of which could be squeezed out under compression.
The force-deformation test indicated an increase in the strength, elastic moduli, and relaxation time of fabricated globules when the chitosan concentration was higher in the casting solution. When the citric acid concentration was higher, elastic moduli generally increased, but the longest relaxation time decreased. The globules sustained up to approximately 0.8 linear strain without fracture. Stress relaxation tests showed that the viscoelastic properties of globules may be represented by a one-element Maxwell model with a relaxation time on the order of 1000 sec and an elastic modulus of 0.05–0.27 g/mm².     

TEXTURE-STRUCTURE RELATIONSHIPS IN HEAT-INDUCED SOY PROTEIN GELS

Structural factors responsible for textural properties of heat-induced soy protein gels were investigated using microscopic and mechanical testing techniques. The gels were prepared by heating 20% soy protein pastes for 30 min at temperatures ranging from 25 to 130°C . Gel hardness increased linearly with the heating temperature up to 80°C , and decreased when the gels were heated at over 90°C , especially over 120°C . The equilibrium modulus estimated by tensile stress relaxation experiments was of the order of 10⁴ - 10⁵ dyne/cm², suggesting the presence of crosslinks, and there was a good correlation between the equilibrium modulus and the hardness of the gels. Solubility in phosphate buffer containing 2 -mercaptoethanol and/or urea suggested that the gel network was formed through crosslinking of the disulfide-, hydrogen- and hydrophobic-bonding types, and that the textural properties were governed by the degree of the network formation controlled by the heating temperature. SEM images of the 80°C -induced hard gels revealed a porous structure having membranous walls of thin compact film. With the 40°C -induced soft gels, the formation of the porous structure was not yet adequate, while a partial collapse of this structure was observed in the 120°C -induced fragile gels.     

EFFECT OF ALKALI METAL IONS ON THE RHEOLOGICAL PROPERTIES OF κ-CARRAGEENAN AND AGAROSE GELS

Stress relaxation and dynamic measurements were carried out on κ-carrageenan and agarose gels to examine the effect of alkali metal ions. The elastic modulus of κ-carrageenan gels increase remarkably by adding alkali metal ions Li⁺, Na⁺, K⁺, Cs⁺. This was explained as follows: the electrostatic repulsion of sulfate groups in κ-carrageenan gels are prevented by the shielding action of the alkali metal ions stabilizing the double helical structure of κ-carrageenan gels. The increase of the modulus was in the order: Cs⁺ > K⁺≫ Na⁺ > Li⁺. The difference between these two groups (Cs⁺, K⁺) and (Na⁺, Li⁺) is that the former group belongs to the structure disordering ions while the latter group belongs to the structure ordering ions. Thus, the former group prevents the repulsion of sulfate groups more directly than the latter. Agarose gel, which lacks sulfate groups, is not influenced so much by adding the alkali metal ions.     

RHEOLOGICAL BEHAVIOUR OF SHEARED JAMS. RELATION WITH FRUIT CONTENT

Eight samples of jam were sheared to destroy gel structure and their flow behaviour was analysed in a concentric cylinder viscometer. Jams were prepared from 4 different fruits—strawberry, peach, plum, and apricot—at 50% and 30% fruit content approximately. Flow of sheared jam showed time dependence, which could be quantified by the Weltmann model and which was eliminated by shearing samples for 8 min at 300 rpm. Casson's yield stress values were obtained at two ranges of shear rates: 0.08–1.01 s⁻¹ (O₀₁) and 2.58–387.30 s⁻¹ (o₀₂). o₀₂ values were about double the o₀₁ values. Flow was adequately described by the Herschel and Bulkley model, introducing either of the yield stress values (o₀₁ or o₀₂). Significant differences were found for some of the rheological parameters studied (Weltmann A and B constants, o₀₁, o₀₂, K₁, and n₁) between samples containing 50% and 30% fruit. These results demonstrate the role played by fruit particles in the rheological behaviour of this type of product and suggest the possibility of using rheological parameters as indices of fruit content in jams.     

VARIATIONS IN FLEXURAL AND COMPRESSIVE FRACTURE BEHAVIOR OF A BRITTLE CELLULAR FOOD (DRIED BREAD) IN RESPONSE TO MOISTURE SORPTION

Mechanical properties of dried bread (a cellular baked product) equilibrated at different water activities (A_w) were measured using three-point bending and uniaxial compression to compare their responses to moisture sorption. The glass-to-rubber transition was clearly demarcated in all the mechanical property-A_w curves, although there were differences in critical A_w (0.32–0.56) at which the dramatic changes in mechanical properties occurred. The role of water appeared to be strictly that of a plasticizer where flexural mechanical parameters were concerned, leading to reduced modulus and fracture stress but increased fracture strain with increasing A_w. Uniaxial compression tests revealed moisture-induced mechanical antiplasticization effects on the material in the glassy state which resulted in maximum compressive fracture stress but minimum fracture strain over the A_w range from 0–0.56. Compressive modulus apparently was not affected much by moisture sorption up to an A_w of 0.43, above which it decreased sharply.     

EFFECTS OF TEMPERATURE AND MOISTURE CONTENT ON THE VISCOELASTIC BEHAVIOR OF COWPEAS

The viscoelastic parameters of cowpeas (Vigna unguiculata) were studied at different temperature and moisture content combinations. Cowpeas were tested at temperatures of 25°, 45° and 70°C and moisture contents of 13.9, 19.6 and 22.4% dry basis on an Instron Universal Testing Machine using stress relaxation techniques. The response of cowpeas was characterized by two Maxwell bodies in parallel without the incorporation of a residual spring. The relaxation curves (uniaxial modulus versus time) were used to calculate temperature and moisture shift factors, which subsequently led to the construction of a single master response curve. Cowpeas are both thermo-rheologically and hydro-rheologically simple biological materials.     

Osmotic Dehydration Behavior of Red Paprika (Capsicum Annuum L.)

ABSTRACT: Osmotic dehydration of red paprika was studied using a combined sucrose (5 to 45 g/100 g) and sodium chloride (0 to 15 g/100g) solution. The effective diffusion coefficients for water and solute were determined using the slope method based on the Fickian diffusion model. The effects of concentration of sucrose, sodium chloride and their complex interaction on water and solute diffusion coefficients as well as on equilibrium moisture and solid contents were studied using central composite rotatable design of experiments. The graphical optimization showed that at optimum conditions (sucrose concentration and sodium chloride concentration were 21.86 g/100 g and 2.02 g/100 g, respectively), the following criteria were achieved: water diffusion coefficient (D_ew) 0.80 × 10⁻⁹ m²/s, solid diffusion coefficient (D_es 0.82 × 10⁻⁹ m²/s, equilibrium moisture content (m∞) 6.85 kg/kg, and equilibrium solid content (s∞) 2.00 kg/kg.     

Mathematical Evaluation of Effective Moisture Diffusivity in Fresh Japanese Noodles (Udon) by Regular Regime Theory

The effect of moisture content and temperature on the effective moisture diffusivity was investigated to have the optimal drying condition of Japanese noodles (Udon) using regular regime theory. The drying of fresh Udon of different moisture contents was carried out under constant conditions of relative humidity and airflow at 20, 30, and 40 °C. The existence of regular regime periods for fresh noodles was experimentally verified. Effective moisture diffusivity obtained ranged from 2.1 × 10 ^-7 to 3.7 × 10 ^-7 cm² s^-1. The effect of temperature on effective moisture diffusivity was adequately modeled by the Arrhenius relationship, although the effect of moisture content was quite small.     

Effects of moisture content and compression axis on mechanical properties of Shea kernel

Some mechanical properties of Shea kernel were investigated in this study. The kernels were divided into two categories sizes namely: small size kernel (SSK) and large size kernel (LSK) and the properties investigated were: rupture force, deformation at rupture and energy consumed at rupture. The tests were carried out at a deformation rate of 50 mm/min and four moisture content levels of 25.9%, 11.60%, 6.88%, 4.98% (db) for SSK and 11.19%, 6.21%, 5.78% and 2.77% (db) for LSK. The variations in these properties were observed considering the effects of moisture content and compression axes on them as the kernels were air-dried. Sample kernels were compressed along the orthogonal axes corresponding to major axes (length), intermediate axes (width) and minor axes (thickness) of Shea kernel. Some physical characteristics of Shea kernel such as dimensions, geometric mean diameter and mass were also evaluated. Results showed that generally, rupture force, deformation and energy at rupture decreased as moisture content decreased. The regression models that best fitted the relationships were polynomial functions of the second order. The highest and lowest forces for Shea kernel to rupture were those through the minor axis (thickness) and major axis (length) respectively. These properties are often required for the design of transportation, storage and grading/sorting machines and other post harvest machines for Shea kernel.     

DYNAMIC VISCOELASTICITY AND STRESS RELAXATION IN STARCH PASTES

The dynamic viscoelasticity and stress relaxation of ten types of starch pastes were measured. The dynamic moduli increased with increasing frequency, and were different for each starch paste, changes in tan δ for cassava and potato starch pastes being about 0.5–0.6. The stress relaxation behaviour of all the samples tested could be represented by a four-element mechanical model. The relationship between spinnability and stress relaxation was determined, the spinning distance increasing with increased relaxation time (τ₂). No satisfactory linear relationship between spinning distance and relaxation time (τ₂) was apparent with the 10 starch paste samples.     

TOTAL NITROGEN CONTENT IN SINGLE KERNEL MALTING BARLEY SAMPLES

It was demonstrated that the Dumas method is suitable to analyse single kernel barley samples for their total nitrogen content directly without milling. The method was compared to the nitrogen analysis in milled samples over a range of 1.5-3.0%N. These samples consisted of kernel size grading fractions from barley cultivated at different N-dressings and using a shading regime. A good correlation was found between milled and whole barley kernels (r²=0.852). The method was used to determine the nitrogen content of individual kernels in the barley grading fractions. The nitrogen content in these fractions decreased with increasing kernel size depending on growth conditions. A large variation in nitrogen content between individual kernels was found for all grading fractions. In a study of barley main spikes the variation in kernel nitrogen content within spikes was smaller than the variation between spikes, especially when the barley was grown at a 60% light reduction regime during the kernel filling period. The average kernel total nitrogen content under the latter condition was about two times as high as in the control experiment. The kernel position along the spike did not clearly affect its nitrogen content. Acid and SDS polyacrylamide gel electrophoresis (PAGE) revealed similar banding patterns for proteins from kernels at different positions of both low and high N barley spikes. The single kernel method for nitrogen may be used by the breeder as a quality criterion for new barley varieties to test their spike development at different cultivation conditions. It can suit the maltster to screen rapidly the homogeneity in nitrogen (protein) content of barley batches.