TEXTURE ANALYSIS OF CHEDDAR CHEESE MADE FROM ULTRAFILTERED MILK

The textural properties of Cheddar cheese made from ultrafiltered milk were assessed. Cheddar cheeses were prepared from 1.5- and 2.0-fold concentrated milk and ripened for three months. Textural characteristics of the UF cheeses were compared to control and commercial Cheddar cheeses by sensory and instrumental measures. The texture of cheese made from UF milk differed from the control commercial Cheddar cheeses. According to the trained sensory panel, the UF cheeses were harder and more rubbery, crumbly, chewy and grainy than the control and commercial Cheddar cheeses (P <0.01). The texture profile analysis (TPA), conducted using the Instron, did not correspond to the sensory measurements nor was it successful in discriminating among the cheese samples. Lack of agreement between the sensory and instrumental tests was attributed to differences in the testing conditions and procedures of the two methods. Instrumental tests should be validated against sensory measures in order to be useful as measures of palatability. Consumer preferences for the commercial, control and UF Cheddar cheeses were significantly different (P < 0.01), the UF cheeses being less preferred in terms of flavor, texture and overall acceptability.     

UNIAXIAL COMPRESSION OF UF-FETA CHEESE RELATED TO SENSORY TEXTURE ANALYSIS

Rheological characteristics of seven Feta cheeses with different textures and produced from ultrafiltered milk (UF-Feta cheeses) were evaluated by uniaxial compression and sensory texture analysis. The effect of uniaxial deformation rate (50–2500 mm/min) on four rheological parameters: Stress at fracture s?_f), Hencky strain at fracture (?_f), deformability modulus (E) and work to fracture (W_f) was examined. Three Principal Components (PC) described 76, 16 and 4% respectively, of the variation in the uniaxial compression data set (4 parameters at 12 deformation rates). Statistically α_f, E and W_f described the same type of information in the data set. Six sensory texture attributes of the UF-Feta cheeses were evaluated by a sensory texture panel: nonoral firmness, nonoral brittleness, nonoral spreadability, oral crumbliness, oral firmness and oral stickiness. One PC described 93% of the variation in the sensory texture data and grouped the sensory variables into two negatively correlated groups: nonoral firmness nonoral brittleness, oral firmness and oral crumbliness versus nonoral spreadability and oral stickiness. Correlations and Partial Least Squares regression (PLS) between instrumental and sensory texture variables showed that nonoral and oral firmness were the nonoral and oral sensory variables best predicted from instrumental measurements. α_f, E and W_f were all able to predict nonoral and oral firmness. Of the instrumental parameters, α_f generally gave the best correlation to nonoral firmness at all deformation rates. Above a deformation rate of 50 mm/min correlations between α_f and nonoral firmness were almost independent of deformation rate, and at any deformation rate correlations between α_f and oral firmness     

RHEOLOGICAL PROPERTIES OF UF-FETA CHEESE DETERMINED BY UNIAXIAL COMPRESSION AND DYNAMIC TESTING

Rheological characteristics of three Feta cheeses produced from ultrafiltered milk (UF-Feta cheeses) with different textures were evaluated using uniaxial compression and dynamic testing (strain and frequency sweeps). Stress at fracture was 20–46 kPa, Hencky strain at fracture was 0.20–0.35, modulus of deformability was 176–465 kPa, and work up to fracture was 4.4–6.7 kj/m³, depending on the type of cheese and the strain rate. Stress at a given strain, and stress at fracture increased with strain rate: the slope of the log (stress at fracture) versus log(in-itial Hencky strain rate) plot was 0.06–0.21, indicating a partially viscous behavior. Stress at fracture discriminated between all three Feta textures, and Hencky strain at fracture discriminated a Tin Feta texture from two Brick Feta textures at every compression rate. In dynamic testing the complex modulus was 40–173 kPa, and tan (δ) was 0.17–0.25 depending on the type of cheese and the frequency of oscillation. The slope of log(complex modulus) or log(storage modulus) versus log (frequency) was 0.12–0.14, and the slope of log(loss modulus) versus log (frequency) was 0.07–0.11 for all three types of cheese. The complex modulus from strain and frequency sweeps in the dynamic testing distinguished the Tin Feta texture from the Brick Feta textures, and the phase angle (δ) measured in strain sweep could differentiate the Blue Brick Feta texture from the Red Brick Feta texture in the strain interval 0.0003–0.024.     

INFLUENCE OF UNIAXIAL COMPRESSION RATE ON RHEOLOGICAL PARAMETERS AND SENSORY TEXTURE PREDICTION OF COOKED POTATOES

The effect of uniaxial compression rate (20–1000 mm/min) on the parameters: Stress (σ_ftrue), strain (ε_fHencky) and work to fracture (W_f), modulus of deformability (E_d), maximum slope before fracture (E_max) and work during 75% compression (W_total) was investigated for ten potato varieties. Multivariate data analysis was used to study the correlation between and within the sensory and nonsensory measurements by Principal Component Analysis (PCA) which showed σ_ftrue, E_max, W_f, and W_total to explain the same type of information in the data, and ε_fHencky versus E_d another type of information in the data. The deformation rate had a large effect on ε_fHencky. Nine sensory texture attributes covering the mechanical, geometrical and moistness attributes were evaluated. Relationships between uniaxial compression data at various deformation rates and the sensory texture attributes were studied by Partial Least Squares Regression (PLSR). A minor effect of deformation rate on the correlation with the sensory texture properties was obtained. Mechanical properties were predicted to a higher extent than the geometrical attributes and moistness. The prediction of the mechanical, geometrical and moistness attributes increased largely by using uniaxial compression supplemented by chemical measures such as dry matter and pectin methylesterase, but here no relevant effect of deformation rate was obtained.     

MILK GEL STRUCTURE. X. TEXTURE AND MICROSTRUCTURE IN CHEDDAR CHEESE MADE FROM WHOLE MILK AND FROM HOMOGENIZED LOW-FAT MILK1

Reduced-fat cheese (17% fat, 44% moisture) was considerably firmer and more elastic than full-fat cheese (35% fat, 35% moisture), even though the moisture levels in the nonfat matter (MNFM) of the cheese were the same, at 54%. Electron microscopy and compositional analysis revealed about 30% more protein matrix in the reduced-fat cheese. Apparently more of this matrix must be cut or deformed in sensorial and texture assessments. A practical implication is that MNFM should be slightly higher in the reduced-fat cheese than in full-fat cheese to achieve more similar texture. Homogenization of milk tended to increase the moisture content and decrease firmness and elasticity, but not markedly. The smaller fat globules, per se, did not apparently affect texture as measured in these experiments. Curd granule junctions were prominent in nonhomogenized-milk cheese, because large fat globules were lost at the granule surfaces leaving protein-dense junctions; those in homogenized-milk cheese were less apparent because the protein-dense areas, which resulted from the loss of small fat globules, were narrower. Sensory and textural parameters for firmness and elasticity were inter-correlated. The Bite Test was more useful than Instron measurements of deformation (20%), apparently because the latter was markedly affected by a slight openness in the cheese.     

SENSORY TEXTURE PROFILE OF AFRICAN FOODS MADE FROM YAM AND CASSAVA

The textural characteristics of African foods made from yam and cassava were characterized by the sensory profile technique. Products with identical processing techniques reconstituted to the same moisture content showed similar characteristics of firmness, adhesiveness and ease of working to a spherical mass. The important attributes of smoothness, springiness or bounciness, and ease of swallowing without mouth coating were common to all the products and are good measures of their overall acceptability. This method is simple and provides a method of quality control that could be used by industrial manufacturers of these products.     

FULL UNIAXIAL COMPRESSION CURVES FOR PREDICTING SENSORY TEXTURE QUALITY OF COOKED POTATOES

The prediction of six different sensory texture attributes of twenty-seven potato samples based on uniaxial compression curve features and full uniaxial compressions curves is reported. The data set comprised five varieties, sorted in dry matter bins, and sampled at two storage times. The predictions of most of the sensory texture attributes from full compression curves performed better than just using curve features. Furthermore, force-deformation curves are shown to give slightly better predictions than stress-strain curves. For most of the texture attributes better predictions were obtained using uniaxial compression data from raw potato samples as compared to cooked samples. This study is meant to open up a debate on interpreting the information in uniaxial compression curves in relation to sensory texture quality. Multivariate analysis can handle this and can further give insight about where in the curve the information relevant for the predictions of the sensory attributes is found.     

EVALUATION OF LENTIL TEXTURE MEASUREMENTS BY COMPRESSION TESTING

The variability in texture for lentils of different size, from different locations and cooked for varying lengths of time was examined in relation to the sample size and the extent to which the sample was compressed during testing. The force to compress the lentils was found to be dependent on all variables examined and also demonstrated significant interactions between these variables. The coefficient of variability was dependent on the size of the lentil, a two-way interaction between sample size and compression and a three-way interaction between location, cooking time and sample size. Regardless of lentil size, location where the lentil was grown and the cooking time used, the variability in the texture readings was lowest when the larger sample size and maximum compression force were used.     

PREDICTION OF INSTRUMENTAL AND SENSORY TEXTURAL CHARACTERISTICS OF MAHON CHEESE FROM ULTRASONIC MEASUREMENTS

Ultrasonic velocity was related to sensory and instrumental texture measurements. A semi-logarithmic model (Weber-Fechner) was used to relate the sensory and instrumental texture measurements. The ultrasonic velocity ranged from 1650 to 1723 m/s for the softest and hardest cheese, respectively. As expected from theoretical equations, the ultrasonic velocity was related to the square root of the instrumental measurements. The deformability modulus (r²=0.93) and the slope in puncture (r²=0.85) were the most closely related parameters. A model developed from the relationship between sensory and instrumental texture and the relationship between ultrasonic velocity and instrumental texture, was used to relate velocity to sensory measurements. Elasticity (r²= 0.84) and firmness (r²= 0.81) were the sensory attributes which best correlated with ultrasonic velocity. From the obtained results, it was concluded that ultrasonic velocity measurements could be used to assess instrumental and sensory properties of Mahon cheese texture nondestructively, and therefore could be used for grading purposes.     

UNIAXIAL COMPRESSION OF GELS MADE FROM PROTEIN AND K-CARRAGEENAN

Investigations of gels (18% total solids) made from pea protein isolates (PPI) or soy protein isolate (SPI) with differing amounts of _K-carrageenan added showed that the gel strength increased with the concentration of _K-carrageenan. When the concentration of_K-carrageenan exceeded 0.4%, gels made with PPI were stronger and more stiff than equivalent gels made with SPI. Addition of _K-carrageenan stabilized gels made with PPI towards variations in brittleness (indicated by strain at fracture) with pH. This was not the case when SPI was used. Preheating (75C, 2 min) suspensions containing protein isolates and _K-carrageenan before gel formation increased the strength and stiffness of the final gels, most pronounced when SPI was used. Addition of NaCl (0.5–2%) reduced strength and stiffness of gels, whereas CaCl₂ had no influence on gel properties. Mixtures of PPI and SPI proved to be weaker and more brittle than gels made from only SPI of PPI. Results indicate that using proteins of different origin can cause differences in gel structure.     

NEW PROCEDURE FOR ESTIMATING THE MODULUS OF DEFORMABILITY OF CHEESE FROM UNIAXIAL COMPRESSION TESTS

The gradient of the inflection at the lowest strain in a stress versus strain curve was used to estimate the modulus of deformability (E_d) of cheese from the commonly used uniaxial compression test. The procedure required a sufficiently high sampling rate (e. g. 50 Hz at an initial strain rate of 0.0332 s⁻¹) to give data that provided fine structure to the measurements which is not usually reported. This procedure was based on the empirical observation that there was an initial concave up region prior to the usually reported concave down region of the curve for all samples studied. Numerical estimation of the gradient was used to locate the inflection point, and to estimate the gradient at that point. The procedure gave a well-defined measurement in the region of interest at small strain. It did not assume that all samples had the same strain region for compaction-dominating and fracture-dominating processes. Thus, in effect, it took account of the different strains at which E_d should be measured and eliminated differences in E_d between samples induced by differences in these processes. This procedure was compared with three existing procedures, for three cheeses. The procedure used responded differently to each cheese at the 1 % level. Values of E_d from the inflection point were similar to those from the gradient over 0.5 to 1.5 times the inflection strain, and higher than those from the gradient over 0 to 0.04 strain or from the linear term in a fiph order polynomial fit to the data up to fracture. The ranking of Ed for each cheese was the same for each procedure and the relative magnitude of Ed for each cheese was similar for each procedure.     

STEADY SHEAR VISCOSITY OF ULTRAFILTERED WHOLE AND SKIM MILK RETENTATES BEFORE AND DURING FERMENTATION

Steady shear viscosities are reported for skim and whole milk retentates of different volume concentrations after ultrafiltration, as well as during fermentation for the most concentrated retentates with and without salt addition. Retentates up to 3X exhibit Newtonian behaviour, while the most concentrated retentates (5X and 5.3X whole and skim) fit the power law model. The fermentation follows a three-phase model, during which the pH decreases from the natural pH of 6.0–6.5 to around 5.0–5.1. The viscosities of the fermented retentates vary significantly with the change of pH, depending on the fat and salt contents.     

SENSORY CHARACTERISTICS OF EWE MILK CHEESE MADE WITH THREE TYPES OF COAGULANT: CALF RENNET, POWDERED VEGETABLE COAGULANT AND CRUDE AQUEOUS EXTRACT FROM CYNARA CARDUNCULUS

This article reports on a study of the sensorial characteristics of ewe milk cheese (Los Pedroches) made with animal rennet and two types of coagulant obtained from the cardoon Cynara cardunculus. The cheeses made with rennet displayed a less odor intensity: pungent odor and acid odor; a less acid taste; and a slightly lighter color. They were harder and firmer, but less creamy than those made with the vegetable coagulant (powdered vegetable coagulant [PVC] and crude aqueous extract [CAE] from C. cardunculus). However, the cheeses made with PVC showed organoleptic characteristics very similar to the cheeses made with CAE from C. cardunculus. After 90 days' ripening, the cheeses made with vegetable coagulant displayed a slightly more bitter taste than those made with rennet. In general terms, increased ripening time prompted the increased scores for most of the sensory attributes studied.     

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.     

BEHAVIOR OF MOZZARELLA, CHEDDAR AND PROCESSED CHEESE SPREAD IN LUBRICATED AND BONDED UNIAXIAL COMPRESSION

The response of a material under uniaxial compression depends both on the bulk material properties and on the frictional effects at the sample-platen interface. Three commercial cheeses (cheddar, mozzarella and processed cheese spread) were studied in uniaxial compression. Frictional effects at the sample surface were examined under three conditions: (1) lubrication of the sample-platen interface; (2) bonding of the sample to the instrument platens; (3) samples neither bonded nor lubricated. The forces required to deform the cylindrical sample to a given strain level were highest for the bonded cases and lowest under lubricated conditions. The stress in lubricated compression, ρ_L, was calculated from Fh(πR_ρ²h_ρ)