COMPARISON OF TWO INSTRUMENTAL METHODS WITH SENSORY TEXTURE OF PROTEIN GELS2

The textural attributes of 8 different heat-induced protein gel preparations evaluated by torsion failure testing and Instron texture profile analysis (TPA) were compared to sensory ratings by a trained texture profile panel. The gels presented a wide range of textural properties as determined by the instrumental and sensory parameters. Among the instrumental parameters, true shear strain at failure was the most frequent and significant predictor of sensory notes. Initial shear modulus and 50% compression force had the poorest correlations with sensory notes. Comparison of the two instrumental tests produced high correlations between shear stress at failure and TPA hardness; true shear strain at failure and TPA cohesiveness; and, initial shear modulus and 50% compression force. High correlations were also observed among various panel notes. Canonical correlation analyses showed that sets of linear combinations of parameters from each one of the 3 tests (torsion, TPA or sensory) were highly correlated to sets from either of the other two. Regression equations relating each of the instrumental tests to sensory notes were developed. Of the torsion failure parameters, the logarithm of true shear strain most commonly appeared in the equations. Of the TPA parameters, cohesiveness and its logarithm were the terms that were most frequent. High R² values were obtained for regression equations developed for predicting torsion failure parameters based on TPA parameters.     

PHYSICAL AND SENSORY CHARACTERISTICS OF COMMERCIALLY AVAILABLE FRANKFURTERS

This study's objective was to identify the range of physical and sensory properties of commercially available frankfurters. Twenty-five types of frankfurters were evaluated by a six-member sensory panel and subjected to Instron texture profiling. A wide range of sensory and textural characteristics was observed for acceptable frankfurters. Salty flavor and juiciness were correlated with fat content, but salt and fat content were inversely correlated. Negative correlations occurred between fat content and Instron fracturability and compression; fat content decreased resistance to force from mechanical stress. Firmness was positively correlated with Warner-Bratzler shear force. The development of an accurate regression equation to predict sensory hardness was not possible with this data set.     

STRESS RELAXATION DURING FORCE-COMPRESSION STUDIES ON FOODS WITH THE INSTRON UNIVERSAL TESTING MACHINE AND ITS IMPLICATIONS

Abstract. The time required to apply the force in force-compression studies with the Instron Universal Testing Machine is long enough for short time relaxation processes to operate, possibly via intermolecular attraction forces. A theoretical analysis is presented whereby stress relaxation can be determined for the stress-strain region in which the Boltzmann Superposition Principle is valid. Application of the analysis is demonstrated using force-compression data obtained on cheeses of different textural properties. After correction for stress relaxation, the calculated and experimental relaxation modulus-time curves agree satisfactorily over a much longer time interval for Edam cheese than for Cheddar cheese. The latter cheese becomes non-linear at much smaller compressions than does Edam cheese, possibly by the propagation of cracks through the sample during compression. Firmness is one of the textural properties evaluated during the first bite of mastication. Since the time associated with the first bite is longer than that required for application of force during the first compression of a sample with the Instron in this study, it is possible that the sensory evaluation of firmness is made under conditions involving stress relaxation.     

FORCE-DEFORMATION CONDITIONS ASSOCIATED WITH THE EVALUATION OF BRITTLENESS AND CRISPNESS IN SELECTED FOODS1

The brittleness and crispness of low moisture foods and the crispness of selected high moisture foods were evaluated both instrumentally by Instron fracture tests and using a sensory panel. Brittleness was evaluated sensorially during the “first bite” whereas crispness was identified at a later stage of mastication. The maximum force at fracture of low moisture foods correlated inversely with panelists’ evaluations of brittleness either in the mouth or using the fingers. Panelists' evaluations of crispness in the mouth correlated reasonably well with the initial linear portion of the Instron force-deformation curves when the sample were supported near their ends and also in their middle regions. The shapes of the force-deformation curves for high moisture foods were very much influenced by the way in which samples were supported in fracture tests, the method of fracture and the Instron cross-head speed.     

CONTROL OF DEFORMATION IN TEXTURE TESTS *

Abstract. The motion of the Instron crosshead during small deformations (e. g. 0.25 mm) in tensile tests performed at the available range of deformation rates was examined. Large errors are introduced in the deformation readings if it is assumed that the deformation rate was constant at the rate selected because, as with any instrument of this type, the crosshead requires time to accelerate to the selected speed. The characteristic behaviour of the food is subject to misinterpretation if the applied deformation profile is unknown. It was found that the errors are larger when the instrument is used incorrectly by performing tensile tests below the crosshead. The work demonstrated some of the limitations that must be recognized when applying the Instron, or any deformation mechanism, to certain texture tests. It is concluded that food behaviour, under small deformations, could be recorded precisely and interpreted correctly providing that both the force and deformation are recorded against time. Control of the crosshead stopping and reversal points was also examined, particularly in relation to the instrumental texture profile analysis. Crosshead acceleration affects the readings and interpretation of the data at the reversal point. If the deformation rate is changed, the stopping point must be adjusted.     

Effect of chemical composition of wheat flour and functional properties of dough on the quality of south Indian parotta

Six flours differing in quality were analysed for their chemical and rheological parameters. South Indian parottas were prepared and evaluated for their textural characteristics using an Instron universal testing machine (UTM) and their sensory characteristics by a trained panel. The correlation coefficient data indicated that among the chemical characteristics of flours, dry gluten, protein and SDS sedimentation value were found to be the best indices in predicting the quality of parotta. The rheological characteristics, such as farinograph water absorption, extensograph ratio figure and area, and Instron apparent biaxial extensional viscosity (ABEV), hardness and cohesiveness were found to be highly correlated to the overall quality score of parotta. Sensory texture of parotta was found to be highly correlated to shear force as well as compression force (r=0.99, P ≤ 0.001) indicating that shear and compression forces could be considered as the best indices of sensory texture of parotta.     

A TECHNIQUE FOR ESTABLISHING INSTRUMENTAL CONDITIONS FOR MEASURING FOOD FIRMNESS TO SIMULATE CONSUMER EVALUATIONS*

Abstract. A method is described for measuring the force and the rate at which it is applied to fruits and vegetables by the consumer's hands in judging firmness. Halves of the product were mounted on a force transducer, squeezed and the forces recorded. Preliminary results from an untrained panel indicated that the rates and maximum forces used by males and females are different and depend on the firmness of the product. The data also suggest that the rate of force application in sensory testing is significantly greater than that customarily used in instrumental tests. Limitations of the technique and its potential usefulness in establishing more rational conditions for objective firmness tests are discussed.     

RELATIONSHIPS BETWEEN SENSORY CRISPNESS AND OTHER SENSORY AND INSTRUMENTAL PARAMETERS1

Twenty subjects judged the crispness, loudness, and firmness of sixteen food samples by both biting and chewing and by only biting the foods. These subjects also scored the foods for thirteen textural qualities. Instrumental measures of slope, peak force, and deformation to fracture were obtained for the sixteen foods from a snap test at four deformation rates. Whether a subject judged an attribute by the bite or the bite and chew technique made little or no difference in the sensory judgments. Crispness appeared to be very closely related to loudness and less closely related to firmness. Loudness of the chewing sounds was more closely related to crispness than to firmness. Of the sensory qualities studied, loud, snap, and crackly were the three most closely related to crispness. Of the instrumental parameters Young's Modulus generally had the highest correlation with the crispness of all foods and peak force generally had the highest correlation with firmness. Deformation rate had minimal effects on measures of flexure or peak force, but its effects on Young's Modulus were frequently large and irregular. A vibrotactile-acoustical hypothesis for crispness is proposed.     

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.     

INSTRUMENTAL AND SENSORY TEXTURAL PROPERTIES OF FURA

ABSTRACT

A uniaxial compression test and sensory textural analysis was conducted of fura samples made from millet flour. Significant differences (p<0.05) existed among the samples for hardness (the force to compress the sample between molar teeth), cohesiveness (extent to which sample falls apart during chewing) and gumminess (denseness and cohesion persisting during mastication). Correlations between sensory and instrumental tests revealed that a significant relationship exists between modulus of deformability and cohesiveness (r=?0.93, p<0.05); gradient and springiness (r=?0.90, p<0.05); deformation at failure and chewiness (r=0.98, p<0.05); energy per unit mass and gumminess (r=?0.95, p<0.05). A fura quality scale was established based on the peak force; soft and poor quality fura have a peak force of <19 kN; acceptable fura has a peak force of 19–24 kN; a firm and good quality fura, 24–25 kN; very hard and very poor quality fura have a peak force of >25 kN.     

EFFECT OF OTHER HYDROCOLLOIDS ON THE TEXTURE OF KAPPA CARRAGEENAN GELS1

The effect of different hydrocolloids on the breaking strength, cohesiveness and rigidity of kappa carrageenan gels was studied using comression tests with the Instron. Instrumental measurements were supplemented with benchtop sensory evaluation of texture by mouth, gel clarity and syneresis. The evaluated hydrocolloids included locust bean gum, iota carrageenan, amidated low methoxyl pectin, xanthan gum, and their selected combinations. Best gels were obtained by using 0.15% kappa carrageenan and 0.85% iota carrageenan, or 0.2% kappa carrageenan, 0.2% locust bean gum and 0.6% amidated LM pectin. Although none duplicated the textural quality of gelatine gels, they represented a wide range of interesting and potentially useful textures.     

TEXTURE OF CARROTS

Abstract Shear and compression strengths of individual carrots were measured with the Instron Universal Testing Machine. Compression correlated highly, but shear poorly, with sensory hardness as judged by compressing and flexing. The study confirmed the usefullness of the coefficient of compression in predicting textural quality of carrots.     

SENSORY AND TEXTURAL EVALUATION OF MAINE WILD BLUEBERRIES FOR THE FRESH PACK MARKET

Maine wild blueberries were sized according to berry diameter into three size classes; ≤ 8 mm, 9–10 mm and 11–12 mm. A consumer sensory panel was asked to indicate their opinion of flavor, texture and overall attributes using a 9-point hedonic scale. Subsamples of berries were subjected to a compression test using an Instron Materials testing machine, measuring force and deformation to point of rupture of individual blueberries. Berries ≤ 8 mm were significantly lower in sensory acceptability for all three attributes evaluated. No significant difference was found between 9–10 mm and 11–12 mm samples. Both were rated "like moderately". Ranked preference data indicated a significant preference for the larger 11–12 mm berries. The results of the compression tests revealed significant differences among all size classes with respect to the apparent modulus. A linear relationship was found between the "texture" sensory attribute and the elastic modulus.     

A PHYSICO-CHEMICAL STUDY OF THE MECHANICAL PROPERTIES OF LOW AND INTERMEDIATE MOISTURE FOODS*

A number of textural properties of precooked, freeze-dried beef were examined by a cutting-extrusion test (force) and by a compression test (seven different properties). The tests were performed at different points of the moisture sorption isotherm over the complete range of water activity, A_w. In cutting-extrusion experiments (Allo Kramer Shear Press), a maximum in the force vs. A_w curve was observed at about A_w= 0.85. In compression experiments (Instron Universal Testing Apparatus), important changes of the textural properties were found in the range A_w= 0.15–0.30. These changes were paralleled by changes in the thermodynamic functions of water vapor sorption, especially in the standard differential entropy. Thermodynamic theory and mechanical measurements were used to interpret the textural changes in terms of increased crystallinity and subsequent swelling of the food structure.     

A STUDY OF FORCE-COMPRESSION CONDITIONS ASSOCIATED WITH HARDNESS EVALUATION IN SEVERAL FOODS

Abstract. The hardness of fourteen foods has been evaluated by panel tests and by compression tests with a table model Instron. Oral evaluation of hardness was correlated with instrumental force -% compression data obtained for compressions extending up to 80% and with crosshead speeds up to 20 cm min⁻¹. With soft foods, agreement between panelists' and instrumental data commences at lower % compressions and lower applied forces than with hard foods. As the Instron crosshead speed increases so does the force required to achieve a desired % compression. With very hard foods exhibiting a short relaxation time, e. g. toffee, stress relaxation may influence the registered force. Crosshead speeds exceeding 20 cm min^-1** cannot be utilised in conjunction with the standard Instron recorder because its response time is too long. It should be replaced by a fast response recorder such as a UV recorder. The procedure whereby panelists evaluate hardness during the first downstroke of mastication appears to change from compression to biting as hardness increases. A limited number of tests with Cheddar cheese and table jelly suggest that hardness evaluation by squeezing samples between the thumb and index finger involves lower % compression and lower forces than the oral evaluation of hardness with the same products.     

A Puncture Testing Method for Monitoring Solid Substrate Fermentation

Meitauza, an indigenous Chinese food made from fermented okara (soymilk residue), was used as a model system for monitoring solid substrate fermentations. The Instron Universal Testing machine and Chatillon hand operated force gauge were used to measure the force to penetrate meitauza as an estimation of mycelial binding. Increased firmness during fermentation was caused by fungal growth and not by water loss and surface crusting. Puncture force readings with the Instron were werll correlated (r = 0.86) with Chatillon measurements. The results of this study indicate that textural measurements using puncture force may have valuable application in monitoring the degree of mycelial growth or fermentation in a solid substrate.