MECHANICAL PROPERTIES AND SENSORY TEXTURE ASSESSMENT OF CHEESES

The viscoelastic behaviour of hard and semi-hard cheeses was investigated in relation to sensory assessment of texture. The experiments consisted of two separate studies which involved sensory and uniaxial compression tests on eight cheeses in each study. The stress-strain data of the cheeses were approximated well by a power law relationship, showing that the strain and the time dependent variables were separable. The cheeses exhibited similar time dependent behaviour, so the degree of correlation between sensory and instrumental measurements was not influenced significantly by changing the deformation rate in the instrumental tests. Sensory firmness appeared to correlate with instrumental stiffness measurements in one study, but not in the other. This was probably due to the use of different panels and methods of sensory assessment.     

CORRELATION OF MECHANICAL PROPERTIES, COMPOSITION AND PERCEIVED TEXTURE OF BEEFBURGERS

Twenty-five brands of beefburgers were bought at retail in the United Kingdom, and their weights and dimensions, chemical composition, compressive strength and expressible fluid measured before and after grilling and compared with sensory evaluations. Compressive strength of grilled burgers measured with a punch and die, averaged 2.6 × 10⁴ Nm⁻² and varied from 1.1 to 4.6 × 10⁴Nm⁻² between brands. Beefburgers with a more rubbery, cohesive and coarser, tougher texture had higher compressive strength, higher total nitrogen, higher defatted meat content and more acceptable texture. The major variation in texture between brands was a combination of the sensory attributes rubberiness and tenderness of particles, and 70% of that principal component was accounted for by linear combination of three objective variables with measurements of strength predominant. The second principal sensory component, composed mainly of moistness and comminution attributes, was related to chemical assays and expressible fluid. These findings support the interpretation of the sensory profile as a primary component involving behaviour under stress and strain and a secondary involving perception of structure, composition and moistness.     

TEXTURE AND STRUCTURE OF CRISPY-PUFFED FOOD PRODUCTS I: MECHANICAL PROPERTIES IN BENDING

Mechanical properties of flat-bread-shaped extrudates were studied in bending. The effects of bending conditions (plunger thickness, support shape and distance between supports) are presented. Bending parameters, the modulus of deformability particularly, are used to study extrudate anisotropy, discriminate between various samples and correlations discussed in relation to cell structure. It is shown that the Ashby analysis of cellular materials applies to bending of extrudates, and that the modulus of deformability is correlated with cell size and cell density.     

SENSORY AND MECHANICAL ATTRIBUTES OF GEL TEXTURE

Eighteen experienced judges evaluated the texture of gels varying in gelatin concentration (22-45 g/L) in terms of firmness by oral and manual shear and compression, cohesiveness, and extent of breakdown in the mouth. Manual compression and biting with the front teeth discriminated well across gel concentrations. All sensory measures except extent of breakdown increased with gelatin concentration. Instron (IUTM) measurements showed that increasing gelatin concentration resulted in an increase in maximum force and force/deformation, but had little effect on deformation at yield and rupture or in elasticity and cohesiveness. Results from mechanical measurements varied with the type of force applied (compression, shear or puncture), the loading rate (50 or 200 mm/min), and the extent of deformation attained (40–90%). The highest discrimination across gel concentrations was achieved with shear force at a rate of 200 mm/min and at greater deformations. Sensory responses correlated most highly with the following IUTM measurements: (1) Compression forces at yield and at deformations of 70 and 85% at the higher crosshead speed; (2) Compression forces below the yield point at the lower crosshead speed; and (3) Shear forces measured at maximum deformation (90%) at 200 mm/min.     

TEXTURE AND STRUCTURE OF CRISPY-PUFFED FOOD PRODUCTS PART II: MECHANICAL PROPERTIES IN PUNCTURE

A puncture test was used to describe the mechanical and textural behavior of crispy-puffed food extrudates. Four criteria were identified from the force-time curves: (1) the average puncturing force, F_m, (2) the spatial frequency of structural ruptures, N_wr, (3) the average specific force of structural ruptures, f_wr, and (4) the crispness work, W_c. The discriminating power of these criteria was shown through the effects of moisture content and recipe composition in the extrusion-cooking process. Relationships between puncture criteria were also studied. The effect of water activity showed that the force related criteria described well the mechanical behavior of expanded extrudates.     

MODELLING THE MECHANICAL AND HISTOLOGICAL PROPERTIES OF CARROT TISSUE DURING COOKING IN RELATION TO TEXTURE AND CELL WALL CHANGES

A tensile test was used to measure four mechanical properties of carrot tissue cooked under various time-temperature conditions. A kinetic model describing the changes of these mechanical properties measured during cooking was developed. The histological properties of the rupture surfaces caused by the mechanical testing were investigated. The kinetic model was found capable of predicting the changes in the rupture mechanism of the cell walls. Determining the percentage of cell wall ruptures proved to be an accurate method to assess the textural state of carrot tissue during cooking as compared to the measurement of the mechanical properties.     

TEXTURAL PROPERTIES OF STORED AND IRRADIATED TIOGA STRAWBERRIES*

Fresh as well as irradiated Tioga strawberries were softer, required smaller forces to puncture and to compress, and exhibited smaller degrees of elasticity and recoverability from applied stress than the stored berries. Thus, fresh or irradiated strawberries should be more susceptible to mechanical damage during handling, shipping and marketing than the stored fruits.     

MECHANICAL AND SENSORY ASSESSMENT OF THE TEXTURE OF REFRIGERATOR-STORED SPRING ROLL PASTRY

Spring roll (or popiah) consists of a filling surrounded by a remarkably thin pastry that is subjected to tension as it is wound around the filling. It cracks easily if stored before use. Textural perception of the pastry in the mouth is also affected. Within 1 day of manufacture, the Young's modulus of the pastry increases ten-fold, the tensile strength and critical stress intensity factor (K_IC) increase to a lesser extent, but the strain to failure decreases. In the single-edge-notched test (mode I fracture) and trousers tear test (mode III fracture), which gave free-running cracks, fresh pastries were tougher than stored pastries because of blunting of the crack tip by large elastic strains. When the radii of curvature of crack tips in both fresh and stored pastries were constrained to be more equal in a cutting test, which induced out-of-plane shear in mode III fracture, fresh pastries were less tough than stored pastries. This paradox could be important in understanding otherwise contradictory textural assessments made by human subjects at the front versus the back of their mouth.     

DATABASE OF PHYSICAL PROPERTIES OF FOODS: SUBGROUP OF MECHANICAL AND RHEOLOGICAL PROPERTIES

An online database of numerical values of selected rheological and mechanical properties of foods has been constructed as part of a general database covering physical properties of foods. The objective is to provide an easy access to data for food engineers and others interested in physical properties. The collected data include viscosity, elasticity modulus, puncture force and more than 70 properties for over 600 foods. Each entry consists of a bibliographic reference. Tables may be attached to the bibliographic record, describing the food in terms of its composition and structure; the measurement method used, a validation and assessment code for the quality of the measured data and a matrix of the numerical values of the given physical property listed as a function of independent variables such as temperature, shear rate, pressure or composition parameters. This paper describes the organisation and management of the database and the processes of interrogating the database and contributing data by users. The database is on http://www.nelfood.com     

DIFFERENCES IN THE STRUCTURAL RESPONSE OF 'GRANNY-SMITH' APPLES UNDER MECHANICAL IMPACT AND COMPRESSION

Apple fruits, cv. Granny Smith, were subjected to mechanical impact and compression loads utilizing a steel rod with a spherical tip 19 mm diameter, 50.6 g mass. Energies applied were low enough to produce enzymatic reaction: 0.0120 J for impact, and 0.0199 J for compression. Bruised material was cut and examined with a transmission electron microscope. In both compression and impact, bruises showed a central region located in the flesh parenchyma, at a distance that approximately equalled the indentor tip radius. The parenchyma cells of this region were more altered than cells from the epidermis and hypodermis. Tissues under compression presented numerous deformed parenchyma cells with broken tonoplasts and tissue degradation as predicted by several investigators. The impacted cells supported different kinds of stresses than compressed cells, resulting in the formation of intensive vesiculation, either in the vacuole or in the middle lamella region between cell walls of adjacent cells.     

MECHANICAL PROPERTIES OF THE FLESH OF SWEET AND SOUR CHERRIES

The mechanical properties of the flesh of sweet and sour cherry varieties were studied using penetration of whole and skinned fruits by a cylindrical pin. Fresh and canned fruits were included in the study. The results obtained, and their relation to results obtained previously, show that the cherry flesh plays a more important role in the deformation process when its apparent modulus of elasticity is greater than approximately 0.15 MPa. At lower values compression behaviour of the cherry flesh seems to resemble the behaviour of liquids, and the fruit skin has a more important role in a fruit integrity.     

机械损伤对富士苹果采后软化生理的影响

以富士苹果为试材,研究了机械损伤后在5℃和18℃贮藏条件下对果肉颜色、果肉硬度、可溶性果胶和原果胶含量、纤维素含量及纤维素酶活性的影响.结果表明,机械损伤导致果肉L*、果肉硬度、原果胶含量、纤维素酶活性均快速下降;a*值显著上升;b*值、纤维素含量、可溶性果胶含量呈前期上升后期下降的趋势:在贮藏过程中,伤害部位的生理生化指标均显示了上升和下降的反复趋势.说明机械损伤破坏了细胞壁的组织结构,促进了果实的快速软化;随着贮藏期的延长,愈伤组织逐渐形成,从而达到伤害部位的自我修复.而且受伤果实在低温下贮藏各种生理代谢缓慢,有效地延缓了受伤果的快速衰老.     

面料力学性能与结构性能的相关性分析

针对当前服装企业中常要对面料进行预测分类以及性能总结,采用KES织物风格评价系统对采集的样品进行织物风格性能测试,并利用SPSS数据分析软件进行分析,以及织物力学性能的相互正交的六个主成分因子,以此来综合表达织物的风格性能,并建立了各类面料主成分因子与织物结构性能间的相关性模型。