MODERNIZATION OF TEXTURE INSTRUMENTATION *

Abstract. The use of electronic instruments to record force and deformation in objective texture measurements is reviewed to point out that much equipment is available for that purpose and to indicate some of the problems associated with its use. Electronic transducers are universally applicable to texture measuring systems and can give precise measurements with a high degree of resolution. Several examples of modernized texture instruments are described to demonstrate different methods of approach. Special purpose or ‘universal units’ can be developed. It is concluded that force and deformation can be recorded by electronic techniques in any textural test but that the interpretation of the data is the major problem.     

Surface texture of foods: perception and characterization

Surface texture is generally accepted as a key sensory factor of food materials and has great impact on consumers' perception and expectation of a food product. However, no authentic definition has been given in the literature for the term surface texture. Its real meaning is often rather confusing, varying from case to case and from person to person. A general consensus is that surface texture is a multi-parameter sensory factor composed of those surface-related features which can be perceived by visual, tactile handfeel, and tactile mouthfeel senses. A list of such surface-related features has been produced in this review, and of those, topographical properties are probably the most intensively investigated features in literature and are discussed in detail in this paper. The surface texture of a food can be characterized by either sensory panel tests or by physical instrument tests. The former uses panellists (trained or untrained) for sensory assessment, while the latter applies physical techniques to characterize the surface. While sensory tests are widely used for studies on consumers' perception and preference of foods, instrumental characterization uses one or few parameters to define a surface (either qualitatively or quantitatively). Physical techniques used for surface characterization are categorized into two groups: surface contacting and non-surface contacting. The former include tribometer, surface force apparatus, contact profilometry, atomic force microscopy, friction force microscopy, etc. Non-surface contacting techniques include gloss metre, fiber optic reflectometer, angle-resolved light scattering apparatus, surface glistening points method, electron microscopy, confocal laser scanning microscopy, etc. The principles and application examples of these techniques were discussed in this review.     

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.     

The Use of Fractional Conversion Technique to Investigate the Effects of Testing Parameters on Texture Degradation Kinetics

ABSTRACT: To study the effects of testing parameters on texture degradation, texture loss of potatoes heated at 80 °C was measured using an Instron universal testing machine as well as a texture analyzer under 2 instrument crosshead speeds, 2 sample sizes, and either compression or shear modes of mechanical deformation. Using the fractional conversion as a texture index, the kinetics of texture degradation of potatoes fitted a single 1^st order reaction model, and the rate constant (or D value) was shown to be independent of the test used to determine the texture index. The average D value was 30 ± 1.2 min at 80 °C.     

ENGINEERING ASSESSMENT AND CRITIQUE OF INSTRUMENTS USED FOR MEAT TENDERNESS EVALUATION*

A review of the methods used to measure meat texture indicates considerable confusion in terminology, test conditions, and interpretation of the readings that makes evaluation of the results a complex task. Standardization of the methods appears premature and until this is accomplished, the applied methodology must be reported fully. Errors due to instrument design can no longer be accepted since modern instruments that overcome this are readily available. A common error in terminology or interpretation is the use of the term shear to describe the rupture imposed on meat samples in popular tests. It is shown that meat generally ruptures in tension which is also the case during mastication; this explains why empirical measurements often relate to sensory readings. It is concluded that there is room for improvement in existing methods, particularly in the interpretation of the results using common sense, close observation and theoretical analysis.     

Textural Characterization of Cheeses Using Vane Rheometry and Torsion Analysis

ABSTRACT Vane rheometry was applied to textural characterization of cheeses and compared with torsion analysis. A Haake VT 550 viscotester was used for both vane and torsion tests at strain rates of 0.003 to 0.524 s^-1. Angular deformation and shear stress in the vane test increased with increasing low strain rate and was rate independent at higher rates. This shear rate dependency of stress and deformation varied with cheese types. Shear stresses from the vane method were lower than torsion shear stresses. Similar texture maps of cheeses were generated by plotting stress and strain or angular deformation values from the 2 testing methods. The findings indicate the vane technique can be used for rapid textural characterization of cheeses.     

INSTRUMENTAL MULTIPLE TEXTURE PROFILE ANALYSIS OF COOKED GROUND BEEF PATTIES AND SMOKED BEEF

An instrumental texture profile for cooked hamburger patties was obtained by repeated tests on the same samples in the wire extrusion cell of the Ottawa Texture Measuring System. The correlation between sensory and instrumental texture profile parameters was increased when two or more instrument test cycles were applied to each sample in the same test cell. Tests with smoked beef and hamburger patties showed that the change in textural characteristics with repeated cycles depended on the texture of the food.     

RESEARCH NOTE A SIMPLE TEXTURE TEST SYSTEM

A simple inexpensive texture test system is described which is suitable for quality control applications. The apparatus is constructed from a drill press stand, a mechanical force gauge and a test cell. The effect of different operators and sample thickness was investigated using apple and potato as test material. The performance of this system was compared with that of the FTC Texture Press (Kramer Shear Press) in the testing of several foods .     

Variations in banana properties

Samples prepared from different bananas and from different parts of a banana may vary in their properties, which may cause variations in the final results in experiments. Therefore, assessment of variation in the samples’ properties is necessary, and it can be evaluated using statistical analysis. In this work, the variation in banana properties—colour, texture, moisture and sugar contents—within and between bananas were assessed statistically using a two-stage nested design test and the two-sample t-test. Results show that the variation of properties is significant for bananas with different degrees of ripeness. This finding suggests that samples can be prepared from different parts of the bananas provided that the bananas are at the same degrees of ripeness. It was also found that the location of sample in the drying chamber did not affect the measured properties of the drying bananas, significantly. The tests performed for banana texture using a laboratory apparatus produced results that were similar to those performed using a dynamic mechanical analyzer. This suggests that the use of highly-sophisticated instruments in the texture analysis of dried fruit in terms of the apparent modulus is not crucial.     

CORRELATING SENSORY WITH INSTRUMENTAL TEXTURE MEASUREMENTS—AN OVERVIEW OF RECENT DEVELOPMENTS1

Reasons for seeking correlations between sensory and instrumental measurements are discussed and factors which affect such correlations are pointed out. Considerable advances made in the last 1–2 decades in this field can be attributed to the general agreement that texture is a sensory and a multiple parameter quality, and to the interdisciplinary nature of new research approaches. Current trends include use of multiple correlations, attempts to understand the rheology of the human sensing apparatus, an engineering treatment of sensory perceptions, and greater attention to the rheological nature of test foods.     

Simplified texture profile analysis of cooked potatoes

Potato specimens (diameter 25 mm, height 10 mm) were cooked in vacuumed plastic bags at 95° C for intervals of 20‐40 min. The specimen texture was determined using modified one bite TPA test (termed as STPA). The classical TPA parameters, that can be determined from one bite were completed and some new parameters were included into the texture profile, mainly Young's modulus, initial elasticity and ratio of fracturability to Young's modulus. The test was performed repeatedly using Instron Testing Machine. The test parameters were determined by evaluating the computer saved deformation curves. Sensory panel test was used as a base for comparison of the instrumental parameters and the sensory texture.     

INSTRUMENTAL TEXTURE STUDIES ON CHOCOLATE

Instrumental methods to analyze texture of plain chocolates and milk chocolate are reviewed. Using a strength testing apparatus and special measuring cells a method to determine the compression strength, shear strength and rupture force during hesion testing are described. By means of a modified penetrometer equipped with a recording device the melting properties were determined. To determine the maximum value of size of disperse components a modified precision thickness testing instrument is applied. The methods offer good reproducibility. The influence of some measuring parameters and sources of error are explained.     

Effects of structural parameters on compressibility and soiling properties of machine woven carpets

Compressibility performance of the machine woven carpet after a static or dynamic loading expresses the texture deformation tendency of the carpet. This study is an experimental attempt to investigate the effects of pile height and pile density on compressibility and soiling property by dynamic loading, prolonged heavy static loading, compression recovery and artificial soiling tests. In this study, a total of 12 carpet samples with three different pile heights and four different pile densities were tested. As a result of this study, it was seen that higher pile density provides a lower thickness loss and so a lower level of texture deformation. On the other hand, pile height has a preventing effect for texture deformation for static loading and compression recovery tests whereas there is no considerable effect on dynamic loading test. There is no considerable difference between the soiling properties of the samples.     

缅甸硬玉岩的结构与显微构造:硬玉质翡翠的成因意义

对翡翠的结构及其成因进行了评述. 依据其形成阶段及岩相学特征将缅甸硬玉岩的结构首次分为三大类: 原生结构、变形变质结构及后生充填结构. 依据各大类结构的具体特征作了进一步分类, 对每一结构进行了详细的描述, 并对每种结构的宝石学意义进行了讨论. 强调了变形变质作用是翡翠形成必不可少的条件, 指出多期、多阶段性和变形机制因硬玉岩所处的位置不同而出现明显差异, 从而导致翡翠具有独特的场口特征.     

Invited review: Sensory and mechanical properties of cheese texture

Instrumental mechanical properties (instrumental tests that measure force and deformation over time) of cheese and cheese texture (sensory perception of cheese structure) are critical attributes. Accurate measurement of these properties requires both instrumental and sensory testing. Fundamental rheological and fracture tests provide accurate measurement of mechanical properties that can be described based on chemical and structural models. Sensory testing likewise covers a range of possible tests with selection of the specific test dependent of the specific goal desired. Establishing relationships between instrumental and sensory tests requires careful selection of tests and consideration and analysis of the results. A review of these tests and a critical analysis of establishing relationships between instrumental and sensory tests is presented.     

EVALUATION OF THE TEXTURE OF FRIED POTATOES

Texture of potatoes with different shapes (slices and strips) were evaluated after frying and in some cases after baking. Blanched and unblanched potato slices (Bintje variety) were fried at four oil temperatures: 160, 170, 180 and 190C until reaching a moisture content of ∼1.7%. A puncture test with three point support for the slices was applied to measure the texture of potato chips using the following parameters extracted from the force versus distance curves: maximum force of break (MFB) and deformation of break (DB). These two parameters were useful to follow the changes in texture of the fried slices with moisture content at different frying temperatures. Blanched and unblanched potato strips were partially fried at 160C and 190C for 60, 90 and 120 s. The par-fried potatoes were frozen at -20C for one day after which they were baked at 200C for 15 min. The texture of the baked potato strips was evaluated using a bending test with two support points. From the force versus distance curves, two parameters were extracted: maximum force of deformation (MFD) and maximum deformation (MD). Significant higher MFB and lower DB values (P > 0.1) for unblanched fried slices indicate that these are crispier than blanched chips for moisture contents lower than 4% (6.59 N and 0.62 mm vs 5.74 N and vs 0.75 mm for unblanched and blanched chips, respectively, average values for the four frying temperatures employed). There was no effect of the frying temperature and the pretreatment (blanching or unblanching) on the texture of the frozen par-fried potatoes after baking when compared at the same residual moisture content, but blanched potato strips lost moisture more slowly both in frying and in baking.     

五种苹果质构测定方法的比较及与感官评价的相关性分析

为比较5种苹果质构不同测定方法,采用剪切法、穿刺法和TPA压缩法测定了辽宁地区5种主栽苹果的质构特征,同时研究了不同测试条件对测定指标的影响,并分析了仪器测定与感官评价结果的相关性。结果表明剪切、穿刺和TPA压缩均能测得苹果的硬度特征,并区分不同品种间的差异,去皮果肉硬度大小依次为王林 > 红富士 > 国光 > 乔纳金 > 黄元帅;穿刺法检测显示果皮对苹果质构有显著影响(P<0.05),且不同穿刺部位的质构差异显著(P<0.05),其中果顶部位穿刺硬度值最大,其次为果肩和赤道;与感官评价相关性分析显示最大穿刺模量与感官脆性极显著相关(r=0.638,P<0.01),可作为苹果脆性的表征指标;对TPA法,随着压缩形变量增加,苹果硬度测定值显著增加(P<0.05),而内聚性显著减小(P<0.05),且形变量为25%时与感官评价相关性最好。本研究表明穿刺法和TPA法均适用于苹果质构的测定,果皮及穿刺位点对穿刺影响显著,最大穿刺模量可用于表征苹果脆性指标;压缩形变量为25%时TPA法所测得质构参数与感官评价结果相关性最好。     

测试条件对苹果TPA质地参数的影响

简要介绍了TPA质地分析方法，并对苹果片进行TPA测试，研究压缩速率和压缩程度对测试结果的影响。结果表明，压缩程度对考察的四个质地参数有显著影响，压缩速率无显著影响。