EVALUATION OF THE VOLAND-STEVENS LFRA TEXTURE ANALYZER FOR MEASURING THE STRENGTH OF PECTIN SUGAR JELLIES

The Voland-Stevens LFRA texture analyzer was compared to the Tarr-Baker gelometer for its applicability to measuring jelly strength. Both instruments showed a linear relationship between jelly break strength and pectin content. The test results from the two instruments were highly correlated (r = 0.94). The coefficient of variation relative to the overall average of measurement was 5.0% for the Voland-Stevens LFRA and 8.4% for the Tarr-Baker gelometer. The Voland-Stevens LFRA instrument may be equal to or better than the Tarr-Baker gelometer for measuring jelly break strength. It offers the advantages of reduced errors in sample preparation and ease of instrument calibration.     

物性分析仪在食品质构测定方面的应用

质地特性是食品极其重要的品质因素。一般采用的感官评定方法主观因素偏重，而物性分析仪所反映的主要是与力学特性有关的食品质地特性，其结果具有较高的灵敏性与客观性，故其使用越来越广泛。本文综述了物性分析仪的原理及其在小麦粉制品、肉制品、水产品和乳制品中的应用，以及存在的问题与展望。     

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.     

RELATIONSHIP BETWEEN THE TEXTURE AND PECTIN CONSTITUENTS OF JAPANESE PEAR

The relationship between texture and pectin constituents and some related compounds of the Japanese pear (Pyrus serotina Render var. culta 'Housui') during fruit enlargement and ripening was studied. The modulus of elasticity, deformation ratio, and relaxation value from the flat plate compression test, and all the properties from the puncture test were affected by the pectin constituents, alcohol insoluble solids, and soluble solids. The hardness and deformation of the fruit obtained from the plate compression test might depend on the combination of the alcohol insoluble solids in fresh weight and weight of the fruit. The oxalate soluble pectin both in alcohol insoluble solids and in fresh weight affected the fruit texture more than the water soluble pectin. The solubitization of nonsoluble pectin to water soluble pectin appeared to influence the textural properties more than that of the nonsoluble pectin to oxalate soluble pectin. The puncture test was superior in analyzing the textural properties of the Japanese pear fruits with regard to changes in the pectin constituents.     

以桔皮果胶为基质的脂肪替代品在重油蛋糕中的应用

研究以桔皮果胶为基质的脂肪替代品在重油蛋糕中替代油脂量分别为20%、40%、60%对于样品理化性质、质构及感官评价指标的影响,结果表明:低脂蛋糕的密度高于对照样品;替代60%油脂的低脂蛋糕感官方面不易被消费者接受;当替代量低于40%时,脂肪替代品可以成功替代重油蛋糕中的油脂.     

THE ANALYSIS OF STRESS RELAXATION DATA OF SOME VISCOELASTIC FOODS USING A TEXTURE ANALYZER*

Uniaxial compression test for dough and several commercial products like jello, mozzarella cheese, cheddar cheese, tofu and sausage (cooked and uncooked) was performed using a texture analyzer (TA). Percent stress relaxation (%SR ), k1 (initial rate of relaxation), k2 (extent of relaxation) and relaxation time (RT) were calculated and compared for different products. The TA software was used to convert the raw SR data into a linear form. Constants k1 and k2 were determined from the intercept and slope of the linear data. Higher values of %SR and k2 (90 and 9, respectively) indicated higher elasticity for jello, whereas wheat flour dough samples showed the lowest values (20–30) for %SR and 1 to 2 for k2. The RT and k1 values were not good indicators for differentiating different products based on their viscoelastic behavior. Measurement of RT was limited by the maximum time for which the data were collected, whereas k1, because of its mathematical form, needed careful interpretation. In this study, %SR was found to be a good measure to interpret viscoelasticity of different food samples.     

POTATO EXTRACTIVES: EFFECT ON FIRMNESS OF PECTIN JELLIES AND VISCOSITY QF POTATO STARCH PASTES

SUMMARY— Pectin jellies and potato starch pastes were prepared with aqueous extracts of potato tissue. All jellies containing potato extractives were weaker than distilled water control jellies. Jellies containing extractives from bud tissue were weaker than those containing extractives from stem tissue. Extractives from tubers stored continuously at 38°F weakened the jellies to a greater extent than those from tubers stored at 38°F and conditioned for 1 wk. Jellies containing extractives from boiled tissue were weaker than those prepared with extractives from blanched or steamed tissue. The most viscous pastes were those made with distilled water. In every case, viscosity of pastes containing extractives from raw tissue was less than half that of distilled water pastes. When extractives from blanched, steamed or boiled tissue were used, the viscosity decreased still further. The rigidity of jellies and the viscosity of pastes prepared with deionized extracts were similar to those of jellies and pastes prepared with distilled water. The data suggest that extractives leached from potato tissue increase sloughing of potato tissue during cooking by weakening the pectic materials in the intercellular cement rather than by enhancing the swelling of starch in the cells.     

SENSORY EVALUATION OF THE TEXTURE OF 49 COMMERCIAL APPLE AND PEAR PUREES

ABSTRACT

The sensory texture of 49 market samples of pear and apple purees were examined by Flash profile and results were treated by Generalized Procustes Analysis. The product set encompassed grocery products, baby foods and drinking snacks. Four main sensory notions were used to describe the texture of this type of products: graininess, viscosity, moisture and grittiness. Pear and apple purees were discriminated by the gritty perception, carried out on the third component. The other three main characteristics were carried out on the first two axes, where six main groups of products were identified. Pear purees were close to baby foods. Thickened baby foods and pear and apple mixtures constituted additional groups. Finally, apple purees were close sensorially, but three groups could be discriminated by grainy and viscous perceptions. The number of products was not an obstacle and the panel managed the task as required.

PRACTICAL APPLICATIONS

Flash profile seems to be a powerful tool to provide a statement of the sensory diversity of a specific market very quickly even when the number of products is quite large.

     

ANALYSIS OF REPEATED STICKINESS MEASURES OF WHEAT DOUGH USING A TEXTURE ANALYZER

Stickiness of wheat dough using 51 international wheat genotypes was measured ten-times per sample using a texture analyzer and the improved Chen-Hoseney stickiness cell. Repeated measures analyses were carried out with the parameters adhesive force, adhesiveness, and stringiness of the force-time curves using the SAS MIXED procedure. The data revealed a high variability among observations from replicates of the same sample preparation. It is suggested to analyze a large (seven to ten) number of repeated measures per sample to account for the variation. Triplicate measures that result in reliable means with low standard errors for the particular lab conditions and test settings can be found by a repeated measure analysis.     

TEXTURE EVALUATION OF FRENCH ACID-TYPE FRESH CHEESES

A range of French acid-type fresh cheeses of various commercial brands was tested by a trained sensory panel which detected significant differences in thickness, smoothness and slipperiness. The cheeses exhibited thixotropic behaviour. The perceived thickness of the samples was highly correlated with the shear stress values obtained for a limited range of shear rates (30–80 _S⁻¹). The area of the hysteresis loop formed during the first shearing cycle of the samples over a wide range of shear rates (4.5–450 _S⁻¹) was negatively correlated to slipperiness. The correlation matrix showed that the sensory attributes were independent of the chemical composition of the products. Principal components analysis indicated the way the three sensory attributes were related to each other and to the rheological parameters.     

PECTIN, STARCH AND TEXTURE OF POTATOES: SOME PRACTICAL AND THEORETICAL IMPLICATIONS

This review emphasizes the interrelationships between starch and pectins as factors determining different textural qualities of potatoes. It includes examples of texture control through processing treatments affecting the different ways in which pectins are involved in textumi qualities and tissue (celi) sloughing. Previously unpublished observations on cell sloughing and cell rupturing also are included.     

SENSORY AND INSTRUMENTAL EVALUATION OF TEXTURE OF COOKED AND RAW MILLED RICES WITH SIMILAR STARCH PROPERTIES

Three pairs of milled rices with similar starch properties (low gelatinization temperature waxy, and low gelatinization temperature low amylose, and intermediate gelatinization temperature intermediate amylose) were assessed for cooked rice properties by two industry taste panels and for raw and cooked rice properties by 30-member Filipino consumer panels. Only slight differences in texture within pairs were noted by the two industry taste panels who had not been trained to assess boiled raw rice or waxy rice. The Filipino consumer panel gave significantly higher ranked scores for one low-amylose variety in both raw and cooked forms. Malagkit Sungsong suman sa antala was ranked higher than modern waxy rices. Instrumental methods for translucency and whiteness of raw rice and Instron hardness and stickiness of cooked rice were not able to detect differences perceived by the Filipino consumer panels.