ANALYSIS OF THE MECHANICS OF THE FRUIT PRESSURE TESTER

The Magness-Taylor pressure tester is used extensively as a firmness measuring device for convex-shaped fruits. Researchers have been interested to learn what is really being measured by this device when its probe is pressed against the fruit to the point of flesh rupture. This investigation analyzes the mechanics of deformation of Rome Beauty apples, with the skin sliced off, in two deformation stages namely prior to and after puncturing of the flesh. Theories of inelasticity and piercing problem are adopted in analyzing the theoretical stress distribution. With the stress distribution, the theoretical force-deformation relations were found which show the effect of probe size, shape, radius of curvature, and the mechanical properties of the fruit. Experimental tests included simple compression of cylindrical specimens of the flesh, punch shear tests of slices of the flesh, and pressure tests of whole pared fruits. With the 5/16-in. probe, agreement between experimental and theoretical results was within 1.5 % and 2.2 % for the first and the second deformation stage, respectively. Results showed that; (1) the Magness-Taylor pressure test involves a combination of shear and compression stresses; (2) an average conversion factor of 1.85 can be used to convert readings by a 5/16-in. rigid die to those by a 7/16-in. die; and (3) shearing strength of the flesh is the only mechanical property needed to predict the maximum force reading after puncturing of the flesh.     

THE TEXTURE TESTER,PRINCIPLES AND SELECTED APPLICATIONS*

An automatic, self-cleaning, recording instrument for testing textural properties of bite-size food pieces is described. The unit can be fitted with several types of test cells; results obtained with the shear cell are reported. Forces to break, compress, shear and push the food through the blades were identified from the recorded force-displacement curves. Typical curves for a variety of foods are given and applications of the unit to testing cold cereals, peas, fruit pieces etc. are described. The instrument lends itself well to generating data for construction of force distribution patterns which may describe geometrically small foods better than the average force reading.     

MEASUREMENT OF TEXTURE PARAMETERS OF FREEZE-DRIED BEEF*

A modified texture profile analysis with the Instron Universal Testing Apparatus was used to measure hardness and chewiness of precooked freeze-dried beef cubes in order to determine the influence of processing and reconditioning. Two different plate temperatures were used during freeze-drying, and the resulting product was reconditioned at four different water activities in addition to the dry and fully rehydrated product. Reconditioning temperatures of 52, 70, and 100°F were investigated. The results revealed that the hardness and chewiness values were the highest at water activities of 0.4 to 0.6 and with the product freeze-dried at a plate temperature of 105°F. The influence of reconditioning temperature was inconsistent, apparently due to an interaction between the water activity and the plate temperature.     

THE INFLUENCE ON BREAD TEXTURE OF PARTIALLY REPLACING WHEAT WITH POTATO PRODUCTS*

The use of potato products in wheat bread manufacture is reviewed with particular reference to their effect on the textural characteristics of bakers' dough and fresh bread, and the changes associated with bread staling. Possible interactions between the proteins in wheat and potato are discussed. Recent developments relating to the partial replacement of wheat by potato flakes are reviewed. Their effectiveness is discussed in terms of the chemical nature of potato starch, the physical state of starch in potato flakes and the influence exerted by additives such as glyceryl monostearate and fats.     

SOME OBSERVATIONS ON THE COLOR MEASUREMENT OF CANNED TUNA

The effect of different sample holders and various sample preparation techniques on the color of albacore, yellowfin and skipjack canned tuna was examined. It was observed that sample holder A, an empty 8 cm diam stainless steel can with a well 1.2 cm deep, gave the highest reflectance values with the lowest standard deviations. In addition, it saved considerable time in the color measurement. Investigations on the effect of various sample preparation techniques on the color of canned tuna showed that a regular meat grinder with a plate with 1/20 in. holes gave more uniform-sized particles which, in turn, resulted in high reflectance values with low standard deviations and reduced the time of sample preparation greatly.     

THE INFLUENCE OF VACUUM PRESSING ON THE TEXTURE OF CHEDDAR CHEESE*

A study was made of the influence of several factors on the texture of young and mature vacuum-pressed rindless cheese. Pressures greater than 26 lb/in² were required for maximum improvement in texture. A vacuum of 15 in was less effective than a vacuum of 25 in. Vacuum pressing of ‘dressed’ cheese for 5 min was almost as effective as vacuum pressing for 17 h; vacuum pressing after dressing was more effective than before dressing; transfer of vacuum-pressed cheese to a normal press for the completion of pressing did not affect texture. Vacuum treatment of curd before hooping and pressing in the normal way had no beneficial effect on texture; vacuum pressing improved the texture of cheese made with mixed-strain starters although this cheese was not as close as vacuum-pressed cheese made with single strain starters. The distinct improvement in cheese texture which resulted from some combinations of vacuum pressing condition was confirmed in commercial scale trials involving 2,540 rindless cheese. This improvement was evident when cheese were graded at two weeks and when regraded at maturity.     

EFFECT OF FRICTION ON THE PERFORMANCE OF TEXTURE TEST CELLS*

The relationship was measured between the normal contact force and the force required to overcome friction between food samples and a surface simulating a typical texture test cell. Peas produced frictional behavior that combined the characteristics of dry friction and fluid flow. Friction coefficients for selected foods ranged from 0.04 to 0.52. Friction force was linearly related to the normal contact force and non-linearly to the area of contact between the sample and the surface, and the speed of the sample relative to the surface. This verifies the fact that, with empirical texture test devices, these test variables must be held constant. The estimated friction forces represented a significant amount of the total force required to operate a wire extrusion cell and a back extrusion cell. It was concluded that standardization of the test cell would be easier to achieve if the contact area between the sample and the cell surfaces was minimized and if low friction materials were used to construct the cells.     

EFFECT OF HIGH PRESSURE PROCESSING ON THE TEXTURE OF SELECTED FRUITS AND VEGETABLES

Prepared fruits and vegetables were subjected to high pressure processing at 100–400 MPa for 5–60 min in an isostatic press and their influence on product texture was evaluated. Pressure had a dual effect on product texture characterized by an initial loss in texture, ascribed to the instantaneous pulse action of pressure, followed by a more gradual change as a result of pressure-hold. The extent of the initial loss and the subsequent partial recovery were pressure dependent with the former more prominent at higher pressures and the latter at lower pressures. The pressure treated samples were generally brighter in color somewhat resembling the appearance of mildly heat treated samples. For all vegetables pressure treated at 100 MPa for 60 min, the initial loss in texture was totally recovered during the pressure hold yielding an overall texture firmer than that of the raw product. There was no recovery of texture during the standing period at atmospheric pressure after the pressure treatment.     

EVALUATION OF TEXTURE OF PECTIN JELLIES WITH THE VOLAND-STEVENS TEXTURE ANALYZER

Texture profile analysis (TPA) parameters were determined with a Voland-Stevens Texture Analyzer-1000 (VSTA) and an Instron Universal Testing Machine. Because of the nature of the design of VSTA, reliable magnitudes of TPA parameters based on the force-time curves recorded during the down stroke can be calculated. With a 2.54 cm diameter plexiglas plunger, the TPA parameters with the VSTA were higher than those with the Instron by 1.45% for hardness to 16.1% for fracturability.     

TEXTURAL AND SENSORY ATTRIBUTES OF CURRIED RAW JACK FRUIT, FRIED AND PRESSURE COOKED

Studies were conducted to improve the texture and sensory qualities of raw jack fruit. Diced tender jack fruit was subjected to steam cooking (1 kg cm^-2 for 20 min) and oil frying at 150 ± 30C for 5 min and 180 ± 20C for 5 min, respectively. Minced mutton at 5% (w/w) of the jack fruit dice was incorporated into the curried recipe prepared from dice fried in oil at 150C to impart mutton flavor and tested for texture. The firmness of fried dice increased significantly as measured by peak force of 11.06 and 11.49 kg. cm^-2 compared to 0.33 kg. cm^-2 of steamcooked dice. Further, the sensory evaluation for texture and flavor of the samples in the curried recipe also revealed that the fry-treated samples (at 150 ± 30C) were better in quality than steam-cooked samples. The frying treatment of raw jack fruit dice increased the oil content of the dice (8.26% on FWB) compared to 0.6% in steamed dice. However, the treatment did not affect salt pick up.     

TEXTURE MEASUREMENT IN MEAT BY SENSORY EVALUATION*

Various sensory evaluation methods have been used to measure texture in meat. While some methods are more suitable than others, more work must be done before any one can be recommended as a standard method. Other aspects which require special attention are cooking of samples, selection of reference samples and the multicomponent nature of texture.     

OBSERVATIONS ON STRAWBERRY TEXTURE A THREE-PRONGED APPROACH

Sensory, instrumental and microscopic methods of evaluation were combined to permit relating textural parameters to structural characteristics of fresh, frozen and rehydrated freeze-dried strawberries. Large cells and thin cell walls appear to account for the ease of textural damage. Degradation of cell walls, cell rupture and plasmolysis caused by senescence or processing are responsible for softening, loss of crispness and easy juice release. A good agreement was obtained between the three methods of texture evaluation.     

EFFECT OF CALCIUM ON THE TEXTURE PROFILE OF IRRADIATED CARROTS,BEETS AND POTATOES *

Abstract. Addition of calcium as a firming agent to fresh vegetable tissues softened by gamma radiation was studied. With tissues given pasteurizing doses (100 Krad), it was found that most of the texture profile parameters could be effectively restored in beets but not in potatoes. With tissues given sterilizing doses (2 Mrad), none of the texture profile parameters could be restored in beets or in carrots.     

TEXTURE MEASUREMENT OF INDIVIDUAL COOKED DRY BEANS BY THE PUNCTURE TEST

TEXTURE MEASUREMENT OF INDIVIDUAL COOKED DRY BEANS BY THE PUNCTURE TEST. M.C. BOURNE. J. Food Sci. 37, 751–753 (1972)-The Instron Universal Testing Machine was set up to puncture test a large number of cooked dry beans, one bean at a time, by using the distance cycling controls on the machine. The punch is caused to cycle between two preset distance limits at a predetermined speed, permitting the operator to devote full attention to placing and removing beans in the puncture cup. 10 beans per minute can be conveniently tested by this procedure. The number of peak force heights in 20 selected force ranges are counted off from the chart, making for rapid retrieval of data. Tests on cooked dry beans show that the number of beans in each texture range follows approximately a normal distribution pattern, except for the presence of a few exceptionally hard beans which cause the distribution curve to tail off into the high puncture-force range.     

THE QUALITATIVE AND QUANTITATIVE MEASUREMENT OF PEAT SMOKE ON DISTILLER'S MALT*

In the course of developing a novel peating process it became apparent that the present methods for determining the intensity of peat smoke on distiller's malt are inadequate. While the colorimetric test for peat phenols is fairly accurate at low levels, it can give misleading results with highly peated malts. Furthermore, the 4-aminophenazone reagent used in this test is not sensitive to some of the major phenol constituents of peat smoke. New qualitative gas chromatographic techniques, which monitor a wider spectrum of peat smoke constituents, are now presented together with some suggested improvements to the existing quantitative colorometric analysis.