Texture characteristics measurements

Campbell (6) was perhaps the first to investigate the relationship between tenderometer values for raw peas and the texture characteristics of collateral samples after freezing and cooking. A high degree of correlation was observed. The investigations of Nielsen and co-workers (31) indicate the usefulness of the instrument for estimation of maturity in peas intended for freezing preservation. In order to secure consistent and reproducible results, the instrument requires standardization and calibration, and the measurements must be made under standardized conditions of temperature and interval after harvest. 

The major property of accurately measured RAI is the independence of its derivative on possible effects of deviations of adsorption potential of a bare surface. This property together with the obvious additivity of adsorption on various parts of a surface allows measuring the textural characteristics of real microporous or modified PSs [3], Indeed, if the PS has parts with increased (e g., micropores) or decreased (e.g., modificators) adsorption potential, in the majority of cases the total AI, that is, q(P/P0), before capillary condensation is expressed as... 

N2 sorption isotherms were measured for the pure carrier and for all the immobilized complexes, respectively. Sorption isotherms and textural characteristics for pure and loaded samples are compared in Fig. 2.1.6.1 and Table 2.1.6.1. In all cases these isotherms presented the characteristic form of mesoporous materials. It is clear that the N2 adsorbed/desorbed volume was higher in the case of pure carrier than in the case of immobilized complexes. 

Clearly, it may be possible to define and accurately measure many aspects of the mechanical and rheological properties of foods, but to try and relate these measures to consumer perceptions of the texture of the foods, is fraught with difficulties. Conversely, it is possible to train human subjects to assess textural characteristics of foods in defined and consistent ways (training them to mimic an instrumental response), however this may be missing the diversity of perceptions of food texture experienced by normal consumers. 

A considerable problem for both the food industry and sensory scientists is the degree of individual variation in texture perceptions. The differences in breakdown pathways in the mouth for standard samples may underlie some of the variability. Indeed Brown et al31 have demonstrated an influence of chewing behaviour on texture perceptions in a model food system. Even if all individuals shared a common system for assessing a particular textural characteristic, the differences in the way they masticate a sample may cause them to come to different conclusions regarding its texture. However, there is also the real possibility that subjects may use different measuring systems for assessment of a textural characteristic they... 

We can determine what features of the chewing sequence influence assessment of particular textural characteristics of food by using this approach to examine the interaction between food and consumer during the mastication process. We should then be able to develop mathematical models for perception of textural qualities which take into account different texture combinations (for example, assessment of hardness in both elastic and brittle foods), and different breakdown patterns. Although currently at an early stage, mastication analysis shows promise for enhancing our measurement of perceived texture in foods. 

Langton et al. (1996) studied correlations existing between microstructure and texture of a particulate proteic gel (spherical particles joined together to form strands). They found that the texture, as measured with destructive methods, was sensitive to pore size and particle size, whereas it was sensitive to the strand characteristics if measured with nondestructive methods. 

A variety of other words and expressions are used to describe textural characteristics, such as body, crisp, greasy, brittle, tender, juicy, mealy, flaky, crunchy, and so forth. Many of these terms have been discussed by Szczesniak (1963) and Sherman (1969) most have no objective physical meaning and cannot be expressed in units of measurement that are universally applicable. Kokini (1985) has attempted to relate some of these ill-defined terms to the physical properties involved in their evaluation. Through the... 

As evidenced by curves on figures 4 and 5, changes in texture characteristics are quasi-linearly related to increasing carbon content. It also appears that calculated surface areas strongly depend on the physisorption conditions, while measured adsorbate volumes are less affected. This observation is in favor of erroneous assumptions on nitrogen molecule area for the calculations of specific surface area [10]. But, as mentioned above, nitrogen molecule could penetrate in smaller pores, increasing measured micropore volume and surface areas. 

Although BF provides a direct SSA measurement, the techniques of PSD, MIP and gas adsorption provide complementary information on texture characteristics to better understand and interpret results from process and formulation development studies. However, in some cases, BF can be considered as a complete and adequate quality control method which can easily be set to work within the frame work of production control provided that the method has been validated and applies well to the powder studied... 

The most important textural characteristic of a pectin gel is gel strength, and there are a number of good reviews on methods and instruments used to determine this (Mitchell, 1976 Crandall and Wicker, 1986 Alexos et al., 1991). Both nondestructive approaches, which measure the elastic properties of the gel, and destructive approaches, which measure the inelastic properties or breaking strength of a gel, are used. 

Limitations of the IFT SAG method with respect to pH have been demonstrated. Similar limitations have been reported by other laboratories (2). Since the Herbstreith Pectinometer and the Voland Stevens Texture Analyser have been developed recently, it could be of interest to see how the jelly characteristics measured by these Instruments correspond to the official results as expressed by IFT SAG. 

Surface area measurements and precious metal dispersion determinations by CO chemisorption were reported previously [2], The chemical composition of the catalysts and their textural characteristics are given in Table 1. Prior to the BET or CO chemisorption measurements, the samples were either reduced by H2 at... 

Taking as a reference the textural characteristics of the heat treated sepiolite support "ST", the data in Table 1 indicated that washing this natural silicate with an acid solution produced an appreciable increase in tlie BET surface area but had little effect on the surface area and pore volume measured by merciuy porosimetry. Thus, this increase must have been in pores of between 1 and 3nm radius, since evaluation of the adsorption isotlierm by use of the t-plot... 

To analyze the textural characteristics of the initial and MCA-treated nanosilicas, LT (77.4 K) nitrogen adsorption-desorption isotherms (Figure 1.188a) were recorded using a Micromeritics ASAP 2405N adsorption analyzer. Before measurements, the samples were heated at 200°C for 2 h to remove adsorbed water. 

Table 3 presents the textural characteristics of the silica-alumina hydrogels as evaluated from thermoporometry measurements. 

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