References Gqe
1. LH Sperling. Introduction to Physical Polymer Science. New York Wiley, 1986. 2. L Slade, H Levine. Beyond water activity recent advances based on an alternative approach to the assessment of food quality and safety. CRC Crit Rev Food Sci Nutr 30 115-360, 1991. 3. YH Roos. Phase Transitions in Foods. San Diego Academic Press, 1995. 4. M Peleg. Mechanical properties of dry brittle cereal products. In DS Reid, ed. The Properties of Water in Foods ISOPOW 6. London Chapman and Hall, 1998, pp...
E Material Properties
Several material properties are required as inputs to the mechanistic models to perform multiple calculations. The thermomechanical model requires the following material properties isotherms, glass transition temperature, storage modulus, diffusion coefficient, and Young's modulus. The material properties required for the stress-strain model include Young's modulus, Poisson's ratio, and failure stress. Material properties are temperature and moisture dependent, and Young's modulus and failure...
A Starch
Starch is present in wheat flour as particles, starch granules, with diameters in the range 1-40 m 17, 18 . In fact, two populations of granules are present large, lenticular A-granules mean diameter around 14 m , and small B-granules mean diameter around 4 m 19 . It has been observed that the ratio between A- and B-granules is important for baking performance, with an optimum proportion of B-granules at about 25-35 by weight 20 . In wheat starch the proportion of amylose is about 29 , the...
Weight Fraction Of Solids
Figure 3 Glass transition temperatures of lactose, with data from Refs. 10 O , 35 , and 36 A , and glucose and fructose A , with data from Ref. 25. 2. Oligosaccharides and Carbohydrate Polymers It is well known that the Tg of synthetic homopolymers is dependent on molecular weight, increasing with increasing molecular weight. Fox and Flory 37 showed that the Tg of polystyrene fractions was related to the number average molecular weight, Mn, according to Eq. 3 . Another equation relating Tg to...
Info Khx
Shear and elongation deformations beyond the rupture limits Elongation deformations below the rupture limits Permeability, diffusivity Gas-cell formation, disproportionation, and coalescence Elongation deformations below the rupture limits Permeability, diffusivity Biopolymers cross-linking and phase transition Gas cell disproportionation and coalescence Water migration Source Estimations of deformation rates from Ref. 4. Source Estimations of deformation rates from Ref. 4. conditions, flow...
A Crystallization of Amorphous Sugars
Water sorption studies of dairy powders have often shown that during storage at above 40 relative humidity RH and room temperature, large amounts of water may be sorbed initially, but during further storage the sorbed water content is reduced with storage time. For example, as early as in 1926, Supplee 5 found a gradual decrease in sorbed water content of milk powder when the material was stored at 50 RH at room temperature. Such decrease in sorbed water content has often been suggested to be a...
Hydrocolloids
The influence of hydrocolloids on the gelatinization behavior of starch has been investigated for some cereal starches, including corn 68 . It was found that To, Tm, and Tc increased with increasing levels of hydrocolloid, resulting in a broadening of AT. AHgel was found to increase, but because the water content changed at the same time as the addition of the hydrocolloid, the interpretation was difficult. However, when the samples were compared at the same volume fraction of water it was...
Vii Caking And Anticaking Agents
A simple definition of caking is ''when two or more macroparticles, each capable of independent translational modes, contact and interact to form an assemblage in which the particles are incapable of independent translations.'' Caking is such a common phenomena that almost every industry dealing with powders must deal with the problems that caking can cause. For many powdered products, such as foods, detergents, pigments, fertilizers, and chemicals, one important quality criterion is whether or...
Info Ror
available energy the material property is Gc, the critical strain energy release rate. The two properties are related through Young's modulus and the Poisson ratio. Compression techniques are popular because of the ease of performing the test 17 . The initiation of the failure may be inside the test piece and advance in a complex manner. Antila et al. 18 used a piston of area 100 mm2 at a speed of 10 mm s-1 to break specimens from flat-bread extrusion and expressed their data in units of energy...
T Pav
pre-exponential term in Arrhenius equation for Tg specific critical hole free volume of the solvent specific critical hole free volume of the polymer
References Duy
1. NL Kent. Technology of Cereals. 3rd ed. New York Pergamon Press, 1983, pp 1196. M Peleg. Flowability of food powders and methods for its evaluation a review. J Food Pro Eng 1 303-328, 1977. G Herdan. Small Particle Statistic. 1st ed. London Butterworths, 1960, pp 73-89. T Allen. Particle Size Measurement. 3rd ed. London Chapman amp Hall, 1981, pp 103-164. Schubert. Food particle technology. Part I Properties of particles and particulate food systems. J Food Eng 6 1-32, 1987. L Svarovsky....
Ii Calorimetry
Differential scanning calorimetry DSC is a thermal analysis technique that detects and monitors thermally induced conformational transitions and phase transitions as a function of temperature. A pair of matching crucibles or sample pans, one containing the sample and one serving as reference, are heated in tandem. As a crucible is heated, its temperature increases, depending on the heat capacity of the contents of the crucible. At temperatures where an endothermic transition occurs, the thermal...
Gelatinization
Differential scanning calorimetry has become perhaps the most widely used method for studying starch gelatinization. Before the DSC epoch, starch gelatini-zation was usually studied by measuring the change in viscosity during the application of heat, and several instruments have been designed for such measurements. The heating rate and stirring rate are usually fixed, thus resulting in shear rates that cannot be varied 33 . Moreover, there are limitations in how high the starch concentration...
References 1
1. L Slade, H Levine. Beyond water activity recent advances based on an alternative approach to the assessment of food quality and safety. Crit Rev Food Sci Nutri 30 115-360, 1991. 2. L Slade, H Levine. Structure-function relationships of cookie and cracker ingredients. In H Faridi, ed. The Science of Cookie and Cracker Production. New York Chapman and Hall, 1994, pp 23-141. 3. L Slade, H Levine. Water and the glass transition dependence of the glass transition on composition and chemical...
Iii Particle Size Distribution
The measurement of particle size and particle size distribution is one of the most widely used methods in the industry 16 , because, in combination, they affect such other physical properties of a powder system as flowability, bulk density, and compressibility 2, 17 . Even segregation will happen in a free-flowing powder mixture because of differences in particle size 18 . Because preprocessed cereal flours are rarely of uniform particle size, it is necessary to measure a great many particles...
A The Staling Endotherm
The staling endotherm of bread crumb is present at the same conditions as the endotherm due to the melting of retrograded amylopectin see Fig. 3 . The development of this endotherm in bread is affected by the same conditions as in a starch gel and will thus be influenced by, for example, water content 161 and the addition of emulsifiers 53, 62 . The staling endotherm has been concluded to be a reliable measure of the retrogradation of amylopectin. However, an exothermic transition, at about 20...
Gluten
The main component, besides starch, in flour is of course protein Table 1 . As discussed earlier, the gluten proteins do not give rise to any detectable endotherms during the DSC scan, but they will shift To and Tm for the thermal transitions related to starch gelatinization 116 . It was found that for the two peaks obtained at water conditions where the gelatinization endotherm has the shoulder G and M1 in Fig. 2 , gluten causes a linear increase in the peak temperatures when added to wheat...
Info Fpy
is beyond the scope of this chapter, and the reader is referred to the book by Hohne et al. 1 . In addition to the conventional linearly increasing temperature protocol utilized in DSC, a recently introduced modulated differential scanning calorimetry MDSC employs a temperature protocol utilizing an oscillating sine wave of known frequency and amplitude superimposed onto the linear temperature increase applied to the sample and reference pans 4 . The MDSC output signal, heat flow, can be...
References
1. GWH H hne, W Hemminger, HJ Flammersheim. Differential Scanning Calorimetry An Introduction for Practitioners. New York Springer-Verlag, 1996, p 21. 2. L Slade, H Levine. Structural stability of intermediate moisture foods a new understanding. In JMV Blanshard, JR Mitchell, eds. Food Structure Its Creation and Evaluation. London Butterworths, 1988, pp 115-147. 3. LH Sperling. Introduction to Physical Polymer Science. New York Wiley, 1992, pp 303-381. 4. M Reading. Modulated differential...