General Heat Treatment Requirements

Liquid sauces—As noted earlier, liquid sauces are typically sold in shelf stable forms. They generally have a low pH that minimizes the heat treatment required for microbial stability. They may be lower fat versions that are thickened by starches and/or hydrocolloides, or high fat products (e.g., hollandaise-based sauces) that obtain their viscosity from the fat emulsion. Each type of sauce has its own unique formulation requirements for retaining its physical properties during both thermal processing and storage. 

The adherend metallurgy also indirectly determines the degree of smut buildup because the rate of smut formation is proportional to the etch rate [54J. For instance, the etch rate of A606 is four times greater than that of A514, due to differences in grain size, etc. As a result, a different etch treatment is required for each. In general, the roles of alloy and heat-treatment differences have not... 

While gelation temperature Is usually considered a characteristic property of a given protein system, the heating conditions required for gel formation may be Interrelated to all of the previously mentioned factors. It has been observed that WPG dispersions In 0.2 M NaCl will gel at 75 C while a temperature of 90 C Is required to gel WPG dispersions In distilled water (1). Heating time, at a specific temperature, required to form a protein gel structure Is generally considered to decrease with Increased protein concentration. Alteration of heat treatment conditions affects the gel s macroscopic and microscopic structural attributes. This has been dramatically shown by Tombs (A) with electromlcroscoplc evaluation of bovine serum albumin gels. 

Detectable concentrations of various antibacterials in milk attained by different microbiological tests are presented in Table 27.2. Milk constitutes a matrix that, apart from heating to destroy natural inhibitory substances, does not generally necessitate further sample treatment. Some antibiotics, however, exhibit some instability to heat treatment (54-56) and, therefore, if further confirmation is required reference frozen samples should always be available. When raw milk is directly analyzed, critical evaluation is generally required because natural inhibitors such as somatic cells, immunoglobulins, and metabolites may cause zones of inhibition (56, 57). Furthermore, several factors including marked pH-devia-tions, use of paper disks that contain inhibitory substances, and work with forceps that are too hot or have not been cleaned properly can readily lead to falsepositive readings (56, 58). 

The name activated alumina is generally applied to an adsorbent alumina (usually an industrial product) prepared by the heat treatment of some form of hydrated alumina (i.e. a crystalline hydroxide, oxide-hydroxide or hydrous alumina gel). It has been known for many years that certain forms of activated alumina can be used as powerful desiccants or for the recovery of various vapours. It was apparent at an early stage that the adsorbent activity was dependent on the conditions of heat treatment. For example, in 1934 Bayley reported that the adsorption of H2S by a commercial sample of activated alumina was affected by prior heating of the adsorbent at different temperatures, the maximum uptake being obtained after heat treatment at SS0°C. During an investigation of the catalytic dehydration of alcohols, Alekseevskii (1930) found that a calcination temperature of c. 400°C was required to optimize the adsorption of the alcohol reactants, whereas calcination at 600°C was preferable for the adsorption of the olefine products. 

The various procedures for the synthesis of this system have previously been described. From now on, reference shall only be made to the preparation procedure requiring MgC co-milling with the Lewis base (generally EB), and subsequent heat treatment with TiCl4, followed by repeated washings with hydrocarbons in order to remove not bonded TiCl4. The main reasons for this choice are ... 

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