Contents 2 Heat Treatment Process

Plain-carbon steels are essentially alloys of iron and carbon together with varying amounts of other elements such as manganese, sulphur, silicon and phosphoms. These additional elements are found in the raw materials used in the steel-making process and are present as impurities. Both sulphur and phosphorus are extremely harmful and cause brittleness in the steel - they are therefore kept to a minimum. The effect of these is offset by the presence of manganese. The carbon content varies up to about 1.4%, and it is this carbon which makes the steel harder and tougher and able to respond to the various heat-treatment processes. 

In contrast to aimealing, this heat-treatment process is designed to produce a steel that is hard. Steel will vary in hardness depending upon the carbon content, the hardness increasing as the carbon content... 

The carbon content varies up to about 1.4%, and it is this carbon which makes the steel harder and tougher and able to respond to the various heat-treatment processes. 

A comparison of the ceU wall fractions of carrots canned by both processes is given in Table 4. Heat treatment during canning process resulted in the solubilization of the major part of HSP and OHSP. This was reflected on an increase in WSP content in carrots canned by conventional process, in OXP content in carrots canned by conventional process with CaCh addition and in WSP and OXP in carrots canned by the new process. The total uronoides content recovered from conventionally canned carrots was 21% lower as compared with... 

Enzyme activity can indicate the exposure of honey to heating and long storage. This criterion is not more accurate than the HMF content value because enzyme activities vary with honey samples. The diastase activity is usually associated with heat treatment. However, its activity gives only an indication about the processing (heat treatment) of the honey but is not suitable for the detection of the origin. 

Taking into account that heat treatment inactivates some oxidative enzymes and causes the rupture of some cellular structures, greater extractability of carotenoids is expected to occur in processed foods. Therefore, when mild temperatures are applied, it is very common to obtain higher carotenoid content in a processed food as compared to its fresh counter part. For example, total... 

Unheated carrot juices produced from carrots blanched at 80°C for lOmin were devoid of di-isomers, and further pasteurization or sterilization process formed only 13-d.v-P-carotene, respectively, at 2% and 5% (Marx et al. 2003). However, extensive carrot blanching (100°C for 60min) caused the losses of 26%-29% in total P-carotene content, along with an increased 13-d.s-P-carotene content up to 10% after pasteurization (Tmax 95°C, F = 3) and to 14% after sterilization (Tmax 121°C, F = 5) (Marx et al. 2003). The addition of grape oil to carrot juice before heat treatment enhanced the 13-di-P-carotene formation (18.8%) as compared to the control (6.0%) (Marx et al. 2003). This fact is probably due to the partial dissolution of crystalline carotene, present in the intact carrot in lipid droplets, since the solubilization of carotenes during blanching is a prerequisite for the formation of di-isomers. 

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