High-temperature short-time

If food can be heated quickly to a temperature of I3I°C a lethaUty equivalent to 6 min at I2I°C can be accumulated in 36 s. This rapid heating and cooling of hquid foods, such as milk, can be performed in a heat exchanger and is known as high temperature—short time (HTST) processing. HTST processing can yield heat-preserved foods of superior quahty because heat-induced flavor, color, and nutrient losses are minimized. 

Pasteurization may be carried out by batch- or continuous-flow processes. In the batch process, each particle of milk must be heated to at least 63°C and held continuously at this temperature for at least 30 min. In the continuous process, milk is heated to at least 72°C for at least 15 s ia what is known as high temperature—short time (HTST) pasteurization, the primary method used for fluid milk. For milk products having a fat content above that of milk or that contain added sweeteners, 66°C is requited for the batch process and 75°C for the HTST process. For either method, foUowiag pasteurization the product should be cooled quickly to <7.2° C. Time—temperature relationships have been estabHshed for other products including ice cream mix, which is heated to 78°C for 15 s, and eggnog, which must be pasteurized at 69°C for 30 min or 80°C for 25 s. 

High Temperature—Short Time Pasteurizers. The principal continuous-flow process is the high temperature—short time (HTST) method. The product is heated to at least 72°C and held at that temperature for not less than 15 s. Other features are similar to the batch hoi ding method. 

The introduction of high temperature-short time pasteurization of mix has emphasized the need for hydrocolloids which are quick-soluble and do not require heat for complete activation. 

Sodium carboxymethylcellulose (commonly known as CMC) was introduced in 1945 by Josephson and Dahle 10) for use in ice cream. It is cold water-soluble, will not react with acid, and has excellent water-binding properties. When properly processed, it is easily dispersible and quickly soluble in the mix. These properties make it well suited for high temperature-short time (HTST) mix. When used alone, it has a tendency to cause separation or wheying off in the mix. Irish moss extract is used with CMC to eliminate this condition. From 0.15 to 0.25% CMC is most often used in ice cream mix. 

High-temperature short time (HTST) pasteurization is used in a majority of plants in the United States. HTST pasteurization is conducted at temperatures > 72 °C and holding time > 15 s in the United States (FDA, 2009). Milk may also be pasteurized using ultrahigh temperature (UHT) pasteurization. 

The waste milk in dairy wastewaters mostly comes from start-up and shut-down operations performed in the high-temperature, short-time pasteurization process. This waste is pure milk raw material mixed with water. Another wastewater of the dairy sector originates from equipment and tank-cleaning wastewaters. These waste streams contain waste milk and sanitary cleaners that are the principal waste constituents of dairy wastewater. Over time, milk waste degrades to form corrosive lactic and formic acids. Approximately 90% of a dairy s wastewater load is milk. 

High temperature short time (HTST) continuous sterilization, in fermentation, 11 35-36, 45 High temperature steam electrolysis, 13 784... 

Figure 3-7 Plot of nominal space times (or reactor residence times) required for several important industrial reactors versus the nominal reactor temperatiwes. Times go from days (for fermentation) down to milliseconds (for ammonia oxidation to form nihic acid). The low-temperature, long-time processes involve liquids, while the high-temperature, short-time processes involve gases, usually at high pressures.

Compatible with protein-rich beverages (e.g., milk-based soy-based) treated with high-temperature short-time (HTST) pasteurization. However, may be issues with flocculation, thickening, or sedimentation due to Ca-protein interactions when subjected to ultra-high temperature (UHT) heat treatment... 

LTLT (low temperature, long time) HTST (high temperature, short time) Fore warming (for sterilization)... 

Edmondson et al (1971), who studied the enrichment of whole milk with iron, found that ferrous compounds normally caused a definite oxidized flavor when added before pasteurization. Aeration before addition of the iron reduced the off-flavor. The authors recommended the addition of ferric ammonium citrate followed by pasteurization at 81 °C. Kurtz et al. (1973) reported that iron salts can be added in amounts equivalent to 20 mg iron per liter of skim milk with no adverse flavor effects when iron-fortified dry milk is reconstituted to skim milk or used in the preparation of 2% milk. Hegenauer et al. (1979A) reported that emulsification of milk fat prior to fortification greatly reduced lipid peroxidation by all metal complexes. These researchers (Hegenauer et al. 1979B) concluded that chelated iron and copper should be added after homogenization but before pasteurization by a high-temperature-short-time process. 

The effects of heat treatment of milk on the oxidation-reduction potential have been studied to a considerable extent (Eilers et al 1947 Gould and Sommer 1939 Harland et al 1952 Josephson and Doan 1939). A sharp decrease in the potential coincides with the liberation of sulfhydryl groups by denaturation of the protein, primarily /3-lactoglobulin. Minimum potentials are attainable by deaeration and high-temperature-short-time heat treatments (Higginbottom and Taylor 1960). Such treatments also produce dried milks of superior stability against oxidative flavor deterioration (Harland et al 1952). 

Hetrick, J. H. and Tracy, P. H. 1948. Effect of high-temperature short-time heat treatment on some properties of milk. II. Inactivation of the lipase enzyme. J. Dairy Sci. 31, 881-887. 

Leviton, A. and Pallansch, M. J. 1960. Laboratory studies on high temperature-short time sterilized evaporated milk. I. Easily constructed eccentric falling ball type bomb microviscometers. J. Dairy Sci. 43, 1389-1395. 

Neotame is an amino acid derivative and is, therefore, hydrolysed under conditions of low or high pH. Its stability will be a function of pH, temperature and time. The optimum pH range is similar to that for aspartame pH 3.2 1.5. In dry form neotame is stable. Products containing neotame and processed by high-temperature short-time (HTST) do not show significant losses to degradation of neotame (The NutraSweet Company, 2003). 

Citrus juices that are pasteurized at the lower temperatures, 65-66°C, can undergo clarification, i.e., a process of separation that results in a lower layer of liquid and sediment and an upper layer of clear liquid. This process is brought about by the natural enzyme, pectinesterase, that occurs in citrus fruits. Studies have shown that processing of the juice at temperatures of 170-210°F (76.7-99°C) for a fraction of a second to 40 seconds will destroy the pectinesterase activity in citrus juices (7-10). The temperature necessary to stabilize the juice is pH dependent. Juices at higher pH require higher temperatures for stabilization. With the new high-temperature short-time techniques and equipment, stabilization can usually be effected in a fraction of a second. Flash pasteurization can be accomplished in either a plate-type or a tube-type heat exchanger. 

The extruder is a continuous high-temperature short-time reactor. Ingredients, moisture, temperature, pressure, and shear can interactively produce many Mail lard-type flavor compounds. As the extrudate exits the extruder, many of the volatile reaction products may be lost with steam since the extrudate passes from a zone of relatively high pressure within the extruder to atmospheric pressure. By controlling formulation variables, the extruder can serve as a useful tool to thermally produce volatile and nonvolatile compounds which make significant contributions to overall flavor. 

Starches have been used by the cereal and snack industries to achieve specific textures, e.g. increased crispness, especially in high-temperature, short-time processes.135,179 Snack market trends emphasize lower fat, including fried textures from baked products, high fiber and simpler processes. Starch can contribute significantly to the achievement of each of these targets. 

H. D. Stahl and T. H. Parliment, Formation of Maillard products in the proline-glucose model system high-temperature short-time kinetics, in Thermally Generated Flavors Maillard, Microwave, and Extrusion Processes, T. H. Parliment, M. J. Morello, and R. J. McGorrin (eds), American Chemical Society, Washington, DC, 1994, 251-262. 

High-temperature short-time (HTST) treatment (72°C x 15 s) of milk almost completely inactivates the enzyme (Luhtala and Antila, 1968 Andrews et al., 1987 Farkye et al., 1995) so that little if any lipolysis caused by milk lipase occurs in pasteurised milk (Downey, 1974). Somewhat higher temperatures are required for cream pasteurization because of the protective effect of the fat (Nilsson and Willart, 1961 Downey and Andrews, 1966). However, some workers have reported that a more severe heat treatment, [e.g., 79°C x 20 s, (Shipe and Senyk, 1981) or 85°C x 10 s (Driessen, 1987)] is required to inactivate completely milk lipase. 

To maintain cloud stability in fruit juices, high-temperature-short-time (HTST) pasteurization is used to deactivate pectolytic enzymes. Pectin is a protective colloid that helps to keep insoluble particles in suspension. Cloudiness is required in commercial products to provide a desirable appearance. The destruction of the high levels of pectin-esterase during the production of tomato juice and puree is of vital importance. The pectinesterase will act quite rapidly once the tomato is broken. In the so-called hot-break method, the tomatoes are broken up at high temperature so that the pectic enzymes are destroyed instantaneously. 

HIGH-TEMPERATURE SHORT-TIME (htst) METHOD. The HTST method is used for two purposes in fruit juice technology to sterilize juices for storage and to precipitate thermolabile protein. 

Further processing after high-temperature short-time treatment and then being left to stand... 

After leaving the press the juice is given high-temperature short-time treatment. Protein is denatured hy the high temperature and is coagulated. After being left to stand for a few hours the protein and the coarse suspended solids are precipitated. The enzymes of the juice are inactivated hy the heat treatment, this being essential for haze stability. 

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