Ultra high temperature treatment

Ultra-high-temperature treatment (UHT) is now the most widely exploited method in the food industry to stabilize microbiologically any foodstuff. It consists of heating at an ultra high-temperature for a short period of time for example, a treatment at 145°C for 2 seconds is sufficient to assure a total microbial- and spore inactivation. The microbial death is principally due to irreversible cell damage (e.g., of proteins, DNA, RNA, vitamins) enzymes are inactivated by heat which modifies their active sites. 

Bucky, A.R., Hayes, P.R., Robinson, D.S. 1987. A modified ultra-high temperature treatment for reducing microbial lipolysis in stored milk. 1. Dairy Res. 54, 275-282. 

Datta, N., Elliott, A. J., Perkins, M. L., and Deeth, H. C. (2002). Ultra-high-temperature (UHT) treatment of milk Comparison of direct and indirect modes of heating. Aust. ]. Dairy Technol. 57, 211-227. 

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... 

Many lipases produced by psychrotrophic bacteria retain activity after pasteurization and ultra-high-temperature (UHT) heat treatments (Cousin 1982 Adams and Brawly 1981). Butter made from cream which supported growth of lipase-producing psychrotrophs became rancid within two days (Kishonti and Sjostrom 1970). UHT milk processed from raw milk contaminated with lipase from a Pseudomo-... 

Temperature The effect of ultra-high temperature (UHT) treatments on aspartame stability is minimal, with losses in the range 0.5-5% (Shazer et al., 1988). 

Rerkrai, S., Jeon, I.J., Bassette, R. 1987. Effect of various direct ultra high temperature heat treatments on flavor of commercially prepared milk. J. Dairy Sci. 70, 2046. 

Heat treatment of milk above 60 °C, which promotes whey protein denaturation and its complexation with K-casein at normal milk pH (6.6), also affects renneting properties. An increase in rennet coagulation time and a decrease in gel firmness were observed with increased heat treatment of milk (Menard and Gamier, 2005). Ultra-high temperature (UHT) treated milk failed to coagulate completely but the coagulation properties were restored by threefold concentration of the UHT milk (McMahon ef al., 1993). 

Ultra-high temperature (UHT) treatment involves thermal processing at 138°C-142°C. At this temperature, only 2-3 s, for example, is needed to achieve commercial sterility of milk. After heat treatment, the milk can then be aseptically placed in sterile containers (Garbutt, 1997). The milk can be kept unopened for... 

Pasteurization of milk apparently does not influence the vitamin content (30). During sterilization of milk (heating to 112 C for 10 min) the vitamin content reportedly decreases by 14%. The mean retention in UHT (ultra-high temperature) sterilized milk was approximately 96% (31). After 6 weeks of storage at room temperature the losses increase to 30%, and the total pantothenic acid losses caused by UHT heat treatment and storage amount to 20% to 35% (32). In dried milk after storage for 8 weeks at 60°C the loss was 18%. The natural vitamin content in fermented milk products was affected only slightly by the fermentation (33,34). 

Raw or gently pasteurised milk (e.g. for 10 seconds at 73 °C) has a fine characteristic odour and sweet taste. Typical components present in low concentrations are dimethylsulfide, biacetyl, 2-methylbutan-l-ol, (Z)-hept-4-enal and ( )-non-2-enal. Milk pasteurised at higher temperatures and Ultra High Temperature (UHT) milk present the so-called cooked flavour, the appearance of which is the first measurable manifestation of the chemical changes that occur in heated milk. The substances responsible for the cooked off-flavour are sulfane and other sulfur compounds. Of particular importance are dimethylsulfide, dimethyldisulfide and dimethyltrisullide that are produced from proteins contained in the membranes of fat particles and from thiamine. Also relevant are alkane-2-ones (methylketones) generated by thermal decarboxylation of P-oxocarboxylic acids (mainly hexane-2-one, heptane-2-one and nonane-2-one), y-lactones and 5-lactones produced by dehydration of y- and 5-hydroxycarboxylic acids (mainly 8-decalactone and y- and 8-dodecalactones). Important carbonyl compounds include biacetyl, hexanal, 3-methylbutanal, (Z)-hept-4-enal and ( )-non-2-enal. In the more intensive thermal treatment of milk (sterilisation), products of the Maillard reaction play a role, such as maltol and isomaltol, 5-hydroxymethylfuran-2-carbaldehyde, 4-hydroxy-2,5-dimethyl-2 f-furan-3-one (furaneol) and 2,5-dimethylpyrazine. 

Carbon fibers also can be produced by the pyrolytic deposition of hydrocarbon gases. Many hydrocarbon gases, such as methane, naphthalene, and benzene, have been used to produce carbon fibers with deposition temperatures of 1000-1200°C. Dining the pyrolysis process, thin tubes of carbon are first formed on ultra-fine particles. The tubes then grow by a surface diffusion mechanism, and the subsequent high temperature treatment with a temperature up to 2500°C results in the formation of carbon fibers with diameters ranging from 10 run to mote than 100 /im. Carbon fibers produced from hydrocarbon gases often have central hollow cores. 

Resistivity measurements are done on meander shaped samples by the standard potentiometrie method in a stirred bath of liquid nitrogen relative to a dummy speeimen For this proeedure of residual re istometry the ultra-high measuring aeeuraey of 3.10 results below 300°C and of 3.10 for annealing treatments at higher temperatures. 

---