High-temperature short-time process

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.

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. 

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. 

It has been known for decades that heat is one of the most destructive factors of anthocyanins in berry fruit juices (Jackman et al., 1987a). With strawberry preserves, it was shown as early as 1953 that the half-life time was 1 h at 100°C, 240 h at 38°C and 1300 h at 20°C. In a storage experiment with concentrates and dry powder of elderberry extracts, the stability increased 6-9 times when the temperature was reduced from 20°C to 4°C (Zajac et al., 1992). Anthocyanin degradation in anthocyanin solutions increased from 30% to 60% after 60 days when storage temperatures were increased from 10°C to 23°C (Cabrita et al., 2000). High-temperature short-time processing is recommended for maximum anthocyanin retention of foods containing anthocyanins (Jackman and Smith, 1996). 

Buckle, K.A. and Edwards, R.A. 1970. Chlorophyll, color, and pH changes in H.T.S.T. (high temperature-short time) processed green pea puree. J. Food Technol 5, 173-186. 

Blasco, R., Esteve, M.J., Frigola, A., and Rodrigo, M. 2004. Ascorbic acid degradation kinetics in mushrooms in a high-temperature short-time process controlled by thermoresistometer. LWT-Food Sci. Technol VI, 171-175. 

Extrusion cooking is a high temperature-short time process which is ideal for the production of flavor volatiles. However, due to the nature of this process there are many opportunities for these volatiles to be lost. This has led many researchers to study the formation and retention of volatiles during extrusion. This review will focus on the flavor related reactions which may occur during extrusion and their occurrence in various flours and due to the addition of reactive precursors. 

HTST high-temperature, short-time (processing)... 

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