Explain holding method of pasteurization
In the holding method of pasteurization (62oC for 30 minutes) or the high-temperature short-time (HTST), 71oC for 15 minutes methods - very little cooked flavour is noticed, but at higher temperatures or longer periods of heating, cooked flavour becomes more apparent. The flavour appears at 70oC on momentary heating.
This cooked flavour has been shown to be due to the production of sulfhydryls (compounds with a -SH group, found in many plant and animal enzymes) by high temperatures. Sulfhydryl compounds are readily oxidized and delay the oxidation of fat in milk or cream heated to high temperatures. Oxidized flavors in milk do not usually appear until the sulfhydryls are oxidized and the cooked flavor has disappeared.