Quality of heated and stored

Chemical Markers for the Protein Quality of Heated and Stored Foods... 

A well-insulated 30-m3 tank is used to store exhaust steam. The tank contains 0.01 m3 of liquid water at 30°C in equilibrium with the water vapor. Determine the amount of wet-exhaust steam, in kg, from a turbine at 1 atm at the end of an adiabatic filling process. The wet steam has the quality of 90%, and the final pressure within the tank is 1 atm. Assume that heat transfer between the liquid water and the steam is negligible. 

The formal definition of this quality factor, Q, is the amount of power stored in the resonator divided by the amount of power dissipated per cycle (at 9.5 GHz a cycle time is l/(9.5 x 109) 100 picoseconds). The dissipation of power is through the resonator walls as heat, in the sample as heat, and as radiation reflected out of the resonator towards the detector. The cycle time is used in the definition because the unit time of one second would be far too long for practical purposes within one second after the microwave source has been shut off, all stored power has long been dissipated away completely. 

Since man first discovered fire, thermal treatment of foods has been one of the most common ways to prepare food. The use of heating improved the eating quality of food in terms of flavour and digestibility and it also became apparent that cooked food could be stored for longer time than the raw material. Cooked foods develop characteristic flavour and colour and the main reactions which take place are the breakdown of lipid, sugars, amino acids, carotenes, thiamine and other trace food components. 

Heat-Resistant Lipases. The heat-resistant lipases and proteinases and their effects on the quality of dairy products have been reviewed (Cogan 1977, 1980). Several reports have linked the lipases from bacteria with the off-flavor development of market milk (Richter 1981 Shipe et al. 1980A Barnard 1979B). The microflora developing in holding tanks at 4°C [and presumably in market milk stored at 40°F (Richter 1981)] may produce exocellular lipases and proteases that may survive ordinary pasteurization and sterilization temperatures. Rancidity of the cheese and gelation of UHT milk appear to be the major defects caused by the heat-resistant enzymes. 

Use of juice concentrate, 40°-60° Brix, is the least common method of sweetening the wines. The quality of the concentrate, and its effect on the wine, is improved if production methods minimize heat damage and the concentrate is stored subsequently at cool temperatures until use. 

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