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Heat treatment. 30th dec.2011


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Heat treatment. 30th dec.2011

  1. 1. Heat Processing• Pasteurization and Appertization –• Pasteurization – Foods are exposed to thermal processing for different reasons, often destruction of microrganisms not the main objective.• However, this is inevitable useful side effect.
  2. 2. Back ground /Discovering the value of heat• Value of heat as a preservative go to French chef, distiller and confectioner, Nicolas Appert.• In 1975 French gov. Offered a prize of 12000francs to any one who develop the new method of food presevation.• Apart from this prize, he also experimented on packing of foods in Glass bottles, sealing them and then heating them in boiling water.
  3. 3. Background• He described this technique in 1811 in a book called “ art of conserving all kinds of animal and vegetable matter for several years.”• A similar technique was used by Englishman in 1807 to preserve fruits.• British patents describing the use of iron or metal containers were issued to Durand and de Heine in 1810 and the firm of Donkin and Hall established a factory for the production of canned foods in London around 1812.
  4. 4. EARLY/ APPERT AIR CONTACT VIEW AND pasteur,s work• Appert held the view that air contcat was the cause of spoilage and the success of this technique was due to the exclusion of air from the product.• This view persisted for another 50 years until Pasteur,s work established the relationship between microbial activity and putrefaction.
  5. 5. Pasteurization and AppertizationToday, two types of heat processes employed to destroy theM.O in food, PASTURIZATION and APPERTIZATION.PASTEURIZATION -Heat processes typically in the range of 60 -80 c for upto fewminutes. This is used for 2 purposes. FIRST is the eliminationof a specific pathogen or pathogens associated with a prduct.
  6. 6. pasteurizationThis type of pasteurization is often a legalrequirement introduced as a public healthmeasure when product has beenfrequently implicated as a vehicle ofillness. e.g; milk, egg, ice cream mix, allthese products have a much improvedsafety record as a result of pasteurization.
  7. 7. pasteurization• Second reason for pasteurization a product is to eliminate a large proportion of potential spoilage organisms, thus extending its shelf life. This is normally the objective when acidic products such as beers, fruit juices, pickles and sauces are pasteurized.
  8. 8. pasteurization• Pasteurization by means of steam, hot water, dry heat or electric current.• In market milk 62.8 c for 30 min or 71.7 c for 15 sec.• 137.8 c for 2 sec in ultrapasteurised for coxiella burnetti• In ice cream 71.1 for 30 min or 82.2 for 20 sec.
  9. 9. Pasteurization with low Ph and awOn its own the contribution of pasteurization to extension of shelf-life can be quite small, particularly if the pasteurized food lacksother contributing preservative factors such as low pH or aw.Spore forming and some Gram positive vegetative species ingenera Enterococcus, Microbacterium and Arthrobacter cansurvive pasteurization temperatures.Reffrigerated storage is often an additional requirement for anacceptable shelf life.
  10. 10. APPERTIZATIONA process where the only organisms that surviveprocessing are non-pathogenic and incapable ofdeveloping within the product under normal conditionsof storage. As a result appertized products have a longshelf life even when stored at ambient temperatures.The term was coined as an alternative to the stillwidely used description “ commercially sterile whichwas objected to on the grounds that sterility is not arelative concept.
  11. 11. APPERTIZATIONAppertized or coomercially sterile food is notnecessarily sterile - completely free from viableorganisms. It is however free from organisms capable ofgrowing in the product under normal storageconditions.Canned in temperate climate is not a matter of concerneven if the viable spores of thermophile are present asthe organism will not grow at the prevailing ambienttemperature.
  12. 12. FACTORS AFFECTING HEAT RESISTANCETHERMAL DEATH TIME – Cells and spores of microorganisms differwidely in their resistance to high temperatures.In a colony/sample, A small number of cells have low resistanceMost of the cells have a medium resistanceAnd small number have higher resistanceConditions of growth may favour one or the other of these groups.
  13. 13. Heat penetration• Conduction – heat passeses from molecule to molecule• Convection – heat is transfered by movements of liquids or gases.
  14. 14. D-value• D-value refers to decimal reduction time is the time required at a certain temperature to kill 90% of the organisms being studied. Thus after a colony is reduced by 1 D, only 10% of the original organisms remain. The population number has been reduced by one decimal place in the counting scheme. Generally, each lot of a sterilization-resistant organism is given a unique D-value. When referring to D values it is proper to give the temperature as a subscript to the D. For example, a hypothetical organism is reduced by 90% after exposure to temperatures of 300 degrees Fahrenheit for 2 minutes, thus the D-value would be written as D300F = 2 minutes. D- value determination is often carried out to measure a disinfectants efficiency to reduce the number of microbes, present in a given environment
  15. 15. What is a Z-value?• A Z-value is defined as the number of degrees (Celsius or Fahrenheit) required to change a D- value by one factor of ten. In the practical sense, it is a measure of how susceptible a spore population is to changes in temperature. For example, if the Z-value of a population is 10 degrees, then increasing the sterilization temperature 10 degrees will result in a log reduction of the D-value.