Unit 9A
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sterility is achieved when ?
all parts of the product have been heated to 121 ( reached by using steam) and held at that temperature for 15 mins
is sterility used for foods, why or why not?
no, this would cause to become inedible or lose all nutritional value
what is used for canning
commercial sterility
definition of commercial sterility
all pathogenic and toxic forming organisms are killed and spores are inactivated gives shelf life of over 2 years- safe while still providing foods quality
for low acidic foods what temperature is needed to achieve commercial sterility?
above boiling point of water these are achieved by steam under pressure
pasteurization vs commercial sterility?
pasteurization is usually below the boiling point of water because of this it results in a shorter shelf life bc the spores normally survive
blanching is used for ?
denature deleterious enzymes such as polyphenol oxidase and lipoxygenase usually used prior to freezing or other preservation techniques
what is D-value
a decimal reduction time: the heating time at a specific temperature to reduce the microbial population by 1 log unit or 90%
if you assume a can has 10^6 spores than a thermal process resulting in _____ while result in 10^-6 spore and represent commercial sterility
12 D ( 12 decimal reductions ) from 10^6 to 10^-6 is 12 decimals
how is d value found
experimentally by a plate count on samples that have been heated to different temps
higher temps would result in
lower D value and a stepper slope
z value
thermal resistance
how do you find z value
plotting log D vs temperature temperature increase corresponding to the reduction of D by 1 log
what does D100= 2 mins mean
it means that it takes 2 mins at a temperature of 100 degrees to reduce the microbial population by 1 log (or 90%) 2D’s would be 4 mins 12D’s would be 12x2= 24 mins ( achieve commercial sterility!)
explain a z-value of 18 degrees
z value is the temperature increase it takes to reduce the D value by 1 log (factor of 10) so if D100=20 mins and the z value is 18 degrees then D118= (20/10)= 2 mins so D12 at D100= 20 x 12= 240 mins D12 at D118= 2x 12= 24 mins
what is best for quality attributes?
short time and high temperature (HTST)
what are the 2 types of thermal processing?
1) conventional processing - traditional canning where you package first and then heat 2) Aseptic ( free from contamination ) processing- process and then package such as tetra brick
explain batch retort
a large pressure cooking that is called a batch retort in which cans are loaded and sealed and than heated with steam under pressure
what are thermocouples
thermocouples are placed inside a can and placed in the slowest to heat up place “cold point” ( centre for conduction and centre 1 third up in convection ) and are used to determine how food heats up in a retort