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BIOPROCESS
AND ENGINEERING
PRESENTATION
EFFECT OF ACTIVATION ENERGY ON
THERMAL DESTRUCTION OF MEDIA
NUTRIENTS
&
DESIGNED ORGANISM
EFFECT
OF ACTIVATION ENERGY ON
THERMAL DESTRUCTION OF MEDIA
NUTRIENTS
&
DESIGNED ORGANISM
Two types of reaction contribute to loss of nutrient
quality during sterilisation:
1.Interactions between nutrient components of
medium:
 Mailard-type browing reaction results:
 discoloration of media.
 Loss of nutrient quality.
 Caused by reaction of carbonyl groups-reducing
sugars with amino groups of amino acids and proteins.
 Resolved by sterilising sugar separately from rest of
media & recombining the two after cooling.
2. Degradation of heat labile components:
 Certain vitamins,amino acids & proteins may degrade during
steam sterilisation regime.
 For such cultures filtration may be used.
Thermal degradation of media nutrients:
 Follows first order kinetics.
 Described by equations similar for destruction of
microbes:
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Effect of temperature on reaction rate constant
expressed by Arrhenius equation:
Plot of natural algorithm of reaction rate against 1/T give
straight line,sloppe-(E/R).
Value of R,gas constant,fixed;slope of graph determined by
value of activation energy(E).
Activation energy for thermal destruction of
B.sterothermolhilus spores has 67.7kcal/mole.
For thermal destruction of the nutrients is 10 -30
kcal/mole .
With increasing temp.,rate of reaction increases more for
reaction having higher activation energy.
At high temp.destruction of designed organism speeds up.
Activation energy for thermal destruction of designed
organism is more than nutrient degradation.
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From this plot, seen that as temp increased, the reaction
rate rises more rapidly for the reaction with higher
activation energy.
Thus, consider difference b/w activation energies for
spore destruction & nutrient degradation an increase in
temp would accelerate spore destruction more than
medium de-naturation.
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In considering del factors, evident that same Del factor be
achieved over a range of temperature/time regimes.
To achieve desired probability of sterility high teperature
for short time would be advantageous.
Cause minimum nutrient degradation.
Ideal technique would be heating medium to high
temperature,held for short period before cooled down
rapidly tp fermentation temperature.
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