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:

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.

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.

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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