Heat, inactivation of enzymes

They also suggested the lipids were released and became extractable primarily through enzymatic reactions after maceration of the leaves for extraction. Thus, they postulated that the time interval between maceration of the plant tissue and the application of heat to coagulate proteins was critical. They recommended heat inactivation of enzymes and precipitation of proteins as quickly as possible after maceration to minimize this interference. 

The heat sterilization of microorganisms and heat inactivation of enzymes are examples of first-order reactions. In the case of an enzyme being irreversibly heat-inactivated as follows ... 

This difference has important practical implications for the food technologist. Many foods are heat-treated to ensure microbiological safety and to enhance keeping quality. In nearly all cases, the desired properties are the result of heat inactivation of enzymes enzymes may themselves cause spoilage, but they are also essential for microbial (and all other) life, implying that irreversible inactivation of some of their enzymes kills the... 

Commonly used technological processes cannot usually remove antivitamins of the first group, the so-called true antivitamins. The remaining two groups of antivitamins can be largely eliminated by suitable processes or culinary practices (such as heat inactivation of enzymes or denaturation of proteins bound in the non-utilisable protein-vitamin complexes. 

Product Heat Treatment. Equivalent heat treatment for destmction of microorganisms or inactivation of enzymes can be represented by plotting the logarithm of time versus temperature. These relationships were originally developed for sterilization of food at 121.1°C, therefore the time to destroy the microorganism is the V value at 121.1°C (250°F). The slope of the curve is and the temperature span is one log cycle. The heat treatment at 131°C for one minute is equivalent to 121.1°C for 10 minutes (Fig. 10). 

The heat inactivation of many enzymes, and in particular of those which are composed of subunits, is not a simple process, and the In at versus t plots are more complex. Usually the oligomeric forms of enzymes are slower inactivating than their monomeric forms (Szajani, Ivoiy and Boross, 1980). Similarly, specific interactions between different protein molecules could result in higher heat resistance. 

Mehta AD, Seidler NW (2005) Beta-alanine suppresses heat inactivation of lactate dehydrogenase. J Enzyme Inhib Med Chem 20 199-203... 

The elimination or inactivation of enzymes used to treat proteins is a critical problem once the desired modification in functionality is achieved. In many instances, product inhibition or self destruction does not occur as noted above for fish protein concentrate. As stated by Puski (20), if heat inactivation is used, the proteins may be denatureT"and revert to insoluble forms. Washing out the enzyme at its isoelectric point would also remove a portion of the protein which is solubilized by the enzyme. Inactivation of enzymes by chemical means may also cause significant changes in the protein. Thus, while desired functional modifications of food ingredients may be obtained through enzyme treatment, the problem of latent enzyme activity in food formulations must be addressed. 

At higher temperatures, the enzyme activity decreases more rapidly with incubation time. The heat inactivation of many enzymes follows such patterns. 

Harper, W. J. and Gould, I. A. 1959. Some factors affecting the heat-inactivation of the milk lipase enzyme system. 15th Int. Dairy Congr. Proc. 6, 455-462. 

The product of the stoichiometric reaction of acetyl-P with ornithine, catalyzed by ornithine transcarbamylase, has been shown unequivocally to be 6-acetylornithine the transcarbamylases from rat liver, frog liver, and bacteria, however, even though yielding the same product, appear to differ in their ratios of activity with carbamyl-P and acetyl-P (Table n). While it is possible that the synthesis of 6-acetylornithine is catalyzed by other enzymes (16), the different ratios may be due to species differences we know now that the ratios of activity with carbamyl-P and acetyl-P of all ornithine transcarbamylases thus far tested remain constant with purification. Further, the ratio of citrulline to acetylornithine formation does not change with a number of treatments, such as heat inactivation of preparations containing orni-... 

Owusu, R.K., Makhzoum, A., Knapp, J.S. 1992, Heat inactivation of lipase from psychrotrophic Pseudomonas fluorescens P38 Activation parameters and enzyme stability at low or ultra high temperature. Food Chem. 44, 261-268. 

After completion of the Nael digestion, heat-inactivate Nael by incubating at 65° for 10 min. Cool the sample on ice and adjust the enzyme buffer for digestion with BamHl. Add BamHl to a concentration of about 1 unit///g of Charon 40 DNA and incubate at 37° for 1 hr. Heat-inactivate the enzyme and then place on ice. 

Heating the seed to increase oil recovery. This was first interpreted as denat-uration, making the protein matrix brittle to surrender the oil on pressing. Later, it was recognized that concurrent inactivation of enzymes also arrests development of various types of degradations. 

Most of the purified alpha-amylases lose activity rapidly above 50°, but, in the presence of an excess of calcium ions, the deactivation may be slowed down. Thus, calcium ions are both essential for the activity and important for the stability of alpha-amylase this is particularly true of the cereal a/p/io-amylases, where binding of calcium is very weak. The heat inactivation of the enzymes is minimized when much inert protein is present, and so, heat treatment at 70° may be used in the purification of plant alpha-amylases without high loss of activity. The enzyme from B. stearothermophilus is remarkably heat-stable, and retains 70 % of the original activity after incubation for 20 hours at 85°. 

Fig. 4. Heat inactivation of human pepsin (I) and gastricsin (II) at pH 2.0 and 3.2. The enzyme solutions were incubated for 10 minutes at the indicated temperature and the proteolytic activity measiued. The losses of activity were expressed as percent of the inactivation relative to that of the solution incubated at 45°. From Tang et al. (T6).

As shown in Fig. 2, rate of heat inactivation at high temperature (90 and 95°C) was almost the same with the wild-type and the mutant. Thus, the tolerance to heat inactivation of Thermus PEPC was not affected by the mutation. On the other hand, catalytic activity of Thermus PEPC and its dependence on the temperature was affected by the mutation (Fig. 3). When assayed below 65°C, Fmax and 5o.5 of PEP of the mutant Thermus PEPC were around 70% and 15-fold, respectively, of those of the wild-type. The optimum temperature was lowered, from 80°C to 65°C, by the mutation. Therefore, the Gly-rich region of Thermus PEPC does not contribute to heat stability of the enzyme, but does to its activity at high temperature. 

Fig. 2 Heat inactivation of Thermus PEPCs. Heat treatments were carried out with 0.1 mg/ml of wild-type ( , A) and mutant (O, A) Thermus PEPCs at 90 ( , O) and 95T (A, A). The residual activities were assayed at 60°C in the reaction mixture containing 10 mM potassium PEP, 10 mM KHCO3,10 mM MgS04,0.3 mM NADPH, 1.0 mM CoASAc, 0.1 M Ches-KOH, pH 8.6,2.0 U malate dehydrogenase from Thermus sp., and the enzyme. Relative activities were plotted against incubation time.

Our data support the statement that the heat sensitivity of each enzyme source remains characteristic and independent of the influence of the others in the mixture, and that the resultant heat inactivation is an additive function of the heat-sensitivities of members of the mixture. Bone enzyme from different sources is very consistently heat-sensitive (85-90%), unlike intestinal (50-65%), and liver enzyme (50-75%). However, the heat sensitivity of the LPSAP of normal serum can vary from 33 to 85% and of the non-LPSAP fraction from 50 to 95%. Therefore one cannot determine the identity of the organ sources of serum alkaline phosphatase with a knowledge of only the heat sensitivity and the total alkaline phosphatase. However, by correcting the heat-inactivation of serum by that contributed by intestinal component, one obtains the heat-inactivation of non-intestinal sources of alkaline phosphatase. If this value is 90% or more, the non-intestinal component could be presumed to be of osseous origin if 60% or less, of hepatic origin. 

FIGURE 7.11 Heat inactivation of some enzymes, expressed as activity divided by initial activity, (a) A bacterial protease as a function of heating time at various heating temperatures (°C, indicated), (b) Luciferase, same variables, (c) A bacterial protease heated during 30 min as a function of heating temperature. 

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