Inactivation by heat treatment

Pseudomonas and Azotobacter transhydrogenases was provided by Cohen and Kaplan (17) and by van den Broek et al. [19), respectively, who showed that inactivation by heat treatment could be reversed by addition of FAD. FAD could not be replaced by FMN. Reduction of the enzyme with either NADH or NADPH largely increased the heat sensitivity, whereas oxidized nicotinamide nucleotides or FAD had the opposite effect (17, 19). The number of flavins per 50,000-dalton molecular weight was calculated to be 0.58 to 1.1 (17). 

This example takes us at once to the heart of a problem which it ought to be the objective of this Discussion finally to resolve. In 1925, a concept of the catalytic surface was formulated which emphasized heterogeneity or, as it came to be expressed, the concept of active centres . A variety of evidence on the properties of technical catalysts, which were the only catalysts then extensively studied, contributed to this concept of active centres. This evidence included observations on adsorption by catalysts both active and inactivated by heat treatment. It attempted to account for the great influence of poisons and promoters, present in... 

Piszkiewicz, D. Thomas, W. Lieu, M.Y. Tse, D. Samo, L. Virus inactivation by heat treatment of lyophilized coagulation factor concentrates. In Virus Inactivation in Plasma Products Morgenthaler, J.J., Ed. Curr. Stud. Hematol. Blood Transfus., Basel, Karger, 1989 56, 44—54. 

Where feasible, microorganisms may be removed by filtration or inactivated by heat treatment and, if possible, processing may be continued under aseptic conditions. 

In comparison to other cereals, oats contain a significant level of lipase. Its high activity is released once the oat kernel is disintegrated, crushed or squeezed. Linoleic acid is released from the acyl lipids that are present. It is then converted into hydroxy fatty acids by lipoxygenase and hydroperoxidase enzymes, giving rise to off-flavors (Fig. 15.11). All these enzymes are inactivated by heat treatment and thus quality deterioration can be avoided (cf. 15.3.2.2.2). 

Fig. 1.18. Yeast growth and survival curves in a grape juice medium containing killer toxin (Barre, 1992) +, 10% K2 strain active culture supernatant O, 10% supernatant inactivated by heat treatment, (a) White juice, pH 3.4 cells in exponential phase introduced at time = 0. (b) Same juice, cells in stationary phase introduced at time = 0. (c) Red juice extracted by heated maceration, pH 3.4 cells in exponential phase introduced at time = 0...

Ultra-high-temperature treatment (UHT) is now the most widely exploited method in the food industry to stabilize microbiologically any foodstuff. It consists of heating at an ultra high-temperature for a short period of time for example, a treatment at 145°C for 2 seconds is sufficient to assure a total microbial- and spore inactivation. The microbial death is principally due to irreversible cell damage (e.g., of proteins, DNA, RNA, vitamins) enzymes are inactivated by heat which modifies their active sites. 

The proteinoids are inactivated by heating in buffer solution or by treatment with alkali at room temperature, and it is proved that the hydrolysis of cyclic imide bonds, in which aspartic acid residues are initially bound, accompanies the inactivation by heat8). 

An active proteinoid fraction which was separated by gel filtration is almost totally inactivated by heating a solution at 80 °C for 5 minutes 9). The fact that similar heat treatment during the processing of the proteinoid did not result in loss of activity suggests that the gel filtration step may have removed an unknown stabilizing factor 9). 

Residual RNA in a DNA preparation can be removed by treatment with ribonuclease (RNase). RNase A, which is free of DNase, is available commercially, or the contaminant DNase in the crude RNase A solution can be heat inactivated by heating RNase A solution (10 mg/mL in 10 mM Tris-Cl, pH 7.5, 15 mMNaCl) at 100°C for 15 minutes [4], DNA solution in TE at a concentration of at least 100 pg/mL is treated with RNase to a final concentration of 1 pg/mL followed by incubation at 37°C for 1 hour [3], RNase... 

Sanchez-Monge, R., Blanco, C., Perales, A.D. et al. 2000. Class I chitinases, the panallergens responsible for the latex-fruit syndrome, are induced by ethylene treatment and inactivated by heating. J Allergy Clin Immunol 106 190-195. 

Abrasive milling removes the outer bran layer to produce partially polished rice or, after polishing to remove the entire bran layer, white rice. Rice bran or polish may be subsequently stabilized by heat treatment to inactivate lipases. Stabilized rice bran has found use as an ingredient in human-grade processed foods. 

Presently, the vast majority of information on the Mn site in these acid phosphatases comes from the enzyme from sweet potato tubers. This 110-kDa enzyme is identical to the previously reported sweet potato enzyme likewise, a 55-kDa subunit was found (78). However, the enzyme possesses only one Mn per enzyme molecule. At 293 and 77 K, no EPR signal could be detected for the native enzyme. Inactivation of the enzyme by heat treatment or the addition of acid results in the appearance of a six-line EPR pattern due to aquated Mn(II). As in the case of Mn SODs, this was taken as evidence for Mn(III) in the native... 

Untreated serum contains a set of 11 proteins called complement. These proteins are not immunoglobulins and do not increase quantitatively after immunization. However, they do bind to antigen-antibody complexes and can cause problems for certain immunochemical applications. These proteins may be inactivated by heating the serum to 56°C for 10 to 20 minutes. This treatment will not harm the immunoglobulin fraction if the temperature is carefully regulated. 

After using toxins, wash every working surface with bleach, which is an efficient decontaminant. During the experiments, disposable materials should be used that can be eliminated as a biological hazard. As proteins, these toxins are heat labile and are completely inactivated by heating at 80°C for 10 min, i.e., conditions met by most standard decontamination treatments (heat autoclave) of medical infectious waste. 

When proteinoids were heated in buffer at pH 6.2 or 6.8, loss of catalytic activity was observed. The extent of loss ranged from 95 to 11% (Table II). Those proteinoids that initially showed higher levels of activity relative to histidine were the most affected by the heat treatment. After heating, the level of activity was comparable to that of the equivalent amount of histidine, or to that of mineral acid hydrolysates of the polymer. Under similar conditions, a-chymotrypsin was 97% inactivated. The fact that the control tests on L-histidine or A -carbo-benzoxy-L-histidine showed no effect is consistent with the inference that inactivation is due to disruption of a macromolecular conformation. Copolymers prepared from only aspartic acid and histidine were also active on NPA and were inactivated by the heat treatment. The percentages of inactivation ranged from 62 to 19. Polymers prepared and processed under aseptic conditions were both catalytically active and subject to inactivation by heat. These experiments were performed as routine verification that the respective phenomena do not result from the presence, and subsequent denaturation, of contaminating microbial enzymes. 

Microorganisms can be inactivated by heat, chemical disinfection, ultraviolet radiation, or ultrasonic treatment. Most town water supplies are chlorinated or have ozone added for chemical disinfection. 

Heating a 1% (w/v) solution of ricin to >85°C for 30 min results in complete inactivation as judged by toxicity in laboratory mice (Hunt et al., 1918). Dry heat of >100°C for 60 min in an ashing oven or steam autoclave treatment at >121 °C for 1 h reduces the activity of pure ricin by >99% (Wannemacher et al., 1989). Heat inactivation of impure toxin preparations (e.g., crude ricin plant extracts) may vary. Heat-denatured ricin can undergo limited refolding (<1%) to yield active toxin. Isolated RTA and RTB are more easily inactivated by heating than is the holotoxin (Olsnes et al., 1975 Taira et al., 1978). 

A simple (and probably oversimplified) example will be discussed, the inactivation of an enzyme by heat treatment. At a high temperature, the protein molecule will unfold, but if nothing else happens, it will probably refold after cooling and thereby regain its enzyme activity. This means that the unfolded molecule must undergo a reaction that prevents it from refolding into its native conformation. In the simplest situation we thus have N- U- I, where N is the native, U the unfolded, and I the inactivated state. The second reaction will mostly involve other molecules, but we will assume here that both the first and the second step are first-order reactions. We then have... 

Complete inactivation of all enzymes by heat treatment is easily achieved. But heating can cause undesirable losses in color, texture, flavor, aroma and nutritive quality. For maximum quality retention, clearly the need is for sufficient heat treatment to stabilize the product against enzymatic deterioration but at the same time to minimize quality losses due to heating. 

Protein immunochemistry has been used also to verify the presence, the nature, and the origin of a number of enzymes currently used in the food industry, since immunochemical techniques allow detection of these additions even after the original activity of the enzyme is lost upon stabilization of the product (e.g., by heat treatment or by addition of enzyme-inactivating agents), or when measurement of the enzyme activity does not provide hints as for its origin (as is the case for many rennetting enzymes used in the dairy industry). 

Air purification processes can either remove the aerosol or inactivate the material composing it. An aerosol particle may be removed from the air by settling, inertial separation, filtering, scrubbing or by electrostatic precipitation, and it may be inactivated by heat, radiation or by chemical treatment. 

Heat shock and ethanol treatment. Reactivative action of the dialysate was demonstrated in E. coli, S. cerevisiae and C. guilliermondii subjected to heat shock (Table 2.17). The efficiency of the reactivation was inversely proportional to the viability of the inactivated cells, thus replicating the regularity detected for UV-irradiated bacteria and yeasts. Moreover, the two dialysate fractions that showed reactivative and protective activity in UV-irradiated E. coli also showed reactivative effects in bacterial cells inactivated by heating. 

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